Table of contents

We uncover a method of calculation that proceeds at every step without fixing the gauge or specifying details of the regularisation scheme. Results are obtained by iterated use of integration by parts and gauge invariance identities. Calculations can be performed almost entirely diagrammatically. The method is formulated within the framework of an exact renormalisation group for QED. We demonstrate the technique with a calculation of the one-loop beta function, achieving a manifestly universal result, and without gauge fixing.

We extend the worldline description of vector and antisymmetric tensor fields coupled to gravity to the massive case. In particular, we derive a worldline path integral representation for the one-loop effective action of a massive antisymmetric tensor field of rank p (a massive p-form) whose dynamics is dictated by a standard Proca-like lagrangian coupled to a background metric. This effective action can be computed in a proper time expansion to obtain the corresponding Seeley-DeWitt coefficients a₀, a₁, a₂. The worldline approach immediately shows that these coefficients are derived from the massless ones by the simple shift D→D+1, where D is the spacetime dimension. Also, the worldline representation makes it simple to derive exact duality relations. Finally, we use such a representation to calculate the one-loop contribution to the graviton self-energy due to both massless and massive antisymmetric tensor fields of arbitrary rank, generalizing results already known for the massless spin 1 field (the photon).

We analyze the production and subsequent decay of the neutral MSSM Higgs bosons (h≡h⁰, H⁰, A⁰) mediated by flavor changing neutral currents (FCNC) in the LHC collider. We have computed the h-production cross-section times the FCNC branching ratio, σ(pp→h→qq')≡σ(pp→h) × B(h→qq'), in the LHC focusing on the strongly-interacting FCNC sector. Here qq' is an electrically neutral pair of quarks of different flavors, the dominant modes being those containing a heavy quark: tc or bs. We determine the maximum production rates for each of these modes and identify the relevant regions of the MSSM parameter space, after taking into account the severe restrictions imposed by low energy FCNC processes. The analysis of σ(pp→h→qq') singles out regions of the MSSM parameter space different from those obtained by maximizing only the branching ratio, due to non-trivial correlations between the parameters that maximize/minimize each isolated factor. The production rates for the bs channel can be huge for a FCNC process (0.1−1 pb), but its detection can be problematic. The production rates for the tc channel are more modest (10⁻³−10⁻² pb), but its detection should be easier due to the clear-cut top quark signature. A few thousand tc events could be collected in the highest luminosity phase of the LHC, with no counterpart in the SM.

We show that in the D1-D5 system with angular momentum, there can be localised tachyonic winding string modes in the interior of the spacetime even if we choose a spin structure which preserves supersymmetry in the asymptotic region. We consider cases where the tachyonic region extends outside the event horizon, and argue that the natural endstate of tachyon condensation in almost all cases is one of the solitonic solutions which correspond to special microstates of the D1-D5 system.

We find new 1/8-BPS giant graviton solutions in AdS₅ × S⁵, carrying three angular momenta along S⁵, and investigate their properties. Especially, we show that nonzero worldvolume gauge fields are admitted preserving supersymmetry. These gauge field modes can be viewed as electromagnetic waves along the compact D3 brane, whose Poynting vector contributes to the BPS angular momenta. We also analyze the (nearly-)spherical giant gravitons with worldvolume gauge fields in detail. Expressing the S³ in Hopf fibration (S¹ fibred over S²), the wave propagates along the S¹ fiber.

We investigate the discretized version of the compact Randall-Sundrum model. By studying the mass eigenstates of the lattice theory, we demonstrate that for warped space, unlike for flat space, the strong coupling scale does not depend on the IR scale and lattice size. However, strong coupling does prevent us from taking the continuum limit of the lattice theory. Nonetheless, the lattice theory works in the manifestly holographic regime and successfully reproduces the most significant features of the warped theory. It is even in some respects better than the KK theory, which must be carefully regulated to obtain the correct physical results. Because it is easier to construct lattice theories than to find exact solutions to GR, we expect lattice gravity to be a useful tool for exploring field theory in curved space.

The possibility of the magnetic monopole decay in the constant electric field is investigated and the exponential factor in the probability is obtained. Corrections due to Coulomb interaction are calculated. The relation between masses of particles for the process to exist is obtained.

We present a study of light-cone distribution amplitudes of the light 1¹P₁ mesons. The first few Gegenbauer moments of leading twist light-cone distribution amplitudes are calculated by using the QCD sum rule technique.

We propose a formula for the eigenvalue integral of the hermitian one matrix model with infinite well potential in terms of dressed twist fields of the su(2) level one WZW model. The expression holds for arbitrary matrix size n, and provides a suggestive interpretation for the monodromy properties of the matrix model correlators at finite n, as well as in the 1/n-expansion.

We consider a cosmological scenario within the KKLT framework for moduli stabilization in string theory. The universal open string tachyon of decaying non-BPS D-brane configurations is proposed to drive eternal topological inflation. Flux-induced `warping' can provide the small slow-roll parameters needed for successful inflation. Constraints on the parameter space leading to sufficient number of e-folds, exit from inflation, density perturbations and stabilization of the Kähler modulus are investigated. The conditions are difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T³ fibrations and other generic Calabi-Yau manifolds. This requires large volume and magnetic fluxes on the D-brane. The end of inflation may or may not lead to cosmic strings depending on the original non-BPS configuration. A careful investigation of initial conditions leading to a phenomenologically viable model for inflation is carried out. The initial conditions are chosen on the basis of Sen's open string completeness conjecture. We find time symmetrical bounce solutions without initial singularities for k = 1 FRW models which are correlated with an inflationary period. Singular big-bang/big-crunch solutions also exist but do not lead to inflation. There is an intriguing correlation between having an inflationary universe in 4 dimensions and 6 compact dimensions or a big-crunch singularity and decompactification.

We study the compactification of the pure spinor superstring down to four dimensions. We find that the compactified string is described by a conformal invariant system for both the four dimensional and for the compact six dimensional variables. The four dimensional sector is found to be invariant under a non-critical N = 2 superconformal transformations.

In this letter we compute the exact effective superpotential of = 1 U(N) supersymmetric gauge theories with N_f fundamental flavors and an arbitrary tree-level polynomial superpotential for the adjoint Higgs field. We use the matrix model approach in the maximally confining phase. When restricted to the case of a tree-level even polynomial superpotential, our computation reproduces the known result of the SU(N) theory.

We analyse the 4-dimensional effective supergravity theories obtained from the Scherk-Schwarz reduction of M-theory on twisted 7-tori in the presence of 4-form fluxes. We implement the appropriate orbifold projection that preserves a G₂-structure on the internal 7-manifold and truncates the effective field theory to an = 1, D = 4 supergravity. We provide a detailed account of the effective supergravity with explicit expressions for the Kähler potential and the superpotential in terms of the fluxes and of the geometrical data of the internal manifold. Subsequently, we explore the landscape of vacua of M-theory compactifications on twisted tori, where we emphasize the role of geometric fluxes and discuss the validity of the bottom-up approach. Finally, by reducing along isometries of the internal 7-manifold, we obtain superpotentials for the corresponding type IIA backgrounds.

We study the problem of instanton generated superpotentials in Calabi-Yau orientifold compactifications directly in type-IIB string theory. To this end, we derive the Dirac equation on a euclidean D3 brane in the presence of background fluxes. We propose an index which governs whether the generation of a superpotential in the effective 4d theory by D3 brane instantons is possible. Applying the formalism to various classes of examples, including the K3 × (T²/₂) orientifold, in the absence and presence of fluxes, we show that our results are consistent with conclusions attainable via duality from an M-theory analysis.

We present a comparative analysis of localization of 4D gravity on a non ₂ -symmetric scalar thick brane in both a 5-dimensional riemannian space time and a pure geometric Weyl integrable manifold in which variations in the length of vectors during parallel transport are allowed and a geometric scalar field is involved in its formulation. This work was mainly motivated by the hypothesis which claims that Weyl geometries mimic quantum behaviour classically. We start by obtaining a classical 4-dimensional Poincaré invariant thick brane solution which does not respect ₂ -symmetry along the (non-)compact extra dimension. This field configuration reproduces the ₂ -symmetric solutions previously found in the literature, in both the Riemann and the Weyl frames, when the parameter k₁ = 1. The scalar energy density of our field configuration represents several series of thick branes with positive and negative energy densities centered at y₀ . Thus, our field configurations can be compared with the standard Randall-Sundrum thin brane case. The only qualitative difference we have encountered when comparing both frames is that the scalar curvature of the riemannian manifold turns out to be singular for the found solution, whereas its weylian counterpart presents a regular behaviour. By studying the transverse traceless modes of the fluctuations of the classical backgrounds, we recast their equations into a Schödinger's equation form with a volcano potential of finite bottom (in both frames). By solving the Schödinger equation for the massless zero mode m² = 0 we obtain a single bound state which represents a stable 4-dimensional graviton in both frames. We also get a continuum gapless spectrum of KK states with positive m²>0 that are suppressed at y₀ , turning into continuum plane wave modes as y approaches spatial infinity. We show that for the considered solution to our setup, the potential is always bounded and cannot adopt the form of a well with infinite walls; thus, we do not get a discrete spectrum of KK states, and we conclude that the claim that weylian structures mimic, classically, quantum behaviour does not constitute a generic feature of these geometric manifolds.

A string theory description of near extremal black rings is proposed. The entropy is computed and the thermodynamic properties are derived for a large family of black rings that have not yet been constructed in supergravity. It is also argued that the most general black ring in N = 8 supergravity has 21 parameters up to duality.

We give an explicit demonstration of the equivalence between the Normal Matrix Model (NMM) of c = 1 string theory at selfdual radius and the Kontsevich-Penner (KP) model for the same string theory. We relate macroscopic loop expectation values in the NMM to condensates of the closed string tachyon, and discuss the implications for open-closed duality. As in c < 1, the Kontsevich-Miwa transform between the parameters of the two theories appears to encode open-closed string duality, though our results also exhibit some interesting differences with the c < 1 case. We also briefly comment on two different ways in which the Kontsevich model originates.

We further investigate the NS5 ring background using the tachyon map. Mapping the radion fields to the rolling tachyon helps to explain the motion of a probe Dp-brane in this background. It turns out that the radion field becomes tachyonic when the brane is confined to one dimensional motion inside the ring. We find explicit solutions for the geometrical tachyon field that describe stable kink solutions which are similar to those of the open string tachyon. Interestingly in the case of the geometric tachyon, the dynamics is controlled by a cosine potential. In addition, we couple a constant electric field to the probe-brane, but find that the only stable kink solutions occur when there is zero electric field or a critical field value. We also investigate the behaviour of Non-BPS branes in this background, and find that the end state of any probe brane is that of tachyonic matter 'trapped' around the interior of the ring. We conclude by considering compactification of the ring solution in one of the transverse directions.

The AdS/CFT correspondence relates deformations of the CFT by ``multi-trace operators'' to ``non-local string theories''. The deformed theories seem to have non-local interactions in the compact directions of space-time; in the gravity approximation the deformed theories involve modified boundary conditions on the fields which are explicitly non-local in the compact directions. In this note we exhibit a particular non-local property of the resulting space-time theory. We show that in the usual backgrounds appearing in the AdS/CFT correspondence, the commutator of two bulk scalar fields at points with a large enough distance between them in the compact directions and a small enough time-like distance between them in AdS vanishes, but this is not always true in the deformed theories. We discuss how this is consistent with causality.

It has recently been proposed that a class of supersymmetric higher-derivative interactions in = 2 supergravity may encapsulate an infinite number of finite size corrections to the microscopic entropy of certain supersymmetric black holes. If this proposal is correct, it allows one to probe the string theory description of black-hole micro-states to far greater accuracy than has been possible before. We test this proposal for ``small'' black holes whose microscopic degeneracies can be computed exactly by counting the corresponding perturbative BPS states. We also study the ``black hole partition sum'' using general properties of of BPS degeneracies. This complements and extends our earlier work in [1].

We construct new two dimensional unoriented superstring theories in two dimensions with a chiral closed string spectrum and show that anomalies cancel upon supplying the appropriate chiral open string degrees of freedom imposed by tadpole cancellation.

We propose and study a supersymmetric version of the Janus domain wall solution of type-IIB supergravity. Janus is dual to = 4 super Yang Mills theory with a coupling constant that jumps across an interface. While the interface in the Janus field theory completely breaks all supersymmetries, it was found earlier that some supersymmetry can be restored in the field theory at the cost of breaking the SO(6) R-symmetry down to at least SU(3). We find the gravity dual to this supersymmetric interface theory by studying the SU(3) invariant subsector of = 8 gauged supergravity in 5d, which is described by 5D = 2 gauged supergravity with one hypermultiplet.

We study the plane wave limit of the Bäcklund transformations for the classical string in AdS space times a sphere and obtain an explicit expression for the local conserved charges. We show that the Pohlmeyer charges become in the plane wave limit the local integrals of motion of the free massive field. This fixes the coefficients in the expansion of the anomalous dimension as the sum of the Pohlmeyer charges.

QCD plasma instabilities, caused by an anisotropic momentum distributions of the particles in the plasma, are likely to play an important role in thermalization in heavy ion collisions. We consider plasmas with two different components of particles, one strongly anisotropic and one isotropic or nearly isotropic. The isotropic component does not eliminate instabilities but it decreases their growth rates. We investigate the impact of plasma instabilities on the first stage of the ``bottom-up'' thermalization scenario in which such a two-component plasma emerges, and find that even in the case of non-abelian saturation instabilities qualitatively change the bottom-up picture.

We study the leptonic CP violation by employing the complete set of dimension-six pure leptonic effective operators. Connection among the observable at different energy scales can be made by the running of the renormalization group equations. Explicitly, we study the charged lepton electric dipole moment, muon Michel decay, and the triple spin-momentum correlations at the Linear Collider. We found the electron electric dipole moment, which starts at 2-loop level, severely constrains the possibilities to detect the CP violating signatures in muon decay and at the linear colliders.

We study gravity mediated supersymmetry breaking in four-dimensional effective theories derived from six-dimensional brane-world supergravity. Using the Noether method we construct a locally supersymmetric action for a bulk-brane system consisting of the minimal six-dimensional supergravity coupled to vector and chiral multiplets located at four-dimensional branes. Couplings of the bulk moduli to the brane are uniquely fixed, in particular, they are flavour universal. We compactify this system on T₂/₂ and derive the four-dimensional effective supergravity. The tree-level effective Kähler potential is not of the sequestered form, therefore gravity mediation may occur at tree-level. We identify one scenario of moduli stabilization in which the soft scalar masses squared are postive.

Following suggestions of Nekrasov and Siegel, a non-minimal set of fields are added to the pure spinor formalism for the superstring. Twisted ĉ = 3 N = 2 generators are then constructed where the pure spinor BRST operator is the fermionic spin-one generator, and the formalism is interpreted as a critical topological string. Three applications of this topological string theory include the super-Poincaré covariant computation of multiloop superstring amplitudes without picture-changing operators, the construction of a cubic open superstring field theory without contact-term problems, and a new four-dimensional version of the pure spinor formalism which computes F-terms in the spacetime action.

We describe a natural UV complete theory with a composite little Higgs. Below a TeV we have the minimal Standard Model with a light Higgs, and an extra neutral scalar. At the TeV scale there are additional scalars, gauge bosons, and vector-like charge 2/3 quarks, whose couplings to the Higgs greatly reduce the UV sensitivity of the Higgs potential. Stabilization of the Higgs mass squared parameter, without finetuning, occurs due to a softly broken shift symmetry — the Higgs is a pseudo Nambu-Goldstone boson. Above the 10 TeV scale the theory has new strongly coupled interactions. A perturbatively renormalizable UV completion, with softly broken supersymmetry at 10 TeV is explicitly worked out. Our theory contains new particles which are odd under an exact ``dark matter parity", (−1)<sup>(2S+3B+L)</sup>. We argue that such a parity is likely to be a feature of many theories of new TeV scale physics. The lightest parity odd particle, or ``LPOP", is most likely a neutral fermion, and may make a good dark matter candidate, with similar experimental signatures to the neutralino of the MSSM. We give a general effective field theory analysis of the calculation of corrections to precision electroweak observables.

We study lump solutions in nonlocal toy models and their cosmological applications. These models are motivated by a description of D-brane decay within string field theory framework. In order to find cosmological solutions we use the simplest local approximation keeping only second derivative terms in nonlocal dynamics. We study validity of this approximation in flat background where time lump solutions can be written explicitly and work out the validity of this approximation. Finally, we show that our models at large time exhibit the phantom behaviour similar to the case of the string kink.

We discuss chiral supersymmetric compactifications of the SO(32) heterotic string on Calabi-Yau manifolds equipped with direct sums of stable bundles with structure group U(n). In addition we allow for non-perturbative heterotic five-branes. These models are S-dual to type I compactifications with D9- and D5-branes, which by themselves are mirror symmetric to general intersecting D6-brane models. For the construction of concrete examples we consider elliptically fibered Calabi-Yau manifolds with SU(n) bundles given by the spectral cover construction. The U(n) bundles are obtained via twisting by line bundles. We present a four-generation Pati-Salam and a three-generation Standard-like model.

We investigate a simple class of type-II string compactifications which incorporate nongeometric ``fluxes'' in addition to ``geometric flux'' and the usual H-field and R-R fluxes. These compactifications are nongeometric analogues of the twisted torus. We develop T-duality rules for NS-NS geometric and nongeometric fluxes, which we use to construct a superpotential for the dimensionally reduced four-dimensional theory. The resulting structure is invariant under T-duality, so that the distribution of vacua in the IIA and IIB theories is identical when nongeometric fluxes are included. This gives a concrete framework in which to investigate the possibility that generic string compactifications may be nongeometric in any duality frame. The framework developed in this paper also provides some concrete hints for how mirror symmetry can be generalized to compactifications with arbitrary H-flux, whose mirrors are generically nongeometric.

A shape-function independent relation is derived between the partial →X_u l⁻ decay rate with a cut on P₊ = E_X−|_X| ⩽ Δ and a weighted integral over the normalized →X_sγ photon-energy spectrum. The leading-power contribution to the weight function is calculated at next-to-next-to-leading order in renormalization-group improved perturbation theory, including exact two-loop matching corrections at the scale μ_i ∼ (m_bΛ_QCD)^1/2. The overall normalization of the weight function is obtained up to yet unknown corrections of order α_s²(m_b). Power corrections from phase-space factors are included exactly, while the remaining subleading contributions are included at first order in Λ_QCD/m_b. At this level unavoidable hadronic uncertainties enter, which are estimated in a conservative way. The combined theoretical accuracy in the extraction of |V_ub| is at the level of 5% if a value of Δ near the charm threshold can be achieved experimentally.

We study the perturbative integrability of the planar sector of a massive SU(N) matrix quantum mechanical theory with global SO(6) invariance and Yang-Mills-like interaction. This model arises as a consistent truncation of maximally supersymmetric Yang-Mills theory on a three-sphere to the lowest modes of the scalar fields. In fact, our studies mimic the current investigations concerning the integrability properties of this gauge theory. Like in the field theory we can prove the planar integrability of the SO(6) model at first perturbative order. At higher orders we restrict ourselves to the widely studied SU(2) subsector spanned by two complexified scalar fields of the theory. We show that our toy model satisfies all commonly studied integrability requirements such as degeneracies in the spectrum, existence of conserved charges and factorized scattering up to third perturbative order. These are the same qualitative features as the ones found in super Yang-Mills theory, which were enough to conjecture the all-loop integrability of that theory. For the SO(6) model, however, we show that these properties are not sufficient to predict higher loop integrability. In fact, we explicitly demonstrate the breakdown of perturbative integrability at fourth order.

The = (2,2) extended super Yang-Mills theory in 2 dimensions is formulated on the lattice as a dimensional reduction of a 4 dimensional lattice gauge theory. We use the plaquette action for a bosonic sector and the Wilson- or the overlap-Dirac operator for a fermion sector. The fermion determinant is real and, moreover, when the overlap-Dirac operator is used, semi-positive definite. The flat directions in the target theory become compact and present no subtlety for a numerical integration along these directions. Any exact supersymmetry does not exist in our lattice formulation; nevertheless we argue that one-loop calculable and finite mass counter terms ensure a supersymmetric continuum limit to all orders of perturbation theory.

Using exact boundary conformal field theory methods we analyze the D-brane physics of a specific four-dimensional non-critical superstring theory which involves the = 2 SL(2)/U(1) Kazama-Suzuki model at level 1. Via the holographic duality of [1] our results are relevant for D-brane dynamics in the background of NS5-branes and D-brane dynamics near a conifold singularity. We pay special attention to a configuration of D3- and D5-branes that realizes = 1 supersymmetric QCD and discuss the massless spectrum and classical moduli of this setup in detail. We also comment briefly on the implications of this construction for the recently proposed generalization of the AdS/CFT correspondence by Klebanov and Maldacena within the setting of non-critical superstrings.

Soft rescattering in hard QCD processes may involve non-perturbative, chiral symmetry breaking interactions. We find that rescattering which changes the helicity of the struck quark gives rise to a leading twist single spin asymmetry in semi-inclusive DIS, the angular dependence of which is the same as that usually ascribed to the Collins effect. We argue that helicity-changing rescattering can contribute also to k_⊥-integrated parton distributions.

We study predictions from perturbative Quantum Chromodynamics (QCD) for the process pp→H→γγ+X . In particular, we compare fully differential calculations at next-to-leading (NLO) and next-to-next-to-leading order (NNLO) in the strong coupling constant to the results obtained with the MC@NLO Monte Carlo (MC) generator, which combines QCD matrix elements at NLO with a parton shower algorithm. Estimates for the systematic uncertainties in the various predictions due to the choice of the renormalization scale and the parton distribution functions are given for the inclusive and accepted cross sections and for the corresponding acceptance corrections, obtained after applying standard selection and acceptance cuts. Furthermore, we compare the distributions for the Higgs signal to those for the irreducible two-photon background, obtained with a NLO MC simulation.

We construct classical solutions of open string field theory which are not invariant under ordinary twist operation. From detailed analysis of the moduli space of the solutions, it turns out that our solutions become nontrivial at boundaries of the moduli space. The cohomology of the modified BRST operator and the CSFT potential evaluated by the level truncation method strongly support the fact that our nontrivial solutions correspond to the closed string vacuum. We show that the nontrivial solutions are equivalent to the twist even solution which was found by Takahashi and Tanimoto, and twist invariance of open string field theory remains after the shift of the classical backgrounds.

We present a complete description of angular distributions in the presence of new interactions for the process e⁺e⁻→Zγ with polarized beams at future linear colliders, by considering the most general form-factors allowed by gauge invariance. We include the possibility of CP violation, and classify the couplings according to their CP properties. Chirality conserving and chirality violating couplings give rise to distinct dependence on beam polarization. We present a comprehensive discussion including both types of couplings and provide a detailed comparison of the effects due to each. We discuss some selected asymmetries which would enable isolating effects of the CP-violating form-factors. We also present sensitivities on the corresponding couplings achievable at a future linear collider with realistic polarization and luminosity.

This paper is devoted to the study of the tachyon kink on the worldvolume of a non-BPS Dp-brane that is embedded in general background, including NS−NS two form B and also general Ramond-Ramond field. We will explicitly show that the dynamics of the kink is described by the equations of motion that arrise from the DBI and WZ action for D(p-1)-brane.

In this paper we investigate dual formulations for massive tensor fields. Usual procedure for construction of such dual formulations based on the use of first order parent lagrangians in many cases turns out to be ambiguous. We propose to solve such ambiguity by using gauge invariant description of massive fields which works both in Minkowski space as well as (Anti) de Sitter spaces. We illustrate our method by two concrete examples: spin-2 "tetrad" field h_μ^a, the dual field being "Lorentz connection" ω_μ^ab and "Riemann" tensor R_μν^ab with the dual Σ_μν^abc.

We build a matrix model of a chiral [SU(N)]^K gauge theory (SQCD₅ deconstructed down to 4D) using random unitary matrices to model chiral bifundamental fields (N,) (without (,N)). We verify the duality by matching the loop equation of the matrix model to the anomaly equations of the gauge theory. Then we evaluate the matrix model's free energy and use it to derive the effective superpotential for the gaugino condensates.

We find the shock wave solutions in a class of cosmological backgrounds with a null singularity, each of these backgrounds admits a matrix description. A shock wave solution breaks all supersymmetry meanwhile indicates that the interaction between two static D0-branes cancel, thus provides basic evidence for the matrix description. The probe action of a D0-brane in the background of another suggests that the usual perturbative expansion of matrix model breaks down.

We study the microstates of the ``small'' black hole in the 1/2-BPS sector of AdS<sub>5</sub> × S<sup>5</sup>, the superstar [1], using the powerful holographic description provided by LLM [2]. The system demonstrates the inherently statistical nature of black holes, with the geometry of [1] emerging only after averaging over an ensemble of geometries. The individual microstate geometries differ in the highly non-trivial topology of a quantum foam at their core, and the entropy can be understood as a partition of N units of flux among 5-cycles, as required by flux quantization. While the system offers confirmation of the most controversial aspect of Mathur and Lunin's recent ``fuzzball'' proposal [3,4], we see signs of a discrepancy in interpreting its details.

Generalizations of GL(n) abelian Toda and (n) abelian affine Toda field theories to the noncommutative plane are constructed. Our proposal relies on the noncommutative extension of a zero-curvature condition satisfied by algebra-valued gauge potentials dependent on the fields. This condition can be expressed as noncommutative Leznov-Saveliev equations which make possible to define the noncommutative generalizations as systems of second order differential equations, with an infinite chain of conserved currents. The actions corresponding to these field theories are also provided. The special cases of GL(2) Liouville and (2) sinh/sine-Gordon are explicitly studied. It is also shown that from the noncommutative (anti-)self-dual Yang-Mills equations in four dimensions it is possible to obtain by dimensional reduction the equations of motion of the two-dimensional models constructed. This fact supports the validity of the noncommutative version of the Ward conjecture. The relation of our proposal to previous versions of some specific Toda field theories reported in the literature is presented as well.

In this article we study the relation between the bubbling construction and the Mathur's microscopic solutions for the D1/D5 system. We have found that the regular near horizon D1/D5 system (after appropriated constraints are imposed) contains all the bubbling regular solutions. Then, we show that the features of this system are rather different from the bubbling in AdS₅ × S⁵, since the perimeter and not the area plays a key role. After setting the main dictionary between the two approaches, we investigate on extensions to non-regular solutions like conical defects and/or naked singular solutions. In particular, among the latter metrics, closed time-like curves are found together with a chronology protection mechanism enforced by the AdS/CFT duality.

An interesting alternative to supersymmetry (SUSY) for extending physics beyond the Standard Model is a model with universal extra dimensions (UED), in which the SUSY superpartners are replaced by Kaluza-Klein excitations of the Standard Model particles. If new particles are discovered at the LHC, even if their mass spectrum favours SUSY or UED, it will be vital to distinguish between their spin assignments in the two models as far as possible. We extend the method proposed by Barr [1] to the UED case and investigate the angular and charge asymmetries of decay distributions for sample mass spectra of both SUSY and UED types. For hierarchical (`SUSY-type') mass spectra there is a good chance of distinguishing the spin structures of the two models. However, a mass spectrum of the quasi-degenerate type expected in UED would make it difficult to observe spin correlations.

In the context of the supersymmetrized seesaw mechanism embedded in the Minimal Supersymmetric Standard Model (MSSM), complex neutrino Yukawa couplings can induce Electric Dipole Moments (EDMs) for the charged leptons, providing an additional route to seesaw parameters. However, the complex neutrino Yukawa matrix is not the only possible source of CP violation. Even in the framework of Constrained MSSM (CMSSM), there are additional sources, usually attributed to the phases of the trilinear soft supersymmetry breaking couplings and the mu-term, which contribute not only to the electron EDM but also to the EDMs of neutron and heavy nuclei. In this work, by combining bounds on various EDMs, we analyze how the sources of CP violation can be discriminated by the present and planned EDM experiments.

The holographic Weyl anomaly associated to Chern-Simons gravity in 2n+1 dimensions is proportional to the Euler term in 2n dimensions, with no contributions from the Weyl tensor. We compute the holographic energy-momentum tensor associated to Chern-Simons gravity directly from the action, in an arbitrary odd-dimensional spacetime. We show, in particular, that the counterterms rendering the action finite contain only terms of the Lovelock type.

We give a construction of type-IIB flux vacua with discrete R-symmetries and vanishing superpotential for hypersurfaces in weighted projective space with any number of moduli. We find that the existence of such vacua for a given space depends on properties of the modular group, and for Fermat models can be determined solely by the weights of the projective space. The periods of the geometry do not in general have arithmetic properties, but live in a vector space whose properties are vital to the construction.

A geometric string solution has background fields in overlapping coordinate patches related by diffeomorphisms and gauge transformations, while for a non-geometric background this is generalised to allow transition functions involving duality transformations. Non-geometric string backgrounds arise from T-duals and mirrors of flux compactifications, from reductions with duality twists and from asymmetric orbifolds. Strings in `T-fold' backgrounds with a local n-torus fibration and T-duality transition functions in O(n,n;) are formulated in an enlarged space with a T²ⁿ fibration which is geometric, with spacetime emerging locally from a choice of a Tⁿ submanifold of each T²ⁿ fibre, so that it is a subspace or brane embedded in the enlarged space. T-duality acts by changing to a different Tⁿ subspace of T²ⁿ. For a geometric background, the local choices of Tⁿ fit together to give a spacetime which is a Tⁿ bundle, while for non-geometric string backgrounds they do not fit together to form a manifold. In such cases spacetime geometry only makes sense locally, and the global structure involves the doubled geometry. For open strings, generalised D-branes wrap a Tⁿ subspace of each T²ⁿ fibre and the physical D-brane is the part of the physical space lying in the generalised D-brane subspace.

We study generic Einstein-Maxwell-Kalb-Ramond-dilaton actions, and derive conditions under which they give rise to static, spherically symmetric black hole solutions. We obtain new asymptotically flat and non-flat black hole solutions which are in general electrically and magnetically charged. They have positive definite and finite quasi-local masses. Existing non-rotating black hole solutions (including those appearing in low energy string theory) are recovered in special limits.

In this paper, a real-time formulation of light-cone pp-wave string field theory at finite temperature is presented. This is achieved by developing the thermo field dynamics (TFD) formalism in a second quantized string scenario. The equilibrium thermodynamic quantities for a pp-wave ideal string gas are derived directly from expectation values on the second quantized string thermal vacuum. Also, we derive the real-time thermal pp-wave closed string propagator. In the flat space limit it is shown that this propagator can be written in terms of Theta functions, exactly as the zero temperature one. At the end, we show how superstrings interactions can be introduced, making this approach suitable to study the BMN dictionary at finite temperature.

Field theory in space-time with boundary has an interesting sub-sector, where propagator is difference of those with Neumann and Dirichlet boundary conditions. Such boundary-induced theory in the bulk is essentially holomorphic and is exactly solvable in the sense that all orders of perturbation theory can be summed up explicitly into effective non-local theory at the boundary. This provides a non-trivial realization of holography principle. In the particular example of scalar fields of dimensions Δ_± = (d ± 1)/2 in AdS_d+1 the corresponding effective conformal theory has propagators | |⁻¹ and vertices (|₁|+...+|_n|)^−s_n of valence n in momentum representation, with s_n = (n−2)Δ₋−1. This extraordinary simplicity of certain amplitudes in AdS seems inspiring and can be helpful for analyzing corollaries of open-closed string duality for particular field-theory sub-sectors of string theory.

We present some properties of hyperkahler torsion (or heterotic) geometry in four dimensions that make it even more tractable than its hyperkahler counterpart. We show that in d = 4 hypercomplex structures and weak torsion hyperkahler geometries are the same. We present two equivalent formalisms describing such spaces, they are stated in the propositions of section 1. The first is reduced to solve a non-linear system for a doublet of potential functions, first found by Plebanski and Finley. The second is equivalent to finding the solutions of a quadratic Ashtekar-Jacobson-Smolin like system, but without a volume preserving condition. This is why heterotic spaces are simpler than usual hyperkahler ones. We also analyze the strong version of this geometry. Certain examples are presented, some of them are metrics of the Callan-Harvey-Strominger type and others are not. In the conclusion we discuss the benefits and disadvantages of both formulations in detail.

We discuss fermionic higher spin gauge symmetry breaking in AdS space from a holographic perspective. Analogously to the recently discussed bosonic case, the higher spin Goldstino mode responsible for the symmetry breaking has a non-vanishing mass in the limit in which the gauge symmetry is restored. This result is precisely in agreement with the AdS/CFT correspondence, which implies that = 4 SYM at vanishing coupling constant is dual to a theory in AdS which exhibits higher spin gauge symmetry enhancement. When the SYM coupling is non-zero, the current conservation condition becomes anomalous, and correspondingly the local higher spin symmetry in the bulk gets spontaneously broken. We also show that the mass of the Goldstino mode is exactly the one predicted by the correspondence. Finally, we obtain the form of a class of fermionic higher spin currents in the SYM side.

We consider a 3-brane in D-dimensional Minkowski space and discuss a correspondence principle analogous to the AdS/CFT correspondence. For a 3-brane of finite thickness in the transverse directions, we obtain a spectrum for vector gravitational perturbations which correspond to vector mesons. The spectrum agrees with the one obtained in truncated AdS space by de Téramond and Brodsky provided D = 10 and the bulk mass scale M is of order the geometric mean of the Planck mass () on the brane and Λ_QCD (M ∼ (Λ_QCD)^1/2 ∼ 10⁹ GeV).

In the recent paper [1], it was argued that the open topological B-model whose target space is a complex (2|4)-dimensional mini-supertwistor space with D3- and D1-branes added corresponds to a super Yang-Mills theory in three dimensions. Without the D1-branes, this topological B-model is equivalent to a dimensionally reduced holomorphic Chern-Simons theory. Identifying the latter with a holomorphic BF-type theory, we describe a twistor correspondence between this theory and a supersymmetric Bogomolny model on ³. The connecting link in this correspondence is a partially holomorphic Chern-Simons theory on a Cauchy-Riemann supermanifold which is a real one-dimensional fibration over the mini-supertwistor space. Along the way of proving this twistor correspondence, we review the necessary basic geometric notions and construct action functionals for the involved theories. Furthermore, we discuss the geometric aspect of a recently proposed deformation of the mini-supertwistor space, which gives rise to mass terms in the supersymmetric Bogomolny equations. Eventually, we present solution generating techniques based on the developed twistorial description together with some examples and comment briefly on a twistor correspondence for super Yang-Mills theory in three dimensions.

We perform a systematic search for all possible massive deformations of IIA supergravity in ten dimensions. We show that there exist exactly two possibilities: Romans supergravity and Howe-Lambert-West supergravity. Along the way we give the full details of the ten-dimensional superspace formulation of the latter. The scalar superfield at canonical mass dimension zero (whose lowest component is the dilaton), present in both Romans and massless IIA supergravities, is not introduced from the outset but its existence follows from a certain integrability condition implied by the Bianchi identities. This fact leads to the possibility for a certain topological modification of massless IIA, reflecting an analogous situation in eleven dimensions.

If non-vanishing chemical potentials are assigned to chiral fermions, then a Chern-Simons term is induced for the corresponding gauge fields. In thermal equilibrium anomalous processes adjust the chemical potentials such that the coefficient of the Chern-Simons term vanishes, but it has been argued that there are non-equilibrium epochs in cosmology where this is not the case and that, consequently, certain fermionic number densities and large-scale (hypermagnetic) field strengths get coupled to each other. We generalise the Chern-Simons term to a real-time situation relevant for dynamical considerations, by deriving the anomalous Hard Thermal Loop effective action for the hypermagnetic fields, write down the corresponding equations of motion, and discuss some exponentially growing solutions thereof.

Hawking radiation is viewed as a tunneling process. In this way the emission rate at which charged massive particles tunnel across the event horizon of the Reissner-Nordström black hole is calculated. The emission spectrum deviates from the pure thermal spectrum, but it is consistent with an underlying unitary theory and takes the same functional form as that of uncharged massless particles.

Real time rearrangement of particle spectra is studied numerically in a U(1) Gauge+Higgs system, in the unitary gauge and in three spatial dimensions. The cold system starts from the symmetric phase. Evolution of the partial energy densities and pressures reveals well-defined equations of state for the longitudinal and transversal gauge fields very early. Longitudinal modes are excited more efficiently and thermalize the slowest. Hausdorff-dimension of the Higgs-defect manifold, eventually seeding vortex excitations is thoroughly discussed. Scaling dependence of the vortex density on the characteristic time of the symmetry breaking transition is established.

Within the scenario of large extra dimensions, the Planck scale is lowered to values soon accessible. Among the predicted effects, the production of TeV mass black holes at the LHC is one of the most exciting possibilities. Though the final phases of the black hole's evaporation are still unknown, the formation of a black hole remnant is a theoretically well motivated expectation. We analyze the observables emerging from a black hole evaporation with a remnant instead of a final decay. We show that the formation of a black hole remnant yields a signature which differs substantially from a final decay. We find the total transverse momentum of the black hole event to be significantly dominated by the presence of a remnant mass providing a strong experimental signature for black hole remnant formation.

We conduct a systematic search for anomaly-free six-dimensional = 1 chiral supergravity theories. Under a certain set of restrictions on the allowed gauge groups and the representations of the hypermultiplets, we enumerate all possible Poincaré and gauged supergravities with one tensor multiplet satisfying the 6D anomaly cancellation criteria.

We construct, to the first two non-trivial orders, the next conserved charge in the su(2|3) sector of = 4 Super Yang-Mills theory. This represents a test of integrability in a sector where the interactions change the number of sites of the chain. The expression for the charge is completely determined by the algebra and can be written in a diagrammatic form in terms of the interactions already present in the hamiltonian. It appears likely that this diagrammatic expression remains valid in the full theory and can be generalized to higher loops and higher charges thus helping in establishing complete integrability for these dynamical chains.

Four-dimensional Quantum Einstein Gravity (QEG) is likely to be an asymptotically safe theory which is applicable at arbitrarily small distance scales. On sub-planckian distances it predicts that spacetime is a fractal with an effective dimensionality of 2. The original argument leading to this result was based upon the anomalous dimension of Newton's constant. In the present paper we demonstrate that also the spectral dimension equals 2 microscopically, while it is equal to 4 on macroscopic scales. This result is an exact consequence of asymptotic safety and does not rely on any truncation. Contact is made with recent Monte Carlo simulations.

In the presence of compact dimensions massive solutions of General Relativity may take one of several forms including the black-hole and the black-string, the simplest relevant background being ³⁺¹ × S¹. It is shown how Morse theory places constraints on the qualitative features of the phase diagram, and a minimalistic diagram is suggested which describes a first order transition whose only stable phases are the uniform string and the black-hole. The diagram calls for a topology changing ``merger'' transition in which the black-hole evolves continuously into an unstable black-string phase. As evidence a local model for the transition is presented in which the cone over S² × S² plays a central role. Horizon cusps do not appear as precursors to black hole merger. A generalization to higher dimensions finds that whereas the cone has a tachyon function for d = 5, its stability depends interestingly on the dimension — it is unstable for d < 10, and stable for d > 10.

It has recently been shown that the electroweak baryogenesis mechanism is feasible in Standard Model extensions containing extra fermions with large Yukawa couplings. We show here that the lightest of these fermionic fields can naturally be a good candidate for cold dark matter. We find regions in the parameter space where the thermal relic abundance of this particle is compatible with the dark matter density of the Universe as determined by the WMAP experiment. We study direct and indirect dark matter detection for this model and compare with current experimental limits and prospects for upcoming experiments. We find, contrary to the standard lore, that indirect detection searches are more promising than direct ones, and they already exclude part of the parameter space.

As a step towards understanding the properties of string theory in time-dependent and singular spacetimes, we study the divergence of density operators for string ensembles in singular scale-invariant plane waves, i.e. those plane waves that arise as the Penrose limits of generic power-law spacetime singularities. We show that the scale invariance implies that the Hagedorn behaviour of bosonic and supersymmetric strings in these backgrounds, even with the inclusion of RR or NS fields, is the same as that of strings in flat space. This is in marked contrast to the behaviour of strings in the BFHP plane wave which exhibit quantitatively and qualitatively different thermodynamic properties.

In this paper, we relate the free energy of the 0A matrix model to the sum of topological and anti-topological string amplitudes. For arbitrary integer multiples of the matrix model self-dual radius we describe the geometry on which the corresponding topological string propagates. This geometry is not the one that follows from the usual ground ring analysis, but in a sense its ``holomorphic square root''. Mixing of terms for different genus in the matrix model free energy yields one-loop terms compatible with type-II strings on compact Calabi-Yau target spaces. As an application, we give an explicit example of how to relate the 0A matrix model free energy to that of a four-dimensional black hole in type-IIB theory, compactified on a compact Calabi-Yau. Variables, Legendre transforms, and large classical terms on both sides match perfectly.

We consider the classical and local thermodynamic stability of non- and near-extremal Dp-branes smeared on a transverse direction. These two types of stability are connected through the correlated stability conjecture for which we give a proof in this specific class of branes. The proof is analogous to that of Reall for unsmeared branes, and includes the construction of an appropriate two-parameter off-shell family of smeared Dp-brane backgrounds. We use the boost/U-duality map from neutral black strings to smeared black branes to explicitly demonstrate that non-and near-extremal smeared branes are classically unstable, confirming the validity of the conjecture. For near-extremal smeared branes in particular, we show that a natural definition of the grand canonical ensemble exists in which these branes are thermodynamically unstable, in accord with the conjecture. Moreover, we examine the connection between the unstable Gregory-Laflamme mode of charged branes and the marginal modes of extremal branes. Some features of T-duality and implications for the finite temperature dual gauge theories are also discussed.

We analyze the effects of zeta-function regularization on the evaluation of quantum corrections to spinning strings. Previously, this method was applied in the (2) subsector and yielded agreement to third order in perturbation theory with the quantum string Bethe ansatz. In this note we discuss related sums and compare zeta-function regularization against exact evaluation of the sums, thereby showing that the zeta-function regularized expression misses out perturbative as well as non-perturbative terms. In particular, this may imply corrections to the proposed quantum string Bethe equations. This also explains the previously observed discrepancy between the semi-classical string and the quantum string Bethe ansatz in the regime of large winding number.

We study the fuzzy or noncommutative Dp-branes in terms of infinitely many unstable D0-branes, from which we can construct any Dp-branes. We show that the tachyon condensation of the unstable D0-branes induces the noncommutativity. In the infinite tachyon condensation limit, most of the unstable D0-branes disappear and remaining D0-branes are actually the BPS D0-branes with the correct noncommutative coordinates. For the fuzzy S² case, we explicitly show only the D0-branes corresponding to the lowest Landau level survive in the limit. We also show that a boundary state for a Dp-brane satisfying the Dirichlet boundary condition on a curved submanifold embedded in the flat space is not localized on the submanifold. This implies that the Dp-brane on it is ambiguous at the string scale and solves the problem for a spherical D2-brane with a unit flux on the world volume which should be equivalent to one D0-brane. We also discuss the diffeomorphism in the D0-brane picture.

We study deconstructed gauge theories in which a warp factor emerges dynamically. We present nonsupersymmetric models in which the potential for the link fields has translational invariance, broken only by boundary effects that trigger an exponential profile of vacuum expectation values. The spectrum of physical states deviates exponentially from that of the continuum for large masses; we discuss the effects of such exponential towers on gauge coupling unification. We also present a supersymmetric example in which a warp factor is driven by Fayet-Iliopoulos terms. The model is peculiar in that it possesses a global supersymmetry that remains unbroken despite nonvanishing D-terms. Inclusion of gravity and/or additional messenger fields leads to the collective breaking of supersymmetry and to unusual phenomenology.

We analyze the numerical determination of the quark mixing factor V_us from hyperon semileptonic decays. The discrepancies between the results obtained in two previous studies are clarified. Our fits indicate sizeable SU(3) breaking corrections, which unfortunately can only be fully determined from the data at the first order. The lack of a reliable theoretical calculation of second-order symmetry breaking effects translates into a large systematic uncertainty, which has not been taken into account previously. Our final result, |V_us| = 0.226±0.005, is not competitive with the existing determinations from K_l3, K_l2 and τ decays.

We use soft-collinear effective theory (SCET) to study the factorization properties of deep inelastic scattering in the region of phase space where (1−x) ∼ Λ_QCD/Q. By applying a regions analysis to loop diagrams in the Breit frame, we show that the appropriate version of SCET includes anti-hard-collinear, collinear, and soft-collinear fields. We find that the effects of the soft-collinear fields spoil perturbative factorization even at leading order in the 1/Q expansion.

The classification of 1/4-supersymmetric solutions of five dimensional gauged supergravity coupled to arbitrary many abelian vector multiplets, which was initiated in [15], is completed. The structure of all solutions for which the Killing vector constructed from the Killing spinor is null is investigated in both the gauged and the ungauged theories and some new solutions are constructed.

There is a common description of different intrinsic geometric flows in two dimensions using Toda field equations associated to continual Lie algebras that incorporate the deformation variable t into their system. The Ricci flow admits zero curvature formulation in terms of an infinite dimensional algebra with Cartan operator ∂/∂t. Likewise, the Calabi flow arises as Toda field equation associated to a supercontinual algebra with odd Cartan operator ∂/∂θ−θ∂/∂t. Thus, taking the square root of the Cartan operator allows to connect the two distinct classes of geometric deformations of second and fourth order, respectively. The algebra is also used to construct formal solutions of the Calabi flow in terms of free fields by Bäcklund transformations, as for the Ricci flow. Some applications of the present framework to the general class of Robinson-Trautman metrics that describe spherical gravitational radiation in vacuum in four space-time dimensions are also discussed. Further iteration of the algorithm allows to construct an infinite hierarchy of higher order geometric flows, which are integrable in two dimensions and they admit immediate generalization to Kähler manifolds in all dimensions. These flows provide examples of more general deformations introduced by Calabi that preserve the Kähler class and minimize the quadratic curvature functional for extremal metrics.

We show that a flavour symmetry à la Froggatt-Nielsen can be naturally incorporated in models with gauge-Higgs unification, by exploiting the heavy fermions that are anyhow needed to realize realistic Yukawa couplings. The case of the minimal five-dimensional model, in which the SU(2)_L × U(1)_Y electroweak group is enlarged to an SU(3)_W group, and then broken to U(1)_em by the combination of an orbifold projection and a Scherk-Schwarz twist, is studied in detail. We show that the minimal way of incorporating a U(1)_F flavour symmetry is to enlarge it to an SU(2)_F group, which is then completely broken by the same orbifold projection and Scherk-Schwarz twist. The general features of this construction, where ordinary fermions live on the branes defined by the orbifold fixed-points and messenger fermions live in the bulk, are compared to those of ordinary four-dimensional flavour models, and some explicit examples are constructed.

It is well known that a D-string ending on a D3, D5 or D7 brane is described in terms of a non-commutative fuzzy funnel geometry. In this article, we give a numerical study of the fluctuations about this leading geometry. This allows us to investigate issues related to the stability and moduli space of these solutions. We comment on the comparison to the linearized fluctuations in supergravity.

A parent action is introduced to formulate (S–) dual of non-anticommutative N = 1/2 supersymmetric U(1) gauge theory. Partition function for parent action in phase space is utilized to establish the equivalence of partition functions of the theories which this parent action produces. Thus, duality invariance of non–anticommutative N = 1/2 supersymmetric U(1) gauge theory follows. The results which we obtained are valid at tree level or equivalently at the first order in the nonanticommutativity parameter C_μν.

In analogy with parton distribution functions, also parton fragmentation functions obey matching conditions when crossing heavy-flavour thresholds. We compute these matching conditions at next-to-leading order in the strong coupling constant α_s in the scheme. Our results can be used for the dynamical generation of the heavy-flavour component in next-to-leading order fits to light-hadrons fragmentation functions. Furthermore, when computing perturbatively the charm fragmentation function from first principles and evolving it to higher scales, our matching conditions should be used for consistency when crossing the bottom threshold.

We argue that closed string tachyons drive two spacetime topology changing transitions — loss of genus in a Riemann surface and separation of a Riemann surface into two components. The tachyons of interest are localized versions of Scherk-Schwarz winding string tachyons arising on Riemann surfaces in regions of moduli space where string-scale tubes develop. Spacetime and world-sheet renormalization group analyses provide strong evidence that the decay of these tachyons removes a portion of the spacetime, splitting the tube into two pieces. We address the fate of the gauge fields and charges lost in the process, generalize it to situations with weak flux backgrounds, and use this process to study the type 0 tachyon, providing further evidence that its decay drives the theory sub-critical. Finally, we discuss the time-dependent dynamics of this topology-changing transition and find that it can occur more efficiently than analogous transitions on extended supersymmetric moduli spaces, which are limited by moduli trapping.

According to Dijkgraaf and Vafa the effective glueball superpotential of the = 1 supersymmetric QCD coupled with an adjoint chiral multiplet is given by the planar amplitude in the 1/N expansion of a matrix model. It was shown that, when the = 1 supersymmetric QCD is coupled with fundamental chiral multiplets as well, the effective glueball superpotential is modified by the disc amplitude of the generalized matrix model. The diagramatic computation of this disc amplitude is fairly involved for the multi-cut solution. Instead we compute it with recourse to the complex analysis of the hyperelliptic curve. The result is given in series of the gluino condensation S_i. The explicit computation for the generic multi-cut solution is done up to order S³. It is systematic so that it can be extended to higher orders.

The dilepton production process at hadron colliders in the Randall-Sundrum (RS) model is studied at next-to-leading order in QCD. The NLO-QCD corrections have been computed for the virtual graviton exchange process in the RS model, in addition to the usual γ, Z-mediated processes of standard Drell-Yan. K-factors for the cross-sections at the LHC and Tevatron for differential in the invariant mass, Q, and the rapidity, Y, of the lepton pair are presented. We find the K-factors are large over substantial regions of the phase space.

We describe a combinatorial approach to the analysis of the shape and orientation dependence of Wilson loop observables on two-dimensional noncommutative tori. Morita equivalence is used to map the computation of loop correlators onto the combinatorics of non-planar graphs. Several strong nonperturbative evidences of symmetry breaking under area-preserving diffeomorphisms are thereby presented. Analytic expressions for correlators of Wilson loops with infinite winding number are also derived and shown to agree with results from ordinary Yang-Mills theory.

In a recent paper, Dokshitzer and Marchesini rederived the anomalous dimension matrix for colour evolution of gg→gg scattering, first derived by Kidonakis, Oderda and Sterman. They noted a weird symmetry that it possesses under interchange of internal (colour group) and external (scattering angle) degrees of freedom and speculated that this may be related to an embedding into a context that correlates internal and external variables such as string theory.

In this short note, I point out another symmetry possessed by all the colour evolution anomalous dimension matrices calculated to date. It is more prosaic, but equally unexpected, and may also point to the fact that colour evolution might be understood in some deeper theoretical framework. To my knowledge it has not been pointed out elsewhere, or anticipated by any of the authors calculating these matrices. It is simply that, in a suitably chosen colour basis, they are complex symmetric matrices.

The Kaluza-Klein monopole is a well known object in both gravity and string theory, related by T-duality to a ``smeared'' NS5-brane which retains the isometry around the duality circle. As the true NS5-brane solution is localized at a point on the circle, duality implies that the Kaluza-Klein monopole should show some corresponding behavior. In this paper, we express the Kaluza-Klein monopole as a gauged linear sigma model in two dimensions and show that worldsheet instantons give corrections to its geometry. These corrections can be understood as a localization in ``winding space'' which could be probed by strings with winding charge around the circle.

We study the hydrodynamics of the high-energy phase of Little String Theory. The poles of the retarded two-point function of the stress energy tensor contain information about the speed of sound and the kinetic coefficients, such as shear and bulk viscosity. We compute this two-point function in the dual string theory and analytically continue it to lorentzian signature. We perform an independent check of our results by the lorentzian supergravity calculation in the background of non-extremal NS5-branes. The speed of sound vanishes at the Hagedorn temperature. The ratio of shear viscosity to entropy density is equal to the universal value 1/4π and does not receive α' corrections. The ratio of bulk viscosity to entropy density equals 1/10π. We also compute the R-charge diffusion constant. In addition to the hydrodynamic singularities, the correlators have an infinite series of finite-gap poles, and a massless pole with zero attenuation.

After orientifold projection, the conifold singularity in hypermultiplet moduli space of Calabi-Yau compactifications cannot be avoided by geometric deformations. We study the non-perturbative fate of this singularity in a local model involving O6-planes and D6-branes wrapping the deformed conifold in type-IIA string theory. We classify possible A-type orientifolds of the deformed conifold and find that they cannot all be continued to the small resolution. When passing through the singularity on the deformed side, the O-plane charge generally jumps by the class of the vanishing cycle. To decide which classical configurations are dynamically connected, we construct the quantum moduli space by lifting the orientifold to M-theory as well as by looking at the superpotential. We find a rich pattern of smooth and phase transitions depending on the total sixbrane charge. Non-BPS states from branes wrapped on non-supersymmetric bolts are responsible for a phase transition. We also clarify the nature of a ₂ valued D0-brane charge in the 6-brane background. Along the way, we obtain a new metric of G₂ holonomy corresponding to an O6-plane on the three sphere of the deformed conifold.

We show that the equivalence between the c = 1 non-critical bosonic string and the = 2 topologically twisted coset SL(2)/U(1) at level one can be checked very naturally on the level of tree-level scattering amplitudes with the use of the Stoyanovsky-Ribault-Teschner map, which recasts H₃⁺ correlation functions in terms of Liouville field theory amplitudes. This observation can be applied equally well to the topologically twisted SL(2)_n/U(1) coset with n > 1, which has been argued recently to be equivalent with a c < 1 non-critical bosonic string whose matter part is defined by a time-like linear dilaton CFT.

We give a prescription for attaching parton showers to next-to-leading order (NLO) partonic jet cross sections in electron-positron annihilation. Our method effectively extends to NLO the scheme of Catani, Krauss, Kuhn, and Webber for matching between m hard jets and (m+1) hard jets. The matching between parton splitting as part of a shower and parton splitting as part of NLO matrix elements is based on the Catani-Seymour dipole subtraction method that is commonly used for removing the singularities from the NLO matrix elements.

We compute two-point functions of lowest weight operators at the next-to-leading order in the couplings for the β-deformed = 4SU(N) SYM. In particular we focus on the CPO Tr(Φ₁²) and the operator Tr(Φ₁Φ₂) not presently listed as BPS. We find that for both operators no anomalous dimension is generated at this order, then confirming the results recently obtained at lowest order in [5]. However, in both cases a finite correction to the two-point function appears.

We study the variations of the worldvolume fields in the non-abelian action for multiple D-branes. Using T-duality we find that the embedding scalars transform non-trivially under NS-NS gauge transformations as δX ∼ [X,X] and prove that the non-abelian Chern-Simons action is invariant under these transformations. Given that T-duality relates the (part of the) NS-NS transformation with (part of the) general coordinate transformations, we can get some insight in the structure of non-abelian coordinate transformations.

We extend the instanton calculus for = 1/2 U(2) supersymmetric gauge theory by including one massless flavor. We write the equations of motion at leading order in the coupling constant and we solve them exactly in the non(anti)commutativity parameter C. The profile of the matter superfield is deformed through linear and quadratic corrections in C. Higher order corrections are absent because of the fermionic nature of the back-reaction. The instanton effective action, in addition to the usual 't Hooft term, includes a contribution of order C²and is = 1/2 invariant. We argue that the = 1 result for the gluino condensate is not modified by the presence of the new term in the effective action.

The focus point region of supersymmetric models is compelling in that it simultaneously features low fine-tuning, provides a decoupling solution to the SUSY flavor and CP problems, suppresses proton decay rates and can accommodate the WMAP measured cold dark matter (DM) relic density through a mixed bino-higgsino dark matter particle. We present the focus point region in terms of a weak scale parameterization, which allows for a relatively model independent compilation of phenomenological constraints and prospects. We present direct and indirect neutralino dark matter detection rates for two different halo density profiles, and show that prospects for direct DM detection and indirect detection via neutrino telescopes such as IceCube and anti-deuteron searches by GAPS are especially promising. We also present LHC reach prospects via gluino and squark cascade decay searches, and also via clean trilepton signatures arising from chargino-neutralino production. Both methods provide a reach out to m ∼ 1.7 TeV. At a TeV-scale linear e⁺e⁻ collider (LC), the maximal reach is attained in the ₁₂ or ₁₃ channels. In the DM allowed region of parameter space, a (s)^1/2 = 0.5 TeV LC has a reach which is comparable to that of the LHC. However, the reach of a 1 TeV LC extends out to m ∼ 3.5 TeV.

We investigate the radiatively induced Chern-Simons-like term in four-dimensional field theory at finite temperature. The Chern-Simons-like term is temperature dependent and breaks the Lorentz and CPT symmetries. We find that this term remains undetermined although it can be found unambiguously in different regularization schemes at finite temperature

The world-line formalism is used for the evaluation of the mixed heavy-quark–gluon condensate in two models of QCD — the stochastic vacuum model and the dual superconductor one. Calculations are performed for an arbitrary dimensionality of space-time d ⩾ 2. While in the stochastic vacuum model, the condensate is UV finite up to d = 8, in the dual superconductor model it is UV divergent at any d ⩾ 2. A regularization of this divergence is proposed, which makes quantitative the condition of the type-II dual superconductor. The obtained results are generalized to the case of finite temperatures. Corrections to the both, mixed and standard, heavy-quark condensates, which appear due to the variation of the gauge field at the scale of the vacuum correlation length, are evaluated within the stochastic vacuum model. These corrections diminish the absolute values of the condensates, as well as the ratio of the mixed condensate to the standard one.

The generating functional for Green functions of quark currents is given in closed form to next-to-leading order in the low-energy expansion for chiral SU(3), including one-loop amplitudes with up to three meson propagators. Matrix elements and form factors for strong and nonleptonic weak processes with at most six external states can be extracted from this functional by performing three-dimensional flavour traces. To implement this procedure, a Mathematica© program is provided that evaluates amplitudes with at most six external mesons, photons (real or virtual) and virtual W^± (semileptonic form factors). The program is illustrated with several examples that can be compared with existing calculations.

Timelike T-duality of string theory appears as a symmetry of time evolution in string field theory, exchanging evolution through times t and 1/t, and exchanging boundary states with backgrounds. This is demonstrated by constructing the string field Schrödinger functional, the generator of time evolution, based on Feynman diagram arguments and in analogy with quantum field theory. There the functional can be described using only properties of first quantised particles on a timelike orbifold. Using new sewing rules applicable to both open and closed strings we generalise this approach to bosonic string theory and express the string field Schrödinger functional in terms of strings on ¹/₂.

We present a formalism for the calculation of multi-particle one-loop amplitudes, valid for an arbitrary number N of external legs, and for massive as well as massless particles. A new method for the tensor reduction is suggested which naturally isolates infrared divergences by construction. We prove that for N ⩾ 5, higher dimensional integrals can be avoided. We derive many useful relations which allow for algebraic simplifications of one-loop amplitudes. We introduce a form factor representation of tensor integrals which contains no inverse Gram determinants by choosing a convenient set of basis integrals. For the evaluation of these basis integrals we propose two methods: An evaluation based on the analytical representation, which is fast and accurate away from exceptional kinematical configurations, and a robust numerical one, based on multi-dimensional contour deformation. The formalism can be implemented straightforwardly into a computer program to calculate next-to-leading order corrections to multi-particle processes in a largely automated way.

We consider the construction of tachyonic backgrounds in two-dimensional string theory, focusing on the Sine-Liouville background. This can be studied in two different ways, one within the context of collective field theory and the other via the formalism of Toda integrable systems. The two approaches are seemingly different. The latter involves a deformation of the original inverted oscillator potential while the former does not. We perform a comparison by explicitly constructing the Fermi surface in each case, and demonstrate that the two apparently different approaches are in fact equivalent.

Recent work suggests that fundamental and Dirichlet strings, and their (p,q) bound states, may be observed as cosmic strings. The evolution of cosmic string networks, and therefore their observational signals, depends on what happens when two strings collide. We study this in string perturbation theory for collisions between all possible pairs of strings; different cases involve sphere, disk, and annulus amplitudes. The result also depends on the details of compactification; the dependence on ratios of scales is only logarithmic, but this is still numerically important. We study a range of models and parameters, and find that in most cases these strings can be distinguished from cosmic strings that arise as gauge theory solitons.

We find non-critical string backgrounds in five and eight dimensions, holographically related to four-dimensional conformal field theories with = 0 and = 1 supersymmetries. In the five-dimensional case we find an AdS₅ background metric for a string model related to non-supersymmetric, conformal QCD with large number of colors and flavors and discuss the conjectured existence of a conformal window from the point of view of our solution. In the eight-dimensional string theory, we build a family of solutions of the form AdS₅ × ³ with ³ a squashed three-sphere. For a special value of the ratio N_f/N_c, the background can be interpreted as the supersymmetric near-horizon limit of a system of color and flavor branes on ^1,3 times a known four-dimensional generalization of the cigar. The = 1 dual theory with fundamental matter should have an IR fixed point only for a fixed ratio N_f/N_c. General features of the string/gauge theory correspondence for theories with fundamental flavors are also addressed.

We show how generalised unitarity cuts in D = 4−2 dimensions can be used to calculate efficiently complete one-loop scattering amplitudes in non-supersymmetric Yang-Mills theory. This approach naturally generates the rational terms in the amplitudes, as well as the cut-constructible parts. We test the validity of our method by re-deriving the one-loop ++++, -+++, --++, -+-+ and +++++ gluon scattering amplitudes using generalised quadruple cuts and triple cuts in D dimensions.

In the context of massless higher spin gauge fields in constant curvature spaces, we compute the surface charges which generalize the electric charge for spin one, the color charges in Yang-Mills theories and the energy-momentum and angular momentum for asymptotically flat gravitational fields. We show that there is a one-to-one map from surface charges onto divergence free Killing tensors. These Killing tensors are computed by relating them to a cohomology group of the first quantized BRST model underlying the Fronsdal action.

Twistor space constructions and actions are given for full Yang-Mills and conformal gravity using almost complex structures that are not, in general, integrable. These are used as the basis of a derivation of the twistor-string generating functionals for tree level perturbative scattering amplitudes of Yang-Mills and conformal gravity. The derivation follows by expanding and resumming the classical approximation to the path integral obtained from the twistor action. It provides a basis for exploring whether the equivalence can be made to extend beyond tree level and allows one to disentangle conformal supergravity modes and super Yang-Mills modes from the standard Yang-Mills modes.

For the gauge massless higher spin 4D, = 1 off-shell supermultiplets previously developed, we provide evidence of a twistor-like oscillator realization that is intrinsically related to the superfield structure of the dynamical variables and gauge transformations. Gauge invariant field strengths and linearized Bianchi identities for these multiplets are worked out. It is further argued, inspired by earlier non-supersymmetric constructions due to Klishevich and Zinoviev, that a massive superspin-s multiplet can be described as a gauge-invariant dynamical system involving massless multiplets of superspins s,s−1/2,...,0. A gauge-invariant formulation for the massive gravitino multiplet is discussed in some detail.

We construct a kappa-symmetric and diffeomorphism-invariant non-relativistic Dp-brane action as a non-relativistic limit of a relativistic Dp-brane action in flat space. In a suitable gauge the world-volume theory is given by a supersymmetric free field theory in flat spacetime in p+1 dimensions of bosons, fermions and gauge fields.

We study the constraints on flavour violating terms in low energy SUSY coming from several processes as l_i→l_jγ, l_i→l_jl_jl_j and μ→e in Nuclei. We show that a combined analysis of these processes allows us to extract additional information with respect to an individual analysis of all the processes. In particular, it makes possible to put bounds on sectors previously unconstrained by l_i→l_jγ. We perform the analysis both in the mass eigenstate and in the mass insertion approximations clarifying the limit of applicability of these approximations.

The light-like linear dilaton background represents a particularly simple time-dependent 1/2 BPS solution of critical type-IIA superstring theory in ten dimensions. Its lift to M-theory, as well as its Einstein frame metric, are singular in the sense that the geometry is geodesically incomplete and the Riemann tensor diverges along a light-like subspace of codimension one. We study this background as a model for a big bang type singularity in string theory/M-theory. We construct the dual Matrix theory description in terms of a (1+1)-d supersymmetric Yang-Mills theory on a time-dependent world-sheet given by the Milne orbifold of (1+1)-d Minkowski space. Our model provides a framework in which the physics of the singularity appears to be under control.

We study a relation between droplet configurations in the bubbling AdS geometries and a complex matrix model that describes the dynamics of a class of chiral primary operators in dual = 4 super Yang Mills (SYM). We show rigorously that a singlet holomorphic sector of the complex matrix model is equivalent to a holomorphic part of two-dimensional free fermions, and establish an exact correspondence between the singlet holomorphic sector of the complex matrix model and one-dimensional free fermions. Based on this correspondence, we find a relation of the singlet holomorphic operators of the complex matrix model to the Wigner phase space distribution. By using this relation and the AdS/CFT duality, we give a further evidence that the droplets in the bubbling AdS geometries are identified with those in the phase space of the one-dimensional fermions. We also show that the above correspondence actually maps the operators of = 4 SYM corresponding to the (dual) giant gravitons to the droplet configurations proposed in the literature.

We use Supersymmetric Ward Identities and quadruple cuts to generate n-pt NMHV amplitudes involving gluinos and adjoint scalars from purely gluonic amplitudes. We present a set of factors that can be used to generate one-loop NMHV amplitudes involving gluinos or adjoint scalars in = 4 Super Yang-Mills from the corresponding purely gluonic amplitude.

Codimension-two objects on a system of brane-antibrane are studied in the context of Born-Infeld type effective field theory with a complex tachyon and U(1) × U(1) gauge fields. When the radial electric field is turned on in D22, we find static regular global and local D-vortex solutions which could be candidates of straight cosmic D-strings in a superstring theory. A natural extension to DF-strings is briefly discussed.

We analyze M-theory compactified on K3 × K3 with fluxes preserving half the supersymmetry and its F-theory limit, which is dual to an orientifold of the type IIB string on K3 × (T²/₂). The geometry of attractive K3 surfaces plays a significant role in the analysis. We prove that the number of choices for the K3 surfaces is finite and we show how they can be completely classified. We list the possibilities in one case. We then study the instanton effects and see that they will generically fix all of the moduli. We also discuss situations where the instanton effects might not fix all the moduli.