Table of contents

We classify potential cosmic strings according to the topological charge measurable outside the string core. We conjecture that in string theory it is this charge that governs the stability of long strings. This would imply that the SO(32) heterotic string can have endpoints, but not the E₈ × E₈ heterotic string. We give various arguments in support of this conclusion.

We propose a perturbative asymptotic Bethe ansatz (PABA) for open spin-chain systems whose Hamiltonians are given by matrices of anomalous dimension for composite operators, and apply it to two types of composite operators related to two different brane configurations. One is an AdS₄ × S²-brane in the bulk AdS₅ × S⁵ which gives rise to a defect conformal field theory (dCFT) in the dual field theory, and the other is a giant graviton system with an open string excitation. In both cases, excitations on open strings attaching to D-branes (a D5-brane for the dCFT case, and a spherical D3-brane for the giant graviton case) can be represented by magnon states in the spin-chains with appropriate boundary conditions, in which informations of the D-branes are encoded. We concentrate on single-magnon problems, and explain how to calculate boundary S-matrices via the PABA technique. We also discuss the energy spectrum in the BMN limit.

Up to now chiral type IIA vacua have been mostly based on intersecting D6-branes wrapping special Lagrangian 3-cycles on a CY₃ manifold. We argue that there are additional BPS D-branes which have so far been neglected, and which seem to have interesting model-building features. They are coisotropic D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional submanifolds of the CY₃ which are trivial in homology, but contain a worldvolume flux that induces D6-brane charge on them. This induced D6-brane charge not only renders the D8-brane BPS, but also creates D = 4 chirality when two D8-branes intersect. We discuss in detail the case of a type IIA T⁶/(₂ × ₂) orientifold, where we provide explicit examples of coisotropic D8-branes. We study the chiral spectrum, SUSY conditions, and effective field theory of different systems of D8-branes in this orientifold, and show how the magnetic fluxes generate a superpotential for untwisted Kähler moduli. Finally, using both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like type IIA vacua.

We construct the complete and minimal (q²) and (q³) three-flavour Lorentz invariant chiral meson-baryon Lagrangians for the first time in the literature. We compare with previous three-flavour studies reducing the number of independent monomials and adding new ones that were missing.

At the horizon, a static extremal black hole solution in N = 2 supergravity in four dimensions is determined by a set of so-called attractor equations which, in the absence of higher-curvature interactions, can be derived as extremization conditions for the black hole potential or, equivalently, for the entropy function. We contrast both methods by explicitly solving the attractor equations for a one-modulus prepotential associated with the conifold. We find that near the conifold point, the non-supersymmetric solution has a substantially different behavior than the supersymmetric solution. We analyze the stability of the solutions and the extrema of the resulting entropy as a function of the modulus. For the non-BPS solution the region of attractivity and the maximum of the entropy do not coincide with the conifold point.

We show that the recent measurements of B_s−_s mass difference, Δm_s, by DØ and CDF collaborations give very strong constraints on MSSM scenario with large flavor mixing in the LL and/or RR sector of down-type squark mass squared matrix. In particular, the region with large mixing angle and large mass difference between scalar strange and scalar bottom is ruled out by giving too large Δm_s. The allowed region is sensitive to the CP violating phases δ_L(R). The Δm_s constraint is most stringent on the scenario with both LL and RR mixing. We also predict the time-dependent CP asymmetry in B_s→ψϕ decay and semileptonic asymmetry in B_s→ℓX decay.

Previous work on DBI inflation, which achieves inflation through the motion of a D3 brane as it moves through a warped throat compactification, has focused on the region far from the tip of the throat. Since reheating and other observable effects typically occur near the tip, a more detailed study of this region is required. To investigate these effects we consider a generalized warp throat where the warp factor becomes nearly constant near the tip. We find that it is possible to obtain 60 or more e-folds in the constant region, however large non-gaussianities are typically produced due to the small sound speed of fluctuations. For a particular well-studied throat, the Klebanov-Strassler solution, we find that inflation near the tip may be generic and it is difficult to satisfy current bounds on non-gaussianity, but other throat solutions may evade these difficulties.

Loop amplitudes in (p,q) minimal string theory are studied in terms of the continuum string field theory based on the free fermion realization of the KP hierarchy. We derive the Schwinger-Dyson equations for FZZT disk amplitudes directly from the W_1+∞ constraints in the string field formulation and give explicitly the algebraic curves of disk amplitudes for general backgrounds. We further give annulus amplitudes of FZZT-FZZT, FZZT-ZZ and ZZ-ZZ branes, generalizing our previous D-instanton calculus from the minimal unitary series (p,p+1) to general (p,q) series. We also give a detailed explanation on the equivalence between the Douglas equation and the string field theory based on the KP hierarchy under the W_1+∞ constraints.

Because of ultraviolet/infrared (UV/IR) mixing, the low energy physics of noncommutative gauge theories in the Moyal-Weyl approach seems to depend crucially on the details of the ultraviolet completion. However, motivated by recent string theory analyses, we argue that their phenomenology with a very general class of UV completions can be accurately modelled by a cutoff close to the Planck scale. In the infrared the theory tends continuously to the commutative gauge theory. If the photon contains contributions from a trace-U(1), we would observe vacuum birefringence, i.e. a polarisation dependent propagation speed, as a residual effect of the noncommutativity. Constraints on this effect require the noncommutativity scale to be close to the Planck scale.

We present arguments for the existence of new black string solutions with negative cosmological constant. These higher-dimensional configurations have no dependence on the `compact' extra dimension, and their conformal infinity is the product of time and S^d−3 × R or H^d−3 × R. The configurations with an event horizon topology S^d−2 × S¹ have a nontrivial, globally regular limit with zero event horizon radius. We discuss the general properties of such solutions and, using a counterterm prescription, we compute their conserved charges and discuss their thermodynamics. Upon performing a dimensional reduction we prove that the reduced action has an effective SL(2,R) symmetry. This symmetry is used to construct non-trivial solutions of the Einstein-Maxwell-Dilaton system with a Liouville-type potential for the dilaton in (d−1)-dimensions.

Using AdS/CFT, we compute the Fourier space profile of ⟨tr F²⟩ generated by a heavy quark moving through a thermal plasma of strongly coupled = 4 super-Yang-Mills theory. We find evidence of directional emission from the quark whose description includes gauge fields with large momenta. We comment on the possible relevance of our results to relativistic heavy ion collisions.

We generalize the calculation of cosmic superstring reconnection probability to non-trivial backgrounds. This is done by modeling cosmic strings as wound tachyon modes in the 0B theory, and the spacetime effective action is then used to couple this to background fields. Simple examples are given including trivial and warped compactifications. Generalization to (p,q) strings is discussed.

We point out that the flavor problem in theories with dynamical electroweak symmetry breaking can be effectively decoupled if the physics above the TeV scale is strongly conformal, and the electroweak order parameter has a scaling dimension d = 1+ with ≃ 1/few. There are many restrictions on small values of : for << 1, electroweak symmetry breaking requires a fine-tuning similar to that of the standard model; large-N conformal field theories (including those obtained from the AdS/CFT correspondence) require fine-tuning for d < 2; `walking technicolor' theories cannot have d < 2, according to gap equation analyses. However, strong small-N conformal field theories with ≃ 1/few avoid all these constraints, and can give rise to natural dynamical electroweak symmetry breaking with a top quark flavor scale of order 10^1/TeV, large enough to decouple flavor. Small-N theories also have an acceptably small Peskin-Takeuchi S parameter. This class of theories provides a new direction for dynamical electroweak symmetry breaking without problems from flavor or electroweak precision tests. A possible signal for these theories is a prominent scalar resonance below the TeV scale with couplings similar to a heavy standard model Higgs.

In this letter we consider a charged black hole in a flux compactification of type IIB string theory. Both the black hole and the fluxes will induce potentials for the complex structure moduli. We choose the compact dimensions to be described locally by a deformed conifold, creating a large hierarchy. We demonstrate that the presence of a black hole typically will not change the minimum of the moduli potential in a substantial way. However, we also point out a couple of possible loop-holes, which in some cases could lead to interesting physical consequences such as changes in the hierarchy.

We make use of the AdS/CFT correspondence to determine the energy of an external quark-antiquark pair that moves through strongly-coupled thermal = 4 super-Yang-Mills plasma, both in the rest frame of the plasma and in the rest frame of the pair. It is found that the pair feels no drag force, has an energy that reproduces the expected 1/L (or γ/L) behavior at small quark-antiquark separations, and becomes unbound beyond a certain screening length whose velocity-dependence we determine. We discuss the relation between the high-velocity limit of our results and the lightlike Wilson loop proposed recently as a definition of the jet-quenching parameter.

We propose the minimal, lepton-number conserving, SU(3)_c × SU(2)_L × U(1)_Y gauge-singlet, or phantom, extension of the Standard Model. The extension is natural in the sense that all couplings are of (1) or forbidden due to a phantom sector global U(1)_Dsymmetry, and basically imitates the standard Majorana see-saw mechanism. Spontaneous breaking of the U(1)_D symmetry triggers consistent electroweak gauge symmetry breaking only if it occurs at a scale compatible with small Dirac neutrino masses and baryogenesis through Dirac leptogenesis. Dirac leptogenesis proceeds through the usual out-of-equilibrium decay scenario, leading to left and right-handed neutrino asymmetries that do not fully equilibrate after they are produced. The model contains two physical Higgs bosons and a massless Goldstone boson. The existence of the Goldstone boson suppresses the Higgs to bb branching ratio and instead the Higgs bosons will mainly decay to invisible Goldstone and/or to visible vector boson pairs. In a representative scenario, we estimate that with 30 fb⁻¹ integrated luminosity, the LHC could discover this invisibly decaying Higgs, with mass ∼ 120 GeV. At the same time a significantly heavier, partner Higgs boson with mass ∼ 210 GeV could be found through its vector boson decays. Electroweak constraints as well as astrophysical and cosmological implications are analysed and discussed.

Following the analysis of [1], we calculate the spectrum of fluctuations of a probe Dk-brane in the background of N Dp-branes, for k = p,p+2,p+4 and p<5. The result corresponds to the mesonic spectrum of a (p+1)-dimensional super-Yang-Mills (SYM) theory coupled to `dynamical quarks', i.e. fields in the fundamental representation — the latter are confined to a defect for k = p and p+2. We find a universal behaviour where the spectrum is discrete and the mesons are deeply bound. The mass gap and spectrum are set by the scale M ∼ m_q/g_eff(m_q), where m_q is the mass of the fundamental fields and g_eff(m_q) is the effective coupling evaluated at the quark mass, i.e. g_eff²(m_q) = g_YM²N m_q^p−3. We consider the evolution of the meson spectra into the far infrared of three-dimensional SYM, where the gravity dual lifts to M-theory. We also argue that the mass scale appearing in the meson spectra is dictated by holography.

We systematically study the spectrum of open strings attached to half BPS giant gravitons in the N = 4 SYM AdS/CFT setup. We find that some null trajectories along the giant graviton are actually null geodesics of AdS₅ × S⁵, so that we can study the problem in a plane wave limit setup. We also find the description of these states at weak 't Hooft coupling in the dual CFT. We show how the dual description is given by an open spin chain with variable number of sites. We analyze this system in detail and find numerical evidence for integrability. We also discover an interesting instability of long open strings in Ramond-Ramond backgrounds that is characterized by having a continuum spectrum of the string, which is separated from the ground state by a gap. This instability arises from accelerating the D-brane on which the strings end via the Ramond-Ramond field. From the integrable spin chain point of view, this instability prevents us from formulating the integrable structure in terms of a Bethe Ansatz construction.

Once supersymmetric neutralinos ⁰ are produced copiously at e⁺e⁻ linear colliders, their characteristics can be measured with high precision. In particular, the fundamental parameters in the gaugino/higgsino sector of the minimal supersymmetric extension of the standard model (MSSM) can be analyzed. Here we focus on the determination of possible CP–odd phases of these parameters. To that end, we exploit the electron/positron beam polarization, including transverse polarization, as well as the spin/angular correlations of the neutralino production e⁺e⁻→⁰_i⁰_j and subsequent 2–body decays ⁰_i→⁰_kh,⁰_kZ,^±_Rℓ^∓, using (partly) optimized CP–odd observables. If no final–state polarizations are measured, the Z and h modes are independent of the ⁰_i polarization, but CP–odd observables constructed from the leptonic decay mode can help in reconstructing the neutralino sector of the CP–noninvariant MSSM. In this situation, transverse beam polarization does not seem to be particularly useful in probing explicit CP violation in the neutralino sector of the MSSM. This can most easily be accomplished using longitudinal beam polarization.

We argue that the complete Klebanov-Witten flow solution must be described by a Calabi-Yau metric on the conifold, interpolating between the orbifold at infinity and the cone over T^(1,1) in the interior. We show that the complete flow solution is characterized completely by a single, simple, quasi-linear, second order PDE, or ``master equation,'' in two variables. We show that the Pilch-Warner flow solution is almost Calabi-Yau: It has a complex structure, a hermitian metric, and a holomorphic (3,0)-form that is a square root of the volume form. It is, however, not Kähler. We discuss the relationship between the master equation derived here for Calabi-Yau geometries and such equations encountered elsewhere and that govern supersymmetric backgrounds with multiple, independent fluxes.

A multiplet calculus is presented for an arbitrary number n of N = 2 tensor supermultiplets. For rigid supersymmetry the known couplings are reproduced. In the superconformal case the target spaces parametrized by the scalar fields are cones over (3n−1)-dimensional spaces encoded in homogeneous SU(2) invariant potentials, subject to certain constraints. The coupling to conformal supergravity enables the derivation of a large class of supergravity Lagrangians with vector and tensor multiplets and hypermultiplets. Dualizing the tensor fields into scalars leads to hypermultiplets with hyperkähler or quaternion-Kähler target spaces with at least n abelian isometries. It is demonstrated how to use the calculus for the construction of Lagrangians containing higher-derivative couplings of tensor multiplets. For the application of the c-map between vector and tensor supermultiplets to Lagrangians with higher-order derivatives, an off-shell version of this map is proposed. Various other implications of the results are discussed. As an example an elegant derivation of the classification of 4-dimensional quaternion-Kähler manifolds with two commuting isometries is given.

We show that if there exists a special kind of Born-Infeld type scalar field, then one can send information from inside a black hole. This information is encoded in perturbations of the field propagating in non-trivial scalar field backgrounds, which serves as a "new ether". Although the theory is Lorentz-invariant it allows, nevertheless, the superluminal propagation of perturbations with respect to the "new ether". We found the stationary solution for background, which describes the accretion of the scalar field onto a black hole. Examining the propagation of small perturbations around this solution we show the signals emitted inside the horizon can reach an observer located outside the black hole. We discuss possible physical consequences of this result.

We study QCD in 1+1 dimensions in the large N_c limit using light-front Hamiltonian perturbation theory in the 1/N_c expansion. We use this formalism to exactly compute hadronic transition matrix elements for arbitrary currents at leading order in 1/N_c. We compute the semileptonic differential decay rate of a heavy meson, dΓ/dx, and its moments, M_N, using the hadronic matrix elements obtained previously. We put some emphasis in trying to understand parity invariance. We also study with special care the kinematic region where the operator product expansion (1/N ∼ 1−x ∼ 1) or non-local effective field theories (1/N ∼ 1−x ∼ Λ_QCD/m_Q) can be applied. We then compare with the results obtained using an effective field theory approach based on perturbative factorization, with the focus to better understand quark-hadron duality. At the end of the day, using effective field theories, we have been able to obtain expressions for the moments with relative accuracy of O(Λ_QCD²/m_Q²) in the kinematic region where the operator product expansion can be applied, and with relative accuracy of O(Λ_QCD/m_Q) in the kinematic region where non-local effective field theories can be applied. These expressions agree, within this precision, with those obtained from the hadronic result using the layer-function approximation plus Euler-McLaurin expansion. Very good numerical agreement for the moments is obtained between the exact result and the result using effective field theories.

We discuss the question of the relevance of perturbative QCD calculations for analyzing the properties of the dense medium produced in heavy ion collisions. Up to now leading order perturbative estimates have been worked out and confronted with data for quenched large p_⊥ hadron spectra. Some of them are giving paradoxical results, contradicting the perturbative framework and leading to speculations such as the formation of a strongly interacting quark-gluon plasma. Trying to bypass some drawbacks of these leading order analysis and without performing detailed numerical investigations, we collect evidence in favour of a consistent description of quenching and of the characteristics of the produced medium within the pQCD framework.

The special properties of scalars having a mass such that the two possible dimensions of the dual scalar respect the unitarity and the Breitenlohner-Freedman bounds and their ratio is integral (``resonant scalars'') are studied in the AdS/CFT correspondence. The role of logarithmic branches in the gravity theory is related to the existence of a trace anomaly and to a marginal deformation in the Conformal Field Theory. The existence of asymptotic charges for the conformal group in the gravity theory is interpreted in terms of the properties of the corresponding CFT.

We study the dual gravity description of supersymmetric Wilson loops whose expectation value is unity. They are described by calibrated surfaces that end on the boundary of anti de-Sitter space and are pseudo-holomorphic with respect to an almost complex structure on an eight-dimensional slice of AdS₅ × S⁵. The regularized area of these surfaces vanishes, in agreement with field theory non-renormalization theorems for the corresponding operators.

We compute the planar finite size corrections to the spectrum of the dilatation operator acting on two-impurity states of a certain limit of conformal = 2 quiver gauge field theory which is a Z_M-orbifold of = 4 supersymmetric Yang-Mills theory. We match the result to the string dual, IIB superstrings propagating on a pp-wave background with a periodically identified null coordinate. Up to two loops, we show that the computation of operator dimensions, using an effective Hamiltonian technique derived from renormalized perturbation theory and a twisted Bethe ansatz which is a simple generalization of the Beisert-Dippel-Staudacher [1] long range spin chain, agree with each other and also agree with a computation of the analogous quantity in the string theory. We compute the spectrum at three loop order using the twisted Bethe ansatz and find a disagreement with the string spectrum very similar to the known one in the near BMN limit of = 4 super-Yang-Mills theory. We show that, like in = 4, this disagreement can be resolved by adding a conjectured ``dressing factor'' to the twisted Bethe ansatz. Our results are consistent with integrability of the = 2 theory within the same framework as that of = 4.

We point out that gauge bosons emissions should be carefully estimated when considering LHC observables, since real Ws and Zs contributions can dramatically change cross sections with respect to tree level values. Here we consider observables that are fully inclusive respect to soft gauge boson emission and where a certain number of nonabelian isospin charges in initial and/or final states are detected. We set up a general formalism to evaluate leading, all order resummed electroweak corrections and we consider the phenomenologically relevant case of third family quark production at the LHC. In the case of b production we find that, due to the interplay between strong and weak interactions, the production cross section can become an order of magnitude bigger than the tree level value.

We consider equivariant dimensional reduction of Yang-Mills theory on Kähler manifolds of the form M × P¹ × P¹. This induces a rank two quiver gauge theory on M which can be formulated as a Yang-Mills theory of graded connections on M. The reduction of the Yang-Mills equations on M × P¹ × P¹ induces quiver gauge theory equations on M and quiver vortex equations in the BPS sector. When M is the noncommutative space _θ²ⁿ both BPS and non-BPS solutions are obtained, and interpreted as states of D-branes. Using the graded connection formalism, we assign D0-brane charges in equivariant K-theory to the quiver vortex configurations. Some categorical properties of these quiver brane configurations are also described in terms of the corresponding quiver representations.

Dimensional Reduction is applied to QCD in order to compute various renormalization constants in the scheme at higher orders in perturbation theory. In particular, the β function and the anomalous dimension of the quark masses are derived to three-loop order. Special emphasis is put on the proper treatment of the so-called ε-scalars and the additional couplings which have to be considered.

We compute the spectrum of color-singlet fermionic operators in the = 2 gauge theory on intersecting D3 and D7-branes using the AdS/CFT correspondence. The operator spectrum is found analytically by solving the equations for the dual D7-brane fluctuations. For the fermionic part of the D7-brane action, we use the Dirac-like form found by Martucci et al. ([26]). We also consider the baryon spectrum of a large class of supersymmetric gauge theories using a phenomenological approach to the gauge/gravity duality.

We present a numerical study of type IIB supergravity solutions with varying Ramond-Ramond flux. We construct solutions that have a regular horizon and contain nontrivial five- and three-form fluxes. These solutions are holographically dual to the deconfined phase of confining field theories at finite temperature. As a calibration of the numerical method we first numerically reproduce various analytically known solutions including singular and regular nonextremal D3 branes, the Klebanov-Tseytlin solution and its singular nonextremal generalization. The horizon of the solutions we construct is of the precise form of nonextremal D3 branes. In the asymptotic region far away from the horizon we observe a logarithmic behavior similar to that of the Klebanov-Tseytlin solution.

We study the minimal unitary representations of non-compact groups and supergroups obtained by quantization of their geometric realizations as quasi-conformal groups and supergroups. The quasi-conformal groups G leave generalized light-cones defined by a quartic norm invariant and have maximal rank subgroups of the form H × SL(2, ) such that G/H × SL(2, ) are para-quaternionic symmetric spaces. We give a unified formulation of the minimal unitary representations of simple non-compact groups of type A₂, G₂, D₄, F₄, E₆, E₇, E₈ and Sp(2n, ). The minimal unitary representations of Sp(2n, ) are simply the singleton representations and correspond to a degenerate limit of the unified construction. The minimal unitary representations of the other noncompact groups SU(m, n), SO(m, n), SO*(2n) and SL(m, ) are also given explicitly. We extend our formalism to define and construct the corresponding minimal representations of non-compact supergroups G whose even subgroups are of the form H × SL(2, ). If H is noncompact then the supergroup G does not admit any unitary representations, in general. The unified construction with H simple or Abelian leads to the minimal representations of G(3), F(4) and O Sp(n|2, ) (in the degenerate limit). The minimal unitary representations of O Sp(n|2, ) with even subgroups SO(n) × SL(2, ) are the singleton representations. We also give the minimal realization of the one parameter family of Lie superalgebras D(2, 1; σ).

We analyze the bound on gauge couplings e ⩾ m/m_p, suggested by Arkani-Hamed et.al. We show this bound can be derived from simple semi-classical considerations and holds in spacetime dimensions greater than or equal to four. Non abelian gauge symmetries seem to satisfy the bound in a trivial manner. We comment on the case of discrete symmetries and close by performing some checks for the bound in higher dimensions in the context of string theory.

We construct black hole attractor solutions for a wide class of = 2 compactifications. The analysis is carried out in ten dimensions and makes crucial use of pure spinor techniques. This formalism can accommodate non-Kähler manifolds as well as compactifications with flux, in addition to the usual Calabi-Yau case. At the attractor point, the charges fix the moduli according to ∑f_k = Im(CΦ), where Φ is a pure spinor of odd (even) chirality in IIB (A). For IIB on a Calabi-Yau, Φ = Ω and the equation reduces to the usual one. Methods in generalized complex geometry can be used to study solutions to the attractor equation.

We show how such important features of QCD as chiral symmetry breaking or the formation of a mass-gap can be directly traced from QCD sum rules for two point functions assuming, in the large number of colors limit, exact duality between the operator product expansion and the spectrum described by linearly (or nearly linear) rising Regge trajectories as predicted by string theory. We see how the presence of chiral symmetry breaking is intimately related to confinement in this scenario, as expected from general arguments, and how Regge trajectories change when chiral symmetry is broken. As a result the whole meson mass spectrum can be parametrized with a good accuracy by the constant f_π only, thus realizing the program proposed by Migdal some time ago.

We study scalar field theories on Poincaré invariant commutative nonassociative spacetimes. We compute the one-loop self-energy diagrams in the ordinary path integral quantization scheme with Feynman's prescription, and find that the Cutkosky rule is satisfied. This property is in contrast with that of noncommutative field theory, since it is known that noncommutative field theory with space/time noncommutativity violates unitarity in the above standard scheme, and the quantization procedure will necessarily become complicated to obtain a sensible Poincaré invariant noncommutative field theory. We point out a peculiar feature of the non-locality in our nonassociative field theories, which may explain the property of the unitarity distinct from noncommutative field theories. Thus commutative nonassociative field theories seem to contain physically interesting field theories on deformed spacetimes.

We examine the fixed points to first-order RG flow of a non-linear sigma model with background metric, dilaton and tachyon fields. We show that on compact target spaces, the existence of fixed points with non-zero tachyon is linked to the sign of the second derivative of the tachyon potential V''(T) (this is the analogue of a result of Bourguignon for the zero-tachyon case). For a tachyon potential with only the leading term, such fixed points are possible. On non-compact target spaces, we introduce a small non-zero tachyon and compute the correction to the Euclidean 2d black hole (cigar) solution at second order in perturbation theory with a tachyon potential containing a cubic term as well. The corrections to the metric, tachyon and dilaton are well-behaved at this order and tachyon `hair' persists. We also briefly discuss solutions to the RG flow equations in the presence of a tachyon that suggest a comparison to dynamical fixed point solutions obtained by Yang and Zwiebach.

Vortex configurations in the two-dimensional torus are considered in noncommutative space. We analyze the BPS equations of the Abelian Higgs model. Numerical solutions are constructed for the self-dual and anti-self dual cases by extending an algorithm originally developed for ordinary commutative space. We work within the Fock space approach to noncommutative theories and the Moyal-Weyl connection is used in the final stage to express the solutions in configuration space.

Among the firm predictions of softly broken supersymmetry is the identity of gauge couplings and the corresponding Yukawa couplings between gauginos, sfermions and fermions. In the event that a SUSY-like spectrum of new particles is discovered at future colliders, a key follow-up will be to test these relations experimentally. In detailed studies it has been found that the SUSY-Yukawa couplings of the electroweak sector can be studied with great precision at the ILC, but a similar analysis for the Yukawa coupling of the SUSY-QCD sector is far more challenging. Here a first phenomenological study for determining this coupling is presented, using a method which combines information from LHC and ILC.

We analyze the dark matter problem in the context of brane cosmology. We investigate the impact of the non-conventional brane cosmology on the relic abundance of non-relativistic stable particles in high and low reheating temperature scenarios. We show that in case of high reheating temperature, the brane cosmology may enhance the dark matter relic density by many order of magnitudes and a stringent lower bound on the five dimensional scale is obtained. We also consider low reheating temperature scenarios with chemical equilibrium and non-equilibrium. We emphasize that in non-equilibrium case, the resulting relic density is very small. While with equilibrium, it is increased by a factor of (10²) with respect to the standard thermal production. Therefore, dark matter particles with large cross section, which is favored by detection expirements, can be consistent with the recent relic density observational limits.

We study the supersymmetric solutions of 11-dimensional supergravity with a factor of AdS₂ made of M2-branes. Such solutions can provide gravity duals of superconformal quantum mechanics, or through double Wick rotation, the generic bubbling geometry of M-theory which are 1/16-BPS. We show that, when the internal manifold is compact, it should take the form of a warped U(1)-fibration over an 8-dimensional Kähler space.

We determine the one-instanton corrections to the universal hypermultiplet moduli space coming both from Euclidean membranes and NS-fivebranes wrapping the cycles of a (rigid) Calabi-Yau threefold. These corrections are completely encoded by a single function characterizing a generic four-dimensional quaternion-Kähler metric without isometries. We give explicit solutions for this function describing all one-instanton corrections, including the fluctuations around the instanton to all orders in the string coupling constant. In the semi-classical limit these results are in perfect agreement with previous supergravity calculations.

Following the nonperturbative prescription for the jet quenching parameter recently proposed by Liu, Rajagopal and Wiedemann, we compute the first correction in the inverse `t Hooft coupling corresponding to string α' corrections in the dual background. We also consider the introduction of a chemical potential for the U(1)³ gauged R-symmetry. While the former mildly diminishes the jet quenching parameter –this suggesting a smooth interpolation between the strong coupling and perturbative results–, the latter generically increases its value. We comment on the extension of this setup to quarks of finite mass.

We study supersymmetric embeddings of D-brane probes of different dimensionality in the AdS₅ × L^a,b,c background of type IIB string theory. In the case of D3-branes, we recover the known three-cycles dual to the dibaryonic operators of the gauge theory and we also find a new family of supersymmetric embeddings. Supersymmetric configurations of D5-branes, representing fractional branes, and of spacetime filling D7-branes (which can be used to add flavor) are also found. Stable non supersymmetric configurations corresponding to fat strings and domain walls are found as well.

The q-deformed fuzzy sphere S_qF²(N) is the algebra of (N+1) × (N+1) dim. matrices, covariant with respect to the adjoint action of U_q(su(2)) and in the limit q→1, it reduces to the fuzzy sphere S_F²(N). We construct the Dirac operator on the q-deformed fuzzy sphere-S_qF²(N) using the spinor modules ofU_q(su(2)). We explicitly obtain the zero modes and also calculate the spectrum for this Dirac operator. Using this Dirac operator, we construct the U_q(su(2)) invariant action for the spinor fields onS_qF²(N) which are regularised and have only finite modes. We analyse the spectrum for both q being root of unity and real, showing interesting features like its novel degeneracy. We also study various limits of the parameter space (q, N) and recover the known spectrum in both fuzzy and commutative sphere.

The prediction of neutralino dark matter is generally regarded as one of the successes of the Minimal Supersymmetric Standard Model (MSSM). However the successful regions of parameter space allowed by WMAP and collider constraints are quite restricted. We discuss fine-tuning with respect to both dark matter and Electroweak Symmetry Breaking (EWSB) and explore regions of MSSM parameter space with non-universal gaugino and third family scalar masses in which neutralino dark matter may be implemented naturally. In particular allowing non-universal gauginos opens up the bulk region that allows Bino annihilation via t-channel slepton exchange, leading to ``supernatural dark matter'' corresponding to no fine-tuning at all with respect to dark matter. By contrast we find that the recently proposed ``well tempered neutralino'' regions involve substantial fine-tuning of MSSM parameters in order to satisfy the dark matter constraints, although the fine tuning may be ameliorated if several annihilation channels act simultaneously. Although we have identified regions of ``supernatural dark matter'' in which there is no fine tuning to achieve successful dark matter, the usual MSSM fine tuning to achieve EWSB always remains.

We study type IIB orientifolds on T^2d/_N with supersymmetry broken by the compactification. We determine tadpole cancellation conditions including antibranes and considering different actions for the parity Ω. Using these conditions we then obtain the spectrum of tachyons and massless states. Various examples with N even correspond to type 0B orientifolds.

The H. Ooguri, A. Strominger and C. Vafa conjecture Z_BH = |Z_top|² is extended for the topological strings on generalized CY manifolds. It is argued that the classical black hole entropy is given by the generalized Hitchin functional, which defines by critical points a generalized complex structure on X. This geometry differs from an ordinary geometry if b₁(X)≠0. In a critical point the generalized Hitchin functional equals to Legendre transform of the free energy of generalized topological string. The examples of T⁶ and T² × K3 are considered in details.

This paper addresses the issue of production of charm or bottom quarks in association with a high p_T process in hadron hadron collision. These quarks can be produced either as part of the hard scattering process or as a remnant from the structure functions. The latter sums terms of the type (α_slog (p_T/m_q))ⁿ. If structure functions of charm or bottom quarks are used together with a hard process which also allows production of these quarks double counting occurs. This paper describes the correct procedure in form of a Monte-Carlo algorithm , which is consistently derived from the factorisation theorem and provides two examples of its implimentation inside a Monte-Carlo event generator in cases of the single top and Drell-Yan process simulation at the LHC.

We investigate some universal features of AdS/CFT models of heavy quark energy loss. In addition, as a specific example, we examine quark damping in the spinning D3-brane solution dual to = 4 SU(N) super Yang-Mills at finite temperature and R-charge chemical potential.

We develop a new and efficient method to systematically analyse four dimensional effective supergravities which descend from flux compactifications. The issue of finding vacua of such systems, both supersymmetric and non-supersymmetric, is mapped into a problem in computational algebraic geometry. Using recent developments in computer algebra, the problem can then be rapidly dealt with in a completely algorithmic fashion. Two main results are (1) a procedure for calculating constraints which the flux parameters must satisfy in these models if any given type of vacuum is to exist; (2) a stepwise process for finding all of the isolated vacua of such systems and their physical properties. We illustrate our discussion with several concrete examples, some of which have eluded conventional methods so far.

We consider a wide class of cascading gauge theories which usually lead to runaway behaviour in the IR, and discuss possible deformations of the superpotential at the bottom of the cascade which stabilize the runaway direction and provide stable non-supersymmetric vacua. The models we find may allow for a weakly coupled supergravity analysis of dynamical supersymmetric breaking in the context of the gauge/string correspondence.

Using the entropy function formalism we compute the entropy of extremal supersymmetric and non-supersymmetric black holes in = 2 supergravity theories in four dimensions with higher derivative corrections. For supersymmetric black holes our results agree with all previous analysis. However in some examples where the four dimensional theory is expected to arise from the dimensional reduction of a five dimensional theory, there is an apparent disagreement between our results for non-supersymmetric black holes and those obtained by using the five dimensional description. This indicates that for these theories supersymmetrization of the curvature squared term in four dimension does not produce all the terms which would come from the dimensional reduction of a five dimensional action with curvature squared terms.

Fermion fields on an M-theory five-brane carry a representation of the double cover of the structure group of the normal bundle. It is shown that, on an arbitrary oriented Lorentzian six-manifold, there is always an Sp₂ twist that allows such spinors to be defined globally. The vanishing of the arising potential obstructions does not depend on spin structure in the bulk, nor does the six-manifold need to be spin or spin. Lifting the tangent bundle to such a generalised spin bundle requires picking a generalised spin structure in terms of certain elements in the integral and modulo-two cohomology of the five-brane world-volume in degrees four and five, respectively.

The phase diagram of large N_c, weakly-coupled = 4 supersymmetric Yang-Mills theory on a three-sphere with non-zero chemical potentials is examined. In the zero coupling limit, a transition line in the μ-Tplane is found, separating a ``confined'' phase in which the Polyakov loop has vanishing expectation value from a ``deconfined'' phase in which this order parameter is non-zero. For non-zero but weak coupling, perturbative methods may be used to construct a dimensionally reduced effective theory valid for sufficiently high temperature. If the maximal chemical potential exceeds a critical value, then the free energy becomes unbounded below and no genuine equilibrium state exists. However, the deconfined plasma phase remains metastable, with a lifetime which grows exponentially with N_c(not N_c²). This metastable phase persists with increasing chemical potential until a phase boundary, analogous to a spinodal decomposition line, is reached. Beyond this point, no long-lived locally stable quasi-equilibrium state exists.

The resulting picture for the phase diagram of the weakly coupled theory is compared with results believed to hold in the strongly coupled limit of the theory, based on the AdS/CFT correspondence and the study of charged black hole thermodynamics. The confinement/deconfinement phase transition at weak coupling is in qualitative agreement with the Hawking-Page phase transition in the gravity dual of the strongly coupled theory. The black hole thermodynamic instability line may be the counterpart of the spinodal decomposition phase boundary found at weak coupling, but no black hole tunneling instability, analogous to the instability of the weakly coupled plasma phase is currently known.

We present a renormalizable 4-dimensional SU() gauge theory with a suitable multiplet of scalar fields, which dynamically develops extra dimensions in the form of a fuzzy sphere S²_N. We explicitly find the tower of massive Kaluza-Klein modes consistent with an interpretation as gauge theory on M⁴ × S², the scalars being interpreted as gauge fields on S². The gauge group is broken dynamically, and the low-energy content of the model is determined. Depending on the parameters of the model the low-energy gauge group can be SU(n), or broken further to SU(n₁) × SU(n₂) × U(1), with mass scale determined by the size of the extra dimension.

We consider the operators with highest anomalous dimension Δ in the compact rank-one sectors (1|1) and (2) of = 4 super Yang-Mills. We study the flow of Δ from weak to strong 't Hooft coupling λ by solving (i) the all-loop gauge Bethe Ansatz, (ii) the quantum string Bethe Ansatz. The two calculations are carefully compared in the strong coupling limit and exhibit different exponents ν in the leading order expansion Δ ∼ λ^ν. We find ν = 1/2 and ν = 1/4 for the gauge or string solution. This strong coupling discrepancy is not unexpected, and it provides an explicit example where the gauge Bethe Ansatz solution cannot be trusted at large λ. Instead, the string solution perfectly reproduces the Gubser-Klebanov-Polyakov law Δ = 2n^1/2 λ^1/4. In particular, we provide an analytic expression for the integer level n as a function of the U(1) charge in both sectors.

We study the classical spectrum of string theory on AdS₅ × S⁵ in the Hofman-Maldacena limit. We find a family of classical solutions corresponding to Giant Magnons with two independent angular momenta on S⁵. These solutions are related via Pohlmeyer's reduction procedure to the charged solitons of the Complex sine-Gordon equation. The corresponding string states are dual to BPS boundstates of many magnons in the spin-chain description of planar = 4 SUSY Yang-Mills. The exact dispersion relation for these states is obtained from a purely classical calculation in string theory.

We consider the possibility of looking for CP-mixing effects in two-Higgs doublet models (and particularly in the MSSM) by studying the lineshape of the CP-even (H) and CP-odd (A) neutral scalars. In most cases H and A come quite degenerate in mass, and their s-channel production would lead to nearly overlapping resonances. CP-violating effects may connect these two Higgs bosons, giving origin to one-loop particle mixing, which, due to their mass proximity, can be resonantly enhanced. The corresponding transition amplitude contains then CP-even and CP-odd components; besides the signal of intereference between both amplitudes, leading to a CP-odd asymmetry, we propose to look for the mixing probability itself, a quantity which, although CP-even, can originate only from a CP-odd amplitude. We show that, in general, the effect of such a mixing probability cannot be mimicked by (or be re-absorbed into) a simple redefinition of the H and A masses in the context of a CP-conserving model. Specifically, the effects of the CP-mixing are such that, either the mass-splitting of the H and A bosons cannot be accounted for in the absence of CP-mixing, and/or the detailed energy dependence of the produced lineshape is clearly different from the one obtained by redefining the masses, but not allowing any mixing. This analysis suggests that the detailed study of the lineshape of this Higgs system may provide valuable information on the CP nature of the underlying theory.

We consider how variations in the moduli of the compactification manifold contribute `pdV' type work terms to the first law for Kaluza-Klein black holes. We give a new proof for the S¹ case, based on Hamiltonian methods, which demonstrates that the result holds for arbitrary perturbations around a static black hole background. We further apply these methods to derive the first law for black holes in 2-torus compactifications, where there are three real moduli. We find that the result can be simply stated in terms of constructs familiar from the physics of elastic materials, the stress and strain tensors. The strain tensor encodes the change in size and shape of the 2-torus as the moduli are varied. The role of the stress tensor is played by a tension tensor, which generalizes the spacetime tension that enters the first law in the S¹ case.

In a recent string theory motivated paper, Nicolini, Smailagic and Spallucci (NSS) presented an interesting model for a noncommutative inspired, Schwarzschild-like black hole solution in 4-dimensions. The essential effect of having noncommutative co-ordinates in this approach is to smear out matter distributions on a scale associated with the turn-on of noncommutativity which was taken to be near the 4-d Planck mass. In particular, NSS took this smearing to be essentially Gaussian. This energy scale is sufficiently large that in 4-d such effects may remain invisible indefinitely. Extra dimensional models which attempt to address the gauge hierarchy problem, however, allow for the possibility that the effective fundamental scale may not be far from ∼ 1 TeV, an energy regime that will soon be probed by experiments at both the LHC and ILC. In this paper we generalize the NSS model to the case where flat, toroidally compactified extra dimensions are accessible at the Terascale and examine the resulting modifications in black hole properties due to the existence of noncommutativity. We show that while many of the noncommutativity-induced black hole features found in 4-d by NSS persist, in some cases there can be significant modifications due the presence of extra dimensions. We also demonstrate that the essential features of this approach are not particularly sensitive to the Gaussian nature of the smearing employed by NSS.

We consider a gravity dual description of time dependent, strongly interacting large-N_c = 4 SYM. We regard the gauge theory system as a fluid with shear viscosity. Our fluid is expanding in one direction following the Bjorken's picture that is relevant to RHIC experiments. We obtain the dual geometry at the late time that is consistent with dissipative hydrodynamics. We show that the integration constants that cannot be determined by hydrodynamics are given by looking at the horizon of the dual geometry. Relationship between time dependence of the energy density and bulk singularity is also discussed.

We study the dynamics of BPS string-like objects obtained by lifting monopole and dyon solutions of N = 2 Super-Yang-Mills theory to five dimensions. We present exact traveling wave solutions which preserve half of the supersymmetries. Upon compactification this leads to macroscopic BPS rings in four dimensions in field theory. Due to the fact that the strings effectively move in six dimensions the same procedure can also be used to obtain rings in five dimensions by using the hidden dimension.

Entanglement entropy for a spatial partition of a quantum system is studied in theories which admit a dual description in terms of the anti-de Sitter (AdS) gravity one dimension higher. A general proof of the holographic formula which relates the entropy to the area of a codimension 2 minimal hypersurface embedded in the bulk AdS space is given. The entanglement entropy is determined by a partition function which is defined as a path integral over Riemannian AdS geometries with non-trivial boundary conditions. The topology of the Riemannian spaces puts restrictions on the choice of the minimal hypersurface for a given boundary conditions. The entanglement entropy is also considered in Randall-Sundrum braneworld models where its asymptotic expansion is derived when the curvature radius of the brane is much larger than the AdS radius. Special attention is payed to the geometrical structure of anomalous terms in the entropy in four dimensions. Modification of the holographic formula by the higher curvature terms in the bulk is briefly discussed.

Mirage mediation reduces the fine-tuning in the minimal supersymmetric standard model by dynamically arranging a cancellation between anomaly-mediated and modulus-mediated supersymmetry breaking. We explore the conditions under which a mirage ``messenger scale'' is generated near the weak scale and the little hierarchy problem is solved. We do this by explicitly including the dynamics of the SUSY-breaking sector needed to cancel the cosmological constant. The most plausible scenario for generating a low mirage scale does not readily admit an extra-dimensional interpretation. We also review the possibilities for solving the μ/Bμ problem in such theories, a potential hidden source of fine-tuning.

We study the strong coupling behaviour of fixed length single trace operators in the scalar SU(2) sector of = 4 SYM. We assume the recently proposed connection with a twisted half-filled Hubbard model. By explicit direct diagonalization of operators with length L = 4,6,8 we study the full perturbative multiplet of those lattice states which have a clear correspondence with gauge theory composite operators. For this multiplet, we follow the weak-strong coupling flow to free fermion states and identify in particular the precise asymptotic fermion configuration. Next, we analyze the Lieb-Wu equations of the twisted Hubbard model. For the antiferromagnetic state we derive its strong coupling expansion working at L up to 32. We also study the lightest state in the perturbative multiplet. This state is non trivial since involves complex solutions of the Lieb-Wu equations. It is particularly interesting for AdS₅ × S⁵ duality since it is dual to the folded string semiclassical solution in the thermodynamical limit. We are able to perform the full analysis and compute the next-to-next-to leading terms in the strong coupling expansion for the non trivial lengths L = 12 and L = 20. A general formula is proposed for the NLO expansion for any L = 4(2k+1), k∊.

Single pion and prompt photon large transverse momentum spectra in p–p and Au-Au collisions are computed in perturbative QCD at RHIC energy, s_NN^1/2 = 200 GeV. Next-to-leading order calculations are discussed and compared with p–p scattering data. Subsequently, quenching factors are computed to leading order for both pions and photons within the same energy loss model. The good agreement with PHENIX preliminary data allows for a lower estimate of the energy density reached in central Au-Au collisions, _RHIC≳ 10 GeV/fm³. Double inclusive γ-π⁰ production in p–p and Au-Au collisions is then addressed. Next-to-leading order corrections prove rather small in p–p scattering. In Au–Au collisions, the quenching of momentum-correlation spectra is seen to be sensitive to parton energy loss processes, which would help to understand how the fragmentation dynamics is modified in nuclear collisions at RHIC.

The MLLA single inclusive distribution inside one high energy (gluon) jet at small x is estimated by the steepest descent method. Its analytical expression is obtained outside the ``limiting spectrum''. It is then used to evaluate 2-particle correlations at the same level of generality. The dependence of both observables on the ratio between the infrared cutoff Q₀ and Λ_QCD is studied. Fong & Webber's results for correlations are recovered at the limits when this ratio goes to 1 and when one stays close to the peak of the single inclusive distribution.

We compute the next-to-leading order strong interaction corrections to gluino-mediated ΔF = 2 box diagrams in the Minimal Supersymmetric Standard Model. These corrections are given by two loop diagrams which we have calculated in three different regularization schemes in the mass insertion approximation. We obtain the next-to-leading order Wilson coefficients of the ΔF = 2 effective Hamiltonian relevant for neutral meson mixings. We find that the matching scale uncertainty is largely reduced at the next-to-leading order, typically from about 10-15% to few percent.

The fourth generation can give the correct trend of _ϕK⁰, _π⁰K⁰<sin 2ϕ₁, as indicated by data, and the effect, being largely leading order, is robust against hadronic uncertainties. The effect on _η'K⁰, however, is diluted away by hadronic effects, and _η'K⁰ ≃ sin 2ϕ₁ is expected. The near maximal arg V*_t'sV_t'b≲90° that is needed could resolve the unequal direct CP violation seen in B→K⁺π⁻ and K⁺π⁰ modes, and is consistent with b→sℓ⁺ℓ⁻ and B_s mixing constraints.

We investigate a class of CSO-gaugings of = 4 supergravity coupled to 6 vector multiplets. Using the CSO-gaugings we do not find a vacuum that is stable against all scalar perturbations at the point where the matter fields are turned off. However, at this point we do find a stable cosmological scaling solution.

We give analytic approximations to the baryon asymmetry produced by thermal leptogenesis with hierarchical right-handed neutrinos. Our calculation includes flavour-dependent washout processes and CP violation in scattering, and neglects gauge interactions and finite temperature corrections. Our approximate formulae depend upon the three CP asymmetries in the individual lepton flavours as well as on three flavour-dependent efficiency factors. We show that the commonly used expressions for the lepton asymmetry, which depend on the total CP asymmetry and one single efficiency factor, may fail to reproduce the correct lepton asymmetry in a number of cases. We illustrate the importance of using the flavour-dependent formulae in the context of a two right-handed neutrino model.

We consider the present absence of ν = 31/32 supersymmetric solutions in supergravity i.e., of solutions describing BPS preons. A recent result indicates that (bosonic) BPS preonic solutions do not exist in type IIB supergravity. We reconsider this analysis by using the G-frame method, extend it to the IIA supergravity case, and show that there are no (bosonic) preonic solutions for type IIA either. For the classical D = 11 supergravity no conclusion can be drawn yet, although the negative IIA results permit establishing the conditions that preonic solutions would have to satisfy. For supergravities with `stringy' (α')³-corrections, the existence of BPS preonic solutions remains fully open.

We further develop on the study of the conditions for the existence of locally stable non-supersymmetric vacua with vanishing cosmological constant in supergravity models involving only chiral superfields. Starting from the two necessary conditions for flatness and stability derived in a previous paper (which involve the Kähler metric and its Riemann tensor contracted with the supersymmetry breaking auxiliary fields) we show that the implications of these constraints can be worked out exactly not only for factorizable scalar manifolds, but also for symmetric coset manifolds. In both cases, the conditions imply a strong restriction on the Kähler geometry and constrain the vector of auxiliary fields defining the Goldstino direction to lie in a certain cone. We then apply these results to the various homogeneous coset manifolds spanned by the moduli and untwisted matter fields arising in string compactifications, and discuss their implications. Finally, we also discuss what can be said for completely arbitrary scalar manifolds, and derive in this more general case some explicit but weaker restrictions on the Kähler geometry.

We revisit the 't Hooft expansion of 1/2 BPS circular Wilson loop in = 4 SYM studied by Drukker and Gross in hep-th/0010274. We find an interesting recursion relation which relates different number of holes on the worldsheet. We also argue that we can turn on the string coupling by applying a certain integral transformation to the planar result.

Using 4D, = 1 superfield techniques, a discussion of the 6D sigma-model possessing simple supersymmetry is given. Two such approaches are described. Foremost it is shown that the simplest and most transparent description arises by use of a doublet of chiral scalar superfields for each 6D hypermultiplet. A second description that is most directly related to projective superspace is also presented. The latter necessarily implies the use of one chiral superfield and one nonminimal scalar superfield for each 6D hypermultiplet. A separate study of models of this class, outside the context of projective superspace, is also undertaken.

We consider instanton effects in a non-supersymmetric gauge theory obtained by marginal deformations of the = 4 SYM. This gauge theory is expected to be dual to type IIB string theory on the AdS₅ times deformed-S⁵ background. From an instanton calculation in the deformed gauge theory we extract the prediction for the dilaton-axion field τ in dual string theory. In the limit of small deformations where the supergravity regime is valid, our instanton result reproduces the expression for τ of the supergravity solution found by Frolov.

The standard prescription for computing Wilson loops in the AdS/CFT correspondence in the large coupling regime and tree-level involves minimizing the string action. In many cases the action has more than one saddle point as in the simple example studied in this paper, where there are two 1/4 BPS string solutions, one a minimum and the other not. Like in the case of the regular circular loop the perturbative expansion seems to be captured by a free matrix model. This gives enough analytic control to extrapolate from weak to strong coupling and find both saddle points in the asymptotic expansion of the matrix model. The calculation also suggests a new BMN-like limit for nearly BPS Wilson loop operators.

Using the language of theory space, i.e. moose models, we develop a unified framework for studying composite Higgs models at the LHC. This framework — denoted little M-theory — is conveniently described by a theoretically consistent three-site moose diagram which implements minimal flavor and isospin violation. By taking different limits of the couplings, one can interpolate between simple group-like and minimal moose-like models with and without T-parity. In this way, little M-theory reveals a large model space for composite Higgs theories. We argue that this framework is suitable as a starting point for a comprehensive study of composite Higgs scenarios. The rich collider phenomenology of this framework is briefly discussed.

We present a new version of our racetrack inflation scenario which, unlike our original proposal, is based on an explicit compactification of type IIB string theory: the Calabi-Yau manifold ⁴_[1,1,1,6,9]. The axion-dilaton and all complex structure moduli are stabilized by fluxes. The remaining 2 Kähler moduli are stabilized by a nonperturbative superpotential, which has been explicitly computed. For this model we identify situations for which a linear combination of the axionic parts of the two Kähler moduli acts as an inflaton. As in our previous scenario, inflation begins at a saddle point of the scalar potential and proceeds as an eternal topological inflation. For a certain range of inflationary parameters, we obtain the COBE-normalized spectrum of metric perturbations and an inflationary scale of M = 3 × 10¹⁴ GeV. We discuss possible changes of parameters of our model and argue that anthropic considerations favor those parameters that lead to a nearly flat spectrum of inflationary perturbations, which in our case is characterized by the spectral index n_s = 0.95.

We investigate classical solutions in closed bosonic string field theory and heterotic string field theory that are obtained order by order starting from solutions of the linearized equations of motion, and we discuss the ``field redefinitions'' which relate massless fields on the string field theory side and the low energy effective theory side. Massless components of the string field theory solutions are not corrected and from them we can infer corresponding solutions in the effective theory: the chiral null model and the pp-wave solution with B-field, which have been known to be α'-exact. These two sets of solutions on the two sides look slightly different because of the field redefinitions. It turns out that T-duality is a useful tool to determine them: We show that some part of the field redefinitions can be determined by using the correspondence between T-duality rules on the two sides, irrespective of the detail of the interaction terms and the integrating-out procedure. Applying the field redefinitions, we see that the solutions on the effective theory side are reproduced from the string field theory solutions.