Table of contents

Juan Barranco Physics Department, Guanajuato University, Loma del Bosque 103, col. Loma del Campestre, 37150, Leon (Mexico) jbarranc@fisica.ugto.mx

Guillermo Contreras Departamento de Fisica Aplicada Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Merida (Mexico) jgcn@mda.cinvestav.mx

David Delepine Physics Department, Guanajuato University, Loma del Bosque 103, col. Loma del Campestre, 37150, Leon (Mexico) delepine@fisica.ugto.mx

Mauro Napsuciale Physics Department, Guanajuato University, Loma del Bosque 103, col. Loma del Campestre, 37150, Leon (Mexico) mauro@fisica.ugto.mx

The XIII Mexican Workshop on Particles and Fields (MWPF) took place from 20–26 October 2011, in the city of León, Guanajuato, México. This is a biennial meeting organized by the Division of Particles and Fields of the Mexican Physical Society designed to gather specialists in different areas of high energy physics to discuss the latest developments in the field. The thirteenth edition of this meeting was hosted by the Department of Cultural Studies of Guanajuato University in a nice environment dedicated to the Arts and Culture.

The XIII MWPF was organized by three working groups who organized the corresponding sessions around three topics. The first one was Strings, Cosmology, Astroparticles and Physics Beyond the Standard Model. In this category we included: Cosmic Rays, Gamma Ray Bursts, Physics Beyond the Standard Model (theory and experimental searches), Strings and Cosmology. The working group for this topic was formed by Arnulfo Zepeda, Oscar Loaiza, Axel de la Macorra and Myriam Mondragón. The second topic was Hadronic Matter which included Perturbative QCD, Jets and Diffractive Physics, Hadronic Structure, Soft QCD, Hadron Spectroscopy, Heavy Ion Collisions and Soft Physics at Hadron Colliders, Lattice Results and Instrumentation. The working group for this topic was integrated by Wolfgang Bietenholz and Mariana Kirchbach. The third topic was Electroweak and Flavor Physics in whose classification we had Quark masses and mixing, Electroweak Symmetry Breaking, Heavy Quark Physics, Neutrinos, CP Violation, CKM and Rare Decays. The working group for this topic was formed by David Delepine, Lorenzo Díaz, Gerardo Herrera and Olga Félix Beltrán.

The three topics included invited talks dedicated to reviewing theoretical and experimental aspects of the corresponding topic. We had also plenary topical sessions during the mornings and early afternoons and parallel thematic sessions were held late in the afternoons. The reviews sessions were delivered by invited speakers of international prestige on the corresponding subjects and having an active collaboration with the Mexican scientific community. The plenary topical sessions and parallel thematic sessions were given by active researchers both from abroad and working in México. The program included also a permanent poster session and the organizing committee awarded the best poster – a decision made by the three working groups – with a silver medal.

On Sunday 23 October, we had an excursion to the ancient archaeological site of Plazuelas near Penjamo (Guanajuato). Plazuelas is a prehispanic archaeological site located just north of San Juan el Alto, some 2.7 kilometers north of federal highway 90 (Penjamo-Guadalajara), and about 11 kilometers west of the city of Penjamo in the state of Guanajuato, Mexico. The site has been recently opened to the public. This site is a very complex city, it was edified following the natural landscape surrounding it. This city was occupied between 600 and 900 a.C.

After spending some time at this very interesting archaeological site, we went to Hacienda Corralejo, an hacienda where Tequila Corralejo is produced and we had a guided visit of the 'Tequilera' where the famous Corralejo blue bottle of Tequila is made. Hacienda Corralejo is very close to the orginal Hacienda where Miguel Hidalgo (a Mexican independence hero) was born which now is just a set of foundations and a portal, considered national monuments. There, we enjoyed a delicious meal in the cellars of the Corralejo Hacienda before returning to Leon.

The XIII MWPF was sponsored by several institutions: Consejo Nacional de Ciencia y Tecnología (CONACyT) through the Red Nacional de Física de Altas Energías and individual research projects, Consejo de Ciencia y Tecnológico del Estado de Guanajuato (CONCyTEG), Universidad de Guanajuato, Universidad Nacional Autónoma de México, Universidad de Guanajuato, Centro de Investigaciones de Estudios Avanzados del IPN (CINVESTAV), Universidad Michoacana de San Nicolás de Hidalgo, Benemérita Universidad Autónoma de Puebla and Universidad Autónoma de San Luis Potosí. Also, we wish to thak to those who helped in the process of getting financial support for the meeting, specially Dr Juan Carlos D'Olivo, President of the Red Nacional de Física de Altas Energías and Dr José Luis Lucio Martínez, Rector of Universidad de Guanajuato, Campus León. These proceedings have been published thanks to the support of PIFI 2011.

This meeting was possible due to the commitment of the working groups and we wish to thank to their members for the decisive collaboration with the organizing committee. At the local level, we thank our graduate students: Carolina Luján, Vannia González, Selim Gomez and Carlos Alberto Vaquera for their invaluable contribution in the organization of the large amount of small but important things around the meeting.

Finally, we would like to thank all the speakers for delivering excellent talks which contributed to the success of the event. We are also grateful to all the participants for the nice academic and social atmosphere during the meeting and for providing their write-ups on time.

The National organizing committee was formed by

• Arnulfo Zepeda (CINVESTAV-DF)

• Guillermo Contreras (CINVESTAV-Mérida)

• David Delepine (DF-UG)

• Axel de la Macorra (IAC/IF-UNAM)

• Lorenzo Díaz (BUAP)

• Gerardo Herrera (CINVESTAV-DF)

• Mariana Kirchbach (IF-UASLP)

• Oscar Loaiza (DF-UG)

• Myriam Mondragón (IF-UNAM)

• Mauro Napsuciale (DF-UG)

• Humberto Salazar Ibarguen (BUAP)

• Andrés Sandoval (IF-UNAM)

• Juan Carlos D_Olivo (ICN-UNAM)

• Wolfgang Bietenholz (ICN-UNAM)

• Olga Félix Beltrán (BUAP)

Dinner in the cellars of Hacienda Corralejo.

Visit to Hacienda Corralejo.

The PDF contains the conference programme.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We show the results and discussions of the study of a possible suppression of the extragalactic neutrino flux during its propagation due to a nonstandard interaction with a candidate field to dark matter. In particular, we show the study of neutrino interaction with an ultra-light scalar field. It is shown that the extragalactic neutrino flux may be suppressed by such an interaction, leading to a mechanism to reduce the ultra-high energy neutrino flux. We calculate both the cases of non-self-conjugate as well as self-conjugate ultra-light dark matter. In the first case, the suppression is independent of the neutrino and dark matter masses. We conclude that care must be taken when explaining limits on the neutrino flux through source acceleration mechanisms only, since there could be other mechanisms, as absorption during propagation, for the reduction of the neutrino flux [1],

We study a type IIB superstring compactification in the presence of nong-eometric fluxes. We study the non supersymmetric solutions to the equations of motion. The corresponding vacuum is found by employing a genetic algorithm constrained by the Bianchi identities. We explore the space of the non supersymmetric vacua and look for possible De Sitter solutions. We find that such vacua are possible if supersymmetry is broken by all the three moduli.

The High Altitude Water Cherenkov detector is a gamma-ray observatory which is able to scan the sky in energy from 100 GeV to 100 TeV and will be localized at Sierra La Negra volcano at 4100 m a.s.l. near to Puebla, México. In 2011 an engineering array called VAMOS was installed and in 2012, it will start the deployment of HAWC first step, the HAWC-30 array, with 30 water Cherenkov detectors. In this work it is presented the results of simulations where the goal is to get Fano factor in order to simulate the HAWC-30 array sensibility to gamma-ray bursts using the single particle technique.

We construct a supersymmetric higher dimensional theory which includes 5D Lorentz violation terms in a superfield formalism. We show that in order to obtain a consistent construction which incorporates the most general terms that explicitly breaks the 5D Lorentz invariance, it is only necessary to redefine the supersymmetric auxiliary fields. We also analyze the meaning of these violation terms and point out the possibility of resizing the radius of compactification to obtain an equivalent 4D Lorentz invariant effective theory.

Centaurus A and M87 are the closest galaxies with active galactic nuclei and TeV γ-ray emission. The existence of such TeV radiation suggests the production of a neutrino flux from the photo-hadronic interactions of the γ-photons and the gas and dust content of the active galaxies. Using a simple model of Centaurus A and M87, the corresponding ν luminosities at source and their fluxes at Earth were calculated. The neutrino fluxes associated with the aforementioned process resulted to be E²Φ_ν+ ≲ 10⁻¹³ s⁻¹ GeVcm⁻², more than 6 orders of magnitude below the modern upper limits from neutrino telescopes. It will be shown that, at high-energies, relevant for neutrino astronomy, these ν fluxes are not competitive with those fluxes derived from astrophysical scenarios involving cosmic ray acceleration.

We present a 10 dimensional supergravity compactification threaded with a simple flux configuration of Neveu-Schwarz-Neveu-Schwarz (NS-NS) and Ramond-Ramond (RR) 3-form fluxes to obtain the near-horizon geometry of an extremal black hole, namely, the Robinson-Bertotti solution. The constraints and conditions that fluxes must fulfill to attain an AdS₂ × S² symmetry in 4d space-time, were found by Einsteins equations, Bianchi identities and by the integrability conditions of 10d chiral spinors.

The Supersymmetric models predicts the existence of light neutralinos with masses around 50 GeV as good candidates for detection of physics beyond the Standard Model, as well as other supersymmetric particles for different channels of Higgs boson decays. It this work, we presented the branching ratios of the lightest Higgs boson to neutralinos and charginos in the context of the Minimal Supersymmetric Standard Model. Although the invisible modes have been studied previously, is not known in detail the region of parameter space for supersymmetric sector where the mode reaches a significant branching ratio. We presented the analysis the parameters space looking for these regions by sampling techniques.

By recalling the relevance of the Sturm-Liouville theory has had on the solutions of quantum mechanics problems, here it is explored the possibility of getting some insight to the solutions for a standard cosmology model for inflation, from a time independent Schrödinger type equation derived from the equations of motion for a single scalar field in a flat space time with a FRW metric and a cosmological constant.

The effects of phase space deformations in standard scalar field cosmology are studied. The deformation is introduced by modifying the symplectic structure of the minisuperspace variables to have a deformed Poisson algebra among the coordinates and the canonical momenta. The resulting theory is knowns as noncomutative cosmology. We show the effects of this deformation in scalar field cosmology and establish a relationship between the noncommutative parameters and Λ. This work is based on the papers, arXiv:1111.6137 and arXiv:1111.6136.

Many theoretical attempts at understanding the Planck-scale structure of spacetime can accommodate minute departures from Lorentz and CPT invariance. At presently attainable energies, such effects are expected to be accurately described within effective field theory. Such a field theory, in turn, can be employed to identify currently feasible experimental tests. This work presents an overview of the theoretical motivations, the low-energy framework, and the phenomenological implications within this context.

We review some of the mechanisms that string theory offers to address phenomenological questions, such as the origin of our observable four-dimensional space-time, the standard model gauge symmetries and matter, as well as the possible source of the inflationary epoch. These notes are not comprehensive but attempt to provide a general view of the current search for physics cases within the context of string model building.

In the last time the cold dark matter (CDM) model has suggested more and more that it is not able to describe all the properties of nearby galaxies that can be observed in great detail as well as that it has some problems in the mechanism by which matter is more rapidly gathered into large-scale structure such as galaxies and clusters of galaxies. In this work we revisit an alternative model, the scalar field dark matter (SFDM) model, which proposes that the galactic haloes form by condensation of a scalar field (SF) very early in the Universe, i.e., in this model the haloes of galaxies are astronomical Bose-Einstein Condensate drops of SF. On the other hand, large-scale structures like clusters or superclusters of galaxies form similar to the ACDM model, by hierarchy, thus all the predictions of the ACDM model at cosmological scales are reproduced by SFDM. This model predicts that all galaxy haloes must be very similar and exist for higher redshifts than in the ACDM model. In the first part of this review we revisit the cosmological evolution of SFDM model with a scalar potential m²Φ²/2 + λΦ⁴/4 with two different frameworks: the field and fluid approach. We derive the evolution equations of the SF in the linear regime of perturbations as well. The scalar fluctuations have an oscillating growing mode and therefore, this kind of dark matter could lead to the early formation of gravitational structures in the Universe. We also revisit how BEC dark matter haloes exhibit a natural cut of the mass power spectrum. In the second part, we study the core central density profiles of BEC dark matter haloes and fit high-resolution rotation curves, we show a sample of some low surface brightness galaxies. The mean value of the logarithmic inner density slopes is α = −0.27 ± 0.18. Using a model independent new definition of the core in the BEC density profile, we show that the recent observation of the constant dark matter central surface density can be reproduced. We conclude that in light of the difficulties that the ΛCDM model is currently facing the SFDM model can be a worthy alternative to keep exploring further.

We calculate the magnetic dipole moment (MDM) and the electric dipole moment (EDM) of a lepton induced by a vector unparticle with both vector and axial-vector couplings to leptons. We consider the most general scenario in which the unparticle induces lepton flavor violation (LFV) and CP violation. Some specific scenarios are examined to obtain constraints on the LFV unparticle couplings from the current limits on the muon MDM and the decay τ → 3μ. While the experimental limit on the muon MDM favor the scenario in which there is dominance of the unparticle vector couplings over the axial-vector couplings, the experimental limit on the τ → 3μ decay strongly constraints the unparticle LFV couplings. We use these constraints to estimate the EDMs of the electron and the muon, which are negligible and far from the current experimental limits.

In this work, discuss neutrino masses and mixings in the framework of a minimal S₃ symmetric extension of the Standard Model. In this model, the mass matrices of all fermions take the same generic form with two texture zeroes. The mass matrices of the neutrinos and charged leptons are re-parameterized in terms of their eigenvalues, then the neutrino mixing matrix, V_PMNS, is computed and exact, explicit analytical expressions for the neutrino mixing angles as functions of the masses of neutrinos and charged leptons are obtained in excellent agreement with the latest experimental data. We also compute the branching ratios of some selected flavour-changing neutral current (FCNC) processes, as well as the contribution of the exchange of neutral flavour-changing scalars to the anomaly of the magnetic moment of the muon, as functions of the masses of charged leptons and the neutral Higgs bosons. We find that the S₃ × Z₂ flavour symmetry and the strong mass hierarchy of the charged leptons strongly suppress the FCNC processes in the leptonic sector, well below the present experimental bounds by many orders of magnitude. The contribution of FCNC's to the anomaly of the muon's magnetic moment is small, but not negligible.

The main ingredients and the importance of the process are described: its contribution to reveal the true nature of the scalar K*₀ particle, what we know about the parametrization of its dynamics, its importance for CPV in the charm physics and possible new physics contributions.

In the framework of the two Higgs doublet model we graphically illustrate the energy dependence of the Higgs masses and the quartic couplings. Our results are based on the theoretical constraints on the quartic Higgs couplings through the stability and triviality principles that are obtained, using the Lagrange multipliers method and the numerical solutions of the Renormalization Group Equations that give the energy dependence of the parameters of the Lagrangian. From these solutions we can also establish the region of validity of the model in terms of the initial conditions of the parameters.

In this work we study the possibility of new tensorial interactions in neutrino electron scattering. Two new physics schemes are considered, the non standard interactions formalism (NSI) as well as the Unparticle stuff case. Constraints in tensorial couplings are obtained for both cases focusing on the TEXONO collaboration recent results. For the case of tensorial unparticles we find that previous limits are improved, for a given region of parameters, with the analysis of TEXONO data, and for the NSI tensorial parameters, the limit obtained is more restrictive than previous bounds reported in the literature.

Single top quark production at lepton (or non-hadronic) colliders like the e⁺e⁻ International Linear Collider (ILC) can be used to obtain high precision measurements of the V_tb CKM matrix element as well as the effective tbW coupling. For the ILC we have calculated the QCD correction for the cross section in the context of an effective vector boson approximation. Our results show a ∼ 10% increase due to the strong interaction.

In this paper we discuss supersymmetric contributions to the direct CP asymmetries of B → πK* and B → ρK decays. We use Soft Collinear Effective Theory as a framework for our study. We show that within the standard model and including the next leading order QCD corrections, the predicted CP asymmetries can not accommodate the experimental measurements. We show that non-minimal flavor SUSY contributions mediated by gluino exchange can enhance the CP asymmetries significantly to accommodate the experimental measurements.

We study the rare top decay t → cl, which involves flavor violation, as a possible probe of new physics. This decay is analyzed with the simplest Standard Model (SM) extensions with additional gauge symmetry U(l) or SU(2), known as generic Z' model or left-right symmetric model, respectively. The considered models allow to obtain this decay at tree level through Flavor Changing Neutral Currents (FCNC). We have considered diagonal non-universal couplings for up-type quark sector and found that BR(t → cl) for 1 TeV < M_z' < 3 TeV can be of order ∼ 10⁻¹¹ in generic Z' model or ∼ 10⁻¹² in left-right symmetric model.

The study of the phenomenology of an extra neutral gauge boson, Z_H, can help us to unravel the underlying theory from which this particle arises. We study the decay of such a particle into two neutral gauge bosons, Z_H → Z_γ and Z_H → ZZ, in the littlest Higgs model. These decays are induced at the one-loop level by a fermion triangle and are interesting as they are strongly dependent on the mechanism of anomaly cancellation of the model. Other relevant tree-level two- and three-body Z_H decays are also calculated. It is found that the branching ratios for the Z_H → γZ decays can be as large as that of a tree-level three-body decay but the Z_H → ZZ decay is very suppressed. We also discuss the experimental prospects for detecting these decays at the LHC.

Flavor violating tu_iH vertex induces top quark couplings tcy and tu_iγγ (u_i = u, c) at the one-loop level, in the effective Yukawa sector through dimension six SU_L(2) × U_Y(1)-invariant operators. The t → cH and t → cγγ decays can reach branching ratios about 5 × 10⁻³ and 10⁻⁴ respectively. As for tc production, it is found that, due to the presence of a resonant effect in the convoluted cross section σ(e⁺e⁻ → γγ → t + c), about (0.5 − 2.7) × 10³tc events may be produced at the ILC for m_H ∼ m_t.

The 2HDM has been one of the most studied extensions of the SM, due to its simple form and wealthy new phenomenology. Most versions are characterized by the mechanism through which the FCNC are controlled. In order to give to the 2HDM the status of an intermediate step in the rank of energies (that is, a low energy limit between the electroweak scale and the characteristic scale of the general theory), a mechanism to relate several versions of the 2HDM is given. This mechanism exploits the flavour symmetry of the Yukawa Lagrangian and the fact that the mass generation comes from a yet unknown property of the vacuum but related with the CKM entries in the case of quarks.

The experimental observation of lepton number violating (LNV) processes, where the total lepton number is violated by two units (ΔL = 2), represents the most appropriate way to address the question of the nature of the neutrinos as Majorana or Dirac particles. LNV processes mediated by the exchange of heavy Majorana neutrinos, such as three-body decays of τ leptons and charged pseudoscalar mesons, have been widely studied. In this work we study the contribution of heavy Majorana neutrinos in LNV four-body semileptonic decays of neutral B mesons and top quarks. We focus in a scenario where a single heavy neutrino can enhance the decay rates of these processes via the resonant mechanism. Using current bounds on heavy neutrino mixings, we find that the branching ratios of these processes can be at the level of 10⁻⁶ to 10⁻⁷. These decay modes seem to be at the reach of the current and forthcoming experiment, and their experimental search can provide complementary constraints on masses and mixings of heavy Majorana neutrinos.

We present the calculation for the strength of the lepton flavor violating Z'μτ coupling, in which the experimental result of the muon magnetic dipole moment was used to bound this vertex, by means of a model-independent approach. The Z'μτ vertex is represented by the Ω_μτ parameter, which is of the order of 10⁻² for a Z' boson mass of 1 TeV.

We discuss the formulation of the general two-Higgs doublet model type III, which incorporates flavor changing neutral scalar interactions (FCNSI) and CP violation from several sources. CP violation can arise either from Yukawa terms or from the Higgs potential, be it explicit or spontaneous. We discuss the limit that includes CP violation and Yukawa four textures to control FCNSI and evaluate the CP asymmetry for the decay h → bcW, which may allow to test the patterns of FCNSI and CP violation, that arises in these models.

We will briefly present a new derivation of the most general form of the Higgs potential with the highest degree of S₃ flavour symmetry. The discussion will be made in the framework of the Minimal S₃-Invariant Extension of the Standard Model (MS₃IESM). In this form of the theory, the Higgs sector has three flavoured Higgs fields that are SU(2)_L doublets and belong to a reducible 1 ⊕ 2 representation of the S₃ flavour symmetry. Requiring the highest degree of S₃ flavour symmetry, the Higgs potential, in its most general form, has only six self-couplings.

The SuperB project is a very ambitious program whose goal is to build, in the immediate vicinity of the Frascati National Laboratory, a e⁺e⁻ collider operating in the Υ(4S) region with a luminosity in excess of 10³⁶ Hz/cm⁻² surpassing by two orders of magnitude the present generation. Such a progress has ben made possible by the new Crab Waist colliding scheme together with the design of very low emittance rings. The physics goal of this machine is to determine the structure of the new physics (NP) at the Terascale that is likely to show up at the LHC. This will be possible through a very detailed scrutiny of all NP induced indirect effects in rare (or even forbidden in the Standard Model)decays and precision measurements in the quark and lepton sectors. The project, an official element of the European HEP Strategy, has been recently approved and fully funded by the Italian government. The site has been selected and the detector collaboration is currently being formed. The first beams are expected in 2016, with a yearly integrated luminosity of 15 ab⁻¹.

The properties of the nuclear modification factor for heavy flavors are usually attributed to the energy loss suffered by the heavy quark propagating in a QCD plasma. Nevertheless it is a bit surprising that the suppression of this factor is as strong as the one suffered by light flavors. In this work we show that when accounting for the momentum shift associated to the opening of the recombination channel to produce hadrons in the QCD plasma, it is not necessary to invoke such a strong energy loss. We show that when the heavy baryon to meson ratio is larger in nuclear than in proton collisions, data from RHIC and LHC for the nuclear modification factor of electrons coming from heavy flavor decays as well as for charmed masons can be accounted for.

The LHCb experiment was presented with emphasis on the performance during the 2010 and 2011 runs. In addition, a selection of the first few competitive physics results were presented.

We present status of a search for two rare of the Z boson, Z⁰ → J/ψγ and Z⁰ → Υγ at CDF. The state of analysis is described at the time of this worksop.

The time evolution of the matter produced in high energy heavy-ion collisions seems to be well described by relativistic viscous hydrodynamics. In addition to the hydrodynamic degrees of freedom related to energy-momentum conservation, degrees of freedom associated with order parameters of broken continuous symmetries must be considered because they are all coupled to each other. Of particular interest is the coupling of degrees of freedom associated with the chiral symmetry of QCD. Quantum and thermal fluctuations of the chiral fields act as noise sources in the classical equations of motion, turning them into stochastic differential equations in the form of Ginzburg-Landau-Langevin (GLL) equations. Analytic solutions of GLL equations are attainable only in very special circumstances and extensive numerical simulations are necessary, usually by discretizing the equations on a spatial lattice. However, a not much appreciated issue in the numerical simulations of GLL equations is that ultraviolet divergences in the form of lattice-spacing dependence plague the solutions. The divergences are related to the well-known Rayleigh-Jeans catastrophe in classical field theory. In the present communication we present a systematic lattice renormalization method to control the catastrophe. We discuss the implementation of the method for a GLL equation derived in the context of a model for the QCD chiral phase transition and consider the nonequilibrium evolution of the chiral condensate during the hydrodynamic flow of the quark-gluon plasma.

We use a second order formalism based on Poincaré symmetry, and known as Covariant Projector Formalism to calculate the electromagnetic currents of spin 1/2, spin 1 and spin 3/2 particles. We restrict to parity conserving processes and obtain the currents in terms of the gyromagnetic factor g alone. This parameter is then fixed by calculating the forward Compton scattering cross section. In the end we reproduce the Dirac moments for the electron from a more general second order Lagrangian, we also reproduce the Standard Model results for the W boson. In the spin 3/2 case we show that the RS current is incomplete as it does not include the spin 1 piece of the vector-spinor representation. As a consequence, when we calculate the spin 3/2 EM moments, instead of the universal value g = 2, we find g = 2/3 as the gyromagnetic ratio for a Rarita-Schwinger particle.

A systematic low-energy effective field theory for hole-doped antiferromagnets on the honeycomb lattice is constructed. The formalism is then used to investigate spiral phases in the staggered magnetization as well as the formation of two-hole bound states.

We perform a variational Monte Carlo simulation of a system consisting of two quarks and two antiquarks. Using a dynamical model of the strong interaction (string-flip model) we explore the formation of mesons and/or a tetraquark for a set of different density conditions. We characterize the single properties of these states and the modifications upon the mixing. The competition among the different configurations and its implications on several observables are exhibited.

We show that though conformal symmetry can be broken by the dilaton, such can happen without breaking the conformal degeneracy patterns in the spectra. Our argumentation goes as follows: We departure from the gauge-gravity duality which predicts on the boundaries of the AdS₅ geometry a conformal theory, associated with QCD at high temperatures, and consider S¹ × S³ slicing. The inverse radius, R, of S³ relates to the temperature of the deconfinement phase transition and has to satisfy, ℏc/R ≫ Λ_QCD. On S³, whose isometry group is SO(4), we then focus on the eigenvalue problem of the conformal Laplacian there, given by , with standing for the Casimir invariant of the so(4) algebra. This eigenvalue problem describes the spectrum of a scalar particle, to be associated with a q system. Such a spectrum is characterized by a (K + l)²-fold degeneracy of its levels, with K ∊ [0, ∞). We then break the conformal S³ metric, ds² = dχ² + sin² χ(dθ² + sin²θdφ²) -in polar chi;,θ, and azimuthal φ coordinates- according to, ds^∼2 = e^−bχ((1 + b²/4)dχ² + sin²chi;(dθ² + sin²θdφ²)), and attribute the symmetry breaking scale bℏ²c²/R² to the dilaton. Next we show that the above metric deformation is equivalent to a breaking of the conformal curvature of S³ by a term proportional to b cot χ, and that the perturbed conformal Laplacian is equivalent to , with c_κ a representation constant, and being again an so(4) Casimir invariant, but this time in a representation unitarily nonequivalent to the 4D rotational one. As long as the spectra before and after the symmetry breaking happen to be determined each by eigenvalues of a Casimir invariant of an so(4), no matter whether or not in a representation that generates the orthogonal group SO(4) as a subgroup of the conformal group SO(2,4), the degeneracy patterns remain unaltered though the conformal symmetry breaks at the level of the representation of the algebra. We fit the S³ radius and the ℏ²c²b/R² scale to the high-lying excitations in the spectra of the unflavored mesons, and observe the correct tendency of the ℏc/R = 373 MeV value to notably exceed Λ_QCD. The size of the symmetry breaking scale is calculated as MeV.

A numerical solution of the coupled Dyson-Schwinger equations for the ghost and gluon propagators in Yang-Mills theory is presented in Landau gauge. Aimed at investigating the infrared behavior of the propagators, the equations are simplified by neglecting the gluon loops, according to the ghost dominance hypothesis motivated by the Gribov-Zwanziger scenario. The equations are solved with an iterative method, eliminating the ultraviolet divergence through a continuous regulator function depending on the cut off scale. The solutions, derived for different values of the Euclidean space-time dimension, present scaling (the infrared exponents are obtained) or decoupling behavior, depending on whether the horizon condition is or not implemented. Moreover, it is shown that the running coupling constant approaches a constant value in the IR, corresponding to an attractive fixed point.

We present a review of some recent results obtained in the unquenched quark model for baryons. The effects of sea quarks are taken into account in an explicit form via a QCD-inspired creation mechanism of the quark-antiquark pairs. In this approach, the contribution of the quark-antiquark pairs can be studied for any inital baryon and for any flavor of the q pairs (uū, d and s). It is shown that, whereas the inclusion of q pairs (or meson loops) does not affect the baryon magnetic moments, it immediately leads to an excess of over ū in the proton and introduces a sizeable contribution of orbital angular momentum to the spin of the proton. The contribution of s pairs to the magnetic moment and the radius of the proton is found to be small, in agreement with the latest experimental results and recent lattice calculations.

We discuss how to compute corrections to one-loop order to the baryon axial-vector current and magnetic moments in heavy baryon chiral perturbation theory in the large-N_c limit, where N_c is the number of colors. Loop graphs with octet and decuplet intermediate states cancel to various orders in N_c as a consequence of the large-N_c spin-flavor symmetry of QCD baryons. These cancellations are explicitly shown for the general case of N_f flavors of light quarks. We also indicate how to compare our resultant expressions with the corresponding ones obtained within conventional heavy baryon chiral perturbation theory at the physical values N_c = 3, N_f = 3. We observe an excellent agreement order by order.

We determine the value of the ω − ρ − π mesons coupling (g_ωρπ), in the context of the vector meson dominance model, from radiative decays, the ω → 3π decay width and the e⁺e⁻ → 3π cross section. For the last two observables we consider the effect of either a heavier resonance (ρ'(1450)) or a contact term . A weighted average of the results from the set of observables yields g_ωρπ = 13.9 ± 0.1 GeV⁻¹ in absence of those contributions, and g_ωρπ = 11.9 ± 0.2 GeV⁻¹ or g_ωρπ = 11.4 ± 0.1 GeV⁻¹ when including the p' or contact term respectively. Improved measurements of these observables and the p'(1450) meson parameters are needed to give a definite answer on the pertinence of the inclusion of this last one in the considered processes.

In gauge theories the field configurations often occur in distinct topological sectors. In a lattice regularised system with chiral fermions, these sectors can be defined by referring to the Atiyah-Singer Index Theorem. However, if such a model is simulated with local updates of the lattice gauge configuration, the Monte Carlo history tends to get stuck in one sector for many steps, in particular on fine lattices. Then expectation values can be measured only within specific sectors. Here we present a pilot study in the 2-flavour Schwinger model which explores methods of approximating the complete result for an observable — corresponding to a suitable sum over all sectors — based on numerical measurements in a few specific topological sectors. We also probe various procedures for an indirect evaluation of the topological susceptibility, starting from such topologically restricted measurements.

The infrared behavior of gluon and ghost propagators in Landau gauge Yang-Mills theory has been at the center of an intense debate over the last decade. Different solutions of the Dyson-Schwinger equations have a different behavior of the propagators in the infrared: in the so-called scaling solutions both propagators follow a power law, while in the decoupling solutions the gluon propagator shows a massive behavior. The latest lattice results favor the decoupling solutions. In this contribution, after giving a brief overview of the present status of analytical and semi-analytical approaches to the infrared regime of Landau gauge Yang-Mills theory, we will show how Callan-Symanzik renormalization group equations in an epsilon expansion reproduce both types of solutions and single out the decoupling solutions as the infrared-stable ones for space-time dimensions greater than two, in agreement with the lattice calculations.