Marcus A. C. Torres

Angular Structure of the In-Medium QCD Cascade.

We study the angular broadening of a medium-induced QCD cascade. We derive the equation that governs the evolution of the average transverse momentum squared of the gluons in the cascade as a function of the medium length, and we solve this equation analytically. Two regimes are identified. For a medium of a not too large size, and for not too soft gluons, the transverse momentum grows with the size of the medium according to standard momentum broadening. The other regime, visible for a medium of a sufficiently large size and very soft gluons, is a regime dominated by multiple branchings: there, the average transverse momentum saturates to a value that is independent of the size of the medium. This structure of the in-medium QCD cascade is, at least qualitatively, compatible with the recent LHC data on dijet asymmetry.

Pion and vector meson form factors in the Kuperstein-Sonnenschein holographic model

We study phenomenological aspects of the holographic model of chiral symmetry breaking recently introduced by Kuperstein and Sonnenschein (KS). As a first step, we calculate the spectrum of vector and axial-vector mesons in the KS model. We numerically compute various coupling constants of the mesons and pions. Our analysis indicates that vector meson dominance is realized in this model. The pion, vector meson and axial-vector meson form factors are obtained and studied in detail. We find good agreement with QCD results. In particular, the pion form factor closely matches available experimental data.

Deep inelastic scattering for vector mesons in holographic D4-D8 model

We study deep inelastic scattering for vector and axial vector mesons in the holographic D4-D8 brane model. We consider tree level contributions with one particle in the final hadronic state. We obtain the unpolarized structure functions F1 and F2 for the ρ and a1 mesons for q2 < 80 GeV2 and 0.2 < x < 1. We find that the ratio F2/(2xF1) is approximately equal to one for some ranges of x and q2, satisfying the Callan-Gross relation.

Form factors of vector and axial-vector mesons in holographic D4-D8 model

We calculate elastic and non-elastic electromagnetic form factors for vector and axial-vector mesons in the holographic D4-D8 brane model. We obtain the mass spectrum and Regge trajectories for these particles. From the elastic form factors we extract the electric radius, the magnetic and quadrupole moments. Form factors for transverse and longitudinal polarizations are also obtained. We find superconvergence sum rules for the vector and axial-vector meson couplings that determine the asymptotic behavior of the form factors at large momentum transfer. Our results show good agreement with other holographic models and QCD.

Scalar and vector mesons of flavor chiral symmetry breaking in the Klebanov-Strassler background

Recently, Dymarsky, Kuperstein and Sonnenschein constructed an embedding of flavor D7- and anti-D7-branes in the Klebanov-Strassler geometry that breaks the super-symmetry of the background, yet is stable. In this article, we study in detail the spectrum of vector mesons in this new model of flavor chiral symmetry breaking and commence an analytical study of the scalar mesons in this setup.

Generalized baryon form factors and proton structure functions in the Sakai–Sugimoto model

Abstract We investigate the production of positive parity baryon resonances in proton electromagnetic scattering within the Sakai–Sugimoto model. The latter is a string model for the non-perturbative regime of large N c QCD. Using holographic techniques we calculate the generalized Dirac and Pauli form factors that describe resonance production. We use these results to estimate the contribution of resonance production to the proton structure functions. Interestingly, we find an approximate Callan–Gross relation for the structure functions in a regime of intermediate values of the Bjorken variable.

Anomalous dimensions and scalar glueball spectroscopy in AdS/QCD

An extended version of the AdS/QCD soft-wall model that incorporates QCD-like anomalous contributions to the dimensions of gauge theory operators is proposed. This exploratory approach leads to a relation between scalar glueball masses and beta functions. Using this relation, the properties of the glueball mass spectroscopy that emerge from phenomenological beta functions proposed in the literature are investigated. The reverse problem is also considered: starting from a linear Regge trajectory which fits the lattice glueball masses, beta functions with different asymptotic infrared behaviors are found. Remarkably, some of them present a fixed point at finite coupling.

Cluster algebras in scattering amplitudes with special 2D kinematics

We study the cluster algebra of the kinematic configuration space

Relativistic baryons in the Skyrme model revisited

{{\mathrm{Conf}}}_n(\mathbb {P}^3)