arXiv subjects

Alfonso Ballon-Bayona

Publications and source records attributed to Alfonso Ballon-Bayona.

24 records · Page 2Linked to original sources

arXiv2016

Soft Pomeron in Holographic QCD

We study the graviton Regge trajectory in Holographic QCD as a model for high energy scattering processes dominated by soft pomeron exchange. This is done by considering spin J fields from the closed string sector that are dual to glueball states of even spin and parity. In particular, we construct a model that governs the analytic continuation of the spin J field equation to the region of real J < 2, which includes the scattering domain of negative Maldelstam variable t. The model leads to approximately linear Regge trajectories and is compatible with the measured values of 1.08 for the intercept and 0.25 GeV$^{-2}$ for the slope of the soft pomeron. The intercept of the secondary pomeron trajectory is in the same region of the subleading trajectories, made of mesons, proposed by Donnachie and Landshoff, and should therefore be taken into account.

hep-ph↗

arXiv2014

Decay constants of the pion and its excitations in holographic QCD

We investigate the leptonic decay constants of the pion and its excitations with a 5-d holographic model for quantum chromodynamics. We prove numerically that the leptonic decay constants of the excited states of the pion vanish in the chiral limit when chiral symmetry is dynamically broken. This nontrivial result is in agreement with a solid prediction of quantum chromodynamics and is based on a generalized Gell-Mann-Oakes-Renner relationship involving the decay constants and masses of the excited states of the pion. We also obtain an extended partially conserved axial-vector current relation that includes the fields of the excited states of the pion, a relation that was proposed long ago in the context of current algebra.

hep-ph↗

arXiv2013

Holographic deconfinement transition in the presence of a magnetic field

We investigate the thermodynamics of the flavour sector of the Sakai-Sugimoto model in the presence of a magnetic field. Renormalizing the euclidean Dirac-Born-Infeld action in the antipodal limit, we find for the confined and deconfined phases positive contributions to the pressures that grow with the magnetic field. We also obtain positive magnetic susceptibilities indicating a paramagnetic behaviour of quarks. Using these results we estimate a λ^2/N_c correction to the deconfinement temperature that decreases as a function of the magnetic field.

hep-th↗

arXiv2013

DBI equations and holographic DC conductivity

We provide a simple method for writing the Dirac-Born-Infeld (DBI) equations of a Dp-brane in an arbitrary static background whose metric depends only on the holographic radial coordinate z. Using this method we revisit the Karch-O'Bannon's procedure to calculate the DC conductivity in the presence of constant electric and magnetic fields for backgrounds where the boundary is four or three dimensional and satisfies homogeneity and isotropy. We find a frame-independent expression for the DC conductivity tensor. For particular backgrounds we recover previous results on holographic metals and strange metals.

hep-th↗

arXiv2012

Production of negative parity baryons in the holographic Sakai-Sugimoto model

We extend our investigation of resonance production in the Sakai-Sugimoto model to the case of negative parity baryon resonances. Using holographic techniques we extract the generalized Dirac and Pauli baryon form factors as well as the helicity amplitudes for these baryonic states. Identifying the first negative parity resonance with the experimentally observed S_{11}(1535), we find reasonable agreement with experimental data from the JLab-CLAS collaboration. We also estimate the contribution of negative parity baryons to the proton structure functions.

hep-ph↗

arXiv2012

A chiral magnetic spiral in the holographic Sakai-Sugimoto model

We investigate the effect of a magnetic field on the vacuum of low-temperature QCD at large-N_c in the presence of a chiral chemical potential, using the holographic Sakai-Sugimoto model. Above some critical chemical potential we find an instability, which triggers a decay of the homogeneous vacuum to a non-homogeneous configuration with a spiral form, which we construct explicitly. We find that this decay is suppressed for sufficiently large magnetic field, and determine the critical strength. We find that the new vacuum does not exhibit the chiral magnetic effect. This is related to the way the chiral chemical potential is introduced. We discuss an alternative way of introducing the chiral chemical potential that leads to a nonzero chiral magnetic effect.

hep-th↗