Chiral symmetry breaking and pions in nonsupersymmetric gauge/gravity duals

Abstract

We study gravity duals of large N non-supersymmetric gauge theories with matter in the fundamental representation by introducing a D7-brane probe into deformed AdS backgrounds. In particular, we consider a D7-brane probe in both the AdS Schwarzschild black hole solution and in the background found by Constable and Myers, which involves a non-constant dilaton and S 5 radius. Both these backgrounds exhibit confinement of fundamental matter and a discrete glueball and meson spectrum.We numerically compute theΨΨ condensate and meson spectrum associated with these backgrounds.In the AdS-black hole background, a quark-bilinear condensate develops only at non-zero quark mass.We speculate on the existence of a third order phase transition at a critical quark mass where the D7 embedding undergoes a geometric transition. In the Constable-Myers background, we find a chiral symmetry breaking condensate as well as the associated Goldstone boson in the limit of small quark mass. The existence of the condensate ensures that the D7-brane never reaches the naked singularity at the origin of the deformed AdS

Heavy-light mesons from the AdS/CFT correspondence

“…Quarks are again introduced by including probe D7 branes into the geometry. Substituting into the DBI action (2) for this geometry we find [4] the equation of motion for the radial separation, v, of the two branes in the 8, 9 directions as a function of the radial coordinate…”

“…Chiral symmetry breaking is forbidden in a supersymmetric theory so we will turn instead to a non-supersymmetric dilaton flow geometry that provides a gravity dual of QCD [4].…”

“…There has been steady progress towards such a description including string theory descriptions of theories that break chiral symmetry [4] - [23]. Most recently these ideas have been adapted to produce phenomenological models of QCD dynamics that describe aspects of the meson and baryon spectrum at the 20% level or better [24] - [43].…”

“…However this model does not include chiral symmetry breaking behaviour. Therefore we move on to the authors' preferred string theory description of chiral symmetry breaking [4] in the non-supersymmetric Constable-Myers background [71,72,73,74]. This model consists of an AdS background deformed by the presence of a non-zero dilaton.…”

Mesons in gauge/gravity duals

“…In the UV, the field theory returns to the fourdimensional N = 2 theory of [16], but the IR is QCDlike with a running gauge coupling. This combination has 84 The European Physical Journal A been used to obtain a gravity dual description of dynamical chiral symmetry breaking by a quark condensate [18]. Moreover, the associated Goldstone boson has been identified: It is obtained from the fluctuations of the probe D7 brane around its minimum energy configuration.…”