On the spectra of scalar mesons from HQCD models

We determine the holographic spectra of scalar mesons from the fluctuations of the embedding of flavor D-brane probes in HQCD models. The models we consider include a generalization of the Sakai Sugimoto model at zero temperature and at the high-temperature intermediate phase, where the system is in a deconfining phase while admitting chiral symmetry breaking and a non-critical 6d model at zero temperature. All these models are based on backgrounds associated with near extremal N-c D4 branes and a set of N-f << N-c flavor probe branes that admit geometrical chiral symmetry breaking. We point out that the spectra of these models include a 0(--) branch which does not show up in nature. At zero temperature we found that the masses of the mesons M-n depend on the constituent quark mass parameter m(q)(c) and on the excitation number n as M-n(2) similar to m(c)(q) M-n(2) similar to n(1.7) for the ten dimensional case and as M-n similar to m(q)(c) and M-n similar to n(0.75) in the non-critical case. At the high temperature intermediate phase we detect a decrease of the masses of low spin mesons as a function of the temperature similar to holographic vector mesons and to lattice calculations.