Toshiya Imoto | Searcharxiv

arXiv2010

Mesons as Open Strings in a Holographic Dual of QCD

We study meson spectrum obtained from massive open string modes in a holographic dual of QCD constructed on the basis of a D4/D8-brane configuration in type IIA string theory. The spectrum includes mesons with spin higher than one. Taking into account the effect of curved background perturbatively, we obtain a mass formula for these mesons, which exhibits the linear Regge behavior at the leading order with subleading non-linear corrections. We argue that the string spectrum captures some features of the observed meson spectrum. For example, a_2(1320), b_1(1235), π(1300), a_0(1450), etc., are identified as the first excited massive open string states and ρ_3(1690), π_2(1670), etc., are identified as the second excited states.

hep-th↗

arXiv2010

O(N) and USp(N) QCD from String Theory

We propose a holographic dual of large N_c QCD with the gauge group O(N_c) and USp(N_c) and N_f flavors of massless quarks. This is constructed by adding O6-planes to an intersecting D4-D8 system in type IIA superstring theory. The holographic dual description is formulated in the Witten's D4-brane background with D8-branes and O6-planes embedded in it as probes. The D4-brane background gives rise to a smooth interpolation of D8-anti-D8 pairs and an O6-anti-O6 pair. We show that the resultant brane configuration explains geometrically the flavor symmetry breaking patterns in O(N_c) and USp(N_c) QCD that are caused by quark bilinear condensates. We next discuss that baryons can be realized as D4-anti-D4 pairs wrapped on S^4 that intersect with the O6-plane. By analyzing the tachyons on it, we reproduce the stability conditions of the baryons that are expected from the gauge theory viewpoint. The stable baryon configurations are classified systematically by using K-theory. We also give a similar analysis for the flux tubes and again reproduce the results that are consistent with QCD.

hep-th↗