Chiral symmetry breaking and restoration from holography

Abstract

We study intersection of $N_c$ color D4 branes with $N_f$ Dp-branes and anti-Dp branes in the strong coupling limit in the probe approximation. The resulting model has $U(N_f)\times U(N_f)$ global symmetry. We see an $n$ dimensional theory for $n$ overlapping directions between color and flavor branes. At zero temperature we do see the breakdown of chiral symmetry, but there arises a puzzle: we do not see any massless NG boson to the break down of the chiral symmetry group for $n=2,3$ for a specific p. At finite temperature we do see the restoration of chiral symmetry group and the associated phase transitions are of first order. The chiral symmetry restoration is described by a curve, which connects L, the asymptotic distance of separation between the auarks, with the temperature, T. In general this quantity is very difficult to compute but if we evaluate it numerically then the curve is described by an equation $L T=c$, where c is a constant and is much smaller than one. It means for $L/R_{\tau}$ above $2\pi c$ there occurs the deconfined phase along with the chiral symmetryrestored phase.