A holographic model for QCD in the Veneziano limit at finite temperature and density

Abstract

A holographic model of QCD in the limit of large number of colors, Nc, and massless fermion flavors, Nf , but constant ratio xf = Nf /Nc is analyzed at finite temperature and chemical potential. The five dimensional gravity model contains three bulk fields: a scalar dilaton sourcing TrF2, a scalar tachyon dual to $ \overline{q}q $ and a 4-vector dual to the baryon current $ \overline{q} $ γμ q. The main result is the μ, T phase diagram of the holographic theory. A first order deconfining transition along Th(μ) and a chiral transition at Tχ(μ) > Th(μ) are found. The chiral transition is of second order for small μ and becomes of first order at larger μ. The two regimes are separated by a tricritical point. The dependence of thermodynamical quantities including the speed of sound and susceptibilities on the chemical potential and temperature is computed. A new quantum critical regime is found at zero temperature and finite chemical potential. It is controlled by an AdS2 × R3 geometry and displays semi-local criticality.