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

A holographic model of QCD in the limit of large number of colors, N-c, and massless fermion flavors, N-f, but constant ratio x(f) = N-f /N-c 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 (q) over barq and a 4-vector dual to the baryon current (q) over bar gamma(mu)q. The main result is the mu, T phase diagram of the holographic theory. A first order deconfining transition along T-h(mu) and a chiral transition at T-x(mu) > T-h (mu) are found. The chiral transition is of second order for small mu and becomes of first order at larger mu. 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 AdS(2) x R-3 geometry and displays semi-local criticality.