Quantum and stringy corrections to the equation of state of holographic QCD matter and the nature of the chiral transition

TL;DR

This paper investigates how quantum and stringy corrections influence the phase transition nature in holographic QCD, suggesting possible shifts from first to second or third order transitions depending on specific conditions.

Contribution

It introduces calculations of string-loop corrections in holographic QCD and explores how these affect the order of the chiral phase transition.

Findings

Classical gravity predicts a first order transition.

Quantum and stringy corrections can change the transition to second or third order.

Repulsive hadron interactions are crucial for third order transition.

Abstract

We consider the finite temperature phase diagram of holographic QCD in the Veneziano limit (Nc large, Nf large with xf=Nf/Nc fixed) and calculate one string-loop corrections to the free energy in certain approximations. Such corrections, especially due to the pion modes are unsuppressed in the Veneziano limit. We find that under some extra assumptions the first order transition following from classical gravity solutions can become second order. If stringy asymptotics are of a special form and there are residual interactions it may even become of third order. Operationally these computations imply modelling the low temperature chiral symmetry breaking phase with a hadron gas containing Nf^2 massless Goldstone bosons and an exponential spectrum of massive hadrons. A third order transition is possible only if repulsive hadron interactions via the excluded volume effect are included.