The Trajectory of the Cosmic Plasma Through the Quark Matter Phase Diagram

TL;DR

This paper investigates the evolution of the early Universe's cosmic quark-gluon plasma through the quark matter phase diagram, using advanced theoretical tools to understand its trajectory assuming Little Inflation occurred.

Contribution

It combines lattice QCD results and gauge-gravity duality to constrain the cosmic plasma's path through the phase diagram during the early Universe.

Findings

Constrained the plasma's trajectory assuming Little Inflation.

Identified the phase boundary where the plasma epoch ends.

Provided insights into initial conditions for the hadronic epoch.

Abstract

Experimental studies of the Quark-Gluon Plasma (QGP) focus on two, in practice distinct, regimes: one in which the baryonic chemical potential $\mu_B$ is essentially zero, the other in which it is of the same order of magnitude as the temperature. The cosmic QGP which dominates the early Universe after reheating is normally assumed to be of the first kind, but recently it has been suggested that it might well be of the second: this is the case in the theory of "Little Inflation". If that is so, then it becomes a pressing issue to fix the trajectory of the Universe, as it cools, through the quark matter phase diagram: in particular, one wishes to know where in that diagram the plasma epoch ends, so that the initial conditions of the hadronic epoch can be determined. Here we combine various tools from strongly coupled QGP theory (the latest lattice results, together with gauge-gravity duality) in order to constrain that trajectory, assuming that Little Inflation did occur.