O áxion em condições extremas: matéria de quarks quente e magnetizada, meios densos e estrelas compactas

Abstract

We investigate the phase diagram of quantum chromodynamics by means of the Nambu- Jona-Lasinio effective model, including the axion - a particle which emerges as a solution of the strong charge-parity (CP) problem and may describe dark matter - contributions. Initially we study quark matter in a hot and magnetized medium, observing their effects on the mechanisms of chiral symmetry and charge-parity spontaneous breaking and restoration. We also verify the magnetic catalysis and inverse magnetic catalysis phenomena via a medium dependent coupling, and calculate quantities related to the axion such as it’s mass and self-coupling. Afterwards, we verify the effects of finite density in the NJL model with the goal of applying it to the study of hybrid stars, composed by a hadronic crust and deconfined quark matter at it’s core. For purposes of generalization of our results, two hadron models are considered. We find that the axion presence helps maintaining the stability of hybrid neutron stars, by weakening the transition between phases and bringing it to lower densities. As such, the results satisfy the constraints coming from gravitational wave detections and pulsar observations.