Conformal anomaly and the vector coupling in dense matter

TL;DR

This paper develops an effective chiral Lagrangian incorporating conformal invariance to study dense nuclear matter, revealing how vector-meson interactions soften the equation of state near the chiral transition, consistent with neutron star observations.

Contribution

It introduces a novel effective Lagrangian with conformal symmetry and analyzes the impact of the dilaton limit on nuclear matter properties at high density.

Findings

Vector-meson Yukawa coupling is suppressed near the chiral transition.

The symmetry energy becomes softer approaching the phase transition.

The resulting equation of state can explain massive neutron stars without exotic matter.

Abstract

We construct an effective chiral Lagrangian for hadrons implemented by the conformal invariance and discuss the properties of nuclear matter at high density. The model is formulated based on two alternative assignment, "naive" and mirror, of chirality to the nucleons. It is shown that taking the dilaton limit, in which the mended symmetry of Weinberg is manifest, the vector-meson Yukawa coupling becomes suppressed and the symmetry energy becomes softer as one approaches the chiral phase transition. This leads to softer equations of state (EoS) and could accommodate the EoS without any exotica consistent with the recent measurement of a $1.97 \pm 0.04\,M_\odot$ neutron star.