Topology change, emergent symmetries and compact star matter

TL;DR

This paper reviews a topological approach to dense nuclear matter in compact stars, highlighting emergent symmetries, topology change, and a pseudo-conformal sound velocity consistent with astrophysical data.

Contribution

It introduces a novel effective field theory based on skyrmion topology, incorporating emergent symmetries and topology change to describe dense nuclear matter and neutron star properties.

Findings

Description of nuclear matter from saturation density to several times that.

Identification of a pseudo-conformal sound velocity at high density.

Consistency with gravitational wave observations GW170817 and GW190425.

Abstract

Topology effects have being extensively studied and confirmed in strongly correlated condensed matter physics. In the large color number limit of QCD, baryons can be regarded as topological objects -- skyrmions -- and the baryonic matter can be regarded as a skyrmion matter. We review in this paper the generalized effective field theory for dense compact-star matter constructed with the robust inputs obtained from the skyrmion approach to dense nuclear matter, relying to possible ``emergent" scale and local flavor symmetries at high density. All nuclear matter properties from the saturation density $n_0$ up to several times $n_0$ can be fairly well described. A uniquely novel -- and unorthdox -- feature of this theory is the precocious appearance of the pseudo-conformal sound velocity $v^2_{s}/c^2 \approx 1/3$, with the non-vanishing trace of the energy momentum tensor of the system. The topology change encoded in the density scaling of low energy constants is interpreted as the quark-hadron continuity in the sense of Cheshire Cat Principle (CCP) at density $\gsim 2n_0$ in accessing massive compact stars. We confront the approach with the data from GW170817 and GW190425.