Flavor Symmetry and Topology Change in Nuclear Symmetry Energy for Compact Stars

TL;DR

This paper explores how flavor symmetry and topology changes influence the nuclear symmetry energy in dense matter, impacting the structure of neutron stars through a novel theoretical framework involving skyrmions, hidden local symmetry, and effective Lagrangians.

Contribution

It introduces a new approach combining skyrmion crystal models and hidden local symmetry to analyze symmetry energy and topology change effects in dense stellar matter.

Findings

High-density matter flows to a dilaton-limit fixed point constrained by mended symmetries.

Hyperons may appear after kaon condensation, not before, in dense matter.

Kaon condensation acts as a gateway to strange-quark matter in neutron stars.

Abstract

The nuclear symmetry energy figures crucially in the structure of asymmetric nuclei and, more importantly, in the equation of state (EoS) of compact stars. At present it is almost totally unknown, both experimentally and theoretically, in the density regime appropriate for the interior of neutron stars. Basing on a strong-coupled structure of dense baryonic matter encoded in the skyrmion crystal approach with a topology change and resorting to the notion of generalized HLS (hidden local symmetry) in hadronic interactions, we address a variety of hitherto unexplored issues of nuclear interactions associated with the symmetry energy, i.e., kaon condensation and hyperons, possible topology change in dense matter, nuclear tensor forces, conformal symmetry and chiral symmetry etc in the EoS of dense compact-star matter. One of the surprising results coming from the hidden local symmetry structure that is distinct from what is given by standard phenomenological approaches is that at high density, baryonic matter is driven by RG flow to the "dilaton-limit fixed point (DLFP)" constrained by "mended symmetries." We further propose how to formulate kaon condensation and hyperons in compact-star matter in a framework anchored on a single effective Lagrangian by treating hyperons as the Callan-Klebanov kaon-skyrmion bound states simulated on crystal lattice. This formulation suggests that hyperons can figure in the stellar matter -- if at all -- when or after kaons condense, in contrast to the standard phenomenological approaches where the hyperons appear as the first strangeness degree of freedom in matter thereby suppressing or delaying kaon condensation. In our simplified description of the stellar structure in terms of symmetry energies which is compatible with that of the 1.97 solar mass star, kaon condensation plays a role of "doorway state" to strange-quark matter.