A pseudo-conformal structure in dense baryonic matter

TL;DR

This paper proposes that at high baryonic densities, a topology change leads to a pseudo-conformal symmetry in dense matter, affecting the equation of state and the properties of compact stars, with implications for the hadron-quark transition.

Contribution

It introduces the concept of a topology change at high density causing pseudo-conformal symmetry and impacts on dense matter's equation of state, linking skyrmion transitions to observable astrophysical phenomena.

Findings

Emergence of pseudo-conformal sound velocity in dense matter.

Topology change from skyrmions to half-skyrmions at high density.

Possible density range for topology change: 2 to 4 times nuclear saturation density.

Abstract

We clarify and extend further the idea developed in \cite{PKLMR,MLPR} that baryonic matter at high density has an emergent "pseudo-conformal symmetry." It is argued that as baryonic density exceeds $n \simeq n_{1/2} \gtrsim 2n_0$, a topology change mimicking the baryon-quark continuity takes place at $n_{1/2}$. In terms of skyrmions, this corresponds to the transition from skyrmions to half-skyrmions and impacts on the equation of state of dense baryonic matter. The emergence in medium at $n_{1/2}$ of parity-doublet symmetry -- which is invisible in QCD in matter-free vacuum -- plays the crucial role. The consequence of the topology change is that massive compact stars carry the "pseudo-conformal sound velocity" $v_s^2/c^2\approx 1/3$ at $n\gsim n_{1/2}$ signaling a precursor to precocious emergence of scale symmetry as well as {a} local symmetry hidden in QCD in the matter-free vacuum. A highly significant prediction of this work is that the topology change density from normal matter to half-skyrmion matter, up-to-date inaccessible either by QCD proper or by terrestrial experiments, could possibly be pinned down within the range $2 < n_{1/2}/n_0 < 4$, commensurate with the range expected for a continuous hadrons-to-quarks/gluons transition.