We clarify and extend further the idea we developed before that baryonic matter at high density has an emergent “pseudoconformal 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 a matter-free vacuum—plays the crucial role. The consequence of the topology change is that massive compact stars carry the “pseudoconformal sound velocity” $v_s^2/c^2\approx 1/3$ at $n\gtrsim n_{1/2}$ signaling a precursor to the 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 or -gluons transition.

• Received 25 October 2018

DOI:https://doi.org/10.1103/PhysRevD.99.014034