2024/06/07 by Cai, Bao-Jun, Li, Bao-An · 2 citations
#85A04 #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #High Energy Physics - Phenomenology (hep-ph) #High Energy Physics - Theory (hep-th) #Nuclear Experiment (nucl-ex) #Nuclear Theory (nucl-th)
paper · doi:10.48550/arxiv.2406.05025
The trace anomaly Δ≡ 1/3-P/ε=1/3-ϕ quantifies the possibly broken conformal symmetry in supradense matter under pressure P at energy density ε. Perturbative QCD (pQCD) predicts a vanishing Δ at extremely high energy or baryon densities when the conformal symmetry is realized but its behavior at intermediate densities reachable in neutron stars (NSs) are still very uncertain. The extraction of Δ from NS observations strongly depends on the employed model for nuclear Equation of State (EOS). Using the IPAD-TOV method based on an Intrinsic and Perturbatively Analysis of the Dimensionless (IPAD) Tolman-Oppenheimer-Volkoff (TOV) equations that are further verified numerically by using 105 EOSs generated randomly with a meta-model in a very broad EOS parameter space constrained by terrestrial nuclear experiments and astrophysical observations, here we first show that the compactness ξ≡ GM_\rmNS/Rc2≡ M_\rmNS/R of a NS with mass M_\rmNS and radius R scales very accurately with Π_\rmc≡Π_\rmc⋅(1+18\x/25)≡\x/(1+3\x2+4\x)⋅(1+18\rmX/25) where \x≡ϕ_\rmc= P_\rmc/ε_\rmc is the ratio of pressure over energy density at NS centers. The scaling of NS compactness thus enables one to readily read off the central trace anomaly Δ_\rmc=1/3-\x directly from the observational data of either the mass-radius or red-shift measurements. We then demonstrate indeed that the available NS data themselves from recent X-ray and gravitational wave observations can determine model-insensitively the trace anomaly as a function of energy density in NS cores, providing a stringent test of existing NS models and a clear guidance in a new direction for further understanding the nature and EOS of supradense matter.