Roughly half of realistic neutron-star equations of state produce stars with negative Ricci scalar inside, and an improved analytic fit links gravitational mass M to baryonic mass Mb with maximum 3 percent variance.
Constraining the speed of sound inside neutron stars with chiral effective field theory interactions and observations
5 Pith papers cite this work. Polarity classification is still indexing.
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abstract
The dense matter equation of state (EOS) determines neutron star (NS) structure but can be calculated reliably only up to one to two times the nuclear saturation density, using accurate many-body methods that employ nuclear interactions from chiral effective field theory constrained by scattering data. In this work, we use physically motivated ansatzes for the speed of sound $c_S$ at high density to extend microscopic calculations of neutron-rich matter to the highest densities encountered in stable NS cores. We show how existing and expected astrophysical constraints on NS masses and radii from X-ray observations can constrain the speed of sound in the NS core. We confirm earlier expectations that $c_S$ is likely to violate the conformal limit of $c_S^2\leq c^2/3 $, possibly reaching values closer to the speed of light $c$ at a few times the nuclear saturation density, independent of the nuclear Hamiltonian. If QCD obeys the conformal limit, we conclude that the rapid increase of $c_S$ required to accommodate a $2 $ M$_\odot$ NS suggests a form of strongly interacting matter where a description in terms of nucleons will be unwieldy, even between one and two times the nuclear saturation density. For typical NSs with masses in the range $1.2-1.4~$ M$_\odot$, we find radii between $10$ and $14$ km, and the smallest possible radius of a $1.4$ M$_{\odot}$ NS consistent with constraints from nuclear physics and observations is $8.4$ km. We also discuss how future observations could constrain the EOS and guide theoretical developments in nuclear physics.
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2026 5representative citing papers
Hybrid neutron-star equations of state remain sensitive to the low-density nucleonic model at transition densities around 2ρ₀, with model spread in radius and tidal deformability exceeding observational uncertainty by factors of ~1.8 and ~1.4.
DM admixture in isentropic neutron stars can mimic quark-matter conformality signatures via competition between thermal effects and dark sector softening.
A physics-informed neural network produces a thermodynamically consistent 4D equation of state for QCD matter that reproduces lattice QCD and hadron resonance gas results while extrapolating to high baryon density for use in hybrid hydrokinetic models.
QCD features at least three phases at zero baryon density and three at high density, including a Quarkyonic phase at high density and low temperature, described via large-N_c and a parameter-free 3D string model.
citing papers explorer
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General gravitational properties of neutron stars: curvature invariants, binding energy, and trace anomaly
Roughly half of realistic neutron-star equations of state produce stars with negative Ricci scalar inside, and an improved analytic fit links gravitational mass M to baryonic mass Mb with maximum 3 percent variance.
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Sensitivity of Neutron Star Observables to Transition Density in Hybrid Equation-of-State Models
Hybrid neutron-star equations of state remain sensitive to the low-density nucleonic model at transition densities around 2ρ₀, with model spread in radius and tidal deformability exceeding observational uncertainty by factors of ~1.8 and ~1.4.
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Observables and conformal properties of dark matter admixed isentropic neutron stars
DM admixture in isentropic neutron stars can mimic quark-matter conformality signatures via competition between thermal effects and dark sector softening.
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Equation of State at High Baryon Densities from a Thermodynamically Informed Neural Network
A physics-informed neural network produces a thermodynamically consistent 4D equation of state for QCD matter that reproduces lattice QCD and hadron resonance gas results while extrapolating to high baryon density for use in hybrid hydrokinetic models.
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Two Lectures on the Phase Diagram of QCD
QCD features at least three phases at zero baryon density and three at high density, including a Quarkyonic phase at high density and low temperature, described via large-N_c and a parameter-free 3D string model.