arXiv subjects

Yong-Jia Huang

Publications and source records attributed to Yong-Jia Huang.

14 recordsLinked to original sources

arXiv2026

Evidence for a Continuous Hadron--Quark Transition in Cold Dense Matter

Statistical evidence for a continuous hadron-quark transition is found in this work. Confronting microscopic descriptions connecting the Parity Doublet Model and the Nambu--Jona-Lasinio model with observationally constrained non-parametric equations of state, Bayesian model comparison decisively favors a boundary-free crossover over the conventional first-order Maxwell construction ($Δ\ln\mathcal{Z} \sim +7.20$) and fixed-boundary crossover ($Δ\ln\mathcal{Z} \sim +5.16 $). The preferred crossover decouples the intermediate stiffening from the intrinsic stiffness of each phase, allowing both sectors to exhibit physical self-consistency. The chiral-invariant nucleon mass is large, $M_0 = 834^{+28}_{-92}\text{ MeV}$, as expected for a substantial baryon mass surviving chiral restoration. While the quark sector accommodates a small pairing gap $Δ_{\rm CFL} = 88^{+83}_{-59}\text{ MeV}$ consistent with perturbative QCD limits, avoiding the excessively large gaps $Δ_{\rm CFL} \gtrsim 200\text{ MeV}$ required by the other constructions. These results demonstrate that a realistic unified description represents a continuous transition deviating substantially from isolated effective models of hadrons and quarks. Exploring genuine phase boundaries is therefore necessary through the emergence of spinodal instabilities within unified frameworks.

nucl-th↗

arXiv2026

Updated estimates of post-merger gravitational wave energy released in GW170817 and the maximum neutron star mass

In this work, benefiting from the increased sample of neutron stars with measured masses and radii as well as the incorporation of the chiral effective field theory and perturbative QCD constraints, the tidal parameter $κ_2^T$ is constrained to be $78^{+17}_{-11}$ (68.3% credible interval, mainly adopted in this work unless mentioned specifically) for the binary neutron stars involved in GW170817. Such a $κ_2^T$ is in favor of strong gravitational wave radiation in the post-merger phase and the corresponding energy is estimated to be $E_{\rm GW,p} \simeq 0.051^{+0.022}_{-0.017}\,M_\odot c^2$. Assuming the remnant from binary neutron star merger is a supramassive neutron star, as suggested by the modeling of the electromagnetic counterparts of GW170817, we examine the maximum mass of nonrotating neutron stars ($M_{\rm TOV}$) while accounting for the uncertainty in the remnant's lifetime ($t_{\rm c}$). Our results show that $M_{\rm TOV}$ varies from $2.09^{+0.11}_{-0.09}\,M_\odot$ for $t_{\rm c}=0.1$ s to $2.18^{+0.10}_{-0.09}\,M_\odot$ for $t_{\rm c}=1$ s. This result is consistent with that independently inferred from the re-construction of the equation of state of neutron star matter, i.e., $M_{\rm TOV,exc}=2.16^{+0.10}_{-0.07}M_\odot$, particularly if the very massive neutron stars with masses measured indirectly have been removed in constructing the prior distribution of $M_{\rm TOV}$. The consistency of the maximum mass of nonrotating neutron stars found in different approaches suggests a reasonable understanding of this key parameter for dense-matter physics.

astro-ph.HE↗

arXiv2026

Post-Merger Gravitational-Wave Uncertainties of Binary Neutron Stars under Multi-Messenger EOS Constraints

The high-frequency gravitational waves emitted by a binary neutron star merger remnant carry information on matter at densities and temperatures beyond those reached in isolated neutron stars. We quantify how tightly current multi-messenger constraints already determine the dominant post-merger frequency $f_{2,\rm mean}$. Adopting a set of cold equations of state (EOSs) constrained jointly by gravitational-wave tidal deformability, NICER mass--radius measurements, massive-pulsar masses, chiral effective field theory at low density, and perturbative QCD at asymptotically high density, for each binary mass we select the softest and stiffest models of the multi-messenger posterior and follow their coalescence with fully general-relativistic hydrodynamics simulations. Together with a broad set of EOSs drawn from the literature ($82$ models in total), these simulations show that, once the binary mass and a single measure of the stellar compactness ($Λ$ or $R$) are held fixed, the residual spread of $f_{2,\rm mean}$ is only $\sim 100\,{\rm Hz}$, a factor of several below the $\gtrsim 500\,{\rm Hz}$ range spanned by an EOSs set including those already disfavored by the data. This tight calibration of the cold-matter prediction implies that a future high-frequency detection departing from it would point directly to additional physics, such as a hadron--quark transition occurring at finite temperature. We further confirm the quasi-universal relation $(f_1+f_3)/2 \approx f_{2,\rm mean}$ to within $\sim 116\,{\rm Hz}$, which provides a model-independent estimate of $f_{2,\rm mean}$ from the secondary spectral peaks.

astro-ph.HE↗

arXiv2026

Neutron Star Observations Challenge a Large Colour-Superconducting Gap in Dense Quark Matter

At asymptotically high density, quantum chromodynamics (QCD) predicts that quark matter becomes a colour superconductor in the colour-flavour-locked (CFL) phase, yet, away from the asymptotic regime, the magnitude of the pairing gap is uncertain. Here we combine multi-messenger neutron star observations with perturbative QCD and chiral effective field theory inputs in a Bayesian inference built on a flexible Gaussian-process--neural-network representation of the equation of state (EOS). By matching the EOS at a baryon chemical potential of 2.6 GeV to the perturbative QCD prediction supplemented by the next-to-leading-order CFL contribution, we infer a gap of $Δ^{*}_{\rm CFL}=34^{+32}_{-28}$ MeV and a 95% credible upper limit of about 66 MeV, which is a factor of two tighter than previous bounds and at the lower edge of most microscopic model predictions. We further place the first data-driven constraint on the unknown high-order constant of the perturbative QCD pressure, i.e., $c_0=-21^{+9}_{-8}$. Our results indicate that colour-superconducting pairing makes only a subdominant contribution to dense matter pressure, tightening the connection between neutron star data and the QCD phase diagram.

astro-ph.HE↗

arXiv2026

The Non-parametric Equation of State Realizes a Generalized Quark-Hadron Crossover

We propose a non-parametric approach to construct the statistical equation of state (EOS) continuously from the nuclear crust to the asymptotic-freedom regime. The combined requirement of supporting two-solar-mass neutron stars (NSs) with relatively small radii at low masses and of reaching the asymptotically soft pQCD boundary forces a squared-sound-speed ($c_s^2$) peak followed by extended softening, with $c_s^2$ returning toward $1/3$ near $\sim\!30\,n_{\rm sat}$. Correspondingly, the trace anomaly $Δ\equiv 1/3 - p/ε$ becomes positive beyond NS densities and approaches the pQCD limit from above. By quantifying the degree of this softening in the posterior, we find evidence for a hadron-quark transition in the cores of the most massive neutron stars. More importantly, this shows that the thermodynamic structure of a complete crust-to-pQCD statistical EOS naturally realizes a generalized quark-hadron crossover. The quark EOS above NS densities is therefore soft and non-perturbative, in contrast to the stiff quark EOS underlying the quark-star picture.

astro-ph.HE↗

arXiv2026

The maximum mass and rotational kinetic energy of rapidly rotating neutron stars

Rapid uniformly-rotating neutron stars are expected to be formed for instance in the collapse of some massive stars, the accretion of compact object binaries, and double neutron star mergers. The huge amount of the rotational energy has been widely believed to be the source of some cosmic gamma-ray bursts and superluminous supernovae. Benefited from the constraints on the equation of state of the neutron star matter set by the latest multi-messenger data, the chiral effective field theory and perturbative quantum chromodynamics, here we present the maximum gravitational mass as well as the rotational energy for a neutron star at a given spin period. Our nonparametric equation of state analysis reveals that the critical Keplerian configurations ($Ω_{\rm kep}^{\rm crit}=1.02_{-0.07}^{+0.06}\times 10^{4}~{\rm rad/s}$) can sustain maximum gravitational masses of $M_{\rm kep}^{\rm crit}=2.73 \pm 0.09 M_\odot$ with corresponding rotational energy reaching $E_{\rm rot,kep}^{\rm crit}=2.36^{+0.24}_{-0.22}\times 10^{53}$ erg. However, the maximum rotational energy that can be feasibly extracted from a neutron star is limited to $1.40^{+0.14}_{-0.13}\times 10^{53}$ erg, which holds for a baryon mass of $2.66^{+0.10}_{-0.09}M_\odot$. All these parameters, obtained via the nonparametric reconstruction of the equation of state, are at the $68.3\%$ confidence level and the adoption of a quarkonic model yields rather similar results. These findings are found to have already set some intriguing constraints on the millisecond magnetar interpretation of some exciting data.

astro-ph.HE↗

arXiv2025

Phase transition and nuclear symmetry energy from neutron star observations: Constraints in light of PSR J0614--3329

The possible occurrence of a first-order hadron-quark phase transition (FOPT) in neutron-star interiors remains an open question. Whether such a transition can be directly tested with improved observations is a key challenge. Here, we incorporate the latest constraints, especially a new NICER radius measurement for PSR J0614--3329, into a nonparametric Gaussian Process (GP) EOS framework that explicitly includes a first-order transition. We find a Bayes factor of $B\approx2.3$ when comparing models with and without an explicit phase transition, marginally favoring its presence. At $68\%$ credibility, the transition onset density $n_{\rm PT}$ is either below $2\,n_s$ (corresponding to masses $\lesssim1\,M_\odot$, with density jump $Δn\sim0.5\,n_s$) or, more prominently, above $4\,n_s$ (near the central density of the heaviest NS, with $Δn\sim3\,n_s$), where $n_s$ represents the nuclear saturation density. In addition, by using symmetry-energy expansion at low densities ($<1.1\,n_s$), we infer a slope parameter $L=40.2^{+19.3}_{-14.3}$ MeV, in good agreement with nuclear-experiment values. Intriguingly, $L$ correlates positively with the radius difference between $1.4\,M_\odot$ and $2.0\,M_\odot$ stars.

astro-ph.HE↗

arXiv2025

Neutron-quark stars: Discerning viable alternatives for the higher-density part of the equation of state of compact stars

We investigate binary neutron star (BNS) mergers using general-relativistic numerical simulations with hadronic and hybrid equations of state (EOSs), incorporating the latest observations and theoretical constraints. We address two viable scenarios for the transition to quark matter: a quark-hadron crossover (QHC) or a strong first-order phase transition (1PT). To distinguish between different models, we define neutron-quark stars (NQS) as configurations where quark effects emerge at masses below the lowest observed neutron-star mass. While traditional "hybrid stars" may be distinguished by purely hadronic configurations through mass-radius measurements, the mass-radius relations of NQSs resemble those of purely hadronic models, with no sharp boundary between hadrons and quarks. The name NQS effectively captures the absence of a phase boundary between hadrons and quarks in QHC scenarios. Our results indicate that QHC models can be distinguished from hadronic ones if both the inspiral and postmerger gravitational waves (GWs) are observed. In particular, the dominant postmerger frequency ($f_2$) tends to be lower than in hadronic models with the same tidal deformability ($Λ$). We also present the first general-relativistic simulations of BNS mergers where the stars already contain quark matter before merging. These involve a strong first-order phase transition (1PT) at 1.8 times nuclear saturation density, followed by a stiff quark EOS. Finally, we identify a robust linear correlation between the total GW energy emitted after the merger and the $f_2$ frequency. Remarkably, this relation holds regardless of the quark presence.

astro-ph.HE↗

arXiv2024

Upper Limit of Sound Speed in Nuclear Matter: A Harmonious Interplay of Transport Calculation and Perturbative Quantum Chromodynamic Constraint

Very recently, it has been shown that there is an upper bound on the squared sound speed of nuclear matter from the transport, which reads $c_{\rm s}^2 \leq 0.781$. In this work, we demonstrate that this upper bound is corroborated by the reconstructed equation of state (EOS; modeled with a nonparametric method) for ultradense matter. The reconstruction integrates multimessenger observation for neutron stars, in particular, the latest radius measurements for PSR J0437-4715 ($11.36^{+0.95}_{-0.63}$ km), PSR J0030+0451 ($11.71^{+0.88}_{-0.83}$ km, in the ST+PDT model), and PSR J0740+6620 ($12.49^{+1.28}_{-0.88}$ km) by NICER have been adopted. The result shows in all cases, the $c_{\rm s}^2 \leq 0.781$ upper limit for EOS will naturally yield the properties of matter near the center of the massive neutron star consistent with the causality-driven constraint from pQCD, where, in practice, the density in implementing the pQCD likelihood ($n_{\rm L}$) is applied at $10n_s$ (where $n_s$ is the nuclear saturation density). We also note that there is a strong correlation for the maximum $c_s^2$ with $n_{\rm L}$, and $c_{\rm s}^2 \leq 0.781$ is somehow violated when $n_{\rm L} = n_{\rm c,TOV}$. The result indicates that a higher $n_{\rm L}$, even considering the uncertainties from statistics, is more natural. Moreover, the remarkable agreement between the outcomes derived from these two distinct and independent constraints (i.e., the transport calculation and pQCD boundary) lends strong support to their validity. In addition, the latest joint constraint for $R_{1.4}$, $R_{2.0}$, $R_{1.4}-R_{2.0}$, and $M_{\rm TOV}$ are $11.94_{-0.68}^{+0.77}$ km, $11.99_{-0.67}^{+0.88}$ km, $-0.1_{-0.27}^{+0.42}$ km, and $2.24_{-0.10}^{+0.13}M_\odot$ (at $90\%$ credible level), respectively.

astro-ph.HE↗

arXiv2024

Mass and radius of the most massive neutron star: The probe of the equation of state and perturbative QCD

Recently, an association of GW190425 and FRB 20190425A had been claimed and a highly magnetized neutron star (NS) remnant was speculated. Given the $\sim 2.5$-h delay of the occurrence of FRB 20190425A, a uniformly rotating supramassive magnetar is favored since the differential rotation would have been promptly terminated by the magnetic braking. The required maximum gravitational mass ($M_{\rm TOV}$) of the nonrotating NS is $\approx 2.77M_\odot$, which is strongly in tension with the relatively low $M_{\rm TOV}\approx 2.25M_\odot$ obtained in current equation of state (EOS) constraints incorporating perturbative quantum chromodynamics (pQCD) information. However, the current mass-radius and mass-tidal deformability measurements of NSs alone do not convincingly exclude the high $M_{\rm TOV}$ possibility. By performing EOS constraints with mock measurements, we find that with a $2\%$ determination for the radius of PSR J0740+6620-like NS it is possible to distinguish between the low and high $M_{\rm TOV}$ scenarios. We further explore the prospect to resolve the issue of the appropriate density to impose the pQCD constraints with future massive NS observations or determinations of $M_{\rm TOV}$ and/or $R_{\rm TOV}$. It turns out that measuring the radius of a PSR J0740+6620-like NS is insufficient to probe the EOSs around 5 nuclear saturation density, where the information from pQCD becomes relevant. The additional precise $M_{\rm TOV}$ measurements anyhow could provide insights into the EOS at such a density. Indeed, supposing the central engine of GRB 170817A is a black hole formed via the collapse of a supramassive NS, the resulting $M_{\rm TOV}\approx 2.2M_\odot$ considerably softens the EOS at the center of the most massive NS, which is in favor of imposing the pQCD constraint at density beyond the one achievable in the NSs.

astro-ph.HE↗

arXiv2023

Plausible presence of new state in neutron stars with masses above $0.98M_{\rm TOV}$

We investigate the neutron star (NS) equation of state (EOS) by incorporating multi-messenger data of GW170817, PSR J0030+0451, PSR J0740+6620, and state-of-the-art theoretical progresses, including the information from chiral effective field theory ($χ$EFT) and perturbative quantum chromodynamics (pQCD) calculation. Taking advantage of the various structures sampling by a single-layer feed-forward neural network model embedded in the Bayesian nonparametric inference, the structure of NS matter's sound speed $c_{\rm s}$ is explored in a model-agnostic way. It is found that a peak structure is common in the $c_{\rm s}^2$ posterior, locating at $2.4-4.8ρ_{\rm sat}$ (nuclear saturation density) and $c_{\rm s}^2$ exceeds ${c^{2}}/{3}$ at 90\% credibility. The non-monotonic behavior suggests evidence of the state deviating from hadronic matter inside the very massive NSs. Assuming the new/exotic state is featured as it is softer than typical hadronic models or even with hyperons, we find that a sizable ($\geq 10^{-3}M_\odot$) exotic core, likely made of quark matter, is plausible for the NS with a gravitational mass above about $0.98M_{\rm TOV}$, where $M_{\rm TOV}$ represents the maximum gravitational mass of a non-rotating cold NS. The inferred $M_{\rm TOV} = 2.18^{+0.27}_{-0.13}M_\odot$ (90\% credibility) is well consistent with the value of $2.17^{+0.15}_{-0.12}M_\odot$ estimated independently with GW170817/GRB 170817A/AT2017gfo assuming a temporary supramassive NS remnant formed after the merger. PSR J0740+6620, the most massive NS detected so far, may host an exotic core with a probability of $\approx 0.36$.

astro-ph.HE↗

arXiv2022

Merger and post-merger of binary neutron stars with a quark-hadron crossover equation of state

Fully general-relativistic binary-neutron-star (BNS) merger simulations with quark-hadron crossover (QHC) equations of state (EOSs) are studied for the first time. In contrast to EOSs with purely hadronic matter or with a first-order quark-hadron phase transition (1PT), in the transition region QHC EOSs show a peak in sound speed, and thus a stiffening. We study the effects of such stiffening in the merger and post-merger gravitational (GW) signals. Through simulations in the binary-mass range $2.5 < M/M_{\odot} < 2.75$, characteristic differences due to different EOSs appear in the frequency of the main peak of the post-merger GW spectrum ($f_2$), extracted through Bayesian inference. In particular, we found that (i) for lower-mass binaries, since the maximum baryon number density ($n_{\rm max}$) after the merger stays below $3\text{--}4$ times the nuclear-matter density ($n_0$), the characteristic stiffening of the QHC models in that density range results in a lower $f_2$ than that computed for the underlying hadronic EOS and thus also than that for EOSs with a 1PT, (ii) for higher-mass binaries, where $n_{\rm max}$ may exceed $4\text{--}5 n_0$ depending on the EOS model, whether $f_2$ in QHC models is higher or lower than that in the underlying hadronic model depends on the height of the sound-speed peak. Comparing the values of $f_2$ for different EOSs and BNS masses gives important clues on how to discriminate different types of quark dynamics in the high-density end of EOSs and is relevant to future kilohertz GW observations with third-generation GW detectors.

astro-ph.HE↗

arXiv2018

Total gravitational mass of the Galactic Double Neutron Star systems: evidence for a bimodal distribution

So far, in total 15 double neutron star systems (DNSs) with a reliable measurement of the total gravitational mass ($M_{\rm T}$) have been detected in the Galaxy. In this work we study the distribution of $M_{\rm T}$. The data prefer the double Gaussian distribution over a single Gaussian distribution and the low and high mass populations center at $M_{\rm T}\sim 2.58M_\odot$ and $\sim 2.72M_\odot$, respectively. The progenitor stars of GW170817 have a $M_{\rm T}=2.74^{+0.04}_{-0.01}M_\odot$, falling into the high mass population. With a local neutron star merger rate of $\sim 10^{3}~{\rm Gpc^{-3}~yr^{-1}}$, supposing the $M_{\rm T}$ of those merging neutron stars also follow the double Gaussian distribution, the upcoming runs of the advanced LIGO/Virgo will soon detect some events with a $M_{\rm T}\lesssim 2.6M_\odot$ that can effectively probe the equation of state of the neutron stars and the distribution function is expected to be reliably reconstructed in the next decade.

astro-ph.HE↗

arXiv2018

GRB 111005A at Z = 0.0133 and the Prospect of Establishing Long-short GRB/GW Association

GRB 111005A, one long duration gamma-ray burst (GRB) occurred within a metal-rich environment that lacks massive stars with $M_{\rm ZAMS}\geq 15M_\odot$, is not coincident with supernova emission down to stringent limit and thus should be classified as a "long-short" GRB (lsGRB; also known as SN-less long GRB or hybrid GRB), like GRB 060505 and GRB 060614. In this work we show that in the neutron star merger model, the non-detection of the optical/infrared emission of GRB 111005A requires a sub-relativistic neutron-rich ejecta with the mass of $\leq 0.01~M_\odot$, (significantly) less massive than that of GRB 130603B, GRB 060614 and GRB 050709. The lsGRBs are found to have a high rate density and the neutron star merger origin model can be unambiguously tested by the joint observations of the second generation gravitational wave (GW) detectors and the full-sky gamma-ray monitors such as Fermi-GBM and the proposing GECAM. If no lsGRB/GW association is observed in 2020s, alternative scenarios have to be systematically investigated. With the detailed environmental information achievable for the very-nearby events, a novel kind of merger or explosion origin may be identified.

astro-ph.HE↗