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Yong-Zhong Qian

Publications and source records attributed to Yong-Zhong Qian.

At least 19 recordsLinked to original sources
arXiv2026

A Data-Driven Model for $r$-Process Production Patterns

Using the elemental abundances in 68 metal-poor (MP) stars, we present a data-driven model for $r$-process production patterns covering Sr to U. We show that essentially all the $r$-process patterns in those and other test stars can be adequately explained as mixtures of Patterns 1 and 2, which provides theoretical insights into the empirical categories of limited-$r$, $r$-I, and $r$-II stars. We carry out an extensive survey of the yield templates produced by parametric $r$-process calculations. We propose that Pattern 2 may be dominated by a single template and points to regularity in $r$-process production by a subset of neutron star mergers (NSMs), while Pattern 1 is the average superposition of multiple templates and reflects production by other NSMs and perhaps also some magneto-rotational supernovae. We raise possible systematic issues with abundance ratios for elements measured in different ionization states, and highlight the need for examining the Os, Ir, and Pt measurements for HD~122563, which is dominated by Pattern 1 with a prominent Pt peak in our model. If this result is confirmed, the meaning of the limited-$r$ category requires drastic revision. Further measurements of a wider range of $r$-process elements in a larger sample of MP stars are critical to test and improve our model.

astro-ph.SR↗
arXiv2026

On the importance of the IGM/CGM enrichment in determining chemical abundances during the first 600 Myr

JWST observations show that galaxies at $z>8$ exhibit a wide range of carbon-to-oxygen (C/O) ratios at fixed metallicity and systematically elevated nitrogen-to-oxygen (N/O) ratios compared to local galaxies. Proposed explanations include finely tuned star-formation histories (SFHs), differential or pristine inflows, top- or bottom-heavy initial mass functions, or enrichment from Wolf-Rayet stars, supermassive stars (SMSs), or Population III stars. The observed abundances reflect both in situ production tied to the SFHs and earlier pre-enrichment of the intergalactic and circumgalactic medium (IGM/CGM), which supply the gas inflow that fuels star formation. At such early epochs, SFHs are necessarily brief, and sustained star formation requires inflows to dominate over outflows, making the chemical state of the IGM/CGM especially important. We develop a chemical evolution model that incorporates (1) enrichment of the IGM/CGM by multiple sources and (2) the observed SFHs of high-redshift galaxies. Applying this model to eight galaxies at $z>8$, we find that only specific pre-enrichment scenarios reproduce their observed abundance ratios. For example, the low C/O and high N/O ratios measured in GN-z11 and CEERS-1019 require an IGM/CGM enriched by SMSs and pre-enriched to an oxygen metallicity of $\sim10^{-5}$ of the solar value. We also find that the log(N/O) vs. 12 + log(O/H) plane provides more stringent constraints on enrichment pathways than the log(C/O) vs. 12 + log(O/H) plane. Overall, our results highlight the crucial role of IGM/CGM chemical composition in chemical evolution models at $z>8$ and underscore the significant influence of SMSs on early carbon, nitrogen, and oxygen abundances.

astro-ph.GA↗
arXiv2026

Gamma-ray Signatures of r-Process Radioactivity from the Collapse of Magnetized White Dwarfs

We predict the gamma-ray line emission from $r$-process nuclei synthesized in the ejecta of the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf. Using ejecta from a two-dimensional general-relativistic neutrino-magnetohydrodynamic simulation, further evolved with a radiation-hydrodynamics code coupled to an in-situ nuclear reaction network, we construct angle-dependent gamma-ray spectra in the $0.01$-$10\,\mathrm{MeV}$ band via composition-dependent ray-tracing through the ejecta. The emission between $\sim$1 and $10\,$d is dominated by $^{132}$I ($t_{1/2} = 2.3\,$h), continuously replenished by the decay of its parent $^{132}$Te ($t_{1/2} = 3.2\,$d), with additional contributions from $^{131}$I, $^{133}$Xe, and $^{132}$Te. At $t\gtrsim 20$ d, $^{56}$Co (from $^{56}$Ni decay) becomes the primary emitter. The simultaneous presence of $r$-process and iron-peak gamma-ray lines is distinctive of AIC ejecta and absent in binary neutron star mergers, where iron-peak nuclei are generally not synthesized. Comparing with the $3σ$ continuum sensitivities of planned MeV gamma-ray telescopes (COSI, AMEGO-X, e-ASTROGAM, GRAMS, GammaTPC), we find the brightest $r$-process lines detectable to $\sim 10\,\mathrm{Mpc}$ by GammaTPC and GRAMS, with the signal approaching their sensitivity threshold at $30\,\mathrm{Mpc}$. The $r$-process spectral features survive time integration over $\sim 30$ d exposures, demonstrating robustness against the long observation times required by gamma-ray detectors.

astro-ph.HE↗
arXiv2026

Propagating Uncertainties from Nuclear Physics to Gamma-rays in Core Collapse Supernovae

Nuclear yields are powerful probes of supernova explosions, their engines and their progenitors. In addition, as we improve our understanding of these explosions, we can use nuclear yields to probe dense matter and neutrino physics, both of which play a critical role in the central supernova engine. Especially with upcoming gamma-ray detectors that can directly detect radioactive isotopes out to increasing distances from gamma-rays emitted during their decay, nuclear yields have the potential to provide some of the most direct probes of supernova engines and stellar burning. To utilize these probes, we must understand and limit the uncertainties in their production. Uncertainties in the nuclear physics can be minimized by combining both laboratory experiments and nuclear theory. Similarly, astrophysical uncertainties caused by simplified explosion trajectories can be minimized by higher-fidelity stellar-evolution and supernova-engine models. This paper reviews the physics and astrophysics uncertainties in modeling nucleosynthetic yields, identifying the key areas of study needed to maximize the potential of supernova yields as probes of astrophysical transients and dense-matter physics.

astro-ph.HE↗
arXiv2025

Binary Neutron Star Mergers as Potential Sources for Ultra-High-Energy Cosmic Rays and High-Energy Neutrinos

Recent studies suggest that the most energetic cosmic rays, exceeding 100 EeV, may primarily consist of $r$-process nuclei. This highlights binary neutron star mergers and collapsars as promising sources of ultra-high-energy cosmic rays (UHECRs). Building on these insights, we examine the conditions that facilitate the efficient production of UHE $r$-process nuclei during the prompt radiation (PR), extended emission (EE), and plateau emission phases of short gamma-ray bursts (sGRBs) following neutron star mergers. Our study reveals that jets associated with the PR phase, characterized by typical bulk Lorentz factors ($\gtrsim 400-500$), dissipation radii, and magnetic field strengths, can accelerate $r$-process nuclei to energies $\gtrsim 100$ EeV while preserving them during propagation within the source. Additionally, we investigate the production of HE neutrinos from photomeson and hadronic interactions, as well as from the $β$ decay of accelerated $r$-process nuclei. We find that the HE neutrino fluxes from sGRBs, mainly produced via photomeson interactions, are significantly limited to preserve the accelerated heavy nuclei, leading to lower fluxes than the predictions without allowing for contributions to UHECRs. Our results suggest that sGRBs may potentially contribute to UHECRs during the PR phase and to HE neutrinos during the EE phase$-$a scenario that can be tested by future neutrino observatories.

astro-ph.HE↗
arXiv2025

Scaling Relations in the Phase-Space Structure of Dark Matter Haloes

We present new scaling relations for the isotropic phase-space distribution functions (DFs) and energy distributions of simulated dark matter haloes. These relations are inspired by those for the singular isothermal sphere with density profile $ρ(r)\propto r^{-2}$, for which the DF satisfies $f(E) \propto r_{\max}^{-2}(E)$ and the energy distribution satisfies $dM/dE \propto r_{\max}(E)$, with $r_{\max}(E)$ being the radius where the gravitational potential equals energy $E$. For the simulated haloes, we find $f(E)\propto r_{\max}^{-2.08}(E)$ and $dM/dE \propto r_{\max}(E)$ across broad energy ranges. In addition, the proportionality coefficients depend on the gravitational constant and the parameters of the best-fit Navarro-Frenk-White density profile. These scaling relations are satisfied by haloes over a wide mass range and provide an efficient method to approximate their DFs and energy distributions. Understanding the origin of these relations may shed more light on halo formation.

astro-ph.GA↗
arXiv2025

emPDF: Inferring the Milky Way mass with data-driven distribution function in phase space

We introduce the emPDF (Empirical Distribution Function), a novel dynamical modeling method that infers the gravitational potential from kinematic tracers with optimal statistical efficiency under the minimal assumption of steady state. emPDF determines the best-fit potential by maximizing the similarity between instantaneous kinematics and the time-averaged phase-space distribution function (DF), which is empirically constructed from observation upon the theoretical foundation of oPDF (Han et al. 2016). This approach eliminates the need for presumed functional forms of DFs or orbit libraries required by conventional DF- or orbit-based methods. emPDF stands out for its flexibility, efficiency, and capability in handling observational effects, making it preferable to the popular Jeans equation or other minimal assumption methods, especially for the Milky Way (MW) outer halo where tracers often have limited sample size and poor data quality. We apply emPDF to infer the MW mass profile using Gaia DR3 data of satellite galaxies and globular clusters, obtaining enclosed masses of $M(<r)=26\pm8, 46\pm8, 90\pm13$, and $149\pm40 \times 10^{10}M_\odot$ at r=30, 50, 100, and 200 kpc, respectively. These are consistent with the updated constraints from simulation-informed DF fitting (Li et al. 2020). While the simulation-informed DF offers superior precision owing to the additional information extracted from simulations, emPDF is independent of such supplementary knowledge and applicable to general tracer populations. emPDF is currently implemented for tracers with complete 6D kinematics within spherical potentials, but it can potentially be extended to address more general problems.

astro-ph.GA↗
arXiv2024

Enhanced Muonization by Active-Sterile Neutrino Mixing in Protoneutron Stars

We study $ν_μ$-$ν_s$ and $\barν_μ$-$\barν_s$ mixing in the protoneutron star (PNS) created in a core-collapse supernova (CCSN). We point out the importance of the feedback on the general composition of the PNS in addition to the obvious feedback on the $ν_μ$ lepton number. We show that for our adopted mixing parameters $δm^2\sim 10^2$~keV$^2$ and $\sin^2 2θ$ consistent with the current constraints, sterile neutrino production is dominated by the Mikheyev-Smirnov-Wolfenstein conversion of $\barν_μ$ into $\barν_s$ and that the subsequent escape of $\barν_s$ increases the $ν_μ$ lepton number, which in turn enhances muonization of the PNS primarily through $ν_μ+n\to p+μ^-$. While these results are qualitatively robust, their quantitative effects on the dynamics and active neutrino emission of CCSNe should be evaluated by including $ν_μ$-$ν_s$ and $\barν_μ$-$\barν_s$ mixing in the simulations.

hep-ph↗
arXiv2024

Effects of Annihilation with Low-Energy Neutrinos on High-Energy Neutrinos from Binary Neutron Star Mergers and Rare Core-Collapse Supernovae

We explore the possibility that high-energy (HE) neutrinos produced from choked jets can be annihilated with low-energy (LE) neutrinos emitted from the accretion disk around a black hole in binary neutron star mergers and rare core-collapse supernovae. For HE neutrinos produced close to the stellar center ($\lesssim 10^{9}-10^{12}$ cm), we find that the emerging all-flavor spectrum for neutrinos of $E\gtrsim 0.1-1$ PeV could be modified by a factor $E^{-n}$ with $n\gtrsim 0.4-0.5$ under realistic conditions. Flavor evolution of LE neutrinos does not affect this result but can change the emerging flavor composition of HE neutrinos. As a consequence, the above annihilation effect may need to be considered for HE neutrinos produced from choked jets at small radii. We briefly discuss the annihilation effects for different HE neutrino production models and point out that such effects could be tested through precise measurements of the diffuse neutrino spectrum and flavor composition.

astro-ph.HE↗
arXiv2024

Phase Space Distribution Functions and Energy Distributions of Dark Matter Particles in Haloes

For a spherical dark matter halo with isotropic velocity distribution, the phase space distribution function (DF), the energy distribution, and the density profile form a set of self-consistent description of its equilibrium state, and knowing one is sufficient to determine the other two. The Navarro-Frenk-White density profile (NFW profile) is known to be a good approximation to the spherically-averaged density distribution in simulated haloes. The DARKexp energy distribution is also known to compare well with the simulated energy distribution. We present a quantitative assessment of the NFW and DARKexp fits to the simulated DF and energy distribution for a wide range of haloes in a dark-matter-only simulation from the IllustrisTNG Project. As expected, we find that the NFW fits work well except at low energy when the density at small radii deviates from the NFW profile. Further, the NFW and DARKexp fits have comparable accuracy in the region where both fit well, but the DARKexp fits are better at low energy because they require matching of the central gravitational potential. We also find an approximate relation between the energy scale parameterizing the DARKexp energy distribution and that defined by the characteristic density and radius of the NFW profile. This relation may be linked to the relaxation process during halo formation.

astro-ph.CO↗
arXiv2024

Neutrinos and nucleosynthesis of elements

Neutrinos are known to play important roles in many astrophysical scenarios from the early period of the big bang to current stellar evolution being a unique messenger of the fusion reactions occurring in the center of our sun. In particular, neutrinos are crucial in determining the dynamics and the composition evolution in explosive events such as core-collapse supernovae and the merger of two neutron stars. In this paper, we review the current understanding of supernovae and binary neutron star mergers by focusing on the role of neutrinos therein. Several recent improvements on the theoretical modeling of neutrino interaction rates in nuclear matter as well as their impact on the heavy element nucleosynthesis in the supernova neutrino-driven wind are discussed, including the neutrino-nucleon opacity at the mean field level taking into account the relativistic kinematics of nucleons, the effect due to the nucleon-nucleon correlation, and the nucleon-nucleon bremsstrahlung. We also review the framework used to compute the neutrino-nucleus interactions and the up-to-date yield prediction for isotopes from neutrino nucleosynthesis occurring in the outer envelope of the supernova progenitor star during the explosion. Here improved predictions of energy spectra of supernova neutrinos of all flavors have had significant impact on the nucleosynthesis yields. Rapid progresses in modeling the flavor oscillations of neutrinos in these environments, including several novel mechanisms for collective neutrino oscillations and their potential impacts on various nucleosynthesis processes are summarized.

astro-ph.HE↗
arXiv2024

Correlations and Distinguishability Challenges in Supernova Models: Insights from Future Neutrino Detectors

This paper explores core-collapse supernovae as crucial targets for neutrino telescopes, addressing uncertainties in their simulation results. We comprehensively analyze eighteen modern simulations and discriminate among supernova models using realistic detectors and interactions. A significant correlation between the total neutrino energy and cumulative counts, driven by massive lepton neutrinos and oscillations, is identified, particularly noticeable with the DUNE detector. Bayesian techniques indicate strong potential for model differentiation during a Galactic supernova event, with HK excelling in distinguishing models based on equation of state, progenitor mass, and mixing scheme.

astro-ph.HE↗
arXiv2023

Evolution of Tau-Neutrino Lepton Number in Protoneutron Stars due to Active-Sterile Neutrino Mixing

We present an approximate treatment of the mixing between $ν_τ$ ($\barν_τ$) and a sterile species $ν_s$ ($\barν_s$) with a vacuum mass-squared difference of $\sim$ 10$^2$-10$^3$ keV$^2$ in protoneutron stars created in core-collapse supernovae. Including production of sterile neutrinos through both resonant flavor conversion and collisions, we track the evolution of the $ν_τ$ lepton number due to both escape of sterile neutrinos and diffusion. Our approach provides a reasonable treatment of the pertinent processes discussed in previous studies and serves a pedagogical purpose to elucidate the relevant physics. We also discuss refinements needed to study more accurately how flavor mixing with sterile neutrinos affects protoneutron star evolution.

hep-ph↗
arXiv2023

A Data-Driven Model for Abundances in Metal-poor Stars and Implications for Nucleosynthetic Sources

We present a data-driven model for abundances of Fe, Sr, Ba, and Eu in metal-poor (MP) stars. The production patterns for core-collapse supernovae (CCSNe) and binary neutron star mergers (BNSMs) are derived from the data of Holmbeck et al. (arXiv:2007.00749) on [Sr/Fe], [Ba/Fe], and [Eu/Fe] for 195 stars. Nearly all the data can be accounted for by mixtures of contributions from these two sources. We find that on average, the Sr contribution to an MP star from BNSMs is $\approx 3$ times that from CCSNe. Our model is also consistent with the solar inventory of Fe, Sr, Ba, and Eu. We carry out a parametric $r$-process study to explore the conditions that can give rise to our inferred production patterns and find that such conditions are largely consistent with those from simulations of CCSNe and BNSMs. Our model can be greatly enhanced by accurate abundances of many $r$-process elements in a large number of MP stars, and future results from this approach can be used to probe the conditions in CCSNe and BNSMs in much more detail.

astro-ph.SR↗
arXiv2023

Signature of Collapsars as Sources for High-energy Neutrinos and $r$-process Nuclei

If collapsars are sources for both high-energy (HE) neutrinos and $r$-process nuclei, the profuse low-energy antineutrinos from $β$-decay of the newly-synthesized nuclei can annihilate the HE neutrinos. Considering HE neutrinos produced at internal shocks induced by intermittent mildly-magnetized jets, we show that such annihilation suppresses the overall HE neutrino spectrum at $\gtrsim 300$~TeV and produces a corresponding flavor composition of $(F_{ν_e+\barν_e}: F_{ν_μ+\barν_μ}: F_{ν_τ+\barν_τ})_\star \approx (1 : 10 : 1)$ at source. We find that the emergent HE neutrino flux can well fit the diffuse flux observed at IceCube if contributions from all similar sources are taken into account. Our results highlight the unique role of HE neutrinos in supporting collapsars as sources for $r$-process nuclei, and can be tested by accurate measurement of the diffuse HE neutrino flux spectrum and flavor composition, as well as detection of HE neutrinos from individual sources.

astro-ph.HE↗
arXiv2023

Symmetry and bipolar motion in collective neutrino flavor oscillations

We identify a geometric symmetry on the two-flavor Bloch sphere for collective flavor oscillations of a homogeneous dense neutrino gas. Based on this symmetry, analytical solutions to the periodic bipolar flavor evolution are derived. Using numerical calculations, we show that for configurations without this symmetry, the flavor evolution displays deviations from the bipolar flavor motion or even exhibits aperiodic patterns. We also discuss the implication of our finding for more general three-flavor and inhomogeneous cases.

hep-ph↗
arXiv2022

Probing Massive Star Nucleosynthesis with Data on Metal-Poor Stars and the Solar System

Metal-poor stars were formed during the early epochs when only massive stars had time to evolve and contribute to the chemical enrichment. Low-mass metal-poor stars survive until the present and provide fossil records of the nucleosynthesis of early massive stars. On the other hand, short-lived radionuclides (SLRs) in the early solar system (ESS) reflect the nucleosynthesis of sources that occurred close to the proto-solar cloud in both space and time. Both the ubiquity of Sr and Ba and the diversity of heavy-element abundance patterns observed in single metal-poor stars suggest that some neutron-capture mechanisms other than the r-process might have operated in early massive stars. Three such mechanisms are discussed: the weak s-process in non-rotating models with initial carbon enhancement, a new s-process induced by rapid rotation in models with normal initial composition, and neutron-capture processes induced by proton ingestion in non-rotating models. In addition, meteoritic data are discussed to constrain the core-collapse supernova (CCSN) that might have triggered the formation of the solar system and provided some of the SLRs in the ESS. If there was a CCSN trigger, the data point to a low-mass CCSN as the most likely candidate. An 11.8 solar mass CCSN trigger is discussed. Its nucleosynthesis, the evolution of its remnant, and the interaction of the remnant with the proto-solar cloud appear to satisfy the meteoritic constraints and can account for the abundances of the SLRs 41Ca, 53Mn, and 60Fe in the ESS.

astro-ph.SR↗
arXiv2022

Prospects for Distinguishing Supernova Models Using a Future Neutrino Signal

The next Galactic core-collapse supernova (SN) should yield a large number of observed neutrinos. Using Bayesian techniques, we show that with an SN at a known distance up to 25 kpc, the neutrino events in a water Cherenkov detector similar to Super-Kamiokande (SK) could be used to distinguish between seven one-dimensional neutrino emission models assuming no flavor oscillations or the standard Mikheyev-Smirnov-Wolfenstein effect. Some of these models could still be differentiated with an SN at a known distance of 50 kpc. We also consider just the relative distributions of neutrino energy and arrival time predicted by the models and find that a detector like SK meets the requirement to distinguish between these distributions with an SN at an unknown distance up to $\sim 10$ kpc.

astro-ph.HE↗