arXiv subjects

Jin-Biao Gu

Publications and source records attributed to Jin-Biao Gu.

11 recordsLinked to original sources

arXiv2026

Isospin-Driven Splitting of Chemical Potentials in Isobar Collisions from Lattice QCD

Strong magnetic fields produced in relativistic heavy-ion collisions can modify fluctuations of conserved charges and, consequently, their associated chemical potentials. We present first-principles $(2+1)$-flavor lattice-QCD results for isospin-driven splittings of conserved-charge chemical potentials between the isobar systems $^{96}_{44}\mathrm{Ru}+^{96}_{44}\mathrm{Ru}$ and $^{96}_{40}\mathrm{Zr}+^{96}_{40}\mathrm{Zr}$ in the QCD crossover region, both at vanishing and nonzero magnetic fields along the pseudo-critical line $T_{pc}(eB)$. We outline a framework that, under strangeness neutrality and charge-to-baryon ratio $r\equiv n_{\rm Q}/n_{\rm B}$, maps the isospin difference between two nuclei, as encoded in $r_{\rm Zr}$ and $r_{\rm Ru}$, onto splitting ratios $Δμ_{\rm Q}/Δμ_{\rm B}$, $Δμ_{\rm S}/Δμ_{\rm B}$, and $Δμ_{\rm S}/Δμ_{\rm Q}$ as functions of $μ_{\rm B}(r_{\rm Ru})/Δμ_{\rm B}$. Using continuum-estimated lattice results for the leading-order coefficients $q_1\equiv(μ_{\rm Q}/μ_{\rm B})_{\rm LO}$ and $s_1\equiv(μ_{\rm S}/μ_{\rm B})_{\rm LO}$, we find that, at vanishing magnetic field, the splitting ratios are of similar magnitude to recent Bayesian extractions from STAR isobar data and yield $Δμ_{\rm Q}<0$ and $Δμ_{\rm S}>0$, with the electric-charge sector dominating. At nonzero magnetic fields, the splitting ratios show only moderate $eB$ dependence. We therefore further examine Ru--Zr differences in the normalized magnetic-field response of chemical-potential ratios, particularly those involving $μ_{\rm Q}/μ_{\rm B}$, which display a pronounced enhancement in lattice QCD. We also present hadron resonance gas (HRG) results and experimentally motivated proxy observables with kinematic cuts to facilitate contact with experiment.

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arXiv2026

QCD in strong magnetic fields: fluctuations of conserved charges and equation of state

We present continuum-estimated (2+1)-flavor lattice QCD results for second-order fluctuations of conserved charges and the leading-order equation of state in the presence of strong magnetic fields at nonzero baryon chemical potential, using the HISQ action at the physical pion mass. The baryon-electric charge correlation $χ^{\rm BQ}_{11}$ exhibits striking sensitivity to the magnetic field: $R_{cp}$-like double ratios $χ^{\rm BQ}_{11}/χ^{\rm Q}_{2}$ and $χ^{\rm BQ}_{11}/χ^{\rm QS}_{11}$ reach enhancements of $\sim2$ and $\sim2.25$ at $eB \simeq 8M_π^2$ along the transition line, establishing $χ^{\rm BQ}_{11}$ as a magnetometer of QCD. To bridge theoretical predictions and experimental observations, we construct HRG-based proxy observables and apply systematic kinematic cuts emulating STAR and ALICE detector acceptances, which retain $\sim80\%$ of the lattice QCD magnetic sensitivity. Extending to the QCD equation of state under strangeness neutrality and isospin asymmetry, we determine the chemical potential ratio $q_1\equiv(μ_{\rm Q}/μ_{\rm B})_{\rm LO}$ and the pressure coefficient $P_2$ for magnetic field strengths up to $eB \simeq 0.8~{\rm GeV}^2 \sim 45 M_π^2$. The results reveal temperature-band crossings, hierarchy reversals, and non-monotonic structures driven by the nontrivial interplay between thermal and magnetic effects.

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arXiv2025

QCD in strong magnetic fields: fluctuations of conserved charges and EoS

Strong magnetic fields can profoundly affect the equilibrium properties, characterized by the equation of state and bulk thermodynamics of strongly interacting matter. Although such fields are expected in off-central heavy-ion collisions, directly measuring their experimental imprints remains extremely challenging. To address this, we propose the baryon-electric charge correlations $χ^{\rm BQ}_{11}$ and the chemical potential ratio $μ_{\rm Q}/μ_{\rm B}$ as magnetic-field-sensitive probes, based on (2+1)-flavor QCD lattice simulations at physical pion masses. Along the transition line, $χ^{\rm BQ}_{11}$ and $(μ_{\rm Q}/μ_{\rm B})_{\rm LO}$ in Pb-Pb collisions increase by factors of 2.1 and 2.4 at $eB \simeq 8M_π^2$, respectively. To bridge theoretical predictions and experimental observations, we construct HRG-based proxies and apply systematic kinematic cuts to emulate STAR and ALICE detector acceptances. Furthermore, we extend this investigation to the QCD equation of state, and examine the leading-order thermodynamic coefficients for strangeness-neutral scenarios up to $eB \simeq 0.8 {\rm GeV}^2 \sim 45 m_π^2$, revealing intriguing non-monotonic structures.

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arXiv2025

Baryon Electric Charge Correlation as QCD Magnetometer

The detection of strong magnetic fields in peripheral heavy-ion collisions is crucial for observing effects such as the chiral magnetic effect but has proven exceptionally difficult. To address this, we propose the baryon electric charge correlation $χ^{\rm BQ}_{11}$ and the chemical potential ratio $μ_{\rm Q}/μ_{\rm B}$ as sensitive probes of magnetic fields, based on (2+1)-flavor lattice QCD simulations at the physical pion mass. Along the transition line, $χ^{\rm BQ}_{11}$ and $(μ_{\rm Q}/μ_{\rm B})_{\rm LO}$ in Pb-Pb collisions increase by factors of 2.1 and 2.4 at $eB \simeq 8M_π^2$, respectively. To bridge theoretical predictions with experimental observables, we implement systematic kinematic cuts that emulate detector acceptances of the STAR and ALICE experiments within the hadron resonance gas model. This allows us to construct experimentally relevant proxy observables. Furthermore, we demonstrate that $(μ_{\rm Q}/μ_{\rm B})_{\rm LO}$ is also sensitive to the collision system, showing a $1.5$-fold increase from Zr-Zr to Ru-Ru isobar collisions. Our findings offer new insights into thermo-magnetic effects and provide experimentally relevant guidance for the detection of magnetic fields in heavy-ion collisions.

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arXiv2025

Leading-Order QCD Equation of State in Strong Magnetic Fields at Nonzero Baryon Chemical Potential

We present continuum-estimated $(2+1)$-flavor lattice QCD results for the leading-order Taylor expansion coefficients of the equation of state in strong magnetic fields and at nonzero baryon chemical potential. Simulations employ the highly improved staggered quark (HISQ) action with physical pion masses on lattices of temporal extent $N_τ= 8,\,12$, covering $145 \lesssim T \lesssim 165~\mathrm{MeV}$ and $eB \lesssim 0.8~\mathrm{GeV}^2$, imposing strangeness neutrality with baseline results at electric charge to baryon number ratio $r = 0.4$. We determine the $T$--$eB$ dependence of $q_1$ and $s_1$ (electric charge and strangeness chemical potential ratios), pressure coefficient $P_2$, baryon number density coefficient $N_1^{\rm B}$, and energy-like coefficients $Θ_2$ (trace anomaly), $ε_2$ (energy density), and $σ_2$ (entropy density). Magnetic fields induce temperature-band crossings for $q_1$ and $P_2$ and non-monotonic structures in the energy-like coefficients, with $Θ_2$ at strong fields possibly vanishing or turning negative at higher $T$, indicating dominance of the pressure term over the energy contribution. We also examine the $r$-dependence, finding that $r=0$ (charge-neutral matter) shows the most muted magnetic-field enhancement of $P_2$ despite larger $|q_1|$, providing a useful reference for neutron-star-like conditions. Comparisons with the hadron resonance gas (HRG) model show qualitative agreement at low $T$ and weak $eB$, with clear deviations near the crossover and at strong fields. These results provide useful input for constraining models and effective theories of QCD matter in strong magnetic fields at finite baryon density.

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arXiv2025

Second order fluctuations of conserved charges in external magnetic fields

We present a first-principles lattice QCD investigation of second-order fluctuations of and correlations among conserved charges -- baryon number (B), electric charge (Q), and strangeness (S) -- in the presence of external magnetic fields. Our study employs lattice simulations of (2+1)-flavor QCD with physical pion masses using highly improved staggered fermions (HISQ) on $48^3 \times 12$ and $32^3 \times 8$ lattices, covering a wide range of magnetic field strengths up to $eB \simeq 0.8$ GeV$ ^2$. We identify clear signals of magnetic field-induced modifications to these fluctuations and correlations, with the baryon-electric charge correlation, $χ^{\rm BQ}_{11}$, exhibiting particularly strong sensitivity to the magnetic field. To bridge theoretical predictions with experimental observables, we implement systematic kinematic cuts that emulate detector acceptances of the STAR and ALICE experiments within the hadron resonance gas (HRG) model and construct proxy observables for fluctuations measurable in heavy-ion collision experiments. Our findings highlight $χ^{\rm BQ}_{11}$ as a promising ``magnetometer" for probing the presence of magnetic fields in QCD matter. Furthermore, we explore experimentally relevant ratios involving $χ^{\rm BQ}_{11}$, demonstrating their potential in mitigating volume effects and enhancing sensitivity to magnetic fields in collision environments. Additionally, we assess the limitations of the HRG model at strong magnetic fields, revealing deviations that indicate nontrivial modifications to hadronic degrees of freedom. These results offer new insights into the interplay between thermal and magnetic effects in the QCD phase diagram and provide experimentally relevant guidance for the detection of magnetic fields in heavy-ion collisions.

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arXiv2025

Chiral condensates and screening masses of neutral pseudoscalar mesons from lattice QCD at physical quark masses

We investigate the effects of temperature $T$ and external magnetic fields $eB$ on the chiral condensates and screening masses of neutral pseudoscalar mesons, including $π^0$, $K^0$, and $η_{s\bar{s}}^0$, in (2+1)-flavor lattice QCD with physical quark masses. The chiral condensates are intrinsically connected to the screening masses via Ward-Takahashi identities, with the latter characterizing the inverse of the spatial correlation length in the pseudoscalar channel. Using highly improved staggered quarks, we perform simulations on lattices with temporal extents $N_τ= 8, 12, 16$ and an aspect ratio of 4, covering five temperatures from 145 MeV to 166 MeV. For each temperature, eight magnetic field strengths are simulated, reaching up to $eB \sim 0.8$ GeV$^2$. These simulations allow us to provide continuum estimates for the chiral condensates and screening masses. We observe intricate behavior in the light ($ud$), strange-light ($ds$) and strange ($s$) quark condensates as functions of the magnetic field and temperature, reflecting the competition between magnetic catalysis and inverse magnetic catalysis effects. This complex behavior is also mirrored in the screening masses of the neutral pseudoscalar mesons. Notably, the screening masses of $π^0$ and $K^0$ exhibit a non-monotonic dependence on $eB$, closely following the variations in their corresponding chiral condensates. Meanwhile, the screening mass of $η_{s\bar{s}}^0$ decreases monotonically with increasing $eB$. These findings provide valuable insights for understanding the behavior of QCD in a thermomagnetic medium and can serve as benchmarks for low-energy QCD models and effective theories.

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arXiv2025

Pseudoscalar Screening Mass at Finite Temperature and Magnetic Field from Lattice QCD with Physical Quark Masses

Understanding the screening mass of pseudoscalar mesons at finite temperature and magnetic field is crucial for comprehending the behavior of strongly interacting matter under extreme conditions, such as those found in the early universe or inside neutron stars. Additionally, in heavy ion collisions, strong magnetic fields are generated, which could significantly influence the properties of the quark-gluon plasma. The study of these screening masses provides insight into the modifications of mesonic properties in such environments, which is essential for the theoretical understanding of Quantum Chromodynamics (QCD) phase transitions and the properties of the quark-gluon plasma. Here, we present continuum estimated lattice QCD results on the screening mass of neutral pseudoscalar mesons at finite temperatures and nonzero magnetic fields. The simulations used (2+1)-flavor lattice QCD simulations using physical quark masses employing the HISQ/tree action. The continuum estimation was carried out using lattices having temporal extents $N_τ$ = 8, 12, and 16, all having aspect ratio $N_σ/N_τ$ = 4. The investigated temperature ranges from 145 MeV to 166 MeV, while the magnetic field strength varies from 0 to 1 GeV$^2$. We discuss the dependence of the screening masses of various neutral pseudoscalar mesons on temperature, magnetic field strength, and quark mass.

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arXiv2025

Baryon-Electric Charge Correlations and Chemical Potentials as Probes of Magnetized QCD

We present the first lattice QCD results of quadratic fluctuations and correlations of conserved charges in (2+1)-flavor lattice QCD in the presence of a background magnetic field. The simulations were performed using the Highly Improved Staggered Quarks with physical pion mass $m_π$ = 135 MeV on $N_τ=8$ and 12 lattices. We find that the correlation between net baryon number and electric charge, denoted as $χ^{\rm BQ}_{11} $, can serve as a magnetometer of QCD. At pseudocritical temperatures ($T_{pc}$) the $χ^{\rm BQ}_{11}$ starts to increase rapidly with magnetic field strength $eB \gtrsim 2M^2_π$ and by a factor 2 at $eB\simeq 8 M^2_π$. By comparing with the hadron resonance gas model, we find that the $eB$ dependence of $χ^{\rm BQ}_{11}$ is mainly due to the doubly charged $Δ$(1232) baryon. Although the doubly charged $Δ$(1232) could not be detected experimentally, its decay products, protons and pions, retain the $eB$ dependence of $Δ$(1232)'s contribution to $χ^{\rm BQ}_{11}$. Furthermore, the ratio of electric charge chemical potential to baryon chemical potential, $μ_{\rm Q}/μ_{\rm B}$, shows significant dependence on the magnetic field strength and varies with the ratio of electric charge to baryon number in the colliding nuclei in heavy ion collisions. These results provide baselines for effective theory and model studies, and both $χ^{\rm BQ}_{11}$ and $μ_{\rm Q}/μ_{\rm B}$ could be useful probes for the detection of magnetic fields in relativistic heavy ion collision experiments as compared with corresponding results from the hadron resonance gas model.

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arXiv2025

QCD Equation of State with Strong Magnetic Fields and Nonzero Baryon Density

In this work, we have carried out lattice simulations of $(2+1)$-flavor QCD using highly improved staggered quarks at the physical pion mass on $32^3 \times 8$ and $48^3 \times 12$ lattices, with magnetic field strengths ranging up to 0.8 GeV$^2$ and nonzero baryon chemical potentials employing the Taylor expansion framework. We present lattice QCD continuum estimate results, along with the magnetized hadron resonance and ideal gas comparisons, for the leading-order Taylor expansion coefficients for bulk thermodynamic quantities such as pressure, number density, energy density, and entropy density, focusing on the significant impact of strong magnetic fields.

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arXiv2024

Baryon electric charge correlation as a magnetometer of QCD

The correlation between net baryon number and electric charge, $χ_{11}^{\rm BQ}$, can serve as a magnetometer of QCD. This is demonstrated by lattice QCD computations using the highly improved staggered quarks with physical pion mass of $M_π=135~$MeV on $N_τ=8$ and 12 lattices. We find that $χ_{11}^{\rm BQ}$ along the transition line starts to increase rapidly with magnetic field strength $eB\gtrsim 2M_π^2$ and by a factor 2 at $eB\simeq 8M_π^2$. Furthermore, the ratio of electric charge chemical potential to baryon chemical potential, $μ_{\rm Q}/μ_{\rm B}$, shows significant dependence on the magnetic field strength and varies from the ratio of electric charge to baryon number in the colliding nuclei in heavy ion collisions. These results can provide baselines for effective theory and model studies, and both $χ_{11}^{\rm BQ}$ and $μ_{\rm Q}/μ_{\rm B}$ could be useful probes for the detection of magnetic fields in relativistic heavy ion collision experiments as compared with corresponding results from the hadron resonance gas model.

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