arXiv subjects

Jia Ni

Publications and source records attributed to Jia Ni.

3 recordsLinked to original sources

arXiv2026

Chiral Response of QCD Topology across the Thermal Crossover

We introduce a novel relation connecting the light-quark-mass derivative of the topological susceptibility in quantum chromodynamics (QCD) to the connected correlation between the squared topological charge and the integrated light-quark scalar density. This relation gives direct access to the chiral response of QCD topology---the local logarithmic light-quark-mass derivative of the susceptibility---from a single ensemble at fixed quark masses for each temperature, without additional simulations at shifted masses. Applying this relation to $(2+1)$-flavor lattice QCD at $m_π\simeq220\,\mathrm{MeV}$ over temperatures ranging from well below to well above the chiral crossover, we find that the response rises rapidly through the crossover from approximately unity toward two. This evolution corresponds to a change from nearly linear to nearly quadratic dependence of the topological susceptibility on the light-quark mass. Using the chiral response as the exponent of a local power law in the light-quark mass, we determine its effective amplitude from the topological susceptibility. This amplitude exhibits a maximum near the crossover temperature, reflecting the competition between the decreasing topological susceptibility and the increasing chiral response. These results reveal a thermal reorganization of the quark-mass dependence of QCD topology beyond the suppression of topological fluctuations alone.

hep-lat↗

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.

hep-lat↗

arXiv2026

Channel-Level Semantic Perturbations: Unlearnable Examples for Diverse Training Paradigms

The unauthorized use of personal data in model training has emerged as a growing privacy threat. Unlearnable examples (UEs) address this issue by embedding imperceptible perturbations into benign examples to obstruct feature learning. However, existing studies mainly evaluate UEs under from-scratch training settings, leaving their behavior under the widely adopted pretraining-finetuning (PF) paradigm largely unexplored. In this work, we provide the first systematic investigation of unlearnable examples across diverse training paradigms. Our analysis reveals that loading and freezing pretrained weights significantly weakens the effectiveness of existing UEs methods. We further explain these findings through semantic filtering: while UEs tend to induce models to overfit non-semantic noise, thereby weakening their semantic extraction capabilities, under the PF paradigm, frozen shallow layers preserve data semantics, effectively filtering out distracting information like unlearnable noise. Guided by these insights, we propose a hierarchical deception strategy, Shallow Semantic Camouflage (SSC), that confines the generation process to a semantically valid subspace, aiming to bypass the semantic suppression introduced by pretrained weights. Extensive experiments demonstrate that our method consistently preserves data unlearnability even under challenging training paradigms, such as shallow-layer freezing and semantic-focused pretraining (SF-Pretrain), bridging the critical gap in pretrain-based unlearnable learning.

cs.LG↗