Nuclear Theory·nucl-th

Tuesday·November 25, 2025

20 papers—7 primary·13 cross-listed

08
Exploring fixed points and eigenstates of quantum systems with reinforcement learning
María Laura Olivera-Atencio🇪🇸 · Jesús Casado-Pascual🇪🇸 · Denis Lacroix🇫🇷
We introduce a reinforcement learning algorithm designed to identify the fixed points of a given quantum operation. The method iteratively constructs the unitary transformation that maps the computational basis onto the basis of fixed points through a reward-penalty scheme based on quantum measurements. In cases where the operation corresponds to a Hamiltonian evolution, this task reduces to determining the Hamiltonian eigenstates. The algorithm is first benchmarked on random Hamiltonians acting on two and three qubits and then applied to many-body systems of up to six qubits, including the transverse-field Ising model and the all-to-all pairing Hamiltonian. In both cases, the algorithm is demonstrated to perform successfully; in the pairing model, it can also reveal hidden symmetries, which can be exploited to restrict learning to specific symmetry sectors. Finally, we discuss the possibility of post-selecting high-fidelity states even when full convergence has not been reached.
↳ quant-phcond-mat.str-elnucl-thPRResearch(2026)·0 citations
09
Geometry-induced azimuthal anisotropy in coherent $J / ψ$ photoproduction
Ding Yu Shao🇨🇳 · Han-Qing Yu🇨🇳 · Cheng Zhang🇨🇳 · Jian Zhou🇨🇳
Azimuthal anisotropies in heavy-ion collisions are conventionally interpreted as signatures of hydrodynamic flow. We demonstrate that in peripheral collisions, a significant $cos 2 ϕ$ asymmetry in the decay leptons of coherently photoproduced $J / ψ$ mesons arises purely from the initial-state geometry of the nuclear electromagnetic field. This modulation originates from the linear polarization of coherent photons, which is radially aligned in impact parameter space and transferred to the vector meson. By employing light-cone perturbation theory within the dipole formalism, we calculate the centrality dependence of this asymmetry for collisions at RHIC and LHC energies. Our predictions quantitatively reproduce STAR data. This observable thus provides a rigorous benchmark for distinguishing electromagnetic initial-state effects from collective medium dynamics.
↳ hep-phnucl-exnucl-thPRD(2026)·3 citations
10
Collinear spin correlations of final-state radiation in dense QCD matter
João M. Silva🇪🇸 · Alba Soto-Ontoso🇪🇸
Spin correlations are required to reproduce the correct azimuthal dependence of matrix elements for successive branchings at disparate angles in QCD jets. In this paper, we study modifications to this, $cos (2 ψ_{12})$ , azimuthal pattern in the presence of a quark-gluon plasma. To that end, we consider a simplified setup in which a narrow and energetic QCD antenna is formed inside a medium of fixed length and radiates a collinear emission outside it. The calculation includes both light and heavy-quarks. Further, we do not include medium-induced spin-flip interactions since they are energy suppressed in our formalism. We show that the amplitude of the azimuthal modulation in the presence of a medium is always suppressed with respect to the vacuum baseline, with its magnitude depending on the medium properties and splitting kinematics. For a medium with a momentum space anisotropy, we find that the azimuthal modulation acquires a phase shift, i.e., $cos (2 ψ_{12}) \to cos (2 ψ_{12} + ϕ_{med})$ , where $ϕ_{med}$ is a process-dependent function that again depends on the medium properties and splitting kinematics. This work provides theory guidance for implementing spin-driven interference effects in phenomenological studies of jet quenching in heavy-ion collisions.
↳ hep-phnucl-thJHEP(2026)·7 citations
11
Tensor network simulations of quasi-GPDs in the massive Schwinger model
Sebastian Grieninger🇺🇸 · Jake Montgomery🇺🇸 · Felix Ringer🇺🇸 · Ismail Zahed🇺🇸
Generalized Parton Distribution functions (GPDs) are off-diagonal light-cone matrix elements that encode the internal structure of hadrons in terms of quark and gluon degrees of freedom. In this work, we present the first nonperturbative study of quasi-GPDs in the massive Schwinger model, quantum electrodynamics in 1+1 dimensions (QED2), within the Hamiltonian formulation of lattice field theory. Quasi-distributions are spatial correlation functions of boosted states, which approach the relevant light-cone distributions in the luminal limit. Using tensor networks, we prepare the first excited state in the strongly coupled regime and boost it to close to the light-cone on lattices of up to 400 lattice sites. We compute both quasi-parton distribution functions and, for the first time, quasi-GPDs, and study their convergence for increasingly boosted states. In addition, we perform analytic calculations of GPDs in the two-particle Fock-space approximation and in the Reggeized limit, providing qualitative benchmarks for the tensor network results. Our analysis establishes computational benchmarks for accessing partonic observables in low-dimensional gauge theories, offering a starting point for future extensions to higher dimensions, non-Abelian theories, and quantum simulations.
↳ hep-lathep-phnucl-thquant-phPRD(2026)·7 citations
12
Proton mass decompositions in the NNLO QCD
Kazuhiro Tanaka (Juntendo Univ.)🇯🇵
Proton matrix elements of the QCD energy-momentum tensor (EMT) are expressed by the gravitational form factors. The forward values of the gravitational form factors allow for a decomposition of the proton mass into contributions from quarks and gluons, and further subdivisions into contributions from quark masses and from the QCD trace anomaly may be considered. We present the most recent evaluations of these mass decompositions, using a recent quantitative evaluation of the forward values of relevant gravitational form factors at the next-to-next-to-leading order (NNLO) QCD. We also calculate the renormalization scale dependence of each component within these decompositions. Furthermore, similar calculations are performed with another decomposition of the proton mass, organized strictly according to the separation into the traceless part and trace part for each of the gauge-invariant quark/gluon parts of the EMT, such that the former (twist-two) quark/gluon contributions of the EMT embody the effects of the partonic motions inside the proton, while the latter (twist-four) contributions are induced as parton correlations by non-perturbative QCD interactions. We demonstrate the advantages of this new decomposition. We also present the results for the pion, which exhibit quite different parton-correlation behaviors from the proton.
↳ hep-phhep-exhep-latnucl-ex+13 citations
13
Pion Valence-Quark TMD from Continuum Schwinger Function Methods and Gaussian GTMD
Minghui Ding🇨🇳
We employ the continuum Schwinger function method to investigate the unpolarized valence-quark transverse-momentum-dependent parton distribution function (TMD) of the pion at the hadron scale. The first seventeen generalized Mellin-transverse moments, constructed from lightlike and transverse vectors, are computed and found to be well described by a factorized ansatz, in which the longitudinal component coincides with the distribution function (DF) and the transverse momentum follows a Gaussian form. The Gaussianity relation between the mean and mean-squared transverse momenta is satisfied with approximately $99%$ accuracy in our numerical results, with the mean-squared transverse momentum equal to $0.231 GeV^{2}$ . Using the extracted TMD, we test the hypothesis that the quark's transverse spatial distribution also follows a Gaussian form and find that the resulting electromagnetic form factor is in good agreement with existing data. These results indicate that the intrinsic transverse-momentum and transverse-spatial distributions of valence quarks in the pion can be accurately approximated by a Gaussian ansatz, supporting its use in phenomenological analyses and experimental fits.
↳ hep-phnucl-th1 citation
14
Tracing the Trace Anomaly of Dense Matter inside Neutron Stars
Shiyue Ren🇨🇳 · Lap-Ming Lin🇨🇳
The trace anomaly $Δ$ is an important quantity that measures the broken conformal symmetry in neutron star matter. In this work, we present quasi-universal relations that connect the stellar profile of $Δ$ to the compactness, moment of inertia, and tidal deformability of neutron stars. We apply the quasi-universal relations to determine the trace anomaly profiles for PSR J0030+0451 and PSR J0740+6620 based on their mass-radius measurements. We also analyze PSR J0737-3039A according to its moment of inertia inferred from Bayesian modeling of nuclear equation of state. A recent multimessenger constraint on the tidal deformability is also studied, resulting in an estimate value of the trace anomaly $Δ_{c} = 0.177 0_{- 0.0432}^{+ 0.0365}$ at the center of a $1.4 M_{⊙}$ canonical neutron star. It is expected that more precise observations from both electromagnetic and gravitational-wave channels in the future will provide tighter constraints on the behavior of $Δ$ inside neutron stars.
↳ astro-ph.HEgr-qcnucl-thPRD(2026)·2 citations
15
A Nambu--Jona-Lasinio model of quantum chromodynamics and hadron structure
Parada T. P. Hutauruk🇰🇷
In this review paper, I present a study of the structure of the hadrons computed in the covariant Nambu-Jona-Lasinio model as the chiral effective quark theory of QCD. I describe how the NJL model is treated to imitate the spontaneous chiral symmetry breaking and confinement QCD properties. The consistency for the parton distribution functions and electromagnetic form factors, as internal structure observables, in comparison with existing data and other theoretical predictions, is also shown. The implications of mimicking the QCD properties in the NJL model for hadron structure observables, as well as the relevance of the results to EIC, EicC, and COMPASS/AMBER future experiments, are discussed.
↳ hep-phnucl-th1 citation
16
Scalarful double beta decay
Jordy de Vries🇳🇱 · Lukáš Gráf🇳🇱 · Vaisakh Plakkot🇳🇱 · Dominik Starý🇨🇿
We revisit scalar emissions in double beta decays of nuclei, often discussed in the context of Majoron models, in light of the latest developments on the study of neutrinoless double beta decay amplitudes from an effective field theory approach. The sensitivity of double beta decay experiments to this process is assessed through an analysis of spectral shapes, and the study is extended to massive scalars, scalars coupling to sterile neutrinos, and exotic right-handed effective couplings.
↳ hep-phnucl-thJHEP(2026)·6 citations
17
Projected Density Matrix Sampling for Lattice Hamiltonians
Abhishek Karna🇺🇸 · Hansen S. Wu🇺🇸 · Shailesh Chandrasekharan🇺🇸 · Ribhu K. Kaul🇺🇸
Quantum Monte Carlo methods are powerful tools for studying quantum many-body systems but face difficulties in accessing excited states and in treating sign problems. We present a continuous-time path-integral Monte Carlo method for computing the low-lying spectrum of generic quantum Hamiltonians within a projection subspace. The method projects the thermal density matrix onto a subspace spanned by a chosen set of linearly independent states. It is free of Trotter discretization errors and systematically converges to the low-energy states which have finite overlap with the projection subspace as the $β$ parameter increases. While most effective for systems without a sign problem, the method also yields information about low-energy spectra when sign problems are present. We illustrate the approach on two problems. For the sign-free case, we compute the first four low-energy levels in the scaling limit of the one-dimensional Ising model with both transverse and longitudinal fields, demonstrating the flow from the conformal limit to the massive $E_{8}$ quantum field theory. For the sign-problem case, we apply the method to the frustrated Shastry-Sutherland model and benchmark it against exact diagonalization on small lattices. We also present results for larger systems beyond the lattice sizes accessible to exact diagonalization, while limited to small $β$ where sign problems occur. Our method provides a general route toward quantum Monte Carlo spectroscopy for lattice Hamiltonians.
↳ cond-mat.str-elhep-latnucl-thPRD(2026)·3 citations
18
Magnetic susceptibility of a hot hadronic medium and quark degrees of freedom near the QCD cross-over point
Rupam Samanta🇵🇱 · Wojciech Broniowski🇵🇱
The lattice QCD results for the temperature-dependent magnetic susceptibility of the medium below the cross-over temperature are not possible to reconcile with the widely used Hadron Resonance Gas model, also amended with the physical magnetic moments of hadrons or the pion--vector-meson loops. As noticed earlier, one observes a substantially too strong diamagnetism at temperatures in the range above $\approx 120$ ~MeV compared to the lattice. This hints at a presence of quarks significantly below the QCD cross-over temperature, which are needed as a source of paramagnetism. However, the pions must be retained to describe the diamagnetism data at low temperatures. Therefore, we consider here a quark-meson approach, where the temperature-dependent quark masses are fixed in a model-free way using the baryon-baryon and baryon-strangeness susceptibilities from the lattice at zero magnetic field. The constituent quarks possess anomalous magnetic moments estimated from the octet baryon magnetic moments. The vacuum quark-loop and meson-loop contributions are duly incorporated. We show that in such a framework, one can describe the magnetic susceptibility up to the cross-over point. The qualitative conclusion is that the QCD degrees of freedom must extend far below the cross-over temperature, down to $\approx 120$ ~MeV.
↳ hep-phhep-latnucl-thPRC(2026)·2 citations
19
Nonlinear causality and stability of perfect spin hydrodynamics and its nonperturbative character
Samapan Bhadury🇵🇱 · Zbigniew Drogosz🇵🇱 · Wojciech Florkowski🇵🇱 · Sudip Kumar Kar🇵🇱 · Valeriya Mykhaylova🇵🇱
Four formulations of perfect spin hydrodynamics for spin-1/2 particles, distinguished by their treatment of spin (classical vs. quantum) and by the underlying particle statistics (Boltzmann vs. Fermi-Dirac), are analyzed and shown to satisfy the requirements of a divergence-type theory. Moreover, for all the formulations, we define the generating functions associated with the relevant thermodynamic currents and demonstrate that the constructed hydrodynamic theory is nonlinearly causal and stable. The latter is achieved by employing the exact expressions for the distribution functions, indicating a nonperturbative character of our approach.
↳ hep-phnucl-thPRD(2026)·5 citations
20
Numerical solution of the nonlinear boson diffusion equation for gluons
J. Rössler🇩🇪 · G. Wolschin🇩🇪
The nonlinear boson diffusion equation is taken as a basis to account for the fast thermalization of gluons in the initial stages of relativistic heavy-ion collisions. For constant drift and diffusion coefficients with schematic initial conditions, this equation has previously been solved exactly. In order to achieve a more realistic time evolution towards thermalization, energy-dependent transport coefficients are introduced, requiring numerical solutions of the nonlinear equation. Their accuracy is tested against the exact analytical results in the limit of constant coefficients. The consequences for transient gluon-condensate formation through elastic scatterings in overoccupied systems are discussed.
↳ hep-phnucl-thPhysica A(2026)·1 citation

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