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Nuclear Theory·nucl-th

Thursday·February 19, 2026

11 papers—4 primary·7 cross-listed

All11Primary4Cross-lists7
  1. 01

    Solving BDNK diffusion using physics-informed neural networks

    Vicente Chomalí-Castro · Nick Clarisse · Nicki Mullins · Jorge Noronha

    In this work, we reformulate the relativistic BDNK (Bemfica-Disconzi-Noronha-Kovtun) diffusion equation in flux-conservative form, and solve the resulting equations in D using both a second-order Kurganov-Tadmor finite volume scheme and physics-informed neural networks (PINNs). In particular, we introduce the SA-PINN-ACTO framework, which combines the self-adaptive PINN technique with an exact enforcement of initial and periodic boundary conditions through an algebraic transform of the network's raw output, allowing the network to focus solely on minimizing the PDE residual. We test both approaches on smooth and discontinuous initial data, for both trivial and dynamically evolving velocity and temperature BDNK backgrounds, and for two characteristic speeds. The SA-PINN-ACTO method matches the converged Kurganov-Tadmor solutions for smooth profiles, while for discontinuous profiles the errors increase, reflecting an expected limitation of PINNs near sharp gradients.

    nucl-thastro-ph.HEgr-qc1 citation
  2. 02

    Rapidity dependence of mean transverse momentum fluctuation and decorrelation in baryon-dense medium

    Tribhuban Parida🇵🇱

    I study the event-by-event fluctuation and rapidity decorrelation of the mean transverse momentum , which has recently been proposed as a sensitive probe of the equation of state at finite baryon density. The investigation reveals that, in a baryon-rich medium, the event-by-event fluctuation of the mean transverse momentum is driven by the combined effects of energy-density and net-baryon-density fluctuations. Consequently, the rapidity dependence of this observable provides a promising handle to probe the three-dimensional structure of both energy and baryon density profiles. Previous studies have shown that decorrelation along rapidity is largely insensitive to shear and bulk viscosity; however, its dependence on baryon diffusion, another key transport coefficient in baryonic matter, has not been explored. I find that baryon diffusion has a negligible impact, establishing this observable as a robust probe of the equation of state. Furthermore, I present predictions for identified hadrons and observe a pronounced splitting in the rapidity decorrelation of mean transverse momentum between protons and antiprotons, indicating different transverse flow dynamics for baryons and antibaryons.

    nucl-thhep-phnucl-exPRC(2026)·1 citation
  3. 03

    The Crusts of Neutron Stars Revisited: Approximations within a Polytropic Equation of State Approach

    F. Köpp · J. E. Horvath · C. A. Z. Vasconcellos

    In this work, we revisit several thin-crust approximations presented in the literature and compare them with the exact solutions of the Tolman--Oppenheimer--Volkoff (TOV) equations. In addition, we employ three different equations of state (EoSs), including one with a pasta phase, each based on a distinct theoretical framework: the variational method, relativistic Brueckner--Hartree--Fock theory, and relativistic mean-field theory. We emphasize that these approximations require only the TOV solutions for the core and the EoS properties at the core--crust interface; in our approach, only the energy density is needed. Finally, the relativistic approximation, as well as the Newtonian approximation with corrections, shows good agreement with the exact solutions. This indicates that a simple treatment of the crust is sufficient for structural purposes, independently of the uncertainties in the sub-nuclear equation of state, which are not very large. The unified EoS SINPA (relativistic mean-field theory), including the pasta phase, was used to study the thin-crust approximation, while degeneracy in the -- relation is demonstrated through: (i) anisotropic pressure in the modified TOV equations, (ii) the gravity model, and (iii) dark matter admixture. As demonstrated, modifications to the description of gravitation introduce degeneracies in the mass--radius relation that are challenging to disentangle or quantify precisely.

    nucl-thEPJC(2026)·1 citation
  4. 04

    Comparison of Pauli projection and supersymetric transformation methods for three-body nuclear structure and reactions

    A. Deltuva

    Three-body Faddeev-type equations for bound, resonant, and scattering states in the systems with a nuclear core and two nucleons are solved using the momentum-space framework. Two approaches for eliminating the Pauli-forbidden deeply-bound states are compared: projecting out those states by a nonlocal term in the potential, and by using a supersymmetric transformation of the potential. While the former method is preferred by the experimental data for the deuteron-{He} scattering, the results for bound and resonant states do not indicate a clear superiority of a single method. Instead, systematic differences between them are found.

    nucl-thnucl-exPRC(2026)·0 citations

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first authorsco-authorsvia INSPIRE