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Nuclear Theory·nucl-th

Wednesday·September 25, 2024

15 papers—4 primary·11 cross-listed

All15Primary4Cross-lists11
  1. 01

    Field redefinition and its impact in relativistic hydrodynamics

    Sayantani Bhattacharyya🇬🇧 · Sukanya Mitra🇮🇳 · Shuvayu Roy🇮🇳 · Rajeev Singh🇮🇳

    In this paper, we explore the impact of field redefinition on the spectrum of linearized perturbations in relativistic hydrodynamics. We observe that the spectrum of hydrodynamics modes is never affected by the local field redefinition, however, the spectrum of the non-hydrodynamic modes is affected. Through an appropriate all-order redefinition, non-hydrodynamic modes can be eliminated, leading to a new frame where the spectrum contains only hydrodynamic modes. We also observe that the resulting stress-energy tensor may have an infinite series in momentum space, with a convergence radius linked to the eliminated non-hydrodynamic mode. In certain special cases, higher-order terms in the stress-energy tensor under field redefinition may cancel, indicating that non-hydrodynamic modes are mere artefacts of the fluid variable choice and hold no physical significance, even if they appear to violate physical constraints. Using a special toy example, we find a criterion to distinguish between physical and unphysical non-hydrodynamic modes.

    nucl-thgr-qchep-phhep-thPRD(2025)·11 citations
  2. 02

    Nucleon thermalization hindered by isospin symmetry: Violation of eigenstate thermalization hypothesis in atomic nuclei

    Dong Bai · Zhongzhou Ren

    Bohr's compound nucleus theory is one of the most important models in nuclear physics, with far-reaching applications in nuclear science and technology. This model generally assumes that the participating nucleons attain a thermal equilibrium characterized by the microcanonical ensemble before subsequent decays. However, from a theoretical viewpoint, it remains uncertain whether this assumption is universally valid. In this Letter, we critically examine this longstanding assumption through the lens of the eigenstate thermalization hypothesis (ETH), a cornerstone of the modern quantum thermalization theory. Utilizing the time-dependent configuration interaction shell model, it is found that, in certain cases, the long-time averages of nucleon occupation numbers can exhibit significant deviations from the microcanonical ensemble averages, in contrast to the conventional expectation. We attribute this discrepancy primarily to the violation of the ETH in the presence of isospin symmetry and discover that incorporating a substantial isospin-breaking term into the shell-model Hamiltonian can effectively restore the nucleon thermalization.

    nucl-th0 citations
  3. 03

    Multicomponent Fermi systems at low densities

    C.J. Pethick · A. Schwenk

    We calculate, to second order in the scattering length between two fermions, the Landau quasiparticle interaction for a low-density mixture of two fermion species with unequal densities at temperature zero. From the Landau parameters we evaluate the energy density and find agreement with the result of Kanno, Prog. Theor. Phys. 44, 813 (1970). The calculations are then extended to the case of two fermion components with different total densities, each with two spin components, a situation of interest in nuclear physics and astrophysics, where the species are neutrons and protons. An interesting finding is that, for low proton concentrations, , the leading term in the energy density, beyond the contribution from the kinetic energy and the one due to the two-body interaction in the mean-field approximation, varies as . This is to be contrasted with the higher powers of implicit in many phenomenological energy-density functionals employed in nuclear physics, such as those of the Skyrme type.

    nucl-thastro-ph.HEcond-mat.quant-gasPRC(2025)·0 citations
  4. 04

    Equilibrium expectations for non-Gaussian fluctuations near a QCD critical point

    Jamie M. Karthein🇺🇸 · Maneesha Sushama Pradeep🇺🇸 · Krishna Rajagopal🇺🇸 · Mikhail Stephanov🇺🇸 · Yi Yin🇨🇳

    With the highly anticipated results from the Beam Energy Scan II program at RHIC being recently revealed, an understanding of particle-number fluctuations and their significance as a potential signature of a possible QCD critical point is crucial. Early works that embarked on this endeavor sought to estimate the fluctuations due to the presence of a critical point assuming they stay in equilibrium. From these results came the proposal to focus efforts on higher, non-Gaussian, moments of the event-by-event distributions, in particular of the number of protons. These non-Gaussian moments are especially sensitive to critical fluctuations, as their magnitudes are proportional to high powers of the critical correlation length. As the equation of state provides key input for hydrodynamical simulations of heavy-ion collisions, we estimate equilibrium fluctuations from the BEST equation of state (EoS) that includes critical features from the 3D Ising Model. In particular, the proton factorial cumulants and their dependence on non-universal mapping parameters is investigated within the BEST EoS. Furthermore, the correlation length, as a central quantity for the assessment of fluctuations in the vicinity of a critical point, is also calculated in a consistent manner with the scaling equation of state. An understanding of the equilibrium estimates of proton factorial cumulants will be useful for further comparison to estimates of out-of-equilibrium fluctuations in order to determine the magnitude of the observable fluctuations to be expected in heavy-ion collision experiments, in which the time spent near a critical point is short.

    nucl-thhep-phEPJ Web Conf.(2025)·4 citations

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