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Nuclear Theory·nucl-th

Thursday·April 1, 2021

8 papers—5 primary·3 cross-listed

All8Primary5Cross-lists3
  1. 01

    Neutron stars with a crossover equation of state

    J. I. Kapusta🇺🇸 · T. Welle🇺🇸

    The question of whether quark matter exists in neutron stars is a long standing one. Generally one finds that a first order phase transition from baryons to quarks softens the equation of state so much that the star would collapse into a black hole. We consider a crossover equation of state, similar to the crossover that is found in lattice QCD studies at finite temperature and zero or small baryon chemical potentials. We find that with reasonable parameters it may be possible to support neutron stars up to about 2.2 solar masses. In that case 1 to 10% of the pressure would be contributed by quark matter in the central core of the highest mass stars.

    nucl-thPRC(2021)·45 citations
  2. 02

    Beta-decay formulas revisited (I): Gamow--Teller and spin-dipole contributions to allowed and first-forbidden transitions

    W. Horiuchi🇯🇵 · T. Sato🇯🇵 · Y. Uesaka🇯🇵 · K. Yoshida🇯🇵

    We propose formulas of the nuclear beta-decay rate that are useful in a practical calculation. The decay rate is determined by the product of the lepton and hadron current densities. A widely used formula relies upon the fact that the low-energy lepton wave functions in a nucleus can be well approximated by a constant and linear to the radius for the -wave and -wave wave functions, respectively. We find, however, the deviation from such a simple approximation is evident for heavy nuclei with large by numerically solving the Dirac equation. In our proposed formulas, the neutrino wave function is treated exactly as a plane wave, while the electron wave function is obtained by iteratively solving the integral equation, thus we can control the uncertainty of the approximate wave function. The leading-order approximation gives a formula equivalent to the conventional one and overestimates the decay rate. We demonstrate that the next-to-leading-order formula reproduces well the exact result for a schematic transition density as well as a microscopic one obtained by a nuclear energy-density functional method.

    nucl-thhep-phPTEP(2021)·8 citations
  3. 03

    Investigation of multi-step effects for proton inelastic scattering to the state in He

    Shoya Ogawa🇯🇵 · Takuma Matsumoto🇯🇵 · Yoshiko Kanada-En'yo🇯🇵 · Kazuyuki Ogata🇯🇵

    Multi-step effects between bound, resonant, and non-resonant states have been investigated by the continuum-discretized coupled-channels method (CDCC). In the CDCC, a resonant state is treated as multiple states fragmented in a resonance energy region, although it is described as a single state in usual coupled-channel calculations. For such the fragmented resonant states, one-step and multi-step contributions to the cross sections should be carefully discussed because the cross sections obtained by the one-step calculation depend on the number of those states, which corresponds to the size of the model space. To clarify the role of the multi-step effects, we propose the one-step calculation without model-space dependence for the fragmented resonant states. Furthermore, we also discuss the multi-step effects between the ground, resonant, and non-resonant states in He for proton inelastic scattering.

    nucl-thPRC(2021)·2 citations
  4. 04

    From noise to information: The transfer function formalism for uncertainty quantification on nuclear density reconstruction

    Giuliani Pablo🇺🇸 · Piekarewicz Jorge🇺🇸

    The neutron distribution of neutron-rich nuclei provides critical information on the structure of finite nuclei and neutron stars. Parity violating experiments -- such as PREX and CREX -- provide a clean and largely model-independent determination of neutron densities. Such experiments, however, are challenging and expensive which is why sound statistical arguments are required to maximize the information gained. For this goal we introduce a new framework, "the transfer function formalism", aimed at uncertainty quantification, model selection, and experimental design in the context of neutron densities. The transfer functions (TFs) are built analytically by expressing the linear response of the objective function to small perturbations of the data. Using the TF formalism, we are able to analyze the expected overall uncertainty -- quantified in terms of bias and variance -- of the mean square radius and interior density of Ca and Pb. Using relativistic mean field models as a proxy for the weak-charge density -- and assuming that a total of five measurements could be performed on the weak form factor of Ca and Pb -- we identify the optimal models and experimental locations that minimize the combined radius and interior uncertainty for both nuclei. We also explore the use of the TF formalism to understand the influence of prior distributions for the model parameters, as well as the optimization of model hyperparameters not constrained by the data.

    nucl-thPRC(2021)·5 citations
  5. 05

    Diffuse relaxation approximation in a heated Fermi system

    S.V. Lukyanov🇺🇦

    An expression for the two-particle relaxation time of collective excitations on a distorted Fermi surface in the diffusion approach to kinetic theory is obtained. The general case of momentum-dependent diffusion and drift coefficients is considered. The temperature dependence of the obtained expression is established.

    nucl-thIJMPE(2021)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE