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Nuclear Theory·nucl-th

Monday·April 30, 2018

6 papers—3 primary·3 cross-listed

All6Primary3Cross-lists3
  1. 01

    [Submitted on 26 Apr 2018]

    Finite-temperature relativistic nuclear field theory: an application to the dipole response

    Elena Litvinova🇺🇸 · Herlik Wibowo🇺🇸

    Nuclear response theory beyond the one-loop approximation is formulated for the case of finite temperature. For this purpose, the time blocking approximation to the time-dependent part of the in-medium nucleon-nucleon interaction amplitude is adopted for the thermal (imaginary-time) Green's function formalism. We found that introducing a soft blocking, instead of a sharp blocking at zero temperature, brings the Bethe-Salpeter equation to a single frequency variable equation also at finite temperatures. The method is implemented self-consistently in the framework of Quantum Hadrodynamics and designed to connect the high-energy scale of heavy mesons and the low-energy domain of nuclear medium polarization effects in a parameter-free way. In this framework, we investigate the temperature dependence of dipole spectra in the even-even nuclei Ca, Sn and Sn with a special focus on the giant dipole resonance's width problem and on the low-energy dipole strength distribution.

    Comments:
    Article; 5 pages, 2 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1804.10228 [pdf]
    PRL(2018)·33 citations
  2. 02

    [Submitted on 27 Apr 2018]

    Review on the progress in nuclear fission

    Karl-Heinz Schmidt🇫🇷 · Beatriz Jurado🇫🇷

    An overview is given on some of the main advances in experimental methods, experimental results and theoretical models and ideas of the last years in the field of nuclear fission. New experimental approaches extended the availability of fissioning systems considerably and provided a full identification of all fission products in A and Z for the first time. In particular, the transition from symmetric to asymmetric fission around 226Th and some unexpected structure in the mass distributions in the fission of systems around Z = 80 to 84 as well as an extended systematics of the odd-even effect in fission fragment Z distributions have been measured [A. N. Andreyev et al., Rep. Progr. Phys. 81 (2018) 016301]. Three classes of theoretical descriptions of fission presently appear to be the most promising or the most successful ones: Self-consistent quantum-mechanical models fully consider the quantum-mechanical features of the fission process. Intense efforts are presently made to develop suitable theoretical tools [N. Schunck, L. M. Robledo, Rep. Prog. Phys. 79 (2016) 116301] for modeling the non-equilibrium, large-amplitude collective motion leading to fission. Stochastic, essentially classical models provide a fully developed technical framework. The main features of the fission-fragment mass distribution are well reproduced from mercury to fermium and beyond [P. Möller, J. Randrup, Phys. Rev. C 91 (2015) 044316]. In an alternative semi-empirical approach [K.-H. Schmidt et al., Nucl. Data Sheets 131 (2016) 107], considerable progress in describing the fission observables has been achieved by combining several general theoretical concepts. This new approach reveals a high degree of regularity and allows calculating high-quality data with a unique parameter set for a large number of systems and an extended excitation-energy range.

    Comments:
    70 pages, 41 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1804.10421 [pdf]
    Rept.Prog.Phys.(2018)·166 citations
  3. 03

    [Submitted on 27 Apr 2018]

    Net baryon diffusion in fluid dynamic simulations of relativistic heavy-ion collisions

    Gabriel S. Denicol🇧🇷 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦 · Akihiko Monnai🇫🇷 · Björn Schenke🇺🇸 · Chun Shen🇺🇸

    A hybrid (hydrodynamics + hadronic transport) theoretical framework is assembled to model the bulk dynamics of relativistic heavy-ion collisions at energies accessible in the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) and the NA61/SHINE experiment at CERN. The system's energy-momentum tensor and net baryon current are evolved according to relativistic hydrodynamics with finite shear viscosity and non-zero net baryon diffusion. Our hydrodynamic description is matched to a hadronic transport model in the dilute region. With this fully integrated theoretical framework, we present a pilot study of the hadronic chemistry, particle spectra, and anisotropic flow. Phenomenological effects of a non-zero net-baryon current and its diffusion on hadronic observables are presented for the first time. The importance of the hadronic transport phase is also investigated.

    Comments:
    22 pages, 22 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1804.10557 [pdf]
    PRC(2018)·217 citations
  4. 04

    [Submitted on 26 Apr 2018] (cross-list from hep-ph)

    Searching for the QCD critical point via the rapidity dependence of cumulants

    Jasmine Brewer🇺🇸 · Swagato Mukherjee🇺🇸 · Krishna Rajagopal🇺🇸 · Yi Yin🇺🇸

    The search for a possible critical point in the QCD phase diagram is ongoing in heavy ion collision experiments at RHIC which scan the phase diagram by scanning the beam energy; a coming upgrade will increase the luminosity and extend the rapidity acceptance of the STAR detector. In fireballs produced in RHIC collisions, the baryon density depends on rapidity. By employing Ising universality together with a phenomenologically motivated freezeout prescription, we show that the resulting rapidity dependence of cumulant observables sensitive to critical fluctuations is distinctive. The dependence of the kurtosis (of the event-by-event distribution of the number of protons) on rapidity near mid-rapidity will change qualitatively if a critical point is passed in the scan. Hence, measuring the rapidity dependence of cumulant observables can enhance the prospect of discovering a critical point, in particular if it lies between two energies in the beam energy scan.

    Comments:
    6 pages, 2 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1804.10215 [pdf]
    PRC(2018)·56 citations
  5. 05

    [Submitted on 26 Apr 2018] (cross-list from cond-mat.quant-gas)

    Polarized fermions in one dimension: density and polarization from complex Langevin calculations, perturbation theory, and the virial expansion

    Andrew C. Loheac🇺🇸 · Jens Braun🇩🇪 · Joaquín E. Drut🇺🇸

    We calculate the finite-temperature density and polarization equations of state of one-dimensional fermions with a zero-range interaction, considering both attractive and repulsive regimes. In the path-integral formulation of the grand-canonical ensemble, a finite chemical potential asymmetry makes these systems intractable for standard Monte Carlo approaches due to the sign problem. Although the latter can be removed in one spatial dimension, we consider the one-dimensional situation in the present work to provide an efficient test for studies of the higher-dimensional counterparts. To overcome the sign problem, we use the complex Langevin approach, which we compare here with other approaches: imaginary-polarization studies, third-order perturbation theory, and the third-order virial expansion. We find very good qualitative and quantitative agreement across all methods in the regimes studied, which supports their validity.

    Comments:
    9 pages, 6 figures
    Subjects:
    Quantum Gases (cond-mat.quant-gas); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1804.10257 [pdf]
    PRD(2018)·17 citations
  6. 06

    [Submitted on 26 Apr 2018] (cross-list from hep-ex)

    A model of antineutron annihilation in experimental searches for neutron-antineutron transformations

    Elena S. Golubeva🇷🇺 · Joshua L. Barrow🇺🇸 · Charles G. Ladd🇺🇸

    Searches for baryon number violation, including searches for proton decay and neutron-antineutron transformation, are expected to play an important role in the evolution of our understanding of beyond Standard Model physics. The neutron-antineutron transformation is a key prediction of certain popular theories of baryogenesis, and the experiments such as the Deep Underground Neutrino Experiment and the European Spallation Source plan to search for this process with bound- and free-neutron systems. Accurate simulation of this process in Monte Carlo will be important for the proper reconstruction and separation of these rare events from background. This article presents developments towards accurate simulation of the annihilation process for use in a cold, free neutron beam for neutron-antineutron searches from antineutron-carbon annihilation, as carbon-12 is the target of choice for the European Spallation Source's NNBar Collaboration. Initial efforts are also made in this paper to perform analogous studies for intra-nuclear transformation searches in argon-40 nuclei, although this latter work will be properly addressed in our next publication.

    Comments:
    24 pages, 13 figures, 5 tables, 54 references, European Spallation Source NNbar Collaboration signal simulation article
    Subjects:
    High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
    arXiv:
    1804.10270 [pdf]
    PRD(2019)·37 citations

Affiliations

first authorsco-authorsvia INSPIRE