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Nuclear Theory·nucl-th

Monday·June 3, 2019

7 papers—2 primary·5 cross-listed

All7Primary2Cross-lists5
  1. 01

    Perey-effect in Continuum-Discretized Coupled-Channel description of reactions

    M. Gómez-Ramos · N. K. Timofeyuk

    The Perey-effect in two-body channels of reactions has been known for a long time. It arises when the nonlocal two-body deuteron-target and/or proton-target problem is approximated by a local one, manifesting itself in a reduction of the scattering channel wave functions in the nuclear interior. However, the reaction mechanism requires explicit accounting for three-body dynamics involving the target and the neutron and proton in the deuteron. Treating nonlocality of the nucleon-target interactions within a three-body context requires significant effort and demands going beyond the widely-used adiabatic approximation, which can be done using a continuum-discretized coupled-channel (CDCC) method. However, the inclusion of nonlocal interactions into the CDCC description of reactions has not been developed yet. Here, we point out that, similarly to the two-body nonlocal case, nonlocality in a three-body channel can be accounted for by introducing the Perey factors. We explain this procedure and present the first CDCC calculations to our knowledge including the Perey-effect.

    nucl-thJ.Phys.G(2019)·3 citations
  2. 02

    Topological defects at the boundary of neutron superfluids in neutron stars

    Shigehiro Yasui🇯🇵 · Chandrasekhar Chatterjee🇯🇵 · Muneto Nitta🇯🇵

    We study surface effects of neutron superfluids in neutron stars. superfluids are in uniaxial nematic (UN), D biaxial nematic (BN), or D BN phase, depending on the strength of magnetic fields from small to large. We suppose a neutron superfluid in a ball with a spherical boundary. Adopting a suitable boundary condition for condensates, we solve the Ginzburg-Landau equation to find several surface properties for the neutron superfluid. First, the phase on the surface can be different from that of the bulk, and symmetry restoration or breaking occurs in general on the surface. Second, the distribution of the surface energy density has an anisotropy depending on the polar angle in the sphere, which may lead to the deformation of the geometrical shape of the surface. Third, the order parameter manifold induced on the surface, which is described by two-dimensional vector fields induced on the surface from the condensates, allows topological defects (vortices) on the surface, and there must exist such defects even in the ground state thanks to the Poincaré-Hopf theorem: although the numbers of the vortices and antivortices depend on the bulk phases, the difference between them is topologically invariant (the Euler number ) irrespective of the bulk phases. These vortices, which are not extended to the bulk, are called boojums in the context of liquid crystals and helium-3 superfluids. The surface properties of the neutron superfluid found in this paper may provide us useful information to study neutron stars.

    nucl-thastro-ph.HEcond-mat.supr-conhep-thPRC(2020)·16 citations
  3. 03

    Universality of the critical point mapping between Ising model and QCD at small quark mass

    Maneesha Sushama Pradeep🇺🇸 · Mikhail Stephanov🇺🇸

    The universality of the QCD equation of state near the critical point is expressed by mapping pressure as a function of temperature and baryon chemical potential in QCD to Gibbs free energy as a function of reduced temperature and magnetic field in the Ising model. The mapping parameters are, in general, not universal, i.e., determined by details of the microscopic dynamics, rather than by symmetries and long-distance dynamics. In this paper we point out that in the limit of small quark masses, when the critical point is close to the tricritical point, the mapping parameters show universal dependence on the quark mass . In particular, the angle between the and lines in the plane vanishes as . We discuss possible phenomenological consequences of these findings.

    ↳ hep-phcond-mat.stat-mechhep-latnucl-thPRD(2019)·46 citations
  4. 04

    Ultracentral Collisions of Small and Deformed Systems at RHIC: , , , , , and Collisions

    J. Noronha-Hostler🇮🇱 · N. Paladino🇺🇸 · S. Rao🇺🇸 · Matthew D. Sievert🇺🇸 · Douglas E. Wertepny🇺🇸

    In this paper, we study a range of collision systems involving deformed ions and compare the elliptic and triangular flow harmonics produced in a hydrodynamics scenario versus a color glass condensate (CGC) scenario. For the hydrodynamics scenario, we generate initial conditions using TRENTO and work within a linear response approximation to obtain the final flow harmonics. For the CGC scenario, we use the explicit calculation of two-gluon correlations taken in the high- ``(semi)dilute-(semi)dilute'' regime to express the flow harmonics in terms of the density profile of the collision. We consider ultracentral collisions of deformed ions as a testbed for these comparisons because the difference between tip-on-tip and side-on-side collisions modifies the multiplicity dependence in both scenarios, even at zero impact parameter. We find significant qualitative differences in the multiplicity dependence obtained in the initial conditions+hydrodynamics scenario and the CGC scenario, allowing these collisions of deformed ions to be used as a powerful discriminator between models. We also find that sub-nucleonic fluctuations have a systematic effect on the elliptic and triangular flow harmonics which are most discriminating in ultracentral symmetric collisions of small deformed ions and in collisions. The collision systems we consider are , , , , , and .

    ↳ hep-phnucl-thNPA(2021)·14 citations
  5. 05

    Exact solution of multi-angle quantum many-body collective neutrino flavor oscillations

    Ermal Rrapaj🇺🇸

    I study the flavor evolution of a dense neutrino gas by considering vacuum contributions, matter effects and neutrino self-interactions. Assuming a system of two flavors in a uniform matter background, the time evolution of the many-body system in discretized momentum space is computed. The multi-angle neutrino-neutrino interactions are treated exactly and compared to both the single-angle approximation and mean field calculations. %The time unit chosen is . The mono-energetic two neutrino beam scenario is solved analytically. I proceed to solve flavor oscillations for mono-energetic cubic lattices and quadratic lattices of two energy levels. In addition I study various configurations of twelve, sixteen, and twenty neutrinos. I find that when all neutrinos are initially of the same flavor, all methods agree. When both flavors are present, I find collective oscillations and flavor equilibration develop in the many body treatment but not in the mean field method. This difference persists in dense matter with tiny mixing angle and it can be ascribed to non-negligible flavor polarization correlations being present. Entanglement entropy is significant in all such cases. The relevance for supernovae or neutron stars mergers is contingent upon the value of the normalization volume and the large dependence of the timescale associated with oscillations. In future work, I intend to study this dependence using larger lattices and also include anti-neutrinos.

    ↳ hep-phnucl-thPRC(2020)·68 citations
  6. 06

    Nuclear level densities and gamma-ray strength functions in samarium isotopes

    F. Naqvi · A. Simon · M. Guttormsen · R. Schwengner · S. Frauendorf · C.S. Reingold · J.T. Burke · N. Cooper · R.O. Hughes · S. Ota · A. Saastamoinen

    The gamma-strength functions and level densities in the quasi-continuum of 147;149Sm isotopes have been extracted from particle-coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148;150Sm targets and the reaction products were recorded by the Hyperion array. An upbend in the low-energy region of the gSF has been observed. The systematic analysis of the gSF for a range of Sm isotopes highlights the interplay between scissors mode and the upbend. Shell-model calculations show reasonable agreement with the experimental gSFs and confirm the correspondence between the upbend and scissors mode.

    ↳ nucl-exnucl-thPRC(2019)·23 citations
  7. 07

    Chiral effective field theory description of neutrino nucleon-nucleon Bremsstrahlung in supernova matter

    Gang Guo🇩🇪 · Gabriel Martínez-Pinedo🇩🇪

    We revisit the rates of neutrino pair emission and absorption from nucleon-nucleon bremsstrahlung in supernova matter using the -matrix formalism in the long-wavelength limit. Based on two-body potentials of chiral effective field theory (EFT), we solve the Lippmann-Schwinger equation for the -matrix including non-diagonal contributions. We consider final-state Pauli blocking and hence our calculations are valid for nucleons with an arbitrary degree of degeneracy. We also explore the in-medium effects on the -matrix and find that they are relatively small for supernova matter. We compare our results with one-pion exchange rates, commonly used in supernova simulations, and calculations using an effective on-shell diagonal -matrix from measured phase shifts. We estimate that multiple-scattering effects and correlations due to the random phase approximation introduce small corrections on top of the -matrix results at subsaturation densities. A numerical table of the structure function is provided that can be used in supernova simulations.

    ↳ astro-ph.HEhep-phnucl-thApJ(2019)·22 citations

Affiliations

first authorsco-authorsvia INSPIRE