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Nuclear Theory·nucl-th

Friday·April 27, 2018

7 papers—4 primary·3 cross-listed

All7Primary4Cross-lists3
  1. 01

    [Submitted on 26 Apr 2018]

    BCS Pairing Gap in the Infrared Limit of the Similarity Renormalization Group

    Sergio Szpigel · Varese Salvador Timoteo · Enrique Ruiz Arriola

    Effective interactions have been used to compute the pairing gap for nuclear and neutron matter in several schemes. In this work we analyze the impact of phase-shift equivalent interactions within the BCS theory on the -channel pairing gap for a translational invariant many-fermion system such as nuclear and neutron matter. We solve the BCS pairing gap equation on a finite momentum grid for a toy model separable Gaussian potential in the -channel explicitly evolved through the Similarity Renormalization Group (SRG) transformation and show that in the on-shell and continuum limits the pairing gap vanishes. For finite size systems the momentum is quantized and the on-shell limit is realized for SRG cutoffs comparable to the momentum resolution. In this case the pairing gap can be computed directly from the scattering phase-shifts by an energy-shift formula. While the momentum grid is usually used as an auxiliary way of solving the BCS pairing gap equation, we show that it actually encodes some relevant physical information, suggesting that in fact finite grids may represent the finite size of the system.

    Comments:
    05 Pages, 03 Figures. Talk presented at the XIV International Workshop on Hadron Physics, Florianopolis, Brazil, March 2018
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1804.09857 [pdf]
    0 citations
  2. 02

    [Submitted on 26 Apr 2018]

    Surface tension of quark droplets in compact stars and in the early universe

    A. G. Grunfeld🇦🇷 · G. Lugones🇧🇷

    We review the role of the surface tension of quark matter droplets in astrophysical conditions, focusing specifically on the thermodynamic conditions prevailing in cold neutron stars (NSs), in hot lepton rich proto NSs, and in early universe conditions. We analyze quark matter in chemical equilibrium under weak interactions, which is relevant for understanding the internal composition of hybrid stars, as well as just deconfined quark matter out of chemical equilibrium, which is the relevant thermodynamic state for describing the nucleation process of quark matter in NSs. We explore the role of temperature, density, trapped neutrinos, droplet size and magnetic fields within the multiple reflection expansion formalism (MRE). Quark matter is described within the frame of different effective models: the MIT bag model and the Nambu-Jona-Lasinio model (NJL), including color superconductivity, neutrino trapping and magnetic fields. We also analyze the deconfinement transition at vanishing chemical potential and finite temperature including the Polyakov loop. We explore some astrophysical consequences of our results.

    Comments:
    Poster presented at the XIV International Workshop on Hadron Physics, Florianópolis, Brazil, March 2018
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1804.09898 [pdf]
    1 citation
  3. 03

    [Submitted on 26 Apr 2018]

    Equilibrium of nuclear matter in QCD sum rules

    E.G. Drukarev🇷🇺 · M.G. Ryskin🇷🇺 · V.A. Sadovnikova (St. Petersburg, PNPI)🇷🇺

    We calculate the nucleon parameters in symmetric nuclear matter employing the QCD sum rules approach. We focus on the average energy per nucleon and study the equilibrium states of the matter. We treat the matter as a relativistic system of interacting nucleons. Assuming the dependence of the nucleon mass on the light quark mass to be more important than that of nucleon interactions we find that the contribution of the relativistic nucleons to the scalar quark condensate can be expressed as that caused by free nucleons at rest multiplied by the density dependent factor . We demonstrate that there are no equilibrium states while we include only the condensates with dimension . There are equilibrium states if we include the lowest order radiative corrections and the condensates with . They manifest themselves for the nucleon sigma term MeV. Including the condensates with we find equilibrium states of nuclear matter for MeV. In all cases the equilibrium states are due to influence of the relativistic motion of the nucleons composing the matter on the scalar quark condensate.

    Comments:
    26 pages, 10 figure
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1804.10031 [pdf]
    EPJA(2019)·3 citations
  4. 04

    [Submitted on 26 Apr 2018]

    Towards a Unified Quark-Hadron Matter Equation of State for Applications in Astrophysics and Heavy-Ion Collisions

    Niels-Uwe F. Bastian🇵🇱 · David Blaschke🇵🇱 · Tobias Fischer🇵🇱 · Gerd Röpke🇩🇪

    We outline an approach to a unified equation of state for quark-hadron matter on the basis of a derivable approach to the generalized Beth-Uhlenbeck equation of state for a cluster decomposition of thermodynamic quantities like the density. To this end we summarize the cluster virial expansion for nuclear matter and demonstrate the equivalence of the Green's function approach and the derivable formulation. For an example, the formation and dissociation of deuterons in nuclear matter is discussed. We formulate the cluster derivable approach to quark-hadron matter which allows to take into account the specifics of chiral symmetry restoration and deconfinement in triggering the Mott-dissociation of hadrons. This approach unifies the description of a strongly coupled quark-gluon plasma with that of a medium-modified hadron resonance gas description which are contained as limiting cases. The developed formalism shall replace the common two-phase approach to the description of the deconfinement and chiral phase transition that requires a phase transition construction between separately developed equations of state for hadronic and quark matter phases. Applications to the phenomenology of heavy-ion collisions and astrophysics are outlined.

    Comments:
    35 pages, 3 figures, Special Issue "Compact Stars in the QCD Phase Diagram"
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1804.10178 [pdf]
    Universe(2018)·44 citations

Affiliations

first authorsco-authorsvia INSPIRE