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Nuclear Theory·nucl-th

Monday·April 20, 2020

8 papers—3 primary·5 cross-listed

All8Primary3Cross-lists5
  1. 04

    Weak magnetic field corrections to light vector or axial mesons mixings and vector meson dominance

    Fábio L. Braghin🇧🇷

    Weak magnetic field induced corrections to effective coupling constants describing light vector mesons mixings and vector meson dominance (VMD) are derived. The magnetic field must be weak with respect to an effective quark mass such that: or .For that, a flavor SU(2) quark-quark interaction due to non perturbative one gluon exchange is considered. By means of methods usually applied to the Nambu Jona Lasinio (NJL) and Global Color Models (GCM), leading light vector/axial mesons couplings to a background electromagnetic field are derived. The corresponding effective coupling constants are resolved in the structureless mesons and longwavelength limits. Some of the resulting coupling constants are redefined such as to become magnetic field induced corrections to vector or axial mesons couplings. Due to the approximated chiral symmetry of the model, light axial mesons mixings induced by the magnetic field are also obtained. Some numerical estimates are presented for the coupling constants and for some of the corresponding momentum dependent vertices. The contributions of the induced VMD and vector mesons mixing couplings for the low momentum pion electromagnetic form factor and for the (off shell) charge symmetry violation potential at the constituent quark level are estimated. The relative overall weak magnetic field-induced anisotropic corrections are of the order of , where or respectively.

    ↳ hep-phnucl-thJ.Phys.G(2020)·8 citations
  2. 05

    Broken SU(6) symmetry and massive hybrid stars

    Luiz L. Lopes🇧🇷 · Debora P. Menezes🇧🇷

    In this work we revisit the quantum hadrodynamics (QHD) formalism to investigate hyperonic and hybrid stars with hyperon-meson couplings fixed via broken SU(6) group, in favor of a more general flavor group SU(3). We also employ an additional channel, the strangeness-hidden meson, which couples only to the hyperons. In hybrid stars, the quark phase is built with the SU(3) NJL model also with an additional vector channel in the Lagrangian. We found that within the models chosen the hyperon puzzle cannot be avoided by the quark-hadron phase transition, once the hyperon threshold always happens at lower density. Also, the contribution of the quark core in a hybrid star is more relavant to the radius than to the mass, and strongly depends on the quark equation of state. We are able to reproduce 2.21 hyperonic star and 2.10 hybrid star. Both results are in agreement with the recently detected hyper massive pulsar MSP J0740+6620.

    ↳ astro-ph.HEnucl-thNPA(2021)·48 citations
  3. 06

    Thermodynamic equilibrium of massless fermions with vorticity, chirality and magnetic field

    Matteo Buzzegoli🇮🇹

    The present thesis aimed to examine the effects of vorticity on the thermodynamics of relativistic quantum systems. We extend the Zubarev's non-equilibrium statistical operator method to address quantum effects induced by vorticity in the presence of chiral matter and external electromagnetic field and keeping full covariant and quantum properties of the system. To investigate the effects of vorticity, this work has been focused on systems consisting of massless chiral fermions. We recovered the significant quantum phenomena known in the literature, namely the chiral magnetic effect, the chiral vortical effect, the axial vortical effect and the chiral separation effect and we also revealed the presence of additional effects at second-order on thermal vorticity. This study has also identified and presented the exact solutions of thermal states for a system at global thermal equilibrium consisting of chiral massless fermions under the action of an external constant homogeneous magnetic field. Taking advantage of these exact solutions and conservation equations, the study also proved that the thermal coefficients related to first-order effects on thermal vorticity do not receive corrections from the external electromagnetic field. The same argument revealed existing relations between those thermal coefficients, even connecting coefficients related to vorticity to other related to electromagnetic field. For instance, this analysis has found that the chiral vortical effect and the chiral magnetic effect conductivities are connected one to the other by a differential equation. Therefore, this research provides the first steps into deriving the relations between the effects and the interplay of electromagnetic fields and vorticity.

    ↳ hep-thgr-qcnucl-th6 citations
  4. 07

    Estimating the values and variations of neutron star observables by dense nuclear matter properties

    Péter Pósfay🇭🇺 · Gergely Gábor Barnaföldi🇭🇺 · Antal Jakovác🇭🇺

    Recent NICER observation data on PSR J0030+0451 has recently added a unique mass-radius constraint on the properties of the superdense nuclear matter existing in the interior of compact stars. Such a macroscopic data restrict further the microscopical models, elementary interactions, and their parameters, however, with reasonable margin because of the masquarade problem. Here our goal is to identify the origin and quantify the magnitude of the theoretical uncertainties of the nuclear matter models. A detailed study on the effect of different interaction terms and the nuclear parameter values in the Lagrangian of the extended - model is presented here. The equation of state was inserted to the Tolman--Oppenheimer--Volkoff equation and observable parameters of the neutron star were calculated. We identified, that the optimal Landau effective mass is the most relevant physical parameter modifying the macroscopic observable values. Moreover, the compressibility and symmetry energy terms just generate one-one order of magnitude smaller effect to this, respectively. We calculated the linear relations between the maximal mass of a compact star and these microscopic nuclear parameter values within the physical relevant parameters range. Based on the mass observational data we estimated the magnitude of the radii of PSR J1614-2230, PSR J0348+0432, and PSR J0740+6620 including theoretical uncertainties arising from the models' interaction terms and their parameter values choices.

    ↳ astro-ph.HEhep-phnucl-th4 citations
  5. 08

    Quarkyonic Matter Equation of State in Beta-Equilibrium

    Tianqi Zhao🇺🇸 · James M. Lattimer🇺🇸

    Quark matter may appear due to a hadronic-quark transition in the core of a hybrid star. Quarkyonic matter is an approach in which both quarks and nucleons appear as quasi-particles in a crossover transition, and provides an explicit realization of early ideas concerning quark matter (e.g., the MIT bag model). This description has recently been employed by McLerran and Reddy to model chargeless (pure neutron) matter with an approach that has the virtue that the speed of sound rises quickly at a neutron-quark transition so as to satisfy observational constraints on the neutron star maximum mass () and the radius of a star ( km). Traditional models involving first-order transitions result in softer pressure-energy density relations that have difficulty satisfying these constraints except with very narrow choices of parameters. We propose a variation of quarkyonic matter involving protons and leptons whose energy can be explicitly minimized to achieve both chemical and beta equilibrium, which cannot be done in the chargeless formulation. Quarkyonic stellar models are able to satisfy observed mass and radius constraints with a wide range of model parameters, avoiding the obligatory fine-tuning of conventional hybrid star models, including requiring the transition density to be very close to the nuclear saturation density. Our formulation fits experimental and theoretical properties of the nuclear symmetry energy and pure neutron matter, and contains as few as three free parameters. This makes it an ideal tool for the study of high-density matter that is an efficient alternative to piecewise polytrope or spectral decomposition methods.

    ↳ astro-ph.HEnucl-thPRD(2020)·142 citations

Affiliations

first authorsco-authorsvia INSPIRE