scholarly journals Influence of the equation of state on a compact star made of hidden-sector nucleons

2020 ◽  
Vol 2020 (3) ◽  
Author(s):  
Shinji Maedan
Keyword(s):  
Equation Of State ◽  
Cold Dark Matter ◽  
Compact Star ◽  
Mean Field ◽  
Field Approximation ◽  
Compact Stars ◽  
Mean Field Approximation ◽  
Effective Theory ◽  
Hidden Sector ◽  
Two Parameters

Abstract We study a compact star made of degenerate hidden-sector nucleons which will be a candidate for cold dark matter. A hidden sector like quantum chromodynamics is considered, and as the low-energy effective theory we take the (hidden-sector) $ SU(2) $ chiral sigma model including a hidden-sector vector meson. With the mean field approximation, we find that one can treat the equation of state (EOS) of our model analytically by introducing a variable which depends on the Fermi momentum. The EOS is specified by the two parameters $ C'_{\sigma} $, $ C'_{\omega} $, and we discuss how these parameters affect the mass–radius relation for a compact star as well as the EOS. The dependence of the maximum stable mass of compact stars on the parameter $ C'_{\sigma} $ will also be discussed.

STELLAR STRUCTURE FROM QCD

2012 ◽  
Vol 18 ◽  
pp. 91-95
Author(s):  
BRUNO FRANZON ◽  
F. S. NAVARRA ◽  
DAVID FOGAÇA
Keyword(s):  
Equation Of State ◽  
Quark Gluon Plasma ◽  
Mean Field ◽  
Gluon Plasma ◽  
Field Approximation ◽  
Compact Stars ◽  
Stellar Structure ◽  
Mean Field Approximation

Using an equation of state based on a mean-field approximation for QCD (MQCD) to describe the cold quark gluon plasma we study the stellar structure of compact stars.

GLUONS IN THE STARS

2011 ◽  
Vol 20 (supp01) ◽  
pp. 183-188 ◽  
Author(s):  
DAVID A. FOGAÇA ◽  
BRUNO FRANZON ◽  
FERNANDO S. NAVARRA
Keyword(s):  
Equation Of State ◽  
Quark Gluon Plasma ◽  
Mean Field ◽  
Gluon Plasma ◽  
Field Approximation ◽  
Compact Stars ◽  
Mean Field Approximation ◽  
Astrophysical Data

Using an equation of state based on a mean-field approximation for QCD to describe the cold quark gluon plasma we study stellar structures of compact stars which are compatible with recent astrophysical data.1

scholarly journals Kinetic field theory: Non-linear cosmic power spectra in the mean-field approximation

2021 ◽  
Vol 10 (6) ◽  
Author(s):  
Matthias Bartelmann ◽  
Johannes Dombrowski ◽  
Sara Konrad ◽  
Elena Kozlikin ◽  
Robert Lilow ◽  
...  
Keyword(s):  
Field Theory ◽  
Power Spectrum ◽  
Mean Field ◽  
Power Spectra ◽  
Field Approximation ◽  
Density Fluctuations ◽  
Mean Field Approximation ◽  
Non Linear ◽  
Two Parameters ◽  
Kinetic Field

We use the recently developed Kinetic Field Theory (KFT) for cosmic structure formation to show how non-linear power spectra for cosmic density fluctuations can be calculated in a mean-field approximation to the particle interactions. Our main result is a simple, closed and analytic, approximate expression for this power spectrum. This expression has two parameters characterising non-linear structure growth which can be calibrated within KFT itself. Using this self-calibration, the non-linear power spectrum agrees with results obtained from numerical simulations to within typically \lesssim10\,\%≲10% up to wave numbers k\lesssim10\,h\,\mathrm{Mpc}^{-1}k≲10hMpc−1 at redshift z = 0z=0. Adjusting the two parameters to optimise agreement with numerical simulations, the relative difference to numerical results shrinks to typically \lesssim 5\,\%≲5%. As part of the derivation of our mean-field approximation, we show that the effective interaction potential between dark-matter particles relative to Zel’dovich trajectories is sourced by non-linear cosmic density fluctuations only, and is approximately of Yukawa rather than Newtonian shape.

scholarly journals ALTERNATIVE LINEAR CHIRAL MODELS FOR NUCLEAR MATTER

1999 ◽  
Vol 14 (24) ◽  
pp. 1615-1623 ◽  
Author(s):  
A. DELFINO ◽  
F. S. NAVARRA ◽  
M. NIELSEN ◽  
R. B. PRANDINI ◽  
M. CHIAPPARINI
Keyword(s):  
Equation Of State ◽  
Nuclear Matter ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Saturation Properties ◽  
The Mean

The equation of state of a family of alternative linear chiral models in the mean field approximation is discussed. We investigate the analogy between some of these models and current models in the literature, and we show that it is possible to reproduce very well the saturation properties of nuclear matter.

scholarly journals Delta Resonance Coupling with Walecka’s Mesons: Implications to Stellar Matter EoS

2017 ◽  
Vol 45 ◽  
pp. 1760034
Author(s):  
William Silva Gomes ◽  
José Carlos Teixeira de Oliveira ◽  
Hilário Rodrigues ◽  
Sérgio B. Duarte
Keyword(s):  
Phase Transition ◽  
Neutron Star ◽  
Equation Of State ◽  
Mean Field ◽  
Field Approximation ◽  
Coupling Constants ◽  
Mean Field Approximation ◽  
Stellar Matter ◽  
Baryonic Resonance ◽  
Resonance Coupling

In this work we have obtained the equation of state to the highly asymmetric dense stellar matter, using the nonlinear Walecka model in the mean field approximation. We discussed the implication of changes in coupling constant of the delta baryonic resonance on the observable of the neutron star. A detailed analysis of the equation of state and of the baryonic effective mass in respect to changes in the delta coupling constants is carried out. We focus attention on a new aspect observed for pressure when varying the baryonic density of the medium; a first order phase transition like a liquid-gas phase transition was observed for an acceptable range of delta coupled constant values. We have explored the implication of this aspect for the neutron star structure and their maximum masses.

KAON CONDENSATION AND THE NUCLEAR EQUATION OF STATE

2011 ◽  
Vol 20 (supp02) ◽  
pp. 140-145
Author(s):  
ROSANA O. GOMES ◽  
DIMITER HADJIMICHEF ◽  
CÉSAR A. Z. VASCONCELLOS ◽  
ALEXANDRE MESQUITA ◽  
MOISÉS RAZEIRA ◽  
...  
Keyword(s):  
Phase Transition ◽  
Equation Of State ◽  
Degrees Of Freedom ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Charge Neutrality ◽  
Nuclear Equation Of State ◽  
Kaon Condensation ◽  
The Mean

We study the effects of phase transition in the equation of state of a neutron star containing a condensate of anti-kaons, using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω, ϱ, and δ meson fields in the presence of electrons and muons to accomplish electric charge neutrality and beta equilibrium. The phase transition to the anti-kaons condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between hadron matter and the condensed of anti-kaons. In conclusion, we have found that isovector meson degrees of freedom contribute to tighten the Equation of State of Neutron Stars.

A MEAN FIELD THEORY FOR THE COLD QUARK GLUON PLASMA APPLIED TO STELLAR STRUCTURE

2012 ◽  
Vol 18 ◽  
pp. 81-85
Author(s):  
D. A. FOGAÇA ◽  
F. S. NAVARRA ◽  
B. FRANZON
Keyword(s):  
Quark Gluon Plasma ◽  
Mean Field Theory ◽  
Mean Field ◽  
Baryon Number ◽  
Gluon Plasma ◽  
Field Approximation ◽  
Compact Stars ◽  
Stellar Structure ◽  
Mean Field Approximation ◽  
Dense Stars

The quark gluon plasma (QGP) at zero temperature and high baryon number is a strongly interacting system that may exist in the core of dense stars. Using an equation of state based on a mean-field approximation of QCD to describe this cold QGP, we study the structure of compact stars and obtain masses which are compatible with recent astrophysical data.

scholarly journals Bosonic collective excitations in Fermi gases

2020 ◽  
pp. 2060009
Author(s):  
Niels Benedikter
Keyword(s):  
Correlation Energy ◽  
Weak Interactions ◽  
Random Phase ◽  
Mean Field ◽  
Quantum Correlations ◽  
Field Approximation ◽  
Collective Excitations ◽  
Mean Field Approximation ◽  
Effective Theory ◽  
Hartree Fock

Hartree–Fock theory has been justified as a mean-field approximation for fermionic systems. However, it suffers from some defects in predicting physical properties, making necessary a theory of quantum correlations. Recently, bosonization of many-body correlations has been rigorously justified as an upper bound on the correlation energy at high density with weak interactions. We review the bosonic approximation, deriving an effective Hamiltonian. We then show that for systems with Coulomb interaction this effective theory predicts collective excitations (plasmons) in accordance with the random phase approximation of Bohm and Pines, and with experimental observation.

The Determination of the Magnetoelectric Coupling Coefficient in Ferroelectric–Ferromagnetic Composite Based on PZT–Ferrite

2013 ◽  
Vol 58 (4) ◽  
pp. 1401-1403 ◽  
Author(s):  
J.A. Bartkowska ◽  
R. Zachariasz ◽  
D. Bochenek ◽  
J. Ilczuk
Keyword(s):  
Dielectric Permittivity ◽  
Coupling Coefficient ◽  
Mean Field ◽  
Field Approximation ◽  
Theoretical Description ◽  
Magnetoelectric Coupling ◽  
Mean Field Approximation ◽  
Dielectric Measurements ◽  
Temperature Dependences ◽  
Multiferroic Composite

Abstract In the present work, the magnetoelectric coupling coefficient, from the temperature dependences of the dielectric permittivity for the multiferroic composite was determined. The research material was ferroelectric-ferromagnetic composite on the based PZT and ferrite. We investigated the temperature dependences of the dielectric permittivity (") for the different frequency of measurement’s field. From the dielectric measurements we determined the temperature of phase transition from ferroelectric to paraelectric phase. For the theoretical description of the temperature dependence of the dielectric constant, the Hamiltonian of Alcantara, Gehring and Janssen was used. To investigate the dielectric properties of the multiferroic composite this Hamiltonian was expressed under the mean-field approximation. Based on dielectric measurements and theoretical considerations, the values of the magnetoelectric coupling coefficient were specified.

scholarly journals Hexagonal-Shaped Spin Crossover Nanoparticles Studied by Ising-Like Model Solved by Local Mean Field Approximation

2021 ◽  
Vol 7 (5) ◽  
pp. 69
Author(s):  
Catherine Cazelles ◽  
Jorge Linares ◽  
Mamadou Ndiaye ◽  
Pierre-Richard Dahoo ◽  
Kamel Boukheddaden
Keyword(s):  
Spin Crossover ◽  
Hexagonal Lattice ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Ligand Field ◽  
Order And Disorder ◽  
The Matrix ◽  
Local Mean ◽  
Parameter Values

The properties of spin crossover (SCO) nanoparticles were studied for five 2D hexagonal lattice structures of increasing sizes embedded in a matrix, thus affecting the thermal properties of the SCO region. These effects were modeled using the Ising-like model in the framework of local mean field approximation (LMFA). The systematic combined effect of the different types of couplings, consisting of (i) bulk short- and long-range interactions and (ii) edge and corner interactions at the surface mediated by the matrix environment, were investigated by using parameter values typical of SCO complexes. Gradual two and three hysteretic transition curves from the LS to HS states were obtained. The results were interpreted in terms of the competition between the structure-dependent order and disorder temperatures (TO.D.) of internal coupling origin and the ligand field-dependent equilibrium temperatures (Teq) of external origin.

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