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A. G. Grunfeld

Publications and source records attributed to A. G. Grunfeld.

48 records · Page 3Linked to original sources
arXiv2007

Equation of state for hybrid compact stars with a nonlocal chiral quark model

We study the thermodynamics of two flavor color superconducting (2SC) quark matter within a nonlocal chiral quark model, using both instantaneous and covariant nonlocal interactions. For applications to compact stars, we impose conditions of electric and color charge neutrality as well as beta equilibrium and construct a phase transition to the hadronic matter phase described within the Dirac-Brueckner-Hartree-Fock (DBHF) approach. We obtain mass-radius relations for hybrid star configurations which fulfill modern observational constraints, including compact star masses above 2 M_sun.

hep-ph↗
arXiv2007

Hybrid stars within a covariant, nonlocal chiral quark model

We present a hybrid equation of state (EoS) for dense matter in which a nuclear matter phase is described within the Dirac-Brueckner-Hartree-Fock (DBHF) approach and a two-flavor quark matter phase is modelled according to a recently developed covariant, nonlocal chiral quark model. We show that modern observational constraints for compact star masses (M ~ 2 M_sun) can be satisfied when a small vector-like four quark interaction is taken into account. The corresponding isospin symmetric EoS is consistent with flow data analyses of heavy ion collisions and points to a deconfinement transition at about 0.55 fm^-3.

nucl-th↗
arXiv2006

On covariant nonlocal chiral quark models with separable interactions

We present a comparative analysis of chiral quark models which include nonlocal covariant four-fermion couplings. We consider two alternative ways of introducing the nonlocality, as well as various shapes for the momentum-dependent form factors governing the effective interactions. In all cases we study the behavior of model parameters and analyze numerical results for constituent quark masses and quark propagator poles. Advantages of these covariant nonlocal schemes over instantaneous nonlocal schemes and the standard NJL model are pointed out.

hep-ph↗
arXiv2006

Phase diagram of neutral quark matter in nonlocal chiral quark models

We consider the phase diagram of two-flavor quark matter under neutron star constraints for two nonlocal, covariant quark models within the mean field approximation. In the first case (Model I) the nonlocality arises from the regularization procedure, motivated by the instanton liquid model, whereas in the second one (Model II) a separable approximation of the one-gluon exchange interaction is applied. We find that Model II predicts a larger quark mass gap and a chiral symmetry breaking (CSB) phase transition line which extends 15-20% further into the phase diagram spanned by temperature (T) and chemical potential (mu). The corresponding critical temperature at mu=0, T_c(0)~140 MeV, is in better accordance to recent lattice QCD results than the prediction of the standard local NJL model, which exceeds 200 MeV. For both Model I and Model II we have considered various coupling strengths in the scalar diquark channel, showing that different low-temperature quark matter phases can occur at intermediate densities: a normal quark matter (NQM) phase, a two-flavor superconducting (2SC) quark matter phase and a mixed 2SC-NQM phase. Although in most cases there is also a gapless 2SC phase, this occurs in general in a small region at nonzero temperatures, thus its effect should be negligible for compact star applications.

hep-ph↗
arXiv2005

Color Neutral Ground State of 2SC Quark Matter

We construct a new color neutral ground state of two-flavor color superconducting quark matter. It is shown that, in contrast with the conventionally considered ground state with diquark pairing in only one color direction, this new state is stable against arbitrary diquark fluctuations. In addition, the thermodynamical potential is found to be lower for this new state than for the conventional one.

hep-ph↗
arXiv2004

Two flavor color superconductivity in nonlocal chiral quark models

We study the competence between chiral symmetry restoration and two flavor color superconductivity (2SC) using a relativistic quark model with covariant nonlocal interactions. We consider two different nonlocal regulators: a Gaussian regulator and a Lorentzian regulator. We find that although the phase diagrams are qualitative similar to those obtained using models with local interactions, in our case the superconducting gaps at medium values of the chemical potential are larger. Consequently, we obtain that in that region the critical temperatures for the disappearance of the 2SC phase might be of the order of 100-120 MeV. We also find that for ratios of the quark-quark and quark-antiquark couplings somewhat above the standard value 3/4, the end point and triple point in the $T-μ$ phase diagram meet and a phase where both the chiral and diquark condensates are non-negligible appears.

hep-ph↗
arXiv2002

The Ideal Mixing Departure in Vector Meson Physics

In this work we study the departure for the ideal $ϕ-ω$ mixing angle in the frame of the Nambu-Jona-Lasinio model. We have shown that in that context, the flavour symmetry breaking is unable to produce the shifting in the mixing angle. We introduce a nonet symmetry breaking in the neutral vector sector to regulate the non-strange content of the $ϕ$ meson. The phenomenon is well reproduced by our proposal.

hep-ph↗
arXiv2001

Radiative decays of mesons in the NJL model

We revisit the theoretical predictions for anomalous radiative decays of pseudoscalar and vector mesons. Our analysis is performed in the framework of the Nambu-Jona-Lasinio model, introducing adequate parameters to account for the breakdown of chiral symmetry. The results are comparable with those obtained in previous approaches.

hep-ph↗
arXiv1998

The Klein-Gordon oscillator and the proper time formalism in a Rigged Hilbert sapace

The implications of manifestly covariant formulation of relativistic quantum mechanics depending on a scalar evolution parameter, canonically conjugated to the variable mass, is still an unsettled issue. In this work we find a complete set of generalized eigenfunctions of the Klein-Gordon Oscillator in the above mentioned formulation, in the Rigged Hilbert Space with Tempered Ultradistributions. We briefly comment on some models where this solution could be applied.

hep-ph↗
arXiv1997

Vacuum static Brans-Dicke wormhole

A simple Lorentzian vacuum wormhole solution of Brans-Dicke gravitation is presented and analysed. It is shown that such solution holds for both, the Brans-Dicke theory endowed with torsion (for a value of the coupling parameter $ω> 1/2$) and for the vacuum -no torsion- case (for $ω< -2$).

gr-qc↗
arXiv1997

Quarkonium spectra with a Klein-Gordon Oscillator as a confining potential

A quantum relativistic model is proposed to represent the confining potential of $c \bar{c}$ and $b \bar{b}$ mesons by using the Klein Gordon oscillator. We have solved the two-body problem obtaining the eigenvalues and the corresponding mass spectra, which fit very well with experimental data. We compare the results of our model with others obtained from different quark binding potentials.

hep-ph↗