arXiv subjects

I. Zakout

Publications and source records attributed to I. Zakout.

13 recordsLinked to original sources

arXiv2011

Polyakov loops, Gross-Witten like point and Hagedorn states

The phase transition for a finite volume system that incorporates the Polyakov loops and maintains the colorless state is explored using the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. The order parameter for Polyakov loops is demonstrated to signal the appearance of a transition for $SU(3)_{c}$ analogous to Gross-Witten (GW-) phase transition instead of the deconfinement phase transition to quark-gluon plasma. The asymptotic restoration of Polyakov loops is conjectured to be a threshold production for meta-stable Hagedorn (or semi-QGP) states and this does not imply a direct deconfinement phase transition. In this context, the GW-like point is the point where the colorless states switches from the low-lying hadronic states to the meta-stable high-lying Hagedorn states. The chiral phase transition takes place within an extended GW-like point depending on the fireball's size. The deconfinement phase transition is determined by Hagedorn's temperature above GW-like temperature.

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arXiv2008

Exact One Loop Running Couplings in the Standard Model

Taking the dominant couplings in the standard model to be the quartic scalar coupling, the Yukawa coupling of the top quark, and the SU(3) gauge coupling, we consider their associated running couplings to one loop order. Despite the non-linear nature of the differential equations governing these functions, we show that they can be solved exactly. The nature of these solutions is discussed and their singularity structure is examined. It is shown that for a sufficiently small Higgs mass, the quartic scalar coupling decreases with increasing energy scale and becomes negative, indicative of vacuum instability. This behavior changes for a Higgs mass greater than 168 GeV, beyond which this couplant increases with increasing energy scales and becomes singular prior to the ultraviolet (UV) pole of the Yukawa coupling. Upper and lower bounds on the Higgs mass corresponding to new physics at the TeV scale are obtained and compare favourably with the numerical results of the one-loop and two-loop analyses with inclusion of electroweak couplings.

hep-ph↗

arXiv2005

Thermal kaons production in the relativistic heavy ions collision

We study the thermal production of kaons in hot and dense symmetric and asymmetric hypernuclear matter in the context of the modified quark-meson coupling model. All the baryon species and kaons are treated as MIT bags that interact with each other via the scalar mesons $σ,σ^*$ and the vector mesons $ω,ϕ$ as well as the isovector meson $ρ$. Furthermore, in our calculations, we use realistic sets of hyperon-hyperon (or $YY$) interactions based on several versions of Nijmegen core potential models. We consider a system of strange hadronic matter and kaons but with zero total net strangeness of the system and conserved small negative fraction of the isospin-charge. We find strange baryons as well as kaons are produced abundantly when the temperature increases and approaches the critical temperature for the phase transition to the quark-gluon plasma. Our results show that the kaons are produced only thermally in the symmetric and asymmetric hypernuclear matter and there is no signature for the onset of kaon condensation in the relativistic heavy ions collision. The kaons appear in the system only by thermal production. However, when the system cools down strange hadrons could survive.

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arXiv2005

Nucleon bound state at finite temperature

We study the nucleon at finite temperature using Bethe-Salpeter equation (BSE) where it is considered as a bound state of a scalar-diquark and a quark. The interaction between the diquark and the quark is taken as an exchange quark.The constituent quark and diquark substructures are considered momentum and temperature dependent based on the lattice QCD and dynamical chiral symmetry breaking (DCSB). The kernel interaction modification with temperature is approximated using the mixed representation in the imaginary time formalism and then we adopt an adiabatic (instantaneous) approximation after evaluating the Matsubara frequencies sum. The results of BSE are compared with those for MIT bag model. We argue the bag pressure is a temperature dependent and it decreases smoothly with temperature to be consistent with the results for BSE. Furthermore, the nucleon bound state obtained by BSE ceases to exist just below the critical temperature and this indicates that the nucleon deconfines to its constituent quarks at the critical temperature. The nucleon mass decreases with temperature as $M_N(T)/M_N(0)\approx {\cal R}^δ(T)$ where ${\cal R}(T)=(1-b\frac{T^2}{T^2_c})^{1/2}$ and $δ\approx 1$ and this suggests $B(T)/B(0)={\cal R}^{4δ}(T)$ for MIT bag.

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arXiv2002

Numerical solution of the color superconductivity gap in a weak coupling constant

We present the numerical solution of the full gap equation in a weak coupling constant $g$. It is found that the standard approximations to derive the gap equation to the leading order of coupling constant are essential for a secure numerical evaluation of the logarithmic singularity with a small coupling constant. The approximate integral gap equation with a very small $g$ should be inverted to a soft integral equation to smooth the logarithmic singularity near the Fermi surface. The full gap equation is solved for a rather large coupling constant $g\ge 2.0$. The approximate and soft integral gap equations are solved for small $g$ values. When their solutions are extrapolated to larger $g$ values, they coincide the full gap equation solution near the Fermi surface. Furthermore, the analytical solution matches the numerical one up to the order one O(1). Our results confirm the previous estimates that the gap energy is of the order tens to 100 MeV for the chemical potential $μ\le 1000$ MeV. They also support the validity of leading approximations applied to the full gap equation to derive the soft integral gap equation and its analytical solution near the Fermi surface.

hep-ph↗

arXiv2002

The C-metric black hole near the IR-brane in the AdS_4 space

We study the black hole shape using the C-metric solution for a matter trapped near the IR-brane in the ${AdS}_4$ space. In the AdS/CFT duality, the IR-brane is introduced by embedding a 2-brane at the ${AdS}_4$ radius $z=l$, while the UV-brane is defined by the ${AdS}_4$ boundary. We find the C-metric solution generates a negative tension IR-brane and a negative thermal energy gas of colliding particles. We analyze the momentum energy tensor at the ${AdS}_4$ boundary. We find that the negative energy black hole solution is entirely unstable even for a small perturbation in the Poincare coordinate space. However, such a black hole decays very rapidly due to the imaginary part emerges in the ADM mass. This imaginary part appears because of the orbifold constraints of the C-metric solution in the unusual coordinates. Moreover, this decay rate diverges at the UV-brane. This implies that the black hole evaporates instantaneously otherwise the boundary itself will collapse.

hep-th↗

arXiv2002

Charmonium dissociation in the context of Bethe-Salpeter equation at finite temperature

We derive the spin-dependent Bethe-Salpeter equation for $q\bar{q}$ bound state at finite temperature in the ladder and cross box diagram approximations. The imaginary time formalism is adopted in the adiabatic approximation where the flux tube thermal excitation is separated from the thermal excitation of the constituent quarks. The thermal excitation of the flux tube is implemented by using a temperature dependent potential inferred from the lattice gauge calculations. The thermal excitations of the constituent quarks are evaluated by summing Matsubara frequencies. The resultant equation is used to study the thermal charmonium spontaneous dissociation mechanism at temperatures below the critical one of the phase transition to the quark gluon plasma. Our results show that when the thermal excitation of the constituent quarks is considered beside the flux tube thermal excitation, the spontaneous dissociation unlikely takes place in the hadronic phase. In contrary, when the thermal excitation of the flux tube is considered only in the calculations, the spontaneous dissociation likely takes place just below the critical temperature.

hep-ph↗

arXiv2001

Properties of Dense Strange Hadronic Matter with Quark Degrees of Freedom

The properties of strange hadronic matter are studied in the context of the modified quark-meson coupling model using two substantially different sets of hyperon-hyperon ($YY$) interactions. The first set is based on the Nijmegen hard core potential model D with slightly attractive $YY$ interactions. The second potential set is based on the recent SU(3) extension of the Nijmegen soft-core potential NSC97 with strongly attractive $YY$ interactions which may allow for deeply bound hypernuclear matter. The results show that, for the first potential set, the $Σ$ hyperon does not appear at all in the bulk at any baryon density and for all strangeness fractions. The binding energy curves of the resulting $NΛΞ$ system vary smoothly with density and the system is stable (or metastable if we include the weak force). However, the situation is drastically changed when using the second set where the $Σ$ hyperons appear in the system at large baryon densities above a critical strangeness fraction. We find strange hadronic matter undergoes a first order phase transition from a $NΛΞ$ system to a $NΣΞ$ for strangeness fractions $f_S>1.2$ and baryonic densities exceeding twice ordinary nuclear matter density. Furthermore, it is found that the system built of $NΣΞ$ is deeply bound. This phase transition affects significantly the equation of state which becomes much softer and a substantial drop in energy density and pressure are detected as the phase transition takes place.

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arXiv2000

Hot nuclear matter in the modified quark-meson coupling model with quark-quark correlations

Short-range quark-quark correlations in hot nuclear matter are examined within the modified quark-meson coupling model (MQMC) by adding repulsive scalar and vector quark-quark interactions. Without these correlations, the bag radius increases with the baryon density. However when the correlations are introduced the bag size shrinks as the bags overlap. Also as the strength of the scalar quark-quark correlation is increased, the decrease of the effective nucleon mass $M^{*}_N$ with the baryonic density is slowed down and tends to saturate at high densities. Within this model we study the phase transition from the baryon-meson phase to the quark-gluon plasma (QGP) phase with the latter modeled as an ideal gas of quarks and gluons inside a bag. Two models for the QGP bag parameter are considered. In one case, the bag is taken to be medium-independent and the phase transition from the hadron phase to QGP is found to occur at 5-8 times ordinary nuclear matter density for temperatures less than 60 MeV. For lower densities, the transition takes place at higher temperature reaching up to 130 MeV at zero density. In the second case, the QGP bag parameter is considered medium-dependent as in the MQMC model for the hadronic phase. In this case, it is found that the phase transition occurs at much lower densities.

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arXiv1999

Neutron star properties in the quark-meson coupling model

The effects of internal quark structure of baryons on the composition and structure of neutron star matter with hyperons are investigated in the quark-meson coupling (QMC) model. The QMC model is based on mean-field description of nonoverlapping spherical bags bound by self-consistent exchange of scalar and vector mesons. The predictions of this model are compared with quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear matter saturation properties. By employing a density dependent bag constant through direct coupling to the scalar field, the QMC model is found to exhibit identical properties as QHD near saturation density. Furthermore, this modified QMC model provides well-behaved and continuous solutions at high densities relevant to the core of neutron stars. Two additional strange mesons are introduced which couple only to the strange quark in the QMC model and to the hyperons in the QHD model. The constitution and structure of stars with hyperons in the QMC and QHD models reveal interesting differences. This suggests the importance of quark structure effects in the baryons at high densities.

astro-ph↗

arXiv1999

Hot Hypernuclear Matter in the Modified Quark Meson Coupling Model

Hot hypernuclear matter is investigated in an explicit SU(3) quark model based on a mean field description of nonoverlapping baryon bags bound by the self-consistent exchange of scalar $σ, ζ$ and vector $ω, ϕ$ mesons. The $σ, ω$ mean fields are assumed to couple to the u,d-quarks while the $ζ, ϕ$ mean fields are coupled to the s-quark. The coupling constants of the mean fields with the quarks are assumed to satisfy SU(6) symmetry. The calculations take into account the medium dependence of the bag parameter on the scalar fields $σ, ζ$. We consider only the octet baryons $N,Λ,Σ,Ξ$ in hypernuclear matter. An ideal gas of the strange mesons $K$ and $K^{*}$ is introduced to keep zero net strangeness density. Our results for symmetric hypernuclear matter show that a phase transition takes place at a critical temperature around 180 MeV in which the scalar mean fields $σ, ζ$ take nonzero values at zero baryon density. Furthermore, the bag contants of the baryons decrease significantly at and above this critical temperature indicating the onset of quark deconfinement. The present results imply that the onset of quark deconfinement in SU(3) hypernuclear matter is much stronger than in SU(2) nuclear matter.

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arXiv1998

Hot Nuclear Matter in the Quark Meson Coupling Model with Dilatons

We study hot nuclear matter in an explicit quark model based on a mean field description of nonoverlapping nucleon bags bound by the self-consistent exchange of scalar and vector mesons as well as the glueball field. The glueball exchange as well as a realization of the broken scale invariance of quantum chromodynamics is achieved through the introduction of a dilaton field. The calculations also take into account the medium-dependence of the bag constant. The effective potential with dilatons is applied to nuclear matter. The nucleon properties at finite temperature as calculated here are found to be appreciably different from cold nuclear matter. The introduction of the dilaton potential improves the shape of the saturation curve at T=0 and is found to affect hot nuclear matter significantly.

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arXiv1998

Deconfinement in the Quark Meson Coupling Model

The Quark Meson Coupling Model which describes nuclear matter as a collection of non-overlapping MIT bags interacting by the self-consistent exchange of scalar and vector mesons is used to study nuclear matter at finite temperature. In its modified version, the density dependence of the bag constant is introduced by a direct coupling between the bag constant and the scalar mean field. In the present work, the coupling of the scalar mean field with the constituent quarks is considered exactly through the solution of the Dirac equation. Our results show that a phase transition takes place at a critical temperature around 200 MeV in which the scalar mean field takes a nonzero value at zero baryon density. Furthermore it is found that the bag constant decreases significantly when the temperature increases above this critical temperature indicating the onset of quark deconfinement.

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