Screening of instantons in the quark gas

The grand partition function of quark matter is developed about an arbitrary classical gauge field configuration in a systematic weak coupling expansion. In the presence of a finite density massless quark gas the instanton induced effective quark interaction is modified by a factor exp[?2N_F(ω?)²], i.e. the baryon number chemical potential μ acts as an intrinsic infrared cutoff on the instanton scale size ?. The equation of state of the quark matter is also briefly discussed.     

Instantons and meson correlation functions in QCD

Various QCD correlators are calculated in the instanton liquid model in zeromode approximation and 1/N _c expansion. Previous works are extended by including dynamical quark loops. In contrast to the original “perturbative” 1/N _c approximation, not all quark loops are suppressed. Renormalization of the instanton density allows the identification of the density with the gluon condensate even in presence of dynamical quark loops. In the flavor singlet meson correlators a chain of quark bubbles survives the N _c → ∞ limit causing a massive η′ in the pseudoscalar correlator while keeping massless pions in the triplet correlator. The correlators are plotted and meson masses and couplings are obtained from a spectral fit. They are compared to the values obtained from numerical studies of the instanton liquid and to experimental results.     

Light quarks mass effect on the color ferromagnet model of the QCD vacuum

We study the effect of quark masses on the energy density of two ferro-magnetic vacua in QCD, corresponding to different vacuum symmetries. In the massless limit the two states have the same energy, while as the quark masses are turned on the state with more symmetry elements becomes the “true” vacuum. The dominant contribution to the energy density splitting is proportional tom ² lnm ²     

Constituent quarks in nuclear matter and the Nolen-Schiffer anomaly

We investigate the density dependence of the neutronproton mass difference using the Nambu and Jona-Las-inio model in combination with the Isgur-Karl constituent quark model. The decrease of the constituent quark masses with increasing density reduces then-p mass difference in the proper way to help resolving the Nolen-Schiffer anomaly. We point out however, that in the presence of vector interactions, this effect is less pronounced than previously suggested.     

String cloud and domain walls with quark matter for a higher dimensional FRW universe in self creation cosmology

In this study, we research a higher dimensional flat Friedmann-Robertson-Walker(FRW) universe in Barber's second theory when strange quark matter(SQM) and normal matter(NM) are attached to the string cloud and domain walls. We obtain zero string tension density for this model. We obtain dust quark matter solutions. This result agrees with Kiran and Reddy, Krori et al, Sahoo and Mishra and Reddy. In our solutions the quark matter transforms to other particles over time. We also obtain two different solutions for domain walls with quark and normal matters by using a deceleration parameter. Also, the features of the obtained solutions are discussed and some physical and kinematical quantities are generalized and discussed. Our results are consistent with Yilmaz, Adcox et al and Back et al in four and five dimensions.     

Finite-size effects in the Gross-Neveu model with allowance for isospin and baryon chemical potentials

The properties of the (1 + 1)-dimensional massless Gross-Neveu model were studied for a compactified space S ¹, as well as with allowance for nonzero values of the baryon (µ) and isospin (µ _I ) chemical potentials. Our investigation was performed in the limit of a large number of fermion colors, N _c . It is shown that, for L→∞(case of an unbounded volume), the pion-condensation phase characterized by zero quark density is formed at any nonzero value of µ _I and a small value of µ. For any finite value of L (case of a bounded volume), the phase portrait of the model contains a pion-condensation phase where the quark density is nonzero. Thus, finite dimensions of the system being considered may serve as a factor that facilitates the formation of a pion-condensation phase in quark matter with a nonzero baryon density. At the same time, the phase where chiral symmetry is broken may exist only at very large values of L.     

Quark condensate in the nuclear matter

We calculate the quark condensate in the nuclear matter, taking into account the single-pion and two-pion exchanges between nucleons. We find the dependence of the averaged value of the quark operator¯qq on the density of the matterρ. At very low density the nonlinear terms are proportional toρ ² and increase the tendency to restoration of the chiral symmetry. At larger values of density the account of interaction inside the matter slower down the restoration of chiral symmetry compared to the gas approximation law. The leading nonlinear term in Fermi momentum power expansion becomes of the orderρ ^4/3 . The value of the condensate at the saturation value of density is obtained. The role of multinucleon effects is analyzed.     

A note on the massive quark matter phase

Using an equation of state which is based on a many-body treatment of a constituent quark model with confinement interaction, the phase transition to a massive quark phase is studied. It is found that in the case of bag constantsB ^1/4>200 MeV and baryon number density of about 5ρ₀ a phase of massive deconfined quarks may become stable.     

Stars of strange matter?

We investigate suggestions that quark matter with strangeness per baryon of order unity may be stable. We model this matter at nuclear matter densities as a gas of close packed Λ-particles. From the known mass of the Λ-particle we obtain an estimate of the energy and chemical potential of strange matter at nuclear densities. These are sufficiently high to preclude any phase transition from neutron matter to strange matter in the region near nucleon matter density. Including effects from gluon exchange phenomenologically, we investigate higher densities, consistently making approximations which underestimate the density of transition. In this way we find a transition density ρ_tr≳7ρ₀, where ρ₀ is nuclear matter density is not far from the maximum density in the center of the most massive neutron stars that can be constructed. Since we have underestimated ρ_tr and still find it to be ∼7ρ₀, we do not believe that the transition from neutron to quark matter is likely in neutron stars. Moreover, measured masses of observed neutron stars are ≅1.4 M_⊙, where M_⊙ is the solar mass. For such masses, the central (maximum) density is ρ_c<5ρ₀. Transition to quark matter is certainly excluded for these densities.     

Dissipative force on an external quark in heavy quark cloud

Within the finite temperature N=4 strongly coupled super-Yang-Mills, we compute the dissipative force on an external quark in the presence of evenly distributed heavy quark cloud. This is computed holographically by constructing the corresponding gravity dual. We study the behaviour of this force as a function of the cloud density. Along the way we also analyze the stability of the gravity dual for vector and tensor perturbations.     

Diquark condensate and quark interaction with an instanton liquid

The interaction of light quarks with an instanton liquid is considered at nonzero density of quark/baryon matter in a phase where the diquark condensate is nonzero. It is shown that the inclusion of the relevant perturbation of the instanton liquid leads to an increase in the quark chemical potential μ_c. This in turn induces a considerable growth of the threshold quark-matter density at which one expects the emergence of color superconductivity.     

Core collapse supernovae in the QCD phase diagram

We compare two classes of hybrid equations of state with a hadron-to-quark matter phase transition in their application to core collapse supernova simulations. The first one uses the quark bag model and describes the transition to three-flavor quark matter at low critical densities. The second one employs a Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model with parameters describing a phase transition to two-flavor quark matter at higher critical densities. These models possess a distinctly different temperature dependence of their transition densities which turns out to be crucial for the possible appearance of quark matter in supernova cores. During the early post-bounce accretion phase quark matter is found only if the phase transition takes place at sufficiently low densities as in the study based on the bag model. The increase critical density with increasing temperature, as obtained for our PNJL parametrization, prevents the formation of quark matter. The further evolution of the core collapse supernova as obtained applying the quark bag model leads to a structural reconfiguration of the central protoneutron star where, in addition to a massive pure quark matter core, a strong hydrodynamic shock wave forms and a second neutrino burst is released during the shock propagation across the neutrinospheres. We discuss the severe constraints in the freedom of choice of quark matter models and their parametrization due to the recently observed 2M _?? pulsar and their implications for further studies of core collapse supernovae in the QCD phase diagram.     

An Exact Family of Einstein–Maxwell Wyman–Adler Solution in General Relativity

This paper presents a family of two-parametric interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with particular choice of charge distribution and the metric component g ₀₀. This family gives us wide range of parameters, n and K, for which the solutions are regular and acceptable on physical grounds and hence suitable for modeling of charged compact star. The maximum allowable mass and corresponding radius, for this family of solutions with the particular form of charge distribution, is determined to be 2.48M _⊙ and 10.56 km respectively by assuming the stellar “surface” density equal to strange (quark) matter density at zero pressure. It is hoped that our investigation may be of some importance in connection with the study of internal structure of electrically charged strange (quark) star.     

Entropy production at RHIC

For central heavy ion collisions at the RHIC energy, the entropy per unit rapidity dS/dy at freeze-out is extracted with minimal model dependence from available experimental measurements of particle yields, spectra, and source sizes estimated from two-particle interferometry. The extracted entropy rapidity density is consistent with lattice gauge theory results for a thermalized quark–gluon plasma with an energy density estimated from transverse energy production at RHIC.     

Theoretical prediction of cosmological constant Λ in Veneziano ghost theory of QCD

Based on the Veneziano ghost theory of QCD, we predict the cosmological constant ??, which is related to energy density of cosmological vacuum by $ \Lambda = \frac{{8\pi G}} {3}\rho _\Lambda $ . In the Veneziano ghost theory, the vacuum energy density ?? _?? is expressed by absolute value of the product of quark vacuum condensate and quark current mass: $ \rho _\Lambda = \frac{{2N_f H}} {{m_{\eta '} }}c|m_q < 0|:\bar qq:|0 > | $ . We calculate the quark local vacuum condensates ??0|: $ \bar q $ q: |0?? by solving Dyson-Schwinger Equations for a fully dressed confining quark propagator S _f (p) with an effective gluon propagator G _???? ^ab (q). The quark current mass m _q is predicted by use of chiral perturbation theory. Our theoretical result of ??, with the resulting ??0|: 471-4 q: |0?? = ?(235 MeV)³ and light quark current mass m _q ? 3.29?C6.15 MeV, is in a good agreement with the observable of the ?? ?? 10^?52 m^?2 used widely in a great amount of literatures.     

Quark exchange effects on 3He and 3H charge densities

The exchange of quarks between nucleons bound in a nucleus leads to a definite and evaluable contribution to the nuclear charge density distribution. Although this exchange contribution is a consequence of finite nucleon size, it cannot be included by the conventional procedure of folding nucleon charge distributions with the density of point nucleons. For the A = 3 nuclei investigated here, the effects of quark exchange were found to be of significance for small distances away from the nuclear centre-of-mass.     

A simple semiempirical equation of state for cold nuclear matter

On the basis of gross properties of nuclei, a simple semiempirical equation of state is developed for cold hadronic matter composed of light quarks of two flavors. The source of binding energy in the model is the decreasing asymmetry between the number of up and down quarks in extended regions of overlapping nucleons. The resulting incompressibility of symmetric nuclear matter at equilibrium density is K=324 MeV. The incompressibility decreases rapidly with decreasing density but increases only slowly with increasing density until homogenous quark matter is reached at a density just above three times ordinary nuclear matter density.     

Cabibbo current and CP violation in a six quark gauge model

The extended Cabibbo current with CP-violation in a six quark gauge model is obtained in terms of quark mass ratios and phases in the quark mass matrices. The model predicts a long-lived heavy quark and its selection rule.     

Neutrino emissivities in 2SC color-superconducting quark matter

The phase structure and equation of state for two-flavor quark matter under compact star constraints is studied within a nonlocal chiral quark model. Chiral symmetry breaking leads to rather large, density dependent quark masses at the phase transition to quark matter. The influence of diquark pairing gaps and quark masses on density dependent emissivities for the direct URCA is discussed. Since m _u > m _d , the direct URCA process due to quark masses cannot occur. We present cooling curves for model quark stars and discuss their relation to observational data. The text was submitted by the author in English.