arXiv subjects

D. Blaschke

Publications and source records attributed to D. Blaschke.

At least 199 records · Page 11Linked to original sources

arXiv1999

Mesonic correlations and quark deconfinement

A simple confining separable interaction Ansatz for the rainbow-ladder truncated QCD Dyson-Schwinger equations is used to implement chiral restoration and quark deconfinement in a study of $\bar q q$ meson states at finite temperature. The model is fixed at T=0 by reproducing selected pi and rho properties. Deconfinement and chiral restoration are found to both occur at T_c=146 MeV. In the pion sector, we investigate M_pi(T) and f_pi(T) along with the exact QCD mass relation and the GMOR relation. For the vector mode, we investigate the 3-space transverse and longitudinal masses M_rho^T(T) and M_ρ^L(T), along with the widthfor the decay rho^0 --> e^+e^-. The equation of state (EOS) for the model is investigated in the T-mu plane, a tri-critical point is identified and the relationship to a bag model is discussed. The deconfinement transition in rapidly rotating neutron stars is considered and a new signal from the pulsar timing in binary systems with mass accretion is suggested. The model is used to discuss the possibility of a superconducting quark matter phase.

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arXiv1999

A dynamical, confining model and hot quark stars

We explore the consequences of an equation of state (EOS) obtained in a confining Dyson-Schwinger equation model of QCD for the structure and stability of nonstrange quark stars at finite-T, and compare the results with those obtained using a bag-model EOS. Both models support a temperature profile that varies over the star's volume and the consequences of this are model independent. However, in our model the analogue of the bag pressure is (T,mu)-dependent, which is not the case in the bag model. This is a significant qualitative difference and comparing the results effects a primary goal of elucidating the sensitivity of quark star properties to the form of the EOS.

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arXiv1998

NJL model with infrared confinement

We consider an extended Nambu--Jona-Lasinio (NJL) model for the light meson sector of QCD where unphysical quark production thresholds are excluded by an infrared cut-off on the momentum integration within quark loop diagrams. This chiral quark model conserves the low energy theorems. The infrared cut-off is fixed selfconsistently by the dynamically generated quark mass (quark condensate). The masses and decay widths of the σ- and ρ-mesons are described in the model.

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arXiv1998

Squeezed Gluon Condensate and Quark Confinement in the Global Color Model of QCD

We discuss how the presence of a squeezed gluon vacuum might lead to quark confinement in the framework of the global colour model of QCD. Using reduced phase space quantization of massive vector theory we construct a Lorentz invariant and colourless squeezed gluon condensate and show that it induces a permanent, nonlocal quark interaction (delta-function in 4-momentum space), which according to Munczek and Nemirovsky might lead to quark confinement. Our approach makes it possible to relate the strength of this effective confining quark interaction to the strength of the physical gluon condensate.

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arXiv1998

Quark deconfinement and meson properties at finite temperature

A simple confining separable interaction Ansatz for the rainbow-ladder truncated QCD Dyson-Schwinger equations is used to study quark deconfinement and meson states at finite temperature. The model is fixed at T=0 to implement quark confinement while preserving the Goldstone mechanism for the $π$. Within the Matsubara formalism, a very slow temperature dependence is found for the $π$ and $ρ$ meson masses $M_H(T)$ until near the deconfinement temperature $T_c=143$ MeV. Related to rapid decrease of the dynamically-generated quark mass function for $T>T_c$, this model produces $π$ and $ρ$ masses that rise significantly and are better interpreted as spatial screening masses. The $T$-dependent screening mass defect $ΔM_H = 2πT-M_H(T)$ is compared to results of lattice gauge theory simulations and also to those of an infrared dominant analytic model.

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arXiv1998

Non-Markovian effects in strong-field pair creation

We analyze a quantum kinetic equation describing both boson and fermion pair production and explore analytically and numerically the solution of the non-Markovian kinetic equation. In the Markovian limit of the kinetic equation we find an analytical solution for the single particle distribution function of bosons and fermions. The numerical investigation for a homogeneous, constant electric field shows an enhancement (bosons) or a suppression (fermions) of the pair creation rate according to the symmetry character of the produced particles. For strong fields non-Markovian effects are important while they disappear for weak fields. Hence it is sufficient to apply the low density limit for weak fields but necessary to take into account memory effects for strong fields.

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arXiv1998

A quantum kinetic equation for particle production in the Schwinger mechanism

A quantum kinetic equation is derived for the description of pair production in a time-dependent homogeneous electric field $E(t)$. As a source term, the Schwinger mechanism for particle creation is incorporated. Possible particle production due to collisions and collisional damping are neglected. The main result is a kinetic equation of non-Markovian character. In the low density approximation, the source term is reduced to the leading part of the well known Schwinger formula for the probability of pair creation. We discuss the momentum and time dependence of the derived source term and compare with other approaches.

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arXiv1998

Analysis of chiral and thermal susceptibilities

We calculate the chiral and thermal susceptibilities for two confining Dyson-Schwinger equation models of QCD with two light flavours, a quantitative analysis of which yields the critical exponents, beta and delta, that characterise the second-order chiral symmetry restoration transition. The method itself is of interest, minimising the influence of numerical noise in the calculation of the order parameter for chiral symmetry breaking near the critical temperature. For the more realistic of the two models we find: T_c approx. 153 MeV, and the non-mean-field values: beta = 0.46 +/- 0.04, delta = 4.3 +/- 0.3 and 1/(beta delta)= 0.54 +/- 0.05, which we discuss in comparison with the results of other models.

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arXiv1998

Charmonium dissociation in hot and dense matter

We investigate $J/ψ$ suppression in ultrarelativistic heavy ion collisions within a generalized GLAUBER model and compare results of a hadronic comover scenario with those of a quark plasma scenario where conditions for MOTT dissociation of charmonium are fulfilled locally at the short time scales before hadronization. We study possible consequences for the theoretical description to be drawn from the observation of ``anomalous'' thresholds in the $J/ψ$ suppression pattern by the NA50 collaboration.

hep-ph↗

arXiv1998

Excess low energy photon pairs from pion annihilation at the chiral phase transition

The photon pair production by pion annihilation in a hot and dense medium at the chiral phase transition is investigated within a chiral quark model. As a direct consequence of this transition the $σ$ meson appears as a bound state in the domain of temperatures and chemical potentials where the condition $M_σ(T,μ) \approx 2 M_π(T,μ)$ is fulfilled. This effect results in a strong enhancement of the cross section for the pion annihilation process $2 π\to 2 γ$ compared with the vacuum case. The calculation of the photon pair production rate as function of the invariant mass shows a strong enhancement and narrowing of the $σ$ meson resonance at threshold due to chiral symmetry restoration.

hep-ph↗

arXiv1997

Dynamical derivation of a quantum kinetic equation for particle production in the Schwinger mechanism

A quantum kinetic equation has been derived for the description of pair production in a time-dependent homogeneous electric field $E(t)$. As a source term, the Schwinger mechanism for particle creation is incorporated. Possible particle production due to collisions and collisional damping are neglected. The main result is a closed kinetic equation of the non-Markovian type. In the low density approximation, the source term is reduced to the leading part of the well known Schwinger formula for the probability of pair creation. We compare the formula obtained with other approaches and discuss the differences.

hep-ph↗

arXiv1997

Squeezed condensate of gluons and the mass of the eta'

The relation between the large mass of the $η'$ and the structure of the gluon vacuum via the $U_A(1)$ anomaly is discussed. A squeezed gluon vacuum is considered as an alternative to existing models. Considering Witten's formula for the $η_0$ mass we show that the contact term can give a sizable contribution and relate it to the physical gluon condensate. The values of the gluon condensate obtained through this relation are compared with the value by Shifman, Vainshtein and Zakharov and the recent update values by Narison.

hep-ph↗

arXiv1997

Scalar correlations in a quark plasma and low mass dilepton production

We investigate possible consequences of resonant scalar interactions for dilepton production from a quark plasma at the chiral phase transition. It is found that this production mechanism is strongly suppressed compared to the Born process and has no significance for present experiments.

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arXiv1997

Relativistic quantum kinetic equation of the Vlasov type for systems with internal degrees of freedom

We present an approach to derive a relativistic kinetic equation of the Vlasov type. Our approach is especially reliable for the description of quantum field systems with many internal degrees of freedom. The method is based on the Heisenberg picture and leads to a kinetic equation which fulfills the conservation laws. We apply the approach to the standard Walecka Lagrangian and an effective chiral Lagrangian.

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arXiv1997

Thermodynamic properties of a simple, confining model

We study the equilibrium thermodynamics of a simple, confining, DSE-model of 2-flavour QCD at finite temperature and chemical potential. The model has two phases: one characterised by confinement and dynamical chiral symmetry breaking; and the other by their absence. The phase boundary is defined by the zero of the vacuum-pressure difference between the confined and deconfined phases. Chiral symmetry restoration and deconfinement are coincident with the transition being of first order, except for $μ=0$, where it is second order. Nonperturbative modifications of the dressed-quark propagator persist into the deconfined domain and lead to a dispersion law modified by a dynamically-generated, momentum-dependent mass-scale. This entails that the Stefan-Boltzmann limit for the bulk thermodynamic quantities is attained only for large values of temperature and chemical potential.

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arXiv1997

Critical Scattering and Two Photon Spectra for a Quark/Meson Plasma

At the Mott transition of a quark/meson plasma, mesons become unbound. This leads to the effect of critical scattering, which is studied by investigating photon pair production due to the process $q\bar q\toγγ$. This process can proceed either via direct annihilation or via the formation of a mesonic resonance. It is shown that the latter channel leads to an enhancement of photon pairs with invariant mass equal to the thermal pion mass. The size of this effect measures the time the temperature stays near the Mott temperature during the evolution. It is particularly pronounced for a first order phase transition. The $π^0\toγγ$ decay gives a strong background contribution and may make the observation of critical scattering in two-photon spectra of present day heavy ion collision experiments difficult.

hep-ph↗

arXiv1997

Mott mechanism and anomalous charmonium suppression

We investigate a scenario where conditions for Mott dissociation of charmonium are fulfilled locally in ultrarelativistic heavy ion collisions at the short time scales before hadronization and study possible consequences to be drawn from observation of ``anomalous'' thresholds in the J/ψsuppression pattern. We suggest that for a compilation of experiments with different kinematics, variables presently in use to display the observed suppression pattern should be rescaled by the $γ$ factor of the $c\bar c$ state relative to the participant center of mass. This systematics can be tested by inverse kinematics experiments as, e.g., Pb-S collisions and by sampling data sets in p_T and y of the dimuon pairs.

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arXiv1996

Squeezed condensate of gluons and $η-η'$ mass difference

We consider a mechanism to create the $η- η'$ mass difference by the gluon anomaly in a squeezed vacuum. We find that the mass shift of the $η_0$ governing this mass difference is determined by the magnetic part of the gluon condensate. For the squeezed vacuum this magnetic part coincides with the total gluon condensate, so that we get a relation between the gluon condensate and the mass shift of the $η_0$ as a function of the strong coupling constant $α_s$. The values of the gluon condensate obtained through this relation are compared with the value by Shifman, Vainshtein and Zakharov and the recent update values by Narison.

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