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F. Karsch

Publications and source records attributed to F. Karsch.

At least 109 records · Page 6Linked to original sources
arXiv2003

Heavy quark free energies, potentials and the renormalized Polyakov loop

We discuss the renormalized free energy of a heavy quark anti-quark pair in the color singlet channel for quenched and full QCD at finite temperature. The temperature and mass dependence, as well as its short distance behavior is analyzed. Using the free energies we calculate the heavy quark potential and entropy in quenched QCD. The asymptotic large distance behavior of the free energy is used to define the non-perturbatively renormalized Polyakov loop which is well behaved in the continuum limit. String breaking is studied in the color singlet channel in 2-flavor QCD.

hep-lat↗
arXiv2003

Where is the chiral critical point in 3-flavor QCD?

We determine the location of the second order endpoint of the line of first order chiral phase transition in 3-flavor QCD at vanishing chemical potential. Using Ferrenberg-Swendsen reweighting for two values of the quark mass we determine the dependence of the transition line on the chemical potential and locate the chiral critical point. For both quantities we find a significant quark mass dependence.

hep-lat↗
arXiv2003

The equation of state for two flavor QCD at finite density

We discuss the equation of state for QCD at non-zero temperature and density. We present results of a simulation for QCD with 2 flavors of p4-improved staggered fermions. Derivatives of $\ln {\cal Z}$ with respect to quark chemical potential $μ_q$ up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of $μ_q$ via a Taylor series expansion. We also discuss the radius of convergence of the expansion as a function of temperature. It is found that the fluctuations in the quark number density increase in the vicinity of the phase transition temperature and the susceptibilities start to develop a pronounced peak as $μ_q$ is increased. This suggests the presence of a critical endpoint in the $(T, μ_q)$ plane.

hep-lat↗
arXiv2003

Charmonium at finite temperature

We study charmoinum correlators and spectral functions at finite temperature within the quenched approximation using isotropic lattices with lattice spacing a^-1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of the ground state charmonium spectral function above deconfinement, we find that ground state charmonia (J/psi and eta_c) exist in the deconfined phase at least up to temperatures as high as 1.5Tc. P-wave charmonia (chi_c) on the other hand are dissociated already at 1.12Tc.

hep-lat↗
arXiv2003

Thermodynamics at Non-Zero Baryon Number Density: A Comparison of Lattice and Hadron Resonance Gas Model Calculations

We compare recent lattice studies of QCD thermodynamics at non-zero quark chemical potential with the thermodynamics of a hadron resonance gas. We argue that for T < Tc the equation of state derived from Monte--Carlo simulations of two flavour QCD at non-zero chemical potential can be well described by a hadron resonance gas when using the same set of approximations as used in current lattice calculations. We estimate the importance of truncation errors arising from the use of a Taylor expansion in terms of the quark chemical potential and examine the influence of unphysically large quark masses on the equation of state and the critical conditions for deconfinement.

hep-ph↗
arXiv2003

Thermodynamics and in-medium hadron properties from lattice QCD

Non-perturbative studies of the thermodynamics of strongly interacting elementary particles within the context of lattice regularized QCD are being reviewed. After a short introduction into thermal QCD on the lattice we report on the present status of investigations of bulk properties. In particular, we discuss the present knowledge of the phase diagram including recent developments of QCD at non-zero baryon number density. We continue with the results obtained so far for the transition temperature as well as the temperature dependence of energy and pressure and comment on screening and the heavy quark free energies. A major section is devoted to the discussion of thermal modifications of hadron properties, taking special account of recent progress through the use of the maximum entropy method.

hep-lat↗
arXiv2003

The Equation of State for Two Flavor QCD at Non-zero Chemical Potential

We present results of a simulation of QCD on a 4x16^3 lattice with 2 continuum flavors of p4-improved staggered fermion with mass m/T=0.4. Derivatives of the thermodynamic grand potential with respect to quark chemical potential mu_q up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of mu_q via Taylor series expansion. Discretisation effects associated with various staggered fermion formulations are discussed in some detail. In addition it is possible to estimate the radius of convergence of the expansion as a function of temperature. We also discuss the calculation of energy and entropy densities which are defined via mixed derivatives of the thermodynamic grand potential with respect to the bare couplings and quark masses.

hep-lat↗
arXiv2003

Infinite temperature limit of meson spectral functions calculated on the lattice

We analyze the cut-off dependence of mesonic spectral functions calculated at finite temperature on Euclidean lattices with finite temporal extent. In the infinite temperature limit we present analytic results for lattice spectral functions calculated with standard Wilson fermions as well as a truncated perfect action. We explicitly determine the influence of `Wilson doublers' on the high momentum structure of the mesonic spectral functions and show that this cut-off effect is strongly suppressed when using an improved fermion action.

hep-lat↗
arXiv2003

Hadron Resonance Mass Spectrum and Lattice QCD Thermodynamics

We confront lattice QCD results on the transition from the hadronic phase to the quark--gluon plasma with hadron resonance gas and percolation models. We argue that for T < T_c the equation of state derived from Monte--Carlo simulations of (2+1) quark--flavor QCD can be well described by a hadron resonance gas. We examine the quark mass dependence of the hadron spectrum on the lattice and discuss its description in terms of the MIT bag model. This is used to formulate a resonance gas model for arbitrary quark masses which can be compared to lattice calculations. We finally apply this model to analyze the quark mass dependence of the critical temperature obtained in lattice calculations. We show that the value of T_c for different quark masses agrees with lines of constant energy density in a hadron resonance gas. For large quark masses a corresponding contribution from a glueball resonance gas is required.

hep-ph↗
arXiv2003

Group projection method in statistical systems

We discuss an application of group theoretical methods to the formulation of the thermodynamics of systems constrained by the conservation laws described by a semi--simple compact Lie group. A general projection method that allows to construct a partition function for a given irreducible representation of the Lie group is outlined. Applications of the method in Lattice Gauge Theory (LGT) for non--zero baryon number and in the phenomenological description of particle production in ultrarelativistic heavy ion collisions are also indicated.

hep-ph↗
arXiv2003

Renormalized quark-anti-quark free energy

We present results on the renormalized quark-anti-quark free energy in SU(3) gauge theory at finite temperatures. We discuss results for the singlet, octet and colour averaged free energies and comment on thermal relations which allow to extract separately the potential energy and entropy from the free energy.

hep-lat↗
arXiv2002

The quark mass and $μ$ dependence of the QCD chiral critical point

In order to study the QCD chiral critical point we investigate Binder Cumulants of the chiral condensate. The results were obtained from simulations of 3 and 2+1 flavors of standard staggered fermions and 3 flavors of p4 improved staggered fermions. The quark masses used are close to the physical quark mass. To extract the dependence on quark mass and chemical potential we apply a new reweighting technique based on a Taylor expansion of the action. The reweighting accuracy is ${\cal O}(m)$ for the standard and ${\cal O}(m^2)$, ${\cal O}(μ^2)$ for the p4 action.

hep-lat↗
arXiv2002

The QCD phase transition at high temperature and low density

We study the thermal properties of QCD in the presence of a small quark chemical potential $μ$. Derivatives of the phase transition point with respect to $μ$ are computed at $μ=0$ for 2 and 3 flavors of p-4 improved staggered fermions on a $16^3\times4$ lattice. Moreover we contrast the case of isoscalar and isovector chemical potentials, quantify the effect of $μ\not=0$ on the equation of state, and comment on the screening effect by dynamical quarks and the complex phase of the fermion determinant in QCD with $μ\not=0$.

hep-lat↗
arXiv2002

The QCD thermal phase transition in the presence of a small chemical potential

We propose a new method to investigate the thermal properties of QCD with a small quark chemical potential $μ$. Derivatives of the phase transition point with respect to $μ$ are computed at $μ=0$ for 2 flavors of p-4 improved staggered fermions with $ma=0.1,0.2$ on a $16^3\times4$ lattice. The resulting Taylor expansion is well behaved for the small values of $μ_{\rm q}/T_c\sim0.1$ relevant for RHIC phenomenology, and predicts a critical curve $T_c(μ)$ in reasonable agreement with estimates obtained using exact reweighting. In addition, we contrast the case of isoscalar and isovector chemical potentials, quantify the effect of $μ\not=0$ on the equation of state, and comment on the complex phase of the fermion determinant in QCD with $μ\not=0$.

hep-lat↗
arXiv2002

The H dibaryon on the lattice

We present our final results for the mass of the six quark flavor singlet state (J^P=0^+, S=-2) called H dibaryon, which would be the lightest possible strangelet in the context of strange quark matter. The calculations are performed in quenched QCD on (8-24)^3 x 30 lattices with the (1,2) Symanzik improved gauge action and the clover fermion action. Furthermore the fuzzing technique for the fermion fields and smearing of the gauge fields is applied in order to enhance the overlap with the ground state. Depending on the lattice size we observe an H mass slightly above or comparable with the ΛΛthreshold for strong decay. Therefore a bound H dibaryon state seemed to be ruled out by our simulation.

hep-lat↗
arXiv2002

Heavy Quark Anti-Quark Free Energy and the Renormalized Polyakov Loop

We calculate the colour averaged and colour singlet free energies of static quark anti-quark sources placed in a thermal gluonic heat bath. We discuss the renormalization of these free energies using the short distance properties of the zero temperature heavy quark potential. This leads to the definition of the renormalized Polyakov loop as an order parameter for the deconfinement phase transition of the SU(3) gauge theory which is well behaved in the continuum limit.

hep-lat↗
arXiv2002

QCD at non-zero chemical potential and temperature from the lattice

A study of QCD at non-zero chemical potential, mu, and temperature, T, is performed using the lattice technique. The transition temperature (between the confined and deconfined phases) is determined as a function of mu and is found to be in agreement with other work. In addition the variation of the pressure and energy density with mu is obtained for small positive mu. These results are of particular relevance for heavy-ion collision experiments.

hep-ph↗