arXiv subjects

F. Karsch

Publications and source records attributed to F. Karsch.

At least 145 records · Page 8Linked to original sources

arXiv2000

QCD Thermodynamics with 2 and 3 Quark Flavors

We discuss the flavor dependence of the pressure and critical temperature calculated in QCD with 2, 2+1 and 3 flavors using improved gauge and staggered fermion actions on lattices with temporal extent Nt=4. For T > 2 Tc we find that bulk thermodynamics of QCD with 2 light and a heavier strange quark is well described by 3-flavor QCD while the transition temperature is closer to that of 2-flavor QCD. Furthermore, we present evidence that the chiral critical point of 3-flavor QCD, i.e. the second order endpoint of the line of first order chiral phase transitions, belongs to the universality class of the 3d Ising model.

hep-lat↗

arXiv2000

Hadron Correlators in the Deconfined Phase

Temporal meson correlators and their spectral functions are calculated in the deconfined phase using the hard thermal loop resummation technique. The spectral functions exhibit strong medium effects coming from the hard thermal loop approximation for the quark propagator. The correlators, on the other hand, do not differ significantly from free correlators, for which bare quark propagators are used. This is in contrast to lattice calculations showing a clear deviation from the free correlations functions.

hep-ph↗

arXiv2000

The Pressure in 2, 2+1 and 3 Flavour QCD

We calculate the pressure in QCD with two and three light quarks on a lattice of size 16^3x4 using tree level improved gauge and fermion actions. We argue that for temperatures T > 2T_c systematic effects due to the finite lattice cut-off and non-vanishing quark masses are below 15% in this calculation and give an estimate for the continuum extrapolated pressure in QCD with massless quarks. We find that the flavour dependence of the pressure is dominated by that of the Stefan-Boltzmann constant. Furthermore we perform a calculation of the pressure using 2 light (m_u,d/T=0.4) and one heavier quark (m_s/T = 1). In this case the pressure is reduced relative to that of three flavour QCD. This effect is stronger than expected from the mass dependence of an ideal Fermi gas.

hep-lat↗

arXiv1999

Propagators of hot SU(2) gauge theory from 3d adjoint Higgs model

We study propagators of the lattice 3d adjoint Higgs model, considered as an effective theory of 4d SU(2) gauge theory at high temperature. The propagators are calculated in so-called lambda-gauges. From the long distance behaviour of the propagators we extract the screening masses. It is shown that the pole masses extracted from the propagators agree well with the screening masses obtained recently in finite temperature SU(2) theory. The gauge dependence of the screening masses is also discussed.

hep-lat↗

arXiv1999

The flavour and quark mass dependence of thermodynamic quantities in lattice QCD

The dependence of thermodynamic properties of QCD on the number of quark flavours is investigated. Lattice results for the equation of state are presented for 2, 2+1 and 3 quark flavours. The simulations have been performed with the improved p4-staggered fermion and a Symanzik improved gluon action on lattices of size 16^3 x 4

hep-lat↗

arXiv1999

Further Evidence for an unstable H-Dibaryon?

We present preliminary results for the mass of the 6q flavor-singlet state ($J^P=0^+$, $S=-2$) called H-dibaryon, calculated in quenched QCD on $16^3$x30 and $24^3$x30 lattices with improved gauge and fermion actions (Symanzik improvement, Clover action). For both lattice sizes we applied the fuzzing technique to enhance the overlap with the ground state. We observe a H-mass above the $ΛΛ$ threshold for strong decay. The difference in mass, $m_H - 2m_Λ$, increases with increasing lattice size.

hep-lat↗

arXiv1999

The non-zero baryon number formulation of QCD

We discuss the non-zero baryon number formulation of QCD in the quenched limit at finite temperature. This describes the thermodynamics of gluons in the background of static quark sources. Although a sign problem remains in this theory, our simulation results show that it can be handled quite well numerically. The transition region gets shifted to smaller temperatures and the transition region broadens with increasing baryon number. Although the action is in our formulation explicitly Z(3) symmetric the Polyakov loop expectation value becomes non-zero already in the low temperature phase and the heavy quark potential gets screened at non-vanishing number density already this phase.

hep-lat↗

arXiv1999

The quenched limit of lattice QCD at non-zero baryon number

We discuss the thermodynamics of gluons in the background of static quark sources. In order to do so we formulate the quenched limit of QCD at non-zero baryon number. A first numerical analysis of this system shows that it undergoes a smooth deconfining transition. We find evidence for a region of coexisting phases that becomes broader with increasing baryon number density. Although the action is in our formulation explicitly Z(3) symmetric the Polyakov loop expectation value becomes non-zero already in the low temperature phase. It indicates that the heavy quark potential stays finite at large distances, ie. the string between static quarks breaks at non-zero baryon number density already in the hadronic phase.

hep-lat↗

arXiv1999

Lattice QCD at non-zero baryon number

We discuss the quenched limit of lattice QCD at non-zero baryon number density. We find evidence for a mixed phase that becomes broader with increasing baryon number. Although the action is explicitly Z(3) symmetric the Polyakov loop expectation value becomes non-zero already in the low temperature phase. It indicates that the heavy quark potential stays finite at large distances, i.e. the string between static quarks breaks at non-zero baryon number density already in the hadronic phase. This behaviour is validated by calculating the heavy quark potential using Polyakov loop correlations.

hep-lat↗

arXiv1999

The Phase Diagram of 2 flavour QCD with improved Actions

It has been proposed, that the chiral continuum limit of 2-flavour QCD with Wilson fermions is brought about by a phase in which flavour and parity symmetry are broken spontaneously at finite lattice spacing. At finite temperature this phase should retract from the weak coupling limit to form 5 cusps. This scenario is studied with tree level Symanzik improved actions for both gauge and fermion fields on lattices of size $8^3\times 4$ and $12^2\times 24\times 4$.

hep-lat↗

arXiv1999

Determination of Anisotropy Coefficients for SU(3) Gauge Actions from the Integral and Matching Methods

We use two non-perturbative methods to obtain the anisotropy derivatives of the coupling constants (the anisotropy coefficients) of SU(3) lattice gauge theory. These coefficients appear in the derivative formulae for the energy density and the pressure. We calculate them for the standard Wilson and two improved actions, the 2x2 and the Square Symanzik action. Both methods lead for all investigated actions to compatible results which are clearly different from their known asymptotic perturbative limits. With increasing beta the limits are however approached in all cases. Our findings strongly support the equivalence of the integral and derivative methods for the calculation of energy density and pressure.

hep-lat↗

arXiv1999

Screening Masses of Hot SU(2) Gauge Theory from the 3D Adjoint Higgs Model

We study the Landau gauge propagators of the lattice SU(2) 3d adjoint Higgs model, considered as an effective theory of high temperature 4d SU(2) gauge theory. From the long distance behaviour of the propagators we extract the screening masses. It is shown that the pole masses extracted from the propagators agree well with the screening masses obtained recently in finite temperature SU(2) theory. The relation of the propagator masses to the masses extracted from gauge invariant correlators is also discussed. In so-called lambda gauges non-perturbative evidence is given for the gauge independence of pole masses within this class of gauges.

hep-ph↗

arXiv1999

Improved Staggered Fermion Actions for QCD Thermodynamics

We analyze the cut-off dependence of the fermion contribution to the finite temperature free energy density in ${\cal O}(g^2)$ lattice perturbation theory for several improved staggered fermion actions. Cut-off effects are drastically reduced for the Naik action and an action with improved rotational symmetry of the quark propagator. We show that improvement of rotational symmetry at ${\cal O}(g^2)$ further reduces cut-off effects in thermodynamic observables. We also show that the introduction of fat-links does not have a significant influence on cut-off distortions at ${\cal O}(g^2)$.

hep-lat↗

arXiv1999

The three flavour chiral phase transition with an improved quark and gluon action in lattice QCD

The finite-temperature chiral phase transition is investigated for three flavours of staggered quarks on a lattice of temporal extent N_t=4. In the simulation we use an improved fermion action which reduces rotational symmetry breaking of the quark propagator (p4-action), include fat-links to improve the flavour symmetry and use the tree level improved (1,2) gluon action. We study the nature of the phase transition for quark masses of ma=0.025, ma=0.05 and ma=0.1 on lattices with spatial sizes of 8^3 and 16^3.

hep-lat↗

arXiv1998

QCD thermodynamics from 3d adjoint Higgs model

The screening masses of hot SU(N) gauge theory, defined as poles of the corresponding propagators are studied in 3d adjoint Higgs model, considered as an effective theory of QCD, using coupled gap equations and lattice Monte-Carlo simulations (for N=2). Using so-called lambda gauges non-perturbative evidence for gauge independence of the pole masses within this class of gauges is given. A possible application of the screening masses for the resummation of the free energy is discussed.

hep-ph↗

arXiv1998

Screening Masses of Hot SU(2) Gauge Theory from the 3d Adjoint Higgs Model

We study the Landau gauge propagators of the lattice SU(2) 3d adjoint Higgs model, considered as an effective theory of high temperature 4d SU(2) gauge theory. From the long distance behaviour of the propagators we extract the screening masses. The propagators are studied both in the symmetric and the broken phases of the 3d Higgs model. It is shown that the pole masses extracted from the propagators in the symmetric phase agree well with the screening masses obtained recently in finite temperature SU(2) theory, while propagators measured in the broken phase show quite a different behaviour. This suggest that the symmetric phase of the 3d model corresponds to the deconfined phase of the 4d SU(2) gauge theory. The relation of the propagator masses to the masses extracted from gauge invariant correlators and the mass gap of pure 3d SU(2) gauge theory is also discussed.

hep-lat↗

arXiv1998

String breaking in Lattice QCD

The separation of a heavy quark and antiquark pair leads to the formation of a tube of flux, or string, which should break in the presence of light quark-antiquark pairs. This expected zero temperature phenomenon has proven elusive in simulations of lattice QCD. We present simulation results that show that the string does break in the confining phase at nonzero temperature.

hep-lat↗

arXiv1998

Thermodynamics of two-colour QCD

We discuss the thermodynamics of two-colour QCD with four flavours of staggered quarks on 8^3x4 and 16^3x4 lattices. In our simulations we use the Naik action for the fermions and a (1,2) tree-level improved gauge action. We analyze the deconfinement and chiral phase transitions for four different quark masses (m=0.1,0.05,0.025,0.015). Contrary to three-colour QCD the peak in the Polyakov loop susceptibility decreases with decreasing quark mass. This reflects an early breaking of the string in the heavy quark potential, which we verify explicitly by calculating the heavy quark potential at finite temperature using Polyakov loop correlations.

hep-lat↗