Searcharxiv⌕ Search

arXiv subjects

J. -F. Lagae

Publications and source records attributed to J. -F. Lagae.

15 recordsLinked to original sources
arXiv1999

High temperature meson propagators with domain-wall quarks

We study the chiral properties of domain-wall quarks at high temperatures on an ensemble of quenched configurations. Low lying eigenmodes of the Dirac operator are calculated and used to check the extent to which the Atiyah-Singer index theorem is obeyed on lattices with finite $N_5$. We calculate the connected and disconnected screening propagators for the lowest mass scalar and pseudoscalar mesons in the sectors of different topological charge and note that they behave as expected. Separating out the would-be zero eigenmodes enables us to accurately estimate the disconnected propagators with far less effort than would be needed otherwise.

hep-lat↗
arXiv1998

Domain wall fermions at finite temperature

We investigate the properties of domain wall fermions on a set of quenched configurations at non-zero temperature. In particular, we compute the low lying eigenvalues of the DWF operator and study their relation with topology, level crossings and chiral symmetry breaking. We also measure the screening correlators and discuss the dependence on the extent of the extra dimension and the quark mass.

hep-lat↗
arXiv1998

Improved staggered quark actions with reduced flavour symmetry violations for lattice QCD

We introduce a new class of actions for staggered quarks in lattice QCD which significantly reduce flavour symmetry violations in the pion mass spectrum. An action introduced by the MILC collaboration for the same purpose is seen to be a special case. We discus how such actions arise from a systematic attempt to reduce flavour symmetry violations in the weak coupling limit. It is shown that for quenched lattice QCD at 6/g^2=5.7, representative actions of this class give a considerable reduction in flavour symmetry violation over the standard staggered action, and a significant reduction over what is achieved by the MILC action.

hep-lat↗
arXiv1998

Thermodynamics of Lattice QCD with 2 Quark Flavours: Chiral Symmetry and Topology

We have studied the restoration of chiral symmetry in lattice QCD at the finite temperature transition from hadronic matter to a quark-gluon plasma. By measuring the screening masses of flavour singlet and non-singlet meson excitations, we have seen evidence that, although flavour chiral symmetry is restored at this transition, flavour singlet (U(1)) axial symmetry is not. We conclude that this indicates that instantons continue to play an important role in the quark-gluon plasma phase.

hep-lat↗
arXiv1998

Thermodynamics of Lattice QCD with Chiral 4-Fermion Interactions

We have studied lattice QCD with an additional, irrelevant 4-fermion interaction having a U(1)xU(1) chiral symmetry, at finite temperatures. Adding this 4-fermion term allowed us to work at zero quark mass, which would have otherwise been impossible. The theory with 2 massless staggered quark flavours appears to have a first order finite temperature phase transition at N_t=4 for the value of 4-fermion coupling we have chosen, in contrast to what is expected for 2-flavour QCD. The pion screening mass is seen to vanish below this transition, only to become massive and degenerate with the sigma (f_0) above this transition where the chiral symmetry is restored, as is seen by the vanishing of the chiral condensate.

hep-lat↗
arXiv1998

Topology, fermionic zero modes and flavor singlet correlators in finite temperature QCD

We compute the screening correlators in the sigma and eta' flavor singlet channels in finite temperature QCD with 2 light quark flavors. Together with the correlators in the pi and delta channels, these are used to discuss several issues related to symmetry restoration and the nature of the QCD phase transition. Our calculations span a range of temperature extending from approximately 125 MeV to 170 MeV and are carried out in the context of a staggered fermion formulation on a 16^3x8 lattice. In addition to the computation at a fixed quark mass (am_q=0.00625), we discuss the issue of the chiral limit. After careful consideration of the zero-mode shift lattice artefact, we present rather strong (topological) arguments in favor of the non-restoration of U_A(1) at T_c.

hep-lat↗
arXiv1997

Improving the staggered quark action to reduce flavour symmetry violations

We investigate a class of actions for lattice QCD with staggered quarks aimed at reducing the flavour symmetry violations associated with using staggered fermions. These actions replace the gauge field link fields in the quark action with covariantly smeared fields. As such they are an extension of actions considered by the MILC collaboration. We show that such actions systematically reduce flavour symmetry violations in the weak coupling limit. Using the mass splitting between Goldstone and non-Goldstone pions as a measure of flavour symmetry violations we find that these actions have considerably less flavour symmetry violations than the standard staggered action, and represent an improvement on what can be achieved with the MILC action, on quenched configurations with $β=5.7$.

hep-lat↗
arXiv1996

Manifestations of the axial anomaly in finite temperature QCD

We compute the flavor singlet meson correlators and screening masses in quenched and $N_f=2$ QCD at $N_t=8$. The consequences of our results for the realization of the $U_A(1)$ symmetry at finite T are discussed and an interpretation of our measurements in terms of the behaviour of the low lying fermionic modes is proposed.

hep-lat↗
arXiv1995

FLAVOR-SINGLET g_A FROM LATTICE QCD

We report on a lattice QCD calculation of the flavor-singlet axial coupling constant $g_A$ of the proton from the axial-vector current. The simulation is carried out at $β= 6$ on a quenched $16^3 \times 24$ lattice. An extrapolation to the chiral limit shows that the connected insertion (valence and cloud parts) is $0.62 \pm 0.09$, which is close to $g_A^8$. The disconnected insertion (vacuum polarization from the sea quark) for the $u$ or $d$ quark is $- 0.12\pm 0.01 $ and the $s$ quark also contributes $-0.12\pm 0.01$. The total $g_A^1$ is thus $0.25 \pm 0.12$ which is in agreement with experiments. In addition, we find $g_A^3 = 1.20 \pm 0.11$, $g_A^8 = 0.61 \pm 0.13$ and $F_A/D_A = 0.60 \pm 0.02$, also in agreement with experiments.

hep-ph↗
arXiv1995

Finite $ma$ corrections for sea quark matrix elements on the lattice

We compute the $ma$ dependence of lattice renormalization factors for sea quark matrix elements. The results differ from the $(1+ma)$ correction factor commonly used for valence quarks and connected current insertions. We find that for sea quarks, the correction factors are in general larger and depend strongly on the Lorentz structure of the current under consideration. Results are presented both for the Wilson action and for the 2-link improved action of Hamber and Wu. Phenomenological implications are also briefly discussed in two examples.

hep-lat↗
arXiv1994

Finite ma corrections for sea quark matrix elements

We discuss the finite $ma$ corrections associated with the computation of sea quark matrix elements. We find them to differ from the standard normalization used for valence quarks and to depend strongly on the Lorentz structure of the current under consideration. Phenomenological implications of these results are briefly discussed in two examples. We also mention how the magnitude of the correction factors can be reduced by using a 2-link improved action.

hep-lat↗
arXiv1994

Quenched QED on a momentum space lattice

We discuss the advantages of using the momentum space lattice method for studying the phase diagram of quenched QED_4. Preliminary results of a numerical simulation are presented. They indicate that the method avoids the contamination by 4-fermi interactions which plagues the conventional position space non-compact formulation.

hep-lat↗
arXiv1993

QED on a momentum lattice

We investigate the possibility of doing momentum space lattice simulations as an alternative to the conventional method. The procedure is introduced and tested for quenched QED2 and quenched QED3. Interesting physical applications to unquenched QED3 and quenched QED4 are also briefly discussed.

hep-lat↗
arXiv1992

Finite temperature QED3 with light fermions

Non-compact QED3 is simulated both in the quenched and unquenched cases. In particular, we investigate the restoration of chiral symmetry at finite temperature. We also compute the zero temperature spectrum of the theory, including (in the quenched case) the dynamical fermion mass. From these two set of data, one can obtain estimates for the ratio of the mass gap to the critical temperature, of particular interest for applications to high-Tc superconductivity.

hep-lat↗