30
30

Sep 21, 2013
09/13

by
J. B. Kogut; J. -F. Lagae

texts

######
eye 30

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9312050v1

31
31

Sep 19, 2013
09/13

by
J. -F. Lagae; D. K. Sinclair

texts

######
eye 31

######
favorite 0

######
comment 0

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...

Source: http://arxiv.org/abs/hep-lat/9709035v1

32
32

Sep 23, 2013
09/13

by
J. -F. Lagae; D. K. Sinclair

texts

######
eye 32

######
favorite 0

######
comment 0

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...

Source: http://arxiv.org/abs/hep-lat/9806014v1

29
29

Sep 19, 2013
09/13

by
J. -F. Lagae; K. -F. Liu

texts

######
eye 29

######
favorite 0

######
comment 0

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...

Source: http://arxiv.org/abs/hep-lat/9501007v1

23
23

Sep 23, 2013
09/13

by
J. B. Kogut; J. -F. Lagae

texts

######
eye 23

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9211059v1

36
36

Sep 18, 2013
09/13

by
J. -F. Lagae; D. K. Sinclair

texts

######
eye 36

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9809134v1

110
110

Sep 18, 2013
09/13

by
J. -F. Lagae; K. -F. Liu

texts

######
eye 110

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9412023v2

123
123

Sep 18, 2013
09/13

by
J. B. Kogut; J. -F. Lagae

texts

######
eye 123

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9412024v1

25
25

Sep 23, 2013
09/13

by
J. -F. Lagae; D. K. Sinclair

texts

######
eye 25

######
favorite 0

######
comment 0

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...

Source: http://arxiv.org/abs/hep-lat/9909097v1

33
33

Sep 19, 2013
09/13

by
J. B. Kogut; J. -F. Lagae; D. K. Sinclair

texts

######
eye 33

######
favorite 0

######
comment 0

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....

Source: http://arxiv.org/abs/hep-lat/9801020v1

34
34

Sep 18, 2013
09/13

by
J. B. Kogut; J. -F. Lagae; D. K. Sinclair

texts

######
eye 34

######
favorite 0

######
comment 0

We have simulated lattice QCD with an irrelevant 4-fermion interaction and 2 zero mass quarks. The chiral phase transition is observed to be second order and we discuss extraction of critical exponents.

Source: http://arxiv.org/abs/hep-lat/9809052v1

31
31

Sep 19, 2013
09/13

by
J. B. Kogut; J. -F. Lagae; D. K. Sinclair

texts

######
eye 31

######
favorite 0

######
comment 0

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...

Source: http://arxiv.org/abs/hep-lat/9801019v1

32
32

Sep 23, 2013
09/13

by
J. B. Kogut; J. -F. Lagae; D. K. Sinclair

texts

######
eye 32

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9608128v1

29
29

Sep 19, 2013
09/13

by
J. B. Kogut; J. F. Lagae; D. K. Sinclair

texts

######
eye 29

######
favorite 0

######
comment 0

We extend our earlier results concerning the breaking of the U_A(1) symmetry in finite temperature QCD. In particular, we use topological arguments to investigate the chiral limit.

Source: http://arxiv.org/abs/hep-lat/9709067v1

37
37

Sep 23, 2013
09/13

by
J. -F. Lagae; D. K. Sinclair; J. B. Kogut

texts

######
eye 37

######
favorite 0

######
comment 0

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.

Source: http://arxiv.org/abs/hep-lat/9806001v1

42
42

Sep 22, 2013
09/13

by
S. J. Dong; J. -F. Lagaë; K. F. Liu

texts

######
eye 42

######
favorite 0

######
comment 0

We report on a lattice QCD calculation of the $\pi N \sigma$ term, the scalar form factor, and $\langle N|\bar{s}s|N\rangle$. The disconnected insertion part of $\sg$ is found to be $1.8 \pm 0.1$ times larger than the connected insertion contribution. The $q^2$ dependence of $\sg(q^2)$ is about the same as $G_E(q^2)$ of the proton so that $\sg(2m_{\pi}^2) - \sg(0) = 6.6 \pm 0.6$ MeV. The ratio $y= \ss/\ud = 0.36 \pm 0.03$. Both results favor a $\sg \sim 53$ MeV, slightly larger than our direct...

Source: http://arxiv.org/abs/hep-ph/9602259v1

31
31

Sep 20, 2013
09/13

by
Ph. de Forcrand; M. Garcia Perez; J. E. Hetrick; E. Laermann; J. F. Lagae; I. O. Stamatescu

texts

######
eye 31

######
favorite 0

######
comment 0

To elucidate the role played by instantons in chiral symmetry breaking, we explore their properties in full QCD, around the critical temperature. We study in particular spatial correlations between low-lying Dirac eigenmodes and instantons. Our measurements are compared with the predictions of instanton-based models.

Source: http://arxiv.org/abs/hep-lat/9810033v1