1,572 research outputs found
A simple construction of fermion measure term in U(1) chiral lattice gauge theories with exact gauge invariance
In the gauge invariant formulation of U(1) chiral lattice gauge theories
based on the Ginsparg-Wilson relation, the gauge field dependence of the
fermion measure is determined through the so-called measure term. We derive a
closed formula of the measure term on the finite volume lattice. The Wilson
line degrees of freedom (torons) of the link field are treated separately to
take care of the global integrability. The local counter term is explicitly
constructed with the local current associated with the cohomologically trivial
part of the gauge anomaly in a finite volume. The resulted formula is very
close to the known expression of the measure term in the infinite volume with a
single parameter integration, and would be useful in practical implementations.Comment: 25 pages, uses JHEP3.cls, the version to appear in JHE
Towards Weyl fermions on the lattice without artefacts
In spite of the breakthrough in non-perturbative chiral gauge theories during
the last decade, the present formulation has stubborn artefacts. Independently
of the fermion representation one is confronted with unwanted CP violation and
infinitely many undetermined weight factors. Renormalization group identifies
the culprit. We demonstrate the procedure on Weyl fermions in a real
representation
Non-perturbatively Renormalized Light-Quark Masses with the Alpha Action
We have computed the light quark masses using the O(a^2) improved Alpha
action, in the quenched approximation. The renormalized masses have been
obtained non-perturbatively. By eliminating the systematic error coming from
the truncation of the perturbative series, our procedure removes the
discrepancies, observed in previous calculations, between the results obtained
using the vector and the axial-vector Ward identities. It also gives values of
the quark masses larger than those obtained by computing the renormalization
constants using (boosted) perturbation theory. Our main results, in the RI
(MOM) scheme and at a renormalization scale \mu=2 GeV, are m^{RI}_s= 138(15)
MeV and m^{RI}_l= 5.6(5) MeV, where m^{RI}_s is the mass of the strange quark
and m^{RI}_l=(m^{RI}_u+m^{RI}_d)/2 the average mass of the up-down quarks. From
these results, which have been obtained non-perturbatively, by using continuum
perturbation theory we derive the \bar{MS} masses, at the same scale, and the
renormalization group invariant (m^{RGI}) masses. We find m^{NLO \bar{MS}}_s=
121(13)$ MeV and m^{NLO\bar{MS}}_l= 4.9(4) MeV at the next-to-leading order;
m^{N^2LO \bar{MS}}_s= 111(12) MeV, m^{N^2LO \bar{MS}}_l= 4.5(4) MeV, m_s^{RGI}=
177(19) MeV and m^{RGI}_l= 7.2(6) MeV at the next-to-next-to-leading order.Comment: 13 pages, 1 figur
Coulomb Energy, Vortices, and Confinement
We estimate the Coulomb energy of static quarks from a Monte Carlo
calculation of the correlator of timelike link variables in Coulomb gauge. We
find, in agreement with Cucchieri and Zwanziger, that this energy grows
linearly with distance at large quark separations. The corresponding string
tension, however, is several times greater than the accepted asymptotic string
tension, indicating that a state containing only static sources, with no
constituent gluons, is not the lowest energy flux tube state. The Coulomb
energy is also measured on thermalized lattices with center vortices removed by
the de Forcrand-D'Elia procedure. We find that when vortices are removed, the
Coulomb string tension vanishes.Comment: 8 pages, 4 EPS figures, RevTeX4; reference adde
Non-perturbative renormalisation and improvement of the local vector current for quenched and unquenched Wilson fermions
By considering the local vector current between nucleon states and imposing
charge conservation, we determine its renormalisation constant and quark mass
improvement coefficient for Symanzik improved Wilson fermions. The
computation is first performed for quenched fermions (and for completeness also
with unimproved fermions) and compared against known results. The two-flavour
unquenched case is then considered.Comment: 15 pages, 5 figures, Latex, Final versio
A construction of the Glashow-Weinberg-Salam model on the lattice with exact gauge invariance
We present a gauge-invariant and non-perturbative construction of the
Glashow-Weinberg-Salam model on the lattice, based on the lattice Dirac
operator satisfying the Ginsparg-Wilson relation. Our construction covers all
SU(2) topological sectors with vanishing U(1) magnetic flux and would be usable
for a description of the baryon number non-conservation. In infinite volume, it
provides a gauge-invariant regularization of the electroweak theory to all
orders of perturbation theory. First we formulate the reconstruction theorem
which asserts that if there exists a set of local currents satisfying cetain
properties, it is possible to reconstruct the fermion measure which depends
smoothly on the gauge fields and fulfills the fundamental requirements such as
locality, gauge-invariance and lattice symmetries. Then we give a closed
formula of the local currents required for the reconstruction theorem.Comment: 32 pages, uses JHEP3.cls, the version to appear in JHE
The Landau Pole at Finite Temperature
We study the Landau pole in the lambda phi^4 field theory at non-zero and
large temperatures. We show that the position of the thermal Landau pole
Lambda_L(T) is shifted to higher energies with respect to the zero temperature
Landau pole Lambda_L(0). We find for high temperatures T > Lambda_L(0),
Lambda_L(T) simeq pi^2 T / log (T / Lambda_L(0)). Therefore, the range of
applicability in energy of the lambda phi^4 field theory increases with the
temperature.Comment: LaTex, 6 pages, 2 .ps figures. Improved version. To appear in Phys.
Rev. D, Rapid Communication
Short distance behaviour of the effective string
We study the Polyakov loop correlator in the (2+1) dimensional Z_2 gauge
model. An algorithm that we have presented recently, allows us to reach high
precision results for a large range of distances and temperatures, giving us
the opportunity to test predictions of the effective Nambu-Goto string model.
Here we focus on the regime of low temperatures and small distances. In
contrast to the high temperature, large distance regime, we find that our
numerical results are not well described by the two loop-prediction of the
Nambu-Goto model. In addition we compare our data with those for the SU(2) and
SU(3) gauge models in (2+1) dimensions obtained by other authors. We generalize
the result of L\"uscher and Weisz for a boundary term in the interquark
potential to the finite temperature case.Comment: 38 pages, 7 figures, version accepted for publication in JHE
Inequalities for low-energy symmetric nuclear matter
Using effective field theory we prove inequalities for the correlations of
two-nucleon operators in low-energy symmetric nuclear matter. For physical
values of operator coefficients in the effective Lagrangian, the S = 1, I = 0
channel correlations must have the lowest energy and longest correlation length
in the two-nucleon sector. This result is valid at nonzero density and
temperature.Comment: 9 page
pion scattering amplitude with Wilson fermions
We present an exploratory calculation of the scattering
amplitude at threshold using Wilson fermions in the quenched approximation,
including all the required contractions. We find good agreement with the
predictions of chiral perturbation theory even for pions of mass 560-700 MeV.
Within the 10\% errors, we do not see the onset of the bad chiral behavior
expected for Wilson fermions. We also derive rigorous inequalities that apply
to 2-particle correlators and as a consequence show that the interaction in the
antisymmetric state of two pions has to be attractive.Comment: This PS file includes 4 tables and figures 1-8 on 25 pages. Los
Alamos Preprint Number LAUR-92-364
- …