342 research outputs found
Higher Loop Results for the Plaquette, Using the Clover and Overlap Actions
We calculate the perturbative value of the free energy in QCD on the lattice.
This quantity is directly related to the average plaquette.
Our calculation is done to 3 loops using the clover action for fermions; the
results are presented for arbitrary values of the clover coefficient, and for a
wide range of fermion masses.
In addition, we calculate the 2 loop result for the same quantity, using the
overlap action.Comment: 3 pages, 1 figure. Presented at Lattice2004(improved
Lattice chiral fermions in the background of non-trivial topology
We address the problem of numerical simulations in the background non-trivial
topology in the chiral Schwinger model. An effective fermionic action is
derived which is in accord with established analytical results, and which
satisfies the anomaly equation. We describe a numerical evaluation of baryon
number violating amplitudes, specifically the 't Hooft vertex.Comment: LATTICE99(Chiral Gauge Theories
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
A practical implementation of the Overlap-Dirac operator
A practical implementation of the Overlap-Dirac operator
is presented. The implementation exploits
the sparseness of and does not require full storage. A simple application
to parity invariant three dimensional SU(2) gauge theory is carried out to
establish that zero modes related to topology are exactly reproduced on the
lattice.Comment: Y-axis label in figure correcte
First-order restoration of SU(Nf) x SU(Nf) chiral symmetry with large Nf and Electroweak phase transition
It has been argued by Pisarski and Wilczek that finite temperature
restoration of the chiral symmetry SU(Nf) x SU(Nf) is first-order for Nf >=3.
This type of chiral symmetry with a large Nf may appear in the Higgs sector if
one considers models such as walking technicolor theories. We examine the
first-order restoration of the chiral symmetry from the point of view of the
electroweak phase transition. The strength of the transition is estimated in
SU(2) x U(1) gauged linear sigma model by means of the finite temperature
effective potential at one-loop with the ring improvement. Even if the mass of
the neutral scalar boson corresponding to the Higgs boson is larger than 114
GeV, the first-order transition can be strong enough for the electroweak
baryogenesis, as long as the extra massive scalar bosons (required for the
linear realization) are kept heavier than the neutral scalar boson. Explicit
symmetry breaking terms reduce the strength of the first-order transition, but
the transition can remain strongly first-order even when the masses of pseudo
Nambu-Goldstone bosons become as large as the current lower bound of direct
search experiments.Comment: 18 pages, 18 figures, minor corrections, references adde
Neutron electric dipole moment from lattice QCD
We carry out a feasibility study for the lattice QCD calculation of the
neutron electric dipole moment (NEDM) in the presence of the term. We
develop the strategy to obtain the nucleon EDM from the CP-odd electromagnetic
form factor at small , in which NEDM is given by where is the momentum transfer and is the
nucleon mass. We first derive a formula which relates , a matrix element
of the electromagnetic current between nucleon states, with vacuum expectation
values of nucleons and/or the current. In the expansion of , the
parity-odd part of the nucleon-current-nucleon three-point function contains
contributions not only from the parity-odd form factors but also from the
parity-even form factors multiplied by the parity-odd part of the nucleon
two-point function, and therefore the latter contribution must be subtracted to
extract . We then perform an explicit lattice calculation employing the
domain-wall quark action with the RG improved gauge action in quenched QCD at
GeV on a lattice. At the quark mass
, corresponding to , we accumulate 730
configurations, which allow us to extract the parity-odd part in both two- and
three-point functions. Employing two different Dirac matrix
projections, we show that a consistent value for cannot be obtained
without the subtraction described above. We obtain 0.024(5) fm for the neutron and
0.021(6) fm for the
proton.Comment: LaTeX2e, 43 pages, 42 eps figures, uses revtex4 and graphicx,
comments added and typos corrected, final version to appear in Phys. Rev.
Domain wall fermion and CP symmetry breaking
We examine the CP properties of chiral gauge theory defined by a formulation
of the domain wall fermion, where the light field variables and
together with Pauli-Villars fields and are utilized. It is shown
that this domain wall representation in the infinite flavor limit is
valid only in the topologically trivial sector, and that the conflict among
lattice chiral symmetry, strict locality and CP symmetry still persists for
finite lattice spacing . The CP transformation generally sends one
representation of lattice chiral gauge theory into another representation of
lattice chiral gauge theory, resulting in the inevitable change of propagators.
A modified form of lattice CP transformation motivated by the domain wall
fermion, which keeps the chiral action in terms of the Ginsparg-Wilson fermion
invariant, is analyzed in detail; this provides an alternative way to
understand the breaking of CP symmetry at least in the topologically trivial
sector. We note that the conflict with CP symmetry could be regarded as a
topological obstruction. We also discuss the issues related to the definition
of Majorana fermions in connection with the supersymmetric Wess-Zumino model on
the lattice.Comment: 33 pages. Note added and a new reference were added. Phys. Rev.D (in
press
Neutron electric dipole moment with external electric field method in lattice QCD
We discuss a possibility that the Neutron Electric Dipole Moment (NEDM) can
be calculated in lattice QCD simulations in the presence of the CP violating
term. In this paper we measure the energy difference between spin-up
and spin-down states of the neutron in the presence of an uniform and static
external electric field. We first test this method in quenched QCD with the RG
improved gauge action on a lattice at 2 GeV,
employing two different lattice fermion formulations, the domain-wall fermion
and the clover fermion for quarks, at relatively heavy quark mass . We obtain non-zero values of NEDM from calculations with both
fermion formulations. We next consider some systematic uncertainties of our
method for NEDM, using lattice at the same lattice spacing only
with the clover fermion. We finally investigate the quark mass dependence of
NEDM and observe a non-vanishing behavior of NEDM toward the chiral limit. We
interpret this behavior as a manifestation of the pathology in the quenched
approximation.Comment: LaTeX2e, 51 pages, 43 figures, uses revtex4 and graphicx, References
and comments added, typos corrected, accepted by PR
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