2,379 research outputs found
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Phase Coexistence of a Stockmayer Fluid in an Applied Field
We examine two aspects of Stockmayer fluids which consists of point dipoles
that additionally interact via an attractive Lennard-Jones potential. We
perform Monte Carlo simulations to examine the effect of an applied field on
the liquid-gas phase coexistence and show that a magnetic fluid phase does
exist in the absence of an applied field. As part of the search for the
magnetic fluid phase, we perform Gibbs ensemble simulations to determine phase
coexistence curves at large dipole moments, . The critical temperature is
found to depend linearly on for intermediate values of beyond the
initial nonlinear behavior near and less than the where no
liquid-gas phase coexistence has been found. For phase coexistence in an
applied field, the critical temperatures as a function of the applied field for
two different are mapped onto a single curve. The critical densities
hardly change as a function of applied field. We also verify that in an applied
field the liquid droplets within the two phase coexistence region become
elongated in the direction of the field.Comment: 23 pages, ReVTeX, 7 figure
SU(N) chiral gauge theories on the lattice
We extend the construction of lattice chiral gauge theories based on
non-perturbative gauge fixing to the non-abelian case. A key ingredient is that
fermion doublers can be avoided at a novel type of critical point which is only
accessible through gauge fixing, as we have shown before in the abelian case.
The new ingredient allowing us to deal with the non-abelian case as well is the
use of equivariant gauge fixing, which handles Gribov copies correctly, and
avoids Neuberger's no-go theorem. We use this method in order to gauge fix the
non-abelian group (which we will take to be SU(N)) down to its maximal abelian
subgroup. Obtaining an undoubled, chiral fermion content requires us to
gauge-fix also the remaining abelian gauge symmetry. This modifies the
equivariant BRST identities, but their use in proving unitarity remains intact,
as we show in perturbation theory. On the lattice, equivariant BRST symmetry as
well as the abelian gauge invariance are broken, and a judiciously chosen
irrelevant term must be added to the lattice gauge-fixing action in order to
have access to the desired critical point in the phase diagram. We argue that
gauge invariance is restored in the continuum limit by adjusting a finite
number of counter terms. We emphasize that weak-coupling perturbation theory
applies at the critical point which defines the continuum limit of our lattice
chiral gauge theory.Comment: 39 pages, 3 figures, A number of clarifications adde
Spontaneous symmetry breaking in strong-coupling lattice QCD at high density
We determine the patterns of spontaneous symmetry breaking in strong-coupling
lattice QCD in a fixed background baryon density. We employ a
next-nearest-neighbor fermion formulation that possesses the SU(N_f)xSU(N_f)
chiral symmetry of the continuum theory. We find that the global symmetry of
the ground state varies with N_f and with the background baryon density. In all
cases the condensate breaks the discrete rotational symmetry of the lattice as
well as part of the chiral symmetry group.Comment: 10 pages, RevTeX 4; added discussion of accidental degeneracy of
vacuum after Eq. (35
Phase structure of the Higgs-Yukawa systems with chirally invariant lattice fermion actions
We develop analytical technique for examining phase structure of ,
, and lattice Higgs-Yukawa systems with radially frozen Higgs
fields and chirally invariant lattice fermion actions. The method is based on
variational mean field approximation. We analyse phase diagrams of such systems
with different forms of lattice fermion actions and demonstrate that it
crucially depends both on the symmetry group and on the form of the action. We
discuss location in the diagrams of possible non-trivial fixed points relevant
to continuum physics, and argue that the candidates can exist only in
system with SLAC action and systems with naive and SLAC actions. [Note:
By a product, missing term in Eq. (3.5) of hep-lat/9309010 is reconstructed,
that, however, affects only the result of Sect. 4.3 (Fig. 3) of that reference
(cf. Fig. 2(c) of this paper).]Comment: KEK-TH-390, KYUSHU-HET-17, 34 pages (harvmac) including 17 figures
(appended in postscript format with uuencoded tar file).(PostScript Files are
fixed.
Hamiltonian domain wall fermions at strong coupling
We apply strong-coupling perturbation theory to gauge theories containing
domain-wall fermions in Shamir's surface version. We construct the effective
Hamiltonian for the color-singlet degrees of freedom that constitute the
low-lying spectrum at strong coupling. We show that the effective theory is
identical to that derived from naive, doubled fermions with a mass term, and
hence that domain-wall fermions at strong coupling suffer both doubling and
explicit breaking of chiral symmetry. Since we employ a continuous fifth
dimension whose extent tends to infinity, our result applies to overlap
fermions as well.Comment: Revtex, 21 pp. Some changes in Introduction, dealing with consistency
with previous wor
Low-lying fermion modes, topology and light hadrons in quenched QCD
We explore the properties of low lying eigenmodes of fermions in the quenched
approximation of lattice QCD. The fermion action is a recently proposed overlap
action and has exact chiral symmetry. We find that chiral zero-eigenvalue modes
are localized in space and their positions correlate strongly with the
locations (as defined through the density of pure gauge observables) of
instantons of the appropriate charge. Nonchiral modes are also localized with
peaks which are strongly correlated with the positions of both charges of
instantons. These correlations slowly die away as the fermion eigenvalue rises.
Correlators made of quark propagators restricted to these modes closely
reproduce ordinary hadron correlators at small quark mass in many channels. Our
results are in qualitative agreement with the expectations of instanton liquid
models.Comment: 21 pages, Revtex, 21 postscript figures. COLO-HEP-45
Spectrum of the U(1) staggered Dirac operator in four dimensions
We compare the low-lying spectrum of the staggered Dirac operator in the
confining phase of compact U(1) gauge theory on the lattice to predictions of
chiral random matrix theory. The small eigenvalues contribute to the chiral
condensate similar as for the SU(2) and SU(3) gauge groups. Agreement with the
chiral unitary ensemble is observed below the Thouless energy, which is
extracted from the data and found to scale with the lattice size according to
theoretical predictions.Comment: 5 pages, 3 figure
Domain wall fermion zero modes on classical topological backgrounds
The domain wall approach to lattice fermions employs an additional dimension,
in which gauge fields are merely replicated, to separate the chiral components
of a Dirac fermion. It is known that in the limit of infinite separation in
this new dimension, domain wall fermions have exact zero modes, even for gauge
fields which are not smooth. We explore the effects of finite extent in the
fifth dimension on the zero modes for both smooth and non-smooth topological
configurations and find that a fifth dimension of around ten sites is
sufficient to clearly show zero mode effects. This small value for the extent
of the fifth dimension indicates the practical utility of this technique for
numerical simulations of QCD.Comment: Updated fig. 3-7, small changes in sect. 3, added fig. 8, added more
reference
Abdominal Compartment Syndrome and Intra-abdominal Ischemia in Patients with Severe Acute Pancreatitis
Severe acute pancreatitis may be complicated by intra-abdominal hypertension (IAH), abdominal compartment syndrome (ACS), and intestinal ischemia. The aim of this retrospective study is to describe the incidence, treatment, and outcome of patients with severe acute pancreatitis and ACS, in particular the occurrence of intestinal ischemia. The medical records of all patients admitted with severe acute pancreatitis admitted to the ICU of a tertiary referral center were reviewed. The criteria proposed by the World Society of the Abdominal Compartment Syndrome (WSACS) were used to determine whether patients had IAH or ACS. Fifty-nine patients with severe acute pancreatitis were identified. Intra-abdominal pressure (IAP) measurements were performed in 29 patients (49.2 %). IAH was present in all patients (29/29). ACS developed in 13/29 (44.8 %) patients. Ten patients with ACS underwent decompressive laparotomy. A large proportion of patients with ACS had intra-abdominal ischemia upon laparotomy: 8/13 (61.5 %). Mortality was high in both the ACS group and the IAH group. This study confirms that ACS is common in severe acute pancreatitis. Intra-abdominal ischemia occurs in a large proportion of patients with ACS. Swift surgical intervention may be indicated when conservative measures fail in patients with ACS. National and international guidelines need to be updated so that routine IAP measurements become standard of care for patients with severe acute pancreatitis in the ICU
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