1,917 research outputs found
Before sailing on a domain-wall sea
We discuss the very different roles of the valence-quark and the sea-quark
residual masses ( and ) in dynamical domain-wall fermions
simulations. Focusing on matrix elements of the effective weak hamiltonian
containing a power divergence, we find that can be a source of a
much bigger systematic error. To keep all systematic errors due to residual
masses at the 1% level, we estimate that one needs
and , at a lattice spacing fm. The
practical implications are that (1) optimal use of computer resources calls for
a mixed scheme with different domain-wall fermion actions for the valence and
sea quarks; (2) better domain-wall fermion actions are needed for both the sea
and the valence sectors.Comment: latex, 25 pages. Improved discussion in appendix, including
correction of some technical mistakes; ref. adde
Chiral Fermions on the Lattice through Gauge Fixing -- Perturbation Theory
We study the gauge-fixing approach to the construction of lattice chiral
gauge theories in one-loop weak-coupling perturbation theory. We show how
infrared properties of the gauge degrees of freedom determine the nature of the
continuous phase transition at which we take the continuum limit. The fermion
self-energy and the vacuum polarization are calculated, and confirm that, in
the abelian case, this approach can be used to put chiral gauge theories on the
lattice in four dimensions. We comment on the generalization to the nonabelian
case.Comment: 31 pages, 5 figures, two refs. adde
A simple derivation of the Overlap Dirac Operator
We derive the vector-like four dimensional overlap Dirac operator starting
from a five dimensional Dirac action in the presence of a delta-function
space-time defect. The effective operator is obtained by first integrating out
all the fermionic modes in the fixed gauge background, and then identifying the
contribution from the localized modes as the determinant of an operator in one
dimension less. We define physically relevant degrees of freedom on the defect
by introducing an auxiliary defect-bound fermion field and integrating out the
original five dimensional bulk field.Comment: 9 pages, LaTe
Existence of Wormholes in Gravity using Symmetries
The current study examines the geometry of static wormholes with anisotropic
matter distribution in context of modified gravity. We
consider the well known Noether and conformal symmetries, which help in
investigating wormholes in gravity. For this purpose, we
develop symmetry generators associated with conserved quantities by taking into
consideration the gravity model. Moreover, we use the
conservation relationship gained from the classical Noether method and
conformal Killing symmetries to develop the metric potential. These symmetries
provide a strong mathematical background to investigate wormhole solutions by
incorporating some suitable initial conditions. The obtained conserved quantity
performs a significant role in defining the essential physical characteristics
of the shape-function and energy conditions. Further, we also describe the
stability of obtained wormholes solutions by employing the equilibrium
condition in modified gravity. It is observed from graphical
representation of obtained wormhole solutions that Noether and conformal
Killing symmetries provide the results with physically accepted patterns.Comment: 10 pages, 7 figure
Gravity Bouncing Universe with Cosmological Parameters
In recent few years, the Gauss-Bonnet
theory of gravity has fascinated considerable researchers owing to its coupling
of trace of the stress-energy tensor with the Gauss-Bonnet term
. In this context, we focuss ourselves to study bouncing universe
with in gravity background. Some important
preliminaries are presented along with the discussion of cosmological
parameters to develop a minimal background about
theory of gravity. The exact bouncing
solutions with physical analysis are provided with the choice of two equation
of state parameters. It is shown that the results do agree with the present
values of deceleration, jerk and snap parameters. Moreover, it is concluded
that the model parameters are quite important for the validity of conservation
equation (as the matter coupled theories do not obey the usual conservation
law).Comment: 12 pages, 10 figure
Running coupling and mass anomalous dimension of SU(3) gauge theory with two flavors of symmetric-representation fermions
We have measured the running coupling constant of SU(3) gauge theory coupled
to Nf=2 flavors of symmetric representation fermions, using the Schrodinger
functional scheme. Our lattice action is defined with hypercubic smeared links
which, along with the larger lattice sizes, bring us closer to the continuum
limit than in our previous study. We observe that the coupling runs more slowly
than predicted by asymptotic freedom, but we are unable to observe fixed point
behavior before encountering a first order transition to a strong coupling
phase. This indicates that the infrared fixed point found with the thin-link
action is a lattice artifact. The slow running of the gauge coupling permits an
accurate determination of the mass anomalous dimension for this theory, which
we observe to be small, gamma_m < 0.6, over the range of couplings we can
reach. We also study the bulk and finite-temperature phase transitions in the
strong coupling region.Comment: 17 pages, 16 figures. Substantial modifications to explain why the
fat-link result for the beta function supersedes our thin-link result; also
updated the phase diagram to reflect additional numerical work. Added
references. Final versio
Toward 'socially constructive' social constructions of leadership
In their introductory editorial essay for this special issue, David Grant and Gail Fairhurst have done us a great service by valiantly producing a "Sailing Guide" to the Social Construction of Leadership (Fairhurst & Grant, 2010). As with rounding the Capes, this is not a task for the faint of heart. A sailing guide is designed to provide vital knowledge about a particular sea or coast, providing us with charts, warnings about potential hazards and an indication where we might find safe havens in a storm. Their sailing guide does this to great effect as it skilfully "boxes the compass" by revealing all of the potential directions that one might set one‟s sail by if one was sufficiently foolhardy to embark on a cruise of the social construction of leadership
The Phase Diagram and Spectrum of Gauge-Fixed Abelian Lattice Gauge Theory
We consider a lattice discretization of a covariantly gauge-fixed abelian
gauge theory. The gauge fixing is part of the action defining the theory, and
we study the phase diagram in detail. As there is no BRST symmetry on the
lattice, counterterms are needed, and we construct those explicitly. We show
that the proper adjustment of these counterterms drives the theory to a new
type of phase transition, at which we recover a continuum theory of (free)
photons. We present both numerical and (one-loop) perturbative results, and
show that they are in good agreement near this phase transition. Since
perturbation theory plays an important role, it is important to choose a
discretization of the gauge-fixing action such that lattice perturbation theory
is valid. Indeed, we find numerical evidence that lattice actions not
satisfying this requirement do not lead to the desired continuum limit. While
we do not consider fermions here, we argue that our results, in combination
with previous work, provide very strong evidence that this new phase transition
can be used to define abelian lattice chiral gauge theories.Comment: 42 pages, 30 figure
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