29,797 research outputs found
Instantons and the Ground State of the Massive Schwinger Model
We study the massive Schwinger model, quantum electrodynamics of massive,
Dirac fermions, in 1+1 dimensions; with space compactified to a circle. In the
limit that transitions to fermion--anti-fermion pairs can be neglected, we
study the full ground state. We focus on the effect of instantons which mediate
tunnelling transitions in the induced potential for the dynamical degree of
freedom in the gauge field.Comment: 17 pages, plain te
Fermionization, Convergent Perturbation Theory, and Correlations in the Yang-Mills Quantum Field Theory in Four Dimensions
We show that the Yang-Mills quantum field theory with momentum and spacetime
cutoffs in four Euclidean dimensions is equivalent, term by term in an
appropriately resummed perturbation theory, to a Fermionic theory with nonlocal
interaction terms. When a further momentum cutoff is imposed, this Fermionic
theory has a convergent perturbation expansion. To zeroth order in this
perturbation expansion, the correlation function of generic components
of pairs of connections is given by an explicit, finite-dimensional integral
formula, which we conjecture will behave as \noindent for where is a positive integer depending
on the gauge group In the case where we conjecture that \noindent so that the rate
of decay of correlations increases as Comment: Minor corrections of notation, style and arithmetic errors;
correction of minor gap in the proof of Proposition 1.4 (the statement of the
Proposition was correct); further remark and references adde
Dirty Black Holes and Hairy Black Holes
An approach based on considerations of the non-classical energy momentum
tensor outside the event horizon of a black hole provides additional physical
insight into the nature of discrete quantum hair on black holes and its effect
on black hole temperature. Our analysis both extends previous work based on the
Euclidean action techniques, and corrects an omission in that work. We also
raise several issues related to the effects of instantons on black hole
thermodynamics and the relation between these effects and results in two
dimensional quantum field theory.Comment: 13 pages, Latex, submitted to Physical Review Letter
Design of experiments for non-manufacturing processes : benefits, challenges and some examples
Design of Experiments (DoE) is a powerful technique for process optimization that has been widely deployed in almost all types of manufacturing processes and is used extensively in product and process design and development. There have not been as many efforts to apply powerful quality improvement techniques such as DoE to improve non-manufacturing processes. Factor levels often involve changing the way people work and so have to be handled carefully. It is even more important to get everyone working as a team. This paper explores the benefits and challenges in the application of DoE in non-manufacturing contexts. The viewpoints regarding the benefits and challenges of DoE in the non-manufacturing arena are gathered from a number of leading academics and practitioners in the field. The paper also makes an attempt to demystify the fact that DoE is not just applicable to manufacturing industries; rather it is equally applicable to non-manufacturing processes within manufacturing companies. The last part of the paper illustrates some case examples showing the power of the technique in non-manufacturing environments
Effects of Radiation Forces on the Frequency of Gravitomagnetic Precession Near Neutron Stars
Gravitomagnetic precession near neutron stars and black holes has received
much recent attention, particularly as a possible explanation of 15--60 Hz
quasi-periodic brightness oscillations (QPOs) from accreting neutron stars in
low-mass X-ray binaries, and of somewhat higher-frequency QPOs from accreting
stellar-mass black holes. Previous analyses of this phenomenon have either
ignored radiation forces or assumed for simplicity that the radiation field is
isotropic, and in particular that there is no variation of the radiation field
with angular distance from the rotational equatorial plane of the compact
object. However, in most realistic accretion geometries (e.g., those in which
the accretion proceeds via a geometrically thin disk) the radiation field
depends on latitude. Here we show that in this case radiation forces typically
have an important, even dominant, effect on the precession frequency of test
particles in orbits that are tilted with respect to the star's rotational
equator. Indeed, we find that even for accretion luminosities only a few
percent of the Eddington critical luminosity, the precession frequency near a
neutron star can be changed by factors of up to . Radiation forces
must therefore be included in analyses of precession frequencies near compact
objects, in such varied contexts as low-frequency QPOs, warp modes of disks,
and trapped oscillation modes. We discuss specifically the impact of radiation
forces on models of low-frequency QPOs involving gravitomagnetic precession,
and show that such models are rendered much less plausible by the effects of
radiation forces.Comment: 15 pages LaTeX including three figures, submitted to Ap
Fate of the false monopoles: induced vacuum decay
We study a gauge theory model where there is an intermediate symmetry
breaking to a meta- stable vacuum that breaks a simple gauge group to a U (1)
factor. Such models admit the existence of meta-stable magnetic monopoles,
which we dub false monopoles. We prove the existence of these monopoles in the
thin wall approximation. We determine the instantons for the collective
coordinate that corresponds to the radius of the monopole wall and we calculate
the semi-classical tunneling rate for the decay of these monopoles. The
monopole decay consequently triggers the decay of the false vacuum. As the
monopole mass is increased, we find an enhanced rate of decay of the false
vacuum relative to the celebrated homogeneous tunneling rate due to Coleman
[1].Comment: 10 pages, 4 figure
Gender and educational leadership in England: a comparison of secondary headteachers' views over time
In the context of gender being a barrier to accessing leadership, this paper presents a comparison of the views of men and women head teacher (principals) of secondary schools in England in the 1990s and in 2004. The same survey instrument was used on both occasions. The perceptions of the head teachers show change in some areas and no change in others. Overall, women are more likely to become head teachers and are now less likely to be categorised into pastoral roles, but in some cases women still meet prejudice from governors and others in the wider community. Women head teachers are more likely to have partners and children than in the 1990s, sharing equally or carrying most of the domestic responsibilities, whereas male colleagues are most likely to have partners who take the majority of responsibility in the home. Essentialist stereotypes about women and men as leaders still prevail, although both the women and men head teachers see themselves as adopting a traditionally ‘feminine’ style of leadership. Women head teachers are likely to see some benefits in being a woman in a role stereotypically associated with men. However, there has been an increase in the proportion of women who feel that they have to prove their worth as a leader, and this may be linked with increased levels of accountability in schools
No supercritical supercurvature mode conjecture in one-bubble open inflation
In the path integral approach to false vacuum decay with the effect of
gravity, there is an unsolved problem, called the negative mode problem. We
show that the appearance of a supercritical supercurvature mode in the
one-bubble open inflation scenario is equivalent to the existence of a negative
mode around the Euclidean bounce solution. Supercritical supercurvature modes
are those whose mode functions diverge exponentially for large spatial radius
on the time constant hypersurface of the open universe. Then we propose a
conjecture that there should be ``no supercritical supercurvature mode''. For a
class of models that contains a wide variety of tunneling potentials, this
conjecture is shown to be correct.Comment: 11 pages, 3 postscript figures, tarred, gzipped. submitted to Phys.
Rev. D1
The O(N) Nonlinear Sigma Model in the Functional Schr\"{o}dinger Picture
We present a functional Schr\"{o}dinger picture formalism of the
(1+1)-dimensional nonlinear sigma model. The energy density has been
calculated to two-loop order using the wave functional of a gaussian form, and
from which the nonperturbative mass gap of the boson fields has been obtained.
The functional Schr\"{o}dinger picture approach combined with the variational
technique is shownto describe the characteristics of the ground state of the
nonlinear sigma model in a transparent way.Comment: 13 pages, no figures, Latex fil
Six-body Light-Front Tamm-Dancoff approximation and wave functions for the massive Schwinger model
The spectrum of the massive Schwinger model in the strong coupling region is
obtained by using the light-front Tamm-Dancoff (LFTD) approximation up to
including six-body states. We numerically confirm that the two-meson bound
state has a negligibly small six-body component. Emphasis is on the usefulness
of the information about states (wave functions). It is used for identifying
the three-meson bound state among the states below the three-meson threshold.
We also show that the two-meson bound state is well described by the wave
function of the relative motion.Comment: 19 pages, RevTeX, 7 figures are available upon request; Minor errors
have been corrected; Final version to appear in Phys.Rev.
- …