914 research outputs found
The Polarisation Signatures of Microlensing
It has already been shown that microlensing can give rise to a non-zero
variable polarisation signal. Here we use realistic simulations to demonstrate
the additional information that can be gained from polarimetric observations of
lensing events.Comment: 4 pages, LaTeX, 2 figures from 6 postscript files. Uses elsart.sty,
graphicx.sty and harvard.sty. To appear in New Astronomy Reviews -
proceedings of the Oxford Workshop `Gravitational Lensing: Nature's Own
Weighing Scales
Higher-Spin Theory and Space-Time Metamorphoses
Introductory lectures on higher-spin gauge theory given at 7 Aegean workshop
on non-Einstein theories of gravity. The emphasis is on qualitative features of
the higher-spin gauge theory and peculiarities of its space-time
interpretation. In particular, it is explained that Riemannian geometry cannot
play a fundamental role in the higher-spin gauge theory. The higher-spin
symmetries are argued to occur at ultra high energy scales beyond the Planck
scale. This suggests that the higher-spin gauge theory can help to understand
Quantum Gravity. Various types of higher-spin dualities are briefly discussed.Comment: 37 pages, no figures; V2: references adde
First order quantum phase transitions
Quantum phase transitions have been the subject of intense investigations in
the last two decades [1]. Among other problems, these phase transitions are
relevant in the study of heavy fermion systems, high temperature
superconductors and Bose-Einstein condensates. More recently there is
increasing evidence that in many systems which are close to a quantum critical
point (QCP) different phases are in competition. In this paper we show that the
main effect of this competition is to give rise to inhomogeneous behavior
associated with quantum first order transitions. These effects are described
theoretically using an action that takes into account the competition between
different order parameters. The method of the effective potential is used to
calculate the quantum corrections to the classical functional. These
corrections generally change the nature of the QCP and give rise to interesting
effects even in the presence of non-critical fluctuations. An unexpected result
is the appearance of an inhomogeneous phase with two values of the order
parameter separated by a first order transition. Finally, we discuss the
universal behavior of systems with a weak first order zero temperature
transition in particular as the transition point is approached from finite
temperatures. The thermodynamic behavior along this line is obtained and shown
to present universal features.Comment: 7 pages, 5 figures. Invited talk at ICM2006, Kyoto. To appear in JMM
Lessons from : Vacuum structure, Asymptotic Series, Instantons and all that
We discuss two dimensional with fermions in the
fundamental as well as adjoint representation. We find factorial growth in the coefficients of
the large order perturbative expansion. We argue that this behavior is related
to classical solutions of the theory, instantons, thus it has nonperturbative
origin. Phenomenologically such a growth is related to highly excited states in
the spectrum. We also analyze the heavy-light quark system within
operator product expansion (which it turns out to be an asymptotic series).
Some vacuum condensates \la\bar{q}(x_{\mu}D_{\mu})^{2n}q\ra\sim (x^2)^n\cdot
n! which are responsible for this factorial growth are also discussed. We
formulate some general puzzles which are not specific for 2D physics, but are
inevitable features of any asymptotic expansion. We resolve these apparent
puzzles within and we speculate that analogous puzzles might occur in
real 4-dimensional QCD as well.Comment: latex, 26 pages. A final version to appear in Phys. Rev.
Fractons in Twisted Multiflavor Schwinger Model
We consider two-dimensional QED with several fermion flavors on a finite
spatial circle. A modified version of the model with {\em flavor-dependent}
boundary conditions ,
is discussed ( is the number of flavors). In this case a non-contactable
contour in the space of the gauge fields is {\em not} determined by large gauge
transformations. The Euclidean path integral acquires the contribution from the
gauge field configurations with fractional topological charge. The
configuration with is responsible for the formation of the fermion
condensate . The condensate dies out as a
power of when the length of the spatial box is sent to infinity.
Implications of this result for non-abelian gauge field theories are discussed
in brief.Comment: 29 pages, 3 figures available upon request, Report TPI-MINN-94-24-T
Plain LATE
Unparticle Physics in the Moller Scattering
We investigate the virtual effects of vector unparticles in the Moller
scattering. We derive the analytic expression for scattering amplitudes with
unpolarized beams. We obtain 95% confidence level limits on the unparticle
couplings and with integrated luminosity of
and and 500 GeV energies. We show
that limits on are more sensitive than .Comment: 10 pages, 5 figures, 4 table
Low uptake of postpartum screening for Type 2 diabetes in women after a diagnosis of gestational diabetes
Postpartum screening rates for Type 2 diabetes after a diagnosis of gestational diabetes are low across many high-income countries, ranging from 20 to 58% up to 1 year after delivery [1,2]. Subsequent annual follow-up rates plateau at 20% [1].We conducted an audit to assess postnatal diabetes screening rates in 233 women living in the city of Southampton with a history of gestational diabetes, diagnosed using WHO criteria. Current local practice involves giving verbal and written information regarding the risks of Type 2 diabetes after pregnancy at the initial consultation. After delivery and before discharge, all women are recommended to undergo postnatal glucose testing and are informed verbally and in writing to contact their general practitioner for annual ongoing screening. A copy of this letter is sent to the woman's general practitioner
Finite Temperature Correlators in the Schwinger Model
We discuss the correlation function of hadronic currents in the Schwinger
model at finite temperature . We explicitly construct the retarded
correlator in real time and obtain analytical results for the Euclidean
correlator on a torus. Both constructions lead to the same finite temperature
spectral function. The spatial screening lengths in the mesonic channels are
related to the dynamical meson mass and not even in
the infinite temperature limit. The relevance of our results for the finite
temperature problem in four dimensions is discussed.Comment: in LATEX, 30 pages; two figures available on request from the
authors; USITP-93-19, SUNY-NTG-43, (explanations to the figures have been
clarified
Classical stability of U(1)_A domain walls in dense matter QCD
It was recently shown that there exists metastable U(1)_A domain wall
configurations in high-density QCD (\mu >> 1 GeV). In the following we will
assess the stability of such non-trivial field configurations at intermediate
densities (\mu < 1 GeV). The existence of such configurations at intermediate
densities could have interesting consequences for the physics of neutron stars
with high core density.Comment: 13 pages, 2 Postscript figures, typos correcte
Spectral properties of the one-dimensional two-channel Kondo lattice model
We have studied the energy spectrum of a one-dimensional Kondo lattice, where
the localized magnetic moments have SU(N) symmetry and two channels of
conduction electrons are present. At half filling, the system is shown to exist
in two phases: one dominated by RKKY-exchange interaction effects, and the
other by Kondo screening. A quantum phase transition point separates these two
regimes at temperature . The Kondo-dominated phase is shown to possess
soft modes, with spectral gaps much smaller than the Kondo temperature.Comment: 4 pages + 2 figures. Submitted for publicatio
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