16,332 research outputs found
The UV behavior of Gravity at Large N
A first step in the analysis of the renormalizability of gravity at Large N
is carried on. Suitable resummations of planar diagrams give rise to a theory
in which there is only a finite number of primitive superficially divergent
Feynman diagrams. The mechanism is similar to the the one which makes
renormalizable the 3D Gross-Neveu model at large N. Some potential problems in
fulfilling the Slavnov-Taylor and the Zinn-Justin equations are also pointed
out.Comment: 17 pages, 9 figures. To appear on Phys. Rev. D. Two more references,
further technical details and the discussion of the KLT relations at large N
have been include
Bi-partite entanglement entropy in massive two-dimensional quantum field theory
Recently, Cardy, Castro Alvaredo and the author obtained the first
exponential correction to saturation of the bi-partite entanglement entropy at
large region length, in massive two-dimensional integrable quantum field
theory. It only depends on the particle content of the model, and not on the
way particles scatter. Based on general analyticity arguments for form factors,
we propose that this result is universal, and holds for any massive
two-dimensional model (also out of integrability). We suggest a link of this
result with counting pair creations far in the past.Comment: 5 pages, 2 figures. v2: improved presentation of result and
calculations, section "discussion" adjusted, references adjuste
Hydrodynamic Thermonuclear Runaways in Superbursts
We calculate the thermal and dynamical evolution of the surface layers of an
accreting neutron star during the rise of a superburst. For the first few hours
following unstable 12C ignition, the nuclear energy release is transported by
convection. However, as the base temperature rises, the heating time becomes
shorter than the eddy turnover time and convection becomes inefficient. This
results in a hydrodynamic nuclear runaway, in which the heating time becomes
shorter than the local dynamical time. Such hydrodynamic burning can drive
shock waves into the surrounding layers and may be the trigger for the normal
X-ray burst found to immediately precede the onset of the superburst in both
cases where the Rossi X-Ray Timing Explorer was observing.Comment: 4 pages, 3 figures (emulateapj), accepted to ApJ Letter
Development of improved amorphous materials for laser systems
Crystallization calculations were performed in order to determine the possibility of forming a particular type of laser glass with the avoidance of devitrification in an outer space laboratory. It was demonstrated that under the homogenuous nucleating conditions obtainable in a zero gravity laboratory this laser glass may be easily quenched to a virtually crystal-free product. Experimental evidence is provided that use of this material as a host in a neodymium glass laser would result in more than a 10 percent increase in efficiency when compared to laser glass rods of a similar composition currently commercially available. Differential thermal analysis, thermal gradient oven, X-ray diffraction, and liquidus determination experiments were carried out to determine the basics of the crystallization behavior of the glass, and small-angle X-ray scattering and splat-cooling experiments were performed in order to provide additional evidence for the feasibility of producing this laser glass material, crystal free, in an outer space environment
Nonmetallic impurities improve mechanical properties of vapor-deposited tungsten
Mechanical properties of vapor deposited tungsten are improved by selective incorporation of various nonmetallic impurities. Addition of trace quantities of carbon, nitrogen, or oxygen can significantly increase both low and high temperature yield strength without greatly affecting ductile-to-brittle transition temperature
Dressing the electromagnetic nucleon current
A field-theory-based approach to pion photoproduction off the nucleon is used
to derive a microscopically consistent formulation of the fully dressed
electromagnetic nucleon current in an effective Lagrangian formalism. It is
shown how the rigorous implementation of local gauge invariance at all levels
of the reaction dynamics provides equations that lend themselves to practically
manageable truncations of the underlying nonlinearities of the problem. The
requirement of consistency also suggests a novel way of treating the pion
photoproduction problem. Guided by a phenomenological implementation of gauge
invariance for the truncated equations that has proved successful for pion
photoproduction, an expression for the fully dressed nucleon current is given
that satisfies the Ward-Takahashi identity for a fully dressed nucleon
propagator as a matter of course. Possible applications include meson photo-
and electroproduction processes, bremsstrahlung, Compton scattering, and
processes off nucleons.Comment: 10 pages, 9 figure
A Test of the Adhesion Approximation for Gravitational Clustering
We quantitatively compare a particle implementation of the adhesion
approximation to fully non--linear, numerical nbody simulations. Our primary
tool, cross--correlation of nbody simulations with the adhesion approximation,
indicates good agreement, better than that found by the same test performed
with the Zel'dovich approximation (hereafter ZA). However, the
cross--correlation is not as good as that of the truncated Zel'dovich
approximation (TZA), obtained by applying the Zel'dovich approximation after
smoothing the initial density field with a Gaussian filter. We confirm that the
adhesion approximation produces an excessively filamentary distribution.
Relative to the nbody results, we also find that: (a) the power spectrum
obtained from the adhesion approximation is more accurate than that from ZA or
TZA, (b) the error in the phase angle of Fourier components is worse than that
from TZA, and (c) the mass distribution function is more accurate than that
from ZA or TZA. It appears that adhesion performs well statistically, but that
TZA is more accurate dynamically, in the sense of moving mass to the right
place.
Subject Heading: Galaxies, formation, clustering--large--scale structure of
the UniverseComment: TeX, 7 pages excluding figures (contact
[email protected]). submitted to Ap
Growth of covariant perturbations in the contracting phase of a bouncing universe
In this paper we examine the validity of the linear perturbation theory near
a bounce in the covariant analysis. Some linearity parameters are defined to
set up conditions for a linear theory. Linear evolution of density perturbation
and gravitational waves have been computed previously. We have calculated the
vector and scalar induced parts of the shear tensor. For radiationlike and
dustlike single fluid dominated collapsing Friedmann-Lemaitre-Robertson-Walker
background it is shown that the linearity conditions are not satisfied near a
bounce.Comment: 9 pages, final versio
Some Simpler Analogues of the Dual Standard Model and their Relation to Bais' Generalisation of the Montenon-Olive Conjecture
We show that the correspondence between SU(5) monopoles and the elementary
particles, which underlies the construction of a dual standard model, has some
simpler analogues associated with the strong, weak and hypercharge
interactions. We then discuss how these analogues relate to Bais'
generalization of the Montenon-Olive conjecture and find the representations of
the monopoles under the dual gauge group; these representations agree with
those of the elementary particles.Comment: 4 pages, LaTe
Signatures of gravitational fixed points at the LHC
We study quantum-gravitational signatures at the CERN Large Hadron Collider (LHC) in the context of theories with extra spatial dimensions and a low fundamental Planck scale in the TeV range. Implications of a gravitational fixed point at high energies are worked out using Wilson¿s renormalization group. We find that relevant cross sections involving virtual gravitons become finite. Based on gravitational lepton pair production we conclude that the LHC is sensitive to a fundamental Planck scale of up to 6 TeV
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