1,942 research outputs found
Gravitational Effects of Quantum Fields in the Interior of a Cylindrical Black Hole
The gravitational back-reaction is calculated for the conformally invariant
scalar field within a black cosmic string interior with cosmological constant.
Using the perturbed metric, the gravitational effects of the quantum field are
calculated. It is found that the perturbations initially strengthen the
singularity. This effect is similar to the case of spherical symmetry (without
cosmological constant). This indicates that the behaviour of quantum effects
may be universal and not dependent on the geometry of the spacetime nor the
presence of a non-zero cosmological constant.Comment: 13 pages, 1 figure, uses AMS package. D.E. solution corrected. Some
qualitative results are change
Shape of Deconstruction
We construct a six-dimensional Maxwell theory using a latticized extra space,
the continuum limit of which is a shifted torus recently discussed by Dienes.
This toy model exhibits the correspondence between continuum theory and
discrete theory, and give a geometrical insight to theory-space model building.Comment: 10 pages, 2 figures, RevTeX4. a citation adde
Multi-graviton theory, a latticized dimension, and the cosmological constant
Beginning with the Pauli-Fierz theory, we construct a model for
multi-graviton theory. Couplings between gravitons belonging to
nearest-neighbor ``theory spaces'' lead to a discrete mass spectrum. Our model
coincides with the Kaluza-Klein theory whose fifth dimension is latticized.
We evaluate one-loop vacuum energy in models with a circular latticized extra
dimension as well as with compact continuous dimensions. We find that the
vacuum energy can take a positive value, if the dimension of the continuous
space time is . Moreover, since the amount of the vacuum energy can
be an arbitrary small value according to the choice of parameters in the model,
our models is useful to explain the small positive dark energy in the present
universe.Comment: 10 pages, No figure. Needs REVTeX4. citations are corrected and minor
correction
Bipolar-Driven Large Magnetoresistance in Silicon
Large linear magnetoresistance (MR) in electron-injected p-type silicon at
very low magnetic field is observed experimentally at room temperature. The
large linear MR is induced in electron-dominated space-charge transport regime,
where the magnetic field modulation of electron-to-hole density ratio controls
the MR, as indicated by the magnetic field dependence of Hall coefficient in
the silicon device. Contrary to the space-charge-induced MR effect in unipolar
silicon device, where the large linear MR is inhomogeneity-induced, our results
provide a different insight into the mechanism of large linear MR in
non-magnetic semiconductors that is not based on the inhomogeneity model. This
approach enables homogeneous semiconductors to exhibit large linear MR at low
magnetic fields that until now has only been appearing in semiconductors with
strong inhomogeneities.Comment: 23 pages, 4 figures (main text), 6 figures (supplemental material
Massive scalar field near a cosmic string
The function of a massive scalar field near a cosmic string is
computed and then employed to find the vacuum fluctuation of the field. The
vacuum expectation value of the energy-momentum tensor is also computed using a
point-splitting approach. The obtained results could be useful also for the
case of self-interacting scalar fields and for the finite-temperature Rindler
space theory.Comment: 15 pages, standard LaTeX, no figures. Reference [14] correcte
Dark matter and stable bound states of primordial black holes
We present three reasons for the formation of gravitational bound states of
primordial black holes,called holeums,in the early universe.Using Newtonian
gravity and nonrelativistic quantum mechanics we find a purely quantum
mechanical mass-dependant exclusion property for the nonoverlap of the
constituent black holes in a holeum.This ensures that the holeum occupies space
just like ordinary matter.A holeum emits only gravitational radiation whose
spectrum is an exact analogue of that of a hydrogen atom. A part of this
spectrum lies in the region accessible to the detectors being built.The holeums
would form haloes around the galaxies and would be an important component of
the dark matter in the universe today.They may also be the constituents of the
invisible domain walls in the universe.Comment: 13 pages,2tables,for wider circulation,PD
Evaporation and Fate of Dilatonic Black Holes
We study both spherically symmetric and rotating black holes with dilaton
coupling and discuss the evaporation of these black holes via Hawking's quantum
radiation and their fates. We find that the dilaton coupling constant
drastically affects the emission rates, and therefore the fates of the black
holes. When the charge is conserved, the emission rate from the non-rotating
hole is drastically changed beyond (a superstring theory) and
diverges in the extreme limit. In the rotating cases, we analyze the slowly
rotating black hole solution with arbitrary as well as three exact
solutions, the Kerr--Newman (), and Kaluza--Klein (), and Sen black hole ( and with axion field). Beyond the
same critical value of , the emission rate becomes very large
near the maximally charged limit, while for it remains finite. The
black hole with may evolve into a naked singularity due to its
large emission rate. We also consider the effects of a discharge process by
investigating superradiance for the non-rotating dilatonic black hole.Comment: 33 pages, LaTex, 14 postscript figure files (appended as a uuencoded
compressed tar file
Exact solutions of Einstein and Einstein-scalar equations in 2 + 1 dimensions
A nonstatic and circularly symmetric exact solution of the Einstein equations
(with a cosmological constant and null fluid) in dimensions is
given. This is a nonstatic generalization of the uncharged spinless BTZ metric.
For , the spacetime is though not flat, the Kretschmann invariant
vanishes. The energy, momentum, and power output for this metric are obtained.
Further a static and circularly symmetric exact solution of the
Einstein-massless scalar equations is given, which has a curvature singularity
at and the scalar field diverges at as well as at infinity .Comment: 8 pages, Latex, no numbe
Periodic ILW equation with discrete Laplacian
We study an integro-differential equation which generalizes the periodic
intermediate long wave (ILW) equation. The kernel of the singular integral
involved is an elliptic function written as a second order difference of the
Weierstrass zeta-function. Using Sato's formulation, we show the integrability
and construct some special solutions. An elliptic solution is also obtained. We
present a conjecture based on a Poisson structure that it gives an alternative
description of this integrable hierarchy. We note that this Poisson algebra in
turn is related to a quantum algebra related with the family of Macdonald
difference operators.Comment: 17 pages. To appear in J. Phys. A: Math. Theo
Quantum W-algebras and Elliptic Algebras
We define quantum W-algebras generalizing the results of Reshetikhin and the
second author, and Shiraishi-Kubo-Awata-Odake. The quantum W-algebra associated
to sl_N is an associative algebra depending on two parameters. For special
values of parameters it becomes the ordinary W-algebra of sl_N, or the
q-deformed classical W-algebra of sl_N. We construct free field realizations of
the quantum W-algebras and the screening currents. We also point out some
interesting elliptic structures arising in these algebras. In particular, we
show that the screening currents satisfy elliptic analogues of the Drinfeld
relations in U_q(n^).Comment: 26 pages, AMSLATE
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