19,852 research outputs found
Redshifts and Killing Vectors
Courses in introductory special and general relativity have increasingly
become part of the curriculum for upper-level undergraduate physics majors and
master's degree candidates. One of the topics rarely discussed is symmetry,
particularly in the theory of general relativity. The principal tool for its
study is the Killing vector. We provide an elementary introduction to the
concept of a Killing vector field, its properties, and as an example of its
utility apply these ideas to the rigorous determination of gravitational and
cosmological redshifts.Comment: 16 Latex pages, 6 postscript figures, submitted to Am. J. Phy
Evanescent Black Holes
A renormalizable theory of quantum gravity coupled to a dilaton and conformal
matter in two space-time dimensions is analyzed. The theory is shown to be
exactly solvable classically. Included among the exact classical solutions are
configurations describing the formation of a black hole by collapsing matter.
The problem of Hawking radiation and backreaction of the metric is analyzed to
leading order in a expansion, where is the number of matter fields.
The results suggest that the collapsing matter radiates away all of its energy
before an event horizon has a chance to form, and black holes thereby disappear
from the quantum mechanical spectrum. It is argued that the matter
asymptotically approaches a zero-energy ``bound state'' which can carry global
quantum numbers and that a unitary -matrix including such states should
exist.Comment: 14 page
Thermal divergences on the event horizons of two-dimensional black holes
The expectation value of the stress-energy tensor \langleT_{\mu\nu}\rangle
of a free conformally invariant scalar field is computed in a general static
two-dimensional black hole spacetime when the field is in either a zero
temperature vacuum state or a thermal state at a nonzero temperature. It is
found that for every static two-dimensional black hole the stress-energy
diverges strongly on the event horizon unless the field is in a state at the
natural black hole temperature which is defined by the surface gravity of the
event horizon. This implies that both extreme and nonextreme two-dimensional
black holes can only be in equilibrium with radiation at the natural black hole
temperature.Comment: 13 pages, REVTe
A rotating black ring in five dimensions
The vacuum Einstein equations in five dimensions are shown to admit a
solution describing an asymptotically flat spacetime regular on and outside an
event horizon of topology S^1 x S^2. It describes a rotating ``black ring''.
This is the first example of an asymptotically flat vacuum solution with an
event horizon of non-spherical topology. There is a range of values for the
mass and angular momentum for which there exist two black ring solutions as
well as a black hole solution. Therefore the uniqueness theorems valid in four
dimensions do not have simple higher dimensional generalizations. It is
suggested that increasing the spin of a five dimensional black hole beyond a
critical value results in a transition to a black ring, which can have an
arbitrarily large angular momentum for a given mass.Comment: 4 pages, 3 figures; v2: minor improvement
Semiclassical Stability of the Extreme Reissner-Nordstrom Black Hole
The stress-energy tensor of a free quantized scalar field is calculated in
the extreme Reissner-Nordstr\"{o}m black hole spacetime in the zero temperature
vacuum state. The stress-energy appears to be regular on the event horizon,
contrary to the suggestion provided by two-dimensional calculations. An
analytic calculation on the event horizon for a thermal state shows that if the
temperature is nonzero then the stress-energy diverges strongly there.Comment: 10 pages, REVTeX, 4 figures in separate uuencoded compressed fil
Calibrated Sub-Bundles in Non-Compact Manifolds of Special Holonomy
This paper is a continuation of math.DG/0408005. We first construct special
Lagrangian submanifolds of the Ricci-flat Stenzel metric (of holonomy SU(n)) on
the cotangent bundle of S^n by looking at the conormal bundle of appropriate
submanifolds of S^n. We find that the condition for the conormal bundle to be
special Lagrangian is the same as that discovered by Harvey-Lawson for
submanifolds in R^n in their pioneering paper. We also construct calibrated
submanifolds in complete metrics with special holonomy G_2 and Spin(7)
discovered by Bryant and Salamon on the total spaces of appropriate bundles
over self-dual Einstein four manifolds. The submanifolds are constructed as
certain subbundles over immersed surfaces. We show that this construction
requires the surface to be minimal in the associative and Cayley cases, and to
be (properly oriented) real isotropic in the coassociative case. We also make
some remarks about using these constructions as a possible local model for the
intersection of compact calibrated submanifolds in a compact manifold with
special holonomy.Comment: 20 pages; for Revised Version: Minor cosmetic changes, some
paragraphs rewritten for improved clarit
Electron cyclotron current drive in low collisionality limit: On parallel momentum conservation
Cosmological Consequences of Spontaneous Lepton Number Violation in Grand Unification, EFI-93-07
Cosmological constraints on grand unified theories with spontaneous lepton
number violation are analysed. We concentrate on , the simplest of the
models possessing this property. It has been noted previously that the
consistency of these models with the observed baryon asymmetry generically
implies strict upper bounds on the light neutrino masses. In this paper, we
analyze the situation in detail. We find that minimal models of fermion masses
face difficulties, but that it is possible for these models to generate an
adequate baryon asymmetry via non-equilibrium lepton number violating processes
when the right-handed neutrino masses are near their maximum possible values.
This condition uniquely picks out the minimal gauge symmetry breaking scheme. A
non-minimal model is also analyzed, with somewhat different conclusions due to
the nature of the imposed symmetries.Comment: uses harvmac.tex, epsf.tex, and tables.tex; 4 figures submitted as
tar-compressed-uuencoded postscript files; beautiful compressed postscript
version available by anonymous ftp from
rainbow.uchicago.edu:/pt-preprints/efi-93-07.ps.
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