15 research outputs found
Anomalous Fermion Production in Gravitational Collapse
The Dirac equation is solved in the Einstein-Yang-Mills background found by
Bartnik and McKinnon. We find a normalizable zero-energy fermion mode in the
-wave sector. As shown recently, their solution corresponds to a
gravitational sphaleron which mediates transitions between topologically
distinct vacua. Since the Bartnik-McKinnon solution is unstable, it will either
collapse to form a black hole or radiate away its energy. In either case, as
the Chern-Simons number of the configuration changes, there will be an
accompanying anomalous change in fermion number.Comment: 12 pages, preprint DAMTP93/R1
Supergeometry of Three Dimensional Black Holes
We show how the supersymmetric properties of three dimensional black holes
can be obtained algebraically. The black hole solutions are constructed as
quotients of the supergroup by a discrete subgroup of its
isometry supergroup. The generators of the action of the isometry supergroup
which commute with these identifications are found. These yield the
supersymmetries for the black hole as found in recent studies as well as the
usual geometric isometries. It is also shown that in the limit of vanishing
cosmological constant, the black hole vacuum becomes a null orbifold, a
solution previously discussed in the context of string theory.Comment: 12 pages, harvmac, discussion of rotating black hole added, some
minor corrections, reference adde
Time-Symmetric Initial Data for Multi-Body Solutions in Three Dimensions
Time-symmetric initial data for two-body solutions in three dimensional
anti-deSitter gravity are found. The spatial geometry has constant negative
curvature and is constructed as a quotient of two-dimensional hyperbolic space.
Apparent horizons correspond to closed geodesics. In an open universe, it is
shown that two black holes cannot exist separately, but are necessarily
enclosed by a third horizon. In a closed universe, two separate black holes can
exist provided there is an additional image mass.Comment: 12 pages, harvmac macro, minor changes in wordin
Yang-Mills Cosmologies and Collapsing Gravitational Sphalerons
Cosmological solutions with a homogeneous Yang-Mills field which oscillates
and passes between topologically distinct vacua are discussed. These solutions
are used to model the collapsing Bartnik-McKinnon gravitational sphaleron and
the associated anomalous production of fermions. The Dirac equation is analyzed
in these backgrounds. It is shown explicitly that a fermion energy level
crosses from the negative to positive energy spectrum as the gauge field
evolves between the topologically distinct vacua. The cosmological solutions
are also generalized to include an axion field.Comment: 12 pages, harvmac, DAMTP93/R3
Ultra--Planck Scattering in D=3 Gravity Theories
We obtain the high energy, small angle, 2-particle gravitational scattering
amplitudes in topologically massive gravity (TMG) and its two non-dynamical
constituents, Einstein and Chern--Simons gravity. We use 't Hooft's approach,
formally equivalent to a leading order eikonal approximation: one of the
particles is taken to scatter through the classical spacetime generated by the
other, which is idealized to be lightlike. The required geometries are derived
in all three models; in particular, we thereby provide the first explicit
asymptotically flat solution generated by a localized source in TMG. In
contrast to =4, the metrics are not uniquely specified, at least by naive
asymptotic requirements -- an indeterminacy mirrored in the scattering
amplitudes. The eikonal approach does provide a unique choice, however. We also
discuss the discontinuities that arise upon taking the limits, at the level of
the solutions, from TMG to its constituents, and compare with the analogous
topologically massive vector gauge field models.Comment: 20 pages, preprint BRX TH--337, DAMTP R93/5, ADP-93-204/M1
An Equivalence Between Momentum and Charge in String Theory
It is shown that for a translationally invariant solution to string theory,
spacetime duality interchanges the momentum in the symmetry direction and the
axion charge per unit length. As one application, we show explicitly that
charged black strings are equivalent to boosted (uncharged) black strings. The
extremal black strings (which correspond to the field outside of a fundamental
macroscopic string) are equivalent to plane fronted waves describing strings
moving at the speed of light.Comment: 10 page