165 research outputs found
Quantum Degenerate Systems
Degenerate dynamical systems are characterized by symplectic structures whose
rank is not constant throughout phase space. Their phase spaces are divided
into causally disconnected, nonoverlapping regions such that there are no
classical orbits connecting two different regions. Here the question of whether
this classical disconnectedness survives quantization is addressed. Our
conclusion is that in irreducible degenerate systems --in which the degeneracy
cannot be eliminated by redefining variables in the action--, the
disconnectedness is maintained in the quantum theory: there is no quantum
tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces
are boundaries separating distinct physical systems, not only classically, but
in the quantum realm as well. The relevance of this feature for gravitation and
Chern-Simons theories in higher dimensions cannot be overstated.Comment: 18 pages, no figure
Back-reaction of a conformal field on a three-dimensional black hole
The first order corrections to the geometry of the (2+1)-dimensional black
hole due to back-reaction of a massless conformal scalar field are computed.
The renormalized stress energy tensor used as the source of Einstein equations
is computed with the Green function for the black-hole background with
transparent boundary conditions. This tensor has the same functional form as
the one found in the nonperturbative case which can be exactly solved. Thus, a
static, circularly symmetric and asymptotically anti-de Sitter black hole
solution of the semiclassical equations is found. The corrections to the
thermodynamic quantities are also computed.Comment: 12 pages, RevTeX, no figure
Topological Invariants, Instantons and Chiral Anomaly on Spaces with Torsion
In a spacetime with nonvanishing torsion there can occur topologically stable
configurations associated with the frame bundle which are independent of the
curvature. The relevant topological invariants are integrals of local scalar
densities first discussed by Nieh and Yan (N-Y). In four dimensions, the N-Y
form is the only closed
4-form invariant under local Lorentz rotations associated with the torsion of
the manifold. The integral of over a compact D-dimensional (Euclidean)
manifold is shown to be a topological invariant related to the Pontryagin
classes of SO(D+1) and SO(D). An explicit example of a topologically nontrivial
configuration carrying nonvanishing instanton number proportional to
is costructed. The chiral anomaly in a four-dimensional spacetime with torsion
is also shown to contain a contribution proportional to , besides the usual
Pontryagin density related to the spacetime curvature. The violation of chiral
symmetry can thus depend on the instanton number of the tangent frame bundle of
the manifold. Similar invariants can be constructed in D>4 dimensions and the
existence of the corresponding nontrivial excitations is also discussed.Comment: 6 pages, RevTeX, no figures, two column
Thermodynamics of Black Holes in Schroedinger Space
A black hole and a black hyperboloid solutions in the space with the
Schroedinger isometries are presented and their thermodynamics is examined. The
on-shell action is obtained by the difference between the extremal and
non-extremal ones with the unusual matching of the boundary metrics. This
regularization method is first applied to the black brane solution in the space
of the Schroedinger symmetry and shown to correctly reproduce the known
thermodynamics. The actions of the black solutions all turn out to be the same
as the AdS counterparts. The phase diagram of the black hole system is obtained
in the parameter space of the temperature and chemical potential and the
diagram contains the Hawking-Page phase transition and instability lines.Comment: 20 page
New Gauge Supergravity in Seven and Eleven Dimensions
Locally supersymmetric systems in odd dimensions whose Lagrangians are
Chern-Simons forms for supersymmetric extensions of anti-de Sitter gravity are
discussed. The construction is illustrated for D=7 and 11. In seven dimensions
the theory is an N=2 supergravity whose fields are the vielbein
(), the spin connection (), two gravitini
() and an gauge connection (). These
fields form a connection for . In eleven dimensions the theory is an
N=1 supergravity containing, apart from and ,
one gravitino , and a totally antisymmetric fifth rank Lorentz
tensor one-form, . These fields form a connection for
. The actions are by construction invariant under local
supersymmetry and the algebra closes off shell without requiring auxiliary
fields. The -theory can be shown to have nonnegative energy around
an AdS background, which is a classical solution that saturates the Bogomolnyi
bound obtained from the superalgebra.Comment: 5pages, RevTeX, no figures, two columns, minor typos correcte
Conserved charges for gravity with locally AdS asymptotics
A new formula for the conserved charges in 3+1 gravity for spacetimes with
local AdS asymptotic geometry is proposed. It is shown that requiring the
action to have an extremum for this class of asymptotia sets the boundary term
that must be added to the Lagrangian as the Euler density with a fixed weight
factor. The resulting action gives rise to the mass and angular momentum as
Noether charges associated to the asymptotic Killing vectors without requiring
specification of a reference background in order to have a convergent
expression. A consequence of this definition is that any negative constant
curvature spacetime has vanishing Noether charges. These results remain valid
in the limit of vanishing cosmological constant.Comment: 5 pages, 2 Columns, revtex. Last version for Phys. Rev. Let
Higher codimension braneworlds from intersecting branes
We study the matching conditions of intersecting brane worlds in Lovelock
gravity in arbitrary dimension. We show that intersecting various codimension 1
and/or codimension 2 branes one can find solutions that represent
energy-momentum densities localized in the intersection, providing thus the
first examples of infinitesimally thin higher codimension braneworlds that are
free of singularities and where the backreaction of the brane in the background
is fully taken into account.Comment: 20 pages; v2. references and comments added to match the published
versio
Predicting total reaction cross sections for nucleon-nucleus scattering
Nucleon total reaction and neutron total cross sections to 300 MeV for 12C
and 208Pb, and for 65 MeV spanning the mass range, are predicted using
coordinate space optical potentials formed by full folding of effective
nucleon-nucleon interactions with realistic nuclear ground state densities.
Good to excellent agreement is found with existing data.Comment: 10 pages, 4 figure
Reply to the comment by D. Kreimer and E. Mielke
We respond to the comment by Kreimer et. al. about the torsional contribution
to the chiral anomaly in curved spacetimes. We discuss their claims and refute
its main conclusion.Comment: 9 pages, revte
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