1,675 research outputs found
Symmetry Breaking Using Value Precedence
We present a comprehensive study of the use of value precedence constraints
to break value symmetry. We first give a simple encoding of value precedence
into ternary constraints that is both efficient and effective at breaking
symmetry. We then extend value precedence to deal with a number of
generalizations like wreath value and partial interchangeability. We also show
that value precedence is closely related to lexicographical ordering. Finally,
we consider the interaction between value precedence and symmetry breaking
constraints for variable symmetries.Comment: 17th European Conference on Artificial Intelligenc
New Reducible Five-brane Solutions in M-theory
We construct new M-theory solutions of M5 branes that are a realization of
the fully localized ten dimensional NS5/D6 and NS5/D5 brane intersections.
These solutions are obtained by embedding self-dual geometries lifted to
M-theory. We reduce these solutions down to ten dimensions, obtaining new
D-brane systems in type IIA/IIB supergravity. The worldvolume theories of the
NS5-branes are new non-local, non-gravitational, six dimensional, T-dual little
string theories with eight supersymmetries.Comment: 19 pages, 4 figures, two paragraphs added in conclusions, typos
correcte
Leptogenesis, neutrino masses and gauge unification
Leptogenesis is considered in its natural context where Majorana neutrinos
fit in a gauge unification scheme and therefore couple to some extra gauge
bosons. The masses of some of these gauge bosons are expected to be similar to
those of the heavy Majorana particles, and this can have important consequences
for leptogenesis. In fact, the effect can go both ways. Stricter bounds are
obtained on one hand due to the dilution of the CP-violating effect by new
decay and scattering channels, while, in a re-heating scheme, the presence of
gauge couplings facilitates the re-population of the Majorana states. The
latter effect allows in particular for smaller Dirac couplings.Comment: 11pages, 7 figures. v2: definition of the lepton asymmetry corrected,
small numerical changes for the baryon number, conclusion does not change;
typos corrected and references adde
Nuttier Bubbles
We construct new explicit solutions of general relativity from double
analytic continuations of Taub-NUT spacetimes. This generalizes previous
studies of 4-dimensional nutty bubbles. One 5-dimensional locally
asymptotically AdS solution in particular has a special conformal boundary
structure of . We compute its boundary stress tensor and
relate it to the properties of the dual field theory. Interestingly enough, we
also find consistent 6-dimensional bubble solutions that have only one timelike
direction. The existence of such spacetimes with non-trivial topology is
closely related to the existence of the Taub-NUT(-AdS) solutions with more than
one NUT charge. Finally, we begin an investigation of generating new solutions
from Taub-NUT spacetimes and nuttier bubbles. Using the so-called Hopf duality,
we provide new explicit time-dependent backgrounds in six dimensions.Comment: 32 pages, 1 figure; v.3. typos corrected. Matches the published
versio
Neutrinos in flat extra dimension: towards a realistic scenario
We consider the simple extension of the Standard Model in which an additional
right handed neutrino propagates along a flat extra dimension, while the
Standard Model fields are confined on a 3-brane. The fifth dimension is
orbifold compactified. In this scenario, the neutrino mass can be
naturally suppressed. By studying systematically the fundamental parameter
space, we show that the strong phenomenological constraints on mixing angles
between active and sterile neutrinos (especially those derived from the SNO
experiment data) do not conflict with the possibility of generating a realistic
neutrino mass spectrum. As a second step, we explore the possibility of a
successful leptogenesis through the decays of the Kaluza-Klein excitations of
the right handed neutrino.Comment: 16 pages, 2 ps figure
The black hole final state
We propose that in quantum gravity one needs to impose a final state boundary
condition at black hole singularities. This resolves the apparent contradiction
between string theory and semiclassical arguments over whether black hole
evaporation is unitary.Comment: 17 pages, harvmac, 1 figure, v2: comment about interactions and
references adde
Exact Gravity Dual of a Gapless Superconductor
A model of an exact gravity dual of a gapless superconductor is presented in
which the condensate is provided by a charged scalar field coupled to a bulk
black hole of hyperbolic horizon in asymptotically AdS spacetime. Below a
critical temperature, the black hole acquires its hair through a phase
transition while an electromagnetic perturbation of the background Maxwell
field determines the conductivity of the boundary theory.Comment: 21 pages, 8 figures, a section on the stability of the MTZ black hole
is added, references are added, version to be published in JHE
Non Uniform Black Strings and Critical Dimensions in
We study the equations of black strings in spacetimes of arbitrary dimensions
with a negative cosmological constant and construct numerically non uniform
black strings solutions. Our results suggest the existence of a localised black
hole in asymptotically locally spacetime. We also present evidences for a
dependence of the critical dimension on the horizon radius.The critical
dimension represents the dimension where the order of the phase transition
between uniform and non uniform black string changes. Finally, we argue that
both, the regular asymptotically locally solution and black string
solutions with a very small horizon radius, present a negative tension. This
turns out to be an unexpected feature of the solutions.Comment: 13 pages, 5 figure
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