74 research outputs found
Fresnel laws at curved dielectric interfaces of microresonators
We discuss curvature corrections to Fresnel's laws for the reflection and
transmission of light at a non-planar refractive-index boundary. The reflection
coefficients are obtained from the resonances of a dielectric disk within a
sequential-reflection model. The Goos-H\"anchen effect for curved light fronts
at a planar interface can be adapted to provide a qualitative and quantitative
extension of the ray model which explains the observed deviations from
Fresnel's laws.Comment: submitted to Phys. Rev.
N=3 Warped Compactifications
Orientifolds with three-form flux provide some of the simplest string
examples of warped compactification. In this paper we show that some models of
this type have the unusual feature of D=4, N=3 spacetime supersymmetry. We
discuss their construction and low energy physics. Although the local form of
the moduli space is fully determined by supersymmetry, to find its global form
requires a careful study of the BPS spectrum.Comment: 27 pages, v2: 32pp., RevTeX4, fixed factors, slightly improved
sections 3D and 4B, v3: added referenc
Closed string tachyons, flips and conifolds
Following the analysis of tachyons and orbifold flips described in
hep-th/0412337, we study nonsupersymmetric analogs of the supersymmetric
conifold singularity and show using their toric geometry description that they
are nonsupersymmetric orbifolds of the latter. Using linear sigma models, we
see that these are unstable to localized closed string tachyon condensation and
exhibit flip transitions between their two small resolutions (involving
2-cycles), in the process mediating mild dynamical topology change. Our
analysis shows that the structure of these nonsupersymmetric conifolds as
quotients of the supersymmetric conifold obstructs the 3-cycle deformation of
such singularities, suggesting that these nonsupersymmetric conifolds decay by
evolving towards their stable small resolutions.Comment: Latex, 22 pgs, 2 figs. v4: matches JHEP version, 29 pgs, 3 figures,
more elaborate Introduction, various clarifications adde
Towards a Stringy Resolution of the Cosmological Singularity
We study cosmological solutions to the low-energy effective action of
heterotic string theory including possible leading order corrections
and a potential for the dilaton. We consider the possibility that including
such stringy corrections can resolve the initial cosmological singularity.
Since the exact form of these corrections is not known the higher-derivative
terms are constructed so that they vanish when the metric is de Sitter
spacetime. The constructed terms are compatible with known restrictions from
scattering amplitude and string worldsheet beta-function calculations. Analytic
and numerical techniques are used to construct a singularity-free cosmological
solution. At late times and low-curvatures the metric is asymptotically
Minkowski and the dilaton is frozen. In the high-curvature regime the universe
enters a de Sitter phase.Comment: 6 pages, 2 Figures; minor revisions; references added; REVTeX 4;
version to appear in Phys. Rev.
From Big Crunch to Big Bang
We consider conditions under which a universe contracting towards a big
crunch can make a transition to an expanding big bang universe. A promising
example is 11-dimensional M-theory in which the eleventh dimension collapses,
bounces, and re-expands. At the bounce, the model can reduce to a weakly
coupled heterotic string theory and, we conjecture, it may be possible to
follow the transition from contraction to expansion. The possibility opens the
door to new classes of cosmological models. For example, we discuss how it
suggests a major simplification and modification of the recently proposed
ekpyrotic scenario.Comment: 16 pages, compressed and RevTex file, including three postscript
figure files. Minor changes, version to appear in Physical Review
Gauge Theory and the Excision of Repulson Singularities
We study brane configurations that give rise to large-N gauge theories with
eight supersymmetries and no hypermultiplets. These configurations include a
variety of wrapped, fractional, and stretched branes or strings. The
corresponding spacetime geometries which we study have a distinct kind of
singularity known as a repulson. We find that this singularity is removed by a
distinctive mechanism, leaving a smooth geometry with a core having an enhanced
gauge symmetry. The spacetime geometry can be related to large-N Seiberg-Witten
theory.Comment: 31 pages LaTeX, 2 figures (v3: references added
Observation of the lateral displacement of surface acoustic beams reflected at boundaries of layered substrates
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