1,174 research outputs found
Metastable Vacua in Brane Worlds
We analyze vacuum decay in brane world setups, where a free scalar field in
five dimensions has a localized potential admitting metastable vacua. We study
in particular the bounce solution and its properties in flat and warped spaces.
In the latter case, placing into a deeply warped region the term in the
potential that lifts the vacuum degeneracy, can increase indefinitely the
lifetime of the false vacuum. We discuss the application to metastable vacua in
supersymmetric brane-world constructions.Comment: LaTeX, 24 page
Flowing to four dimensions
We analyze the properties of a model with four-dimensional brane-localized
Higgs type potential of a six dimensional scalar field satisfying the Dirichlet
boundary condition on the boundary of a transverse two-dimensional compact
space. The regularization of the localized couplings generates classical
renormalization group running. A tachyonic mass parameter grows in the
infrared, in analogy with the QCD gauge coupling in four dimensions. We find a
phase transition at a critical value of the bare mass parameter such that the
running mass parameter becomes large in the infrared precisely at the
compactification scale. Below the critical coupling, the theory is in symmetric
phase, whereas above it spontaneous symmetry breaking occurs. Close to the
phase transition point there is a very light mode in the spectrum. The massive
Kaluza-Klein spectrum at the critical coupling becomes independent of the UV
cutoff.Comment: 22 pages, LaTe
Arc stability and melting characteristics of welding wire for use with 2219 aluminum alloy plate
Arc stability and melting characteristics of welding wire for arc welding of 2219 aluminum alloy plat
Solitons in the Horava-Witten supergravity
We study classical BPS five-brane solutions in the Horava-Witten supergravity. The presence of the eleventh dimension add a new feature, namely the dependence of the solution on this new coordinate. For gauge five-branes with an instanton size less than the eleventh radius and in the neighborhood of the center of the neutral five-brane, important corrections to the ten-dimensional solution appear for all values of the string coupling constant. We compute the mass and magnetic charge of the five-brane solitons and the result is shown to agree with the membrane and five-brane quantization conditions. Compactified to four dimensions, our solutions are interpreted as axionic strings
Non-tachyonic Scherk-Schwarz compactifications, cosmology and moduli stabilization
It is well-known that Scherk-Schwarz compactifications in string theory have
a tachyon in the closed string spectrum appearing for a critical value of a
compact radius. The tachyon can be removed by an appropriate orientifold
projection in type II strings, giving rise to tachyon-free compactifications.
We present explicit examples of this type in various dimensions, including six
and four-dimensional chiral examples, with softly broken supersymmetry in the
closed sector and non-BPS configurations in the open sector. These vacua are
interesting frameworks for studying various cosmological issues. We discuss
four-dimensional cosmological solutions and moduli stabilization triggered by
nonperturbative effects like gaugino condensation on D-branes and fluxes.Comment: 36 pages, LaTeX; added reference
Volume modulus inflation and a low scale of SUSY breaking
The relation between the Hubble constant and the scale of supersymmetry
breaking is investigated in models of inflation dominated by a string modulus.
Usually in this kind of models the gravitino mass is of the same order of
magnitude as the Hubble constant which is not desirable from the
phenomenological point of view. It is shown that slow-roll saddle point
inflation may be compatible with a low scale of supersymmetry breaking only if
some corrections to the lowest order Kahler potential are taken into account.
However, choosing an appropriate Kahler potential is not enough. There are also
conditions for the superpotential, and e.g. the popular racetrack
superpotential turns out to be not suitable. A model is proposed in which
slow-roll inflation and a light gravitino are compatible. It is based on a
superpotential with a triple gaugino condensation and the Kahler potential with
the leading string corrections. The problem of fine tuning and experimental
constraints are discussed for that model.Comment: 28 pages, 8 figures, comments and references added, minor change in
notation, version to be publishe
Brane solutions in strings with broken supersymmetry and dilaton tadpoles
The tachyon-free nonsupersymmetric string theories in ten dimensions have
dilaton tadpoles which forbid a Minkowski vacuum. We determine the maximally
symmetric backgrounds for the Type I string and the heterotic string. The static solutions exhibit nine dimensional
Poincar\'e symmetry and have finite 9D Planck and Yang-Mills constants. The low
energy geometry is given by a ten dimensional manifold with two boundaries
separated by a finite distance which suggests a spontaneous compactification of
the ten dimensional string theory.Comment: 13 page
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