378 research outputs found
Twisted supersymmetry and the topology of theory space
We present examples of four dimensional, non-supersymmetric field theories in
which ultraviolet supersymmetry breaking effects, such as bose-fermi splittings
and the vacuum energy, are suppressed by , where
is a weak coupling factor and can be made arbitrarily large. The particle
content and interactions of these models are conveniently represented by a
graph with sites and links, describing the gauge theory space structure. While
the theories are supersymmetric ``locally'' in theory space, supersymmetry can
be explicitly broken by topological obstructions.Comment: 9 pages, revtex
Is There A String Theory Landscape
We examine recent claims of a large set of flux compactification solutions of
string theory. We conclude that the arguments for AdS solutions are plausible.
The analysis of meta-stable dS solutions inevitably leads to situations where
long distance effective field theory breaks down. We then examine whether these
solutions are likely to lead to a description of the real world. We conclude
that one must invoke a strong version of the anthropic principle. We explain
why it is likely that this leads to a prediction of low energy supersymmetry
breaking, but that many features of anthropically selected flux
compactifications are likely to disagree with experiment.Comment: 39 pages, Latex, ``Terminology surrounding the anthropic principle
revised to conform with accepted usage. More history of the anthropic
principle included. Various references added.
Nonabelian D-branes and Noncommutative Geometry
We discuss the nonabelian world-volume action which governs the dynamics of N
coincident Dp-branes. In this theory, the branes' transverse displacements are
described by matrix-valued scalar fields, and so this is a natural physical
framework for the appearance of noncommutative geometry. One example is the
dielectric effect by which Dp-branes may be polarized into a noncommutative
geometry by external fields. Another example is the appearance of
noncommutative geometries in the description of intersecting D-branes of
differing dimensions, such as D-strings ending on a D3- or D5-brane. We also
describe the related physics of giant gravitons.Comment: 21 pages, Latex, ref. adde
Distributions of flux vacua
We give results for the distribution and number of flux vacua of various
types, supersymmetric and nonsupersymmetric, in IIb string theory compactified
on Calabi-Yau manifolds. We compare this with related problems such as counting
attractor points.Comment: 43 pages, 7 figures. v2: improved discussion of finding vacua with
discrete flux, references adde
Meta-Stable Dynamical Supersymmetry Breaking Near Points of Enhanced Symmetry
We show that metastable supersymmetry breaking is generic near certain
enhanced symmetry points of gauge theory moduli spaces. Our model consists of
two sectors coupled by a singlet and combines dynamical supersymmetry breaking
with an O'Raifeartaigh mechanism in terms of confined variables. All relevant
mass parameters, including the supersymmetry breaking scale, are generated
dynamically. The metastable vacua appear as a result of a balance between
non-perturbative and perturbative quantum effects along a pseudo-runaway
direction.Comment: 27 pages, harvmac, 6 figure
Tachyon Tunnelling in D-brane-anti-D-brane
Using the tachyon DBI action proposal for the effective theory of
non-coincident D-brane-anti-D-brane system, we study the decay of this
system in the tachyon channel. We assume that the branes separation is held
fixed, i.e. no throat formation, and then find the bounce solution which
describe the decay of the system from false to the true vacuum of the tachyon
potential. We shall show that due to the non-standard form of the kinetic term
in the effective action, the thin wall approximation for calculating the bubble
nucleation rate gives a result which is independent of the branes separation.
This unusual result might indicate that the true decay of this metastable
system should be via a solution that represents a throat formation as well as
the tachyon tunneling.Comment: 15 pages, 4 figures, Latex file, minor changes, reference adde
Massive IIA flux compactifications and U-dualities
We attempt to find a rigorous formulation for the massive type IIA
orientifold compactifications of string theory introduced in hep-th/0505160. An
approximate double T-duality converts this background into IIA string theory on
a twisted torus, but various arguments indicate that the back reaction of the
orientifold on this geometry is large. In particular, an AdS calculation of the
entropy suggests a scaling appropriate for N M2-branes, in a certain limit of
the compactification, though not the one studied in hep-th/0505160. The
M-theory lift of this specific regime is not 4 dimensional. We suggest that the
generic limit of the background corresponds to a situation analogous to
F-theory, where the string coupling is small in some regions of a compact
geometry, and large in others, so that neither a long wavelength 11D SUGRA
expansion, nor a world sheet expansion exists for these compactifications. We
end with a speculation on the nature of the generic compactification.Comment: JHEP3 LaTeX - 34 pages - 3 figures; v2: Added references; v3: mistake
in entropy scaling corrected, major changes in conclusions; v4: changed
claims about original DeWolfe et al. setup, JHEP versio
A Matrix Model for AdS2
A matrix quantum mechanics with potential and an SL(2,R)
conformal symmetry is conjectured to be dual to two-dimensional type 0A string
theory on AdS with units of RR flux.Comment: 12 page
Generally Covariant Actions for Multiple D-branes
We develop a formalism that allows us to write actions for multiple D-branes
with manifest general covariance. While the matrix coordinates of the D-branes
have a complicated transformation law under coordinate transformations, we find
that these may be promoted to (redundant) matrix fields on the transverse space
with a simple covariant transformation law. Using these fields, we define a
covariant distribution function (a matrix generalization of the delta function
which describes the location of a single brane). The final actions take the
form of an integral over the curved space of a scalar single-trace action built
from the covariant matrix fields, tensors involving the metric, and the
covariant distribution function. For diagonal matrices, the integral localizes
to the positions of the individual branes, giving N copies of the single-brane
action.Comment: 34 pages, LaTeX. v2: comments and refs adde
One in a Billion: MSSM-like D-Brane Statistics
Continuing our recent work hep-th/0411173, we study the statistics of
four-dimensional, supersymmetric intersecting D-brane models in a toroidal
orientifold background. We have performed a vast computer survey of solutions
to the stringy consistency conditions and present their statistical
implications with special emphasis on the frequency of Standard Model features.
Among the topics we discuss are the implications of the K-theory constraints,
statistical correlations among physical quantities and an investigation of the
various statistical suppression factors arising once certain Standard Model
features are required. We estimate the frequency of an MSSM like gauge group
with three generations to be one in a billion.Comment: 36 pages, 12 figures; v2: typos corrected, one ref. added; v3: minor
changes, version to appear in JHE
- …