267 research outputs found
Supergravitational Conformal Galileons
The worldvolume actions of 3+1 dimensional bosonic branes embedded in a
five-dimensional bulk space can lead to important effective field theories,
such as the DBI conformal Galileons, and may, when the Null Energy Condition is
violated, play an essential role in cosmological theories of the early
universe. These include Galileon Genesis and "bouncing" cosmology, where a
pre-Big Bang contracting phase bounces smoothly to the presently observed
expanding universe. Perhaps the most natural arena for such branes to arise is
within the context of superstring and -theory vacua. Here, not only are
branes required for the consistency of the theory, but, in many cases, the
exact spectrum of particle physics occurs at low energy. However, such theories
have the additional constraint that they must be supersymmetric. This
motivates us to compute the worldvolume actions of supersymmetric
three-branes, first in flat superspace and then to generalize them to
supergravitation. In this paper, for simplicity, we begin the process, not
within the context of a superstring vacuum but, rather, for the conformal
Galileons arising on a co-dimension one brane embedded in a maximally symmetric
bulk space. We proceed to supersymmetrize the associated
worldvolume theory and then generalize the results to supergravity,
opening the door to possible new cosmological scenarios.Comment: 39 pages, 1 figure. Version 4: Typos corrected, minor points on
notation clarifie
Flux, Gaugino Condensation and Anti-Branes in Heterotic M-theory
We present the potential energy due to flux and gaugino condensation in
heterotic M-theory compactifications with anti-branes in the vacuum. For
reasons which we explain in detail, the contributions to the potential due to
flux are not modified from those in supersymmetric contexts. The discussion of
gaugino condensation is, however, changed by the presence of anti-branes. We
show how a careful microscopic analysis of the system allows us to use standard
results in supersymmetric gauge theory in describing such effects - despite the
explicit supersymmetry breaking which is present. Not surprisingly, the
significant effect of anti-branes on the threshold corrections to the gauge
kinetic functions greatly alters the potential energy terms arising from
gaugino condensation.Comment: 40 pages, 1 figur
Natural Supergravity Inflation
We show that a single uncharged chiral superfield, canonically coupled to
\mbox{} supergravity with vanishing superpotential, naturally drives
inflation in the early universe for a class of simple Kahler potentials.
Inflation occurs due to the one-loop generation of a Kahler anomaly
proportional to . The coefficient of this term is of the correct
magnitude to describe all aspects of an inflationary cosmology, including
sufficient amplitude perturbations and reheating. Higher order terms
proportional to for are naturally suppressed relative to the
term and, hence, do not destabilize the theory.Comment: 13 pages, CERN-TH.6685/92, UPR-0526
Two Higgs Pair Heterotic Vacua and Flavor-Changing Neutral Currents
We present a vacuum of heterotic M-theory whose observable sector has the
MSSM spectrum with the addition of one extra pair of Higgs-Higgs conjugate
superfields. The quarks/leptons have a realistic mass hierarchy with a
naturally light first family. The double elliptic structure of the Calabi-Yau
compactification threefold leads to two ``stringy'' selection rules. These
classically disallow Yukawa couplings to the second Higgs pair and, hence,
Higgs mediated flavor-changing neutral currents. Such currents are induced in
higher-dimensional interactions, but are naturally suppressed. We show that our
results fit comfortably below the observed upper bounds on neutral
flavor-changing processes.Comment: 52 pages, 3 figures, 1 table, requires feynm
Five--Branes and Supersymmetry Breaking in M--Theory
Supersymmetry breaking via gaugino condensation is studied in vacua of
heterotic M-theory with five-branes. We show that supersymmetry is still broken
by a global mechanism and that the non-perturbative superpotential takes the
standard form. When expressed in terms of low energy fields, a modification
arises due to a threshold correction in the gauge kinetic function that depends
on five-brane moduli. We also determine the form of the low energy matter field
Kahler potential. These results are used to discuss the soft supersymmetry
breaking parameters, in particular the question of universality.Comment: 28 pages, Late
Supersymmetric Cubic Galileons Have Ghosts
Galileons are higher-derivative theories of a real scalar which nevertheless
admit second order equations of motion. They have interesting applications as
dark energy models and in early universe cosmology, and have been conjectured
to arise as descriptions of brane dynamics in string theory. In the present
paper, we study the bosonic sector of globally N=1 supersymmetric extensions of
the cubic Galileon Lagrangian in detail. Supersymmetry requires that the
Galileon scalar now becomes paired with a second real scalar field. We prove
that the presence of this second scalar causes the equations of motion to
become higher than second order, thus leading to the appearance of ghosts. We
also analyze the energy scales up to which, in an effective field theory
description, the ghosts can be tamed.Comment: 18 pages, v4: discussion updated in light of arXiv:1306.2961 by
Farakos et a
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