333 research outputs found
(Weak) G_2 Holonomy from Self-duality, Flux and Supersymmetry
The aim of this paper is two-fold. First, we provide a simple and pedagogical
discussion of how compactifications of M-theory or supergravity preserving some
four-dimensional supersymmetry naturally lead to reduced holonomy or its
generalization, reduced weak holonomy. We relate the existence of a (conformal)
Killing spinor to the existence of certain closed and co-closed p-forms, and to
the metric being Ricci flat or Einstein. Then, for seven-dimensional manifolds,
we show that octonionic self-duality conditions on the spin connection are
equivalent to G_2 holonomy and certain generalized self-duality conditions to
weak G_2 holonomy. The latter lift to self-duality conditions for
cohomogeneity-one spin(7) metrics. To illustrate the power of this approach, we
present several examples where the self-duality condition largely simplifies
the derivation of a G_2 or weak G_2 metric.Comment: references added, 25 pages, no figures, Late
Non-perturbative Temperature Instabilities in N=4 Strings
We derive a universal thermal effective potential, which describes all
possible high-temperature instabilities of the known N=4 superstrings, using
the properties of gauged N=4 supergravity. These instabilities are due to three
non-perturbative thermal dyonic modes, which become tachyonic in a region of
the thermal moduli space. The latter is described by three moduli, s,t,u, which
are common to all non-perturbative dual-equivalent strings with N=4
supersymmetry in five dimensions: the heterotic on T^4xS^1, the type IIA on
K3xS^1, the type IIB on K3xS^1 and the type I on T^4x S^1. The non-perturbative
instabilities are analysed. These strings undergo a high-temperature transition
to a new phase in which five-branes condense. This phase is described in
detail, using both the effective supergravity and non-critical string theory in
six dimensions. In the new phase, supersymmetry is perturbatively restored but
broken at the non-perturbative level. In the infinite-temperature limit the
theory is topological with an N=2 supersymmetry based on a topologically
non-trivial hyper-Kahler manifold.Comment: 45 pages, LATEX file, no figure
Non-perturbative Supersymmetry Breaking and Finite Temperature Instabilities in N=4 Superstrings
We obtain the non-perturbative effective potential for the dual
five-dimensional N=4 strings in the context of finite-temperature regarded as a
breaking of supersymmetry into four space-time dimensions. Using the properties
of gauged N=4 supergravity we derive the universal thermal effective potential
describing all possible high-temperature instabilities of the known N=4
superstrings. These strings undergo a high-temperature transition to a new
phase in which five-branes condense. This phase is described in detail, using
both the effective supergravity and non-critical string theory in six
dimensions. In the new phase, supersymmetry is perturbatively restored but
broken at the non-perturbative level.Comment: 21 pages. Proceedings of the Corfu Summer Institute on Elementary
Particle Physics, Corfu, Greece, September 199
GAUGINO CONDENSATES AND CHIRAL-LINEAR DUALITY: AN EFFECTIVE LAGRANGIAN ANALYSIS
We show how to formulate the phenomenon of gaugino condensation in a
super-Yang-Mills theory with a field-dependent gauge coupling described with a
linear multiplet. We prove the duality equivalence of this approach with the
more familiar formulation using a chiral superfield. In so doing, we resolve a
longstanding puzzle as to how a linear-multiplet formulation can be consistent
with the dynamical breaking of the Peccei-Quinn symmetry which is thought to
occur once the gauginos condense. In our approach, the composite gauge degrees
of freedom are described by a real vector superfield, , rather than the
chiral superfield that is obtained in the traditional dual formulation. Our
dualization, when applied to the case of several condensing gauge groups,
provides strong evidence that this duality survives strong-coupling effects in
string theory.Comment: We have improved our discussion of the case where several factors of
the gauge group condense. We also show that the antisymmetric tensor acquires
a mass in this case in a novel way
Gaugino Condensates and Fluxes in N = 1 Effective Superpotentials
In the framework of orbifold compactifications of heterotic and type II
orientifolds, we study effective N = 1 supergravity potentials arising from
fluxes and gaugino condensates. These string solutions display a broad
phenomenology which we analyze using the method of N = 4 supergravity gaugings.
We give examples in type II and heterotic compactifications of combined fluxes
and condensates leading to vacua with naturally small supersymmetry breaking
scale controlled by the condensate, cases where the supersymmetry breaking
scale is specified by the fluxes even in the presence of a condensate and also
examples where fluxes and condensates conspire to preserve supersymmetry.Comment: 31 page
Fluxes, Gaugings and Gaugino Condensates
Based on the correspondence between the N = 1 superstring compactifications
with fluxes and the N = 4 gauged supergravities, we study effective N = 1
four-dimensional supergravity potentials arising from fluxes and gaugino
condensates in the framework of orbifold limits of (generalized) Calabi-Yau
compactifications. We give examples in heterotic and type II orientifolds in
which combined fluxes and condensates lead to vacua with small supersymmetry
breaking scale. We clarify the respective roles of fluxes and condensates in
supersymmetry breaking, and analyze the scaling properties of the gravitino
mass.Comment: 17 pages, C
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