58 research outputs found
Volume Stabilization via Corrections in Type IIB Theory with Fluxes
We consider the Type IIB string theory in the presence of various extra
-brane pairs compactified on a warped Calabi-Yau threefold that
admits a conifold singularity. We demonstrate that the volume modulus can be
stabilized perturbatively at a non-supersymmetric vacuum by the
effective potential that includes the stringy correction
obtained by Becker {\it et al.} together with a combination of positive tension
and anomalous negative tension terms generated by the additional
7-brane-antibrane pairs.Comment: 20 pages, 4 figures, parts of introduction and conclusions are
modifie
Large-Volume Flux Compactifications: Moduli Spectrum and D3/D7 Soft Supersymmetry Breaking
We present an explicit calculation of the spectrum of a general class of
string models, corresponding to Calabi-Yau flux compactifications with
h_{1,2}>h_{1,1}>1 with leading perturbative and non-perturbative corrections,
in which all geometric moduli are stabilised as in hep-th/0502058. The volume
is exponentially large, leading to a range of string scales from the Planck
mass to the TeV scale, realising for the first time the large extra dimensions
scenario in string theory. We provide a general analysis of the relevance of
perturbative and non-perturbative effects and the regime of validity of the
effective field theory. We compute the spectrum in the moduli sector finding a
hierarchy of masses depending on inverse powers of the volume. We also compute
soft supersymmetry breaking terms for particles living on D3 and D7 branes. We
find a hierarchy of soft terms corresponding to `volume dominated' F-term
supersymmetry breaking. F-terms for Kahler moduli dominate both those for
dilaton and complex structure moduli and D-terms or other de Sitter lifting
terms. This is the first class of string models in which soft supersymmetry
breaking terms are computed after fixing all geometric moduli. We outline
several possible applications of our results, both for cosmology and
phenomenology and point out the differences with the less generic KKLT vacua.Comment: 64 pages, 4 figures; v2. references added; v3. typos, reference
added, matches published versio
Type IIB Flux Vacua from M-theory via F-theory
We study in detail some aspects of duality between type IIB and M-theory. We
focus on the duality between type IIB string theory on K3 x T^2/Z_2 orientifold
and M-theory on K3 x K3, in the F-theory limit. We give the explicit map
between the fields and in particular between the moduli of compactification,
studying their behavior under the F-theory limit. Turning on fluxes generates a
potential for the moduli both in type IIB and in M-theory. We verify that the
type IIB analysis gives the same results of the F-theory analysis. In
particular, we check that the two potentials match.Comment: 24 pages; reference correcte
Gaugino Condensation and Nonperturbative Superpotentials in Flux Compactifications
There are two known sources of nonperturbative superpotentials for K\"ahler
moduli in type IIB orientifolds, or F-theory compactifications on Calabi-Yau
fourfolds, with flux: Euclidean brane instantons and low-energy dynamics in D7
brane gauge theories. The first class of effects, Euclidean D3 branes which
lift in M-theory to M5 branes wrapping divisors of arithmetic genus 1 in the
fourfold, is relatively well understood. The second class has been less
explored. In this paper, we consider the explicit example of F-theory on with flux. The fluxes lift the D7 brane matter fields, and stabilize
stacks of D7 branes at loci of enhanced gauge symmetry. The resulting theories
exhibit gaugino condensation, and generate a nonperturbative superpotential for
K\"ahler moduli. We describe how the relevant geometries in general contain
cycles of arithmetic genus (and how divisors can
contribute to the superpotential, in the presence of flux). This second class
of effects is likely to be important in finding even larger classes of models
where the KKLT mechanism of moduli stabilization can be realized. We also
address various claims about the situation for IIB models with a single
K\"ahler modulus.Comment: 24 pages, harvmac, no figures, references adde
Classification of All 1/2 BPS Solutions of the Tiny Graviton Matrix Theory
The tiny graviton matrix theory [hep-th/0406214] is proposed to describe DLCQ
of type IIB string theory on the maximally supersymmetric plane-wave or
AdS_5xS^5 background. In this paper we provide further evidence in support of
the tiny graviton conjecture by focusing on the zero energy, half BPS
configurations of this matrix theory and classify all of them. These vacua are
generically of the form of various three sphere giant gravitons. We clarify the
connection between our solutions and the half BPS configuration in N=4 SYM
theory and their gravity duals. Moreover, using our half BPS solutions, we show
how the tiny graviton Matrix theory and the mass deformed D=3, N=8
superconformal field theories are related to each other.Comment: 40 pages, 12 figures, v
Enhanced Symmetries in Multiparameter Flux Vacua
We give a construction of type IIB flux vacua with discrete R-symmetries and
vanishing superpotential for hypersurfaces in weighted projective space with
any number of moduli. We find that the existence of such vacua for a given
space depends on properties of the modular group, and for Fermat models can be
determined solely by the weights of the projective space. The periods of the
geometry do not in general have arithmetic properties, but live in a vector
space whose properties are vital to the construction.Comment: 32 pages, LaTeX. v2: references adde
Non-Perturbative Corrections and Modularity in N=1 Type IIB Compactifications
Non-perturbative corrections and modular properties of four-dimensional type
IIB Calabi-Yau orientifolds are discussed. It is shown that certain
non-perturbative alpha' corrections survive in the large volume limit of the
orientifold and periodically correct the Kahler potential. These corrections
depend on the NS-NS two form and have to be completed by D-instanton
contributions to transform covariantely under symmetries of the type IIB
orientifold background. It is shown that generically also the D-instanton
superpotential depends on the two-form moduli as well as on the complex
dilaton. These contributions can arise through theta-functions with the dilaton
as modular parameter. An orientifold of the Enriques Calabi-Yau allows to
illustrate these general considerations. It is shown that this compactification
leads to a controlled four-dimensional N=1 effective theory due to the absence
of various quantum corrections. Making contact to the underlying topological
string theory the D-instanton superpotential is proposed to be related to a
specific modular form counting D3, D1, D(-1) degeneracies on the Enriques
Calabi-Yau.Comment: 35 page
Answering a Basic Objection to Bang/Crunch Holography
The current cosmic acceleration does not imply that our Universe is basically
de Sitter-like: in the first part of this work we argue that, by introducing
matter into *anti-de Sitter* spacetime in a natural way, one may be able to
account for the acceleration just as well. However, this leads to a Big Crunch,
and the Euclidean versions of Bang/Crunch cosmologies have [apparently]
disconnected conformal boundaries. As Maldacena and Maoz have recently
stressed, this seems to contradict the holographic principle. In the second
part we argue that this "double boundary problem" is a matter not of geometry
but rather of how one chooses a conformal compactification: if one chooses to
compactify in an unorthodox way, then the appearance of disconnectedness can be
regarded as a *coordinate effect*. With the kind of matter we have introduced
here, namely a Euclidean axion, the underlying compact Euclidean manifold has
an unexpectedly non-trivial topology: it is in fact one of the 75 possible
underlying manifolds of flat compact four-dimensional Euclidean spaces.Comment: 29 pages, 3 figures, added references and comparison with "cyclic"
cosmology, JHEP versio
Negative Energy in String Theory and Cosmic Censorship Violation
We find asymptotically anti de Sitter solutions in N=8 supergravity which
have negative total energy. This is possible since the boundary conditions
required for the positive energy theorem are stronger than those required for
finite mass (and allowed by string theory). But stability of the anti de Sitter
vacuum is still ensured by the positivity of a modified energy, which includes
an extra surface term. Some of the negative energy solutions describe classical
evolution of nonsingular initial data to naked singularities. Since there is an
open set of such solutions, cosmic censorship is violated generically in
supergravity. Using the dual field theory description, we argue that these
naked singularities will be resolved in the full string theory.Comment: 23 pages, 2 figures, v2: argument for forming naked singularities
clarified, references adde
D-brane instantons and the effective field theory of flux compactifications
We provide a description of the effects of fluxes on euclidean D-brane
instantons purely in terms of the 4d effective action. The effect corresponds
to the dressing of the effective non-perturbative 4d effective vertex with 4d
flux superpotential interactions, generated when the moduli fields made massive
by the flux are integrated out. The description in terms of effective field
theory allows a unified description of non-perturbative effects in all flux
compactifications of a given underlying fluxless model, globally in the moduli
space of the latter. It also allows us to describe explicitly the effects on
D-brane instantons of fluxes with no microscopic description, like
non-geometric fluxes. At the more formal level, the description has interesting
connections with the bulk-boundary map of open-closed two-dimensional
topological string theory, and with the \NN=1 special geometry.Comment: 33 page
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