29 research outputs found
Refining the boundaries of the classical de Sitter landscape
We derive highly constraining no-go theorems for classical de Sitter
backgrounds of string theory, with parallel sources; this should impact the
embedding of cosmological models. We study ten-dimensional vacua of type II
supergravities with parallel and backreacted orientifold Op-planes and
Dp-branes, on four-dimensional de Sitter space-time times a compact manifold.
Vacua for p=3, 7 or 8 are completely excluded, and we obtain tight constraints
for p=4, 5, 6. This is achieved through the derivation of an enlightening
expression for the four-dimensional Ricci scalar. Further interesting
expressions and no-go theorems are obtained. The paper is self-contained so
technical aspects, including conventions, might be of more general interest.Comment: 15 pages + appendices and references; v2: few additions; v3:
requirements on the sources and internal geometry clarified, version accepted
for publication; v4: erratum added, minor impact on the result
Accelerated Universes from type IIA Compactifications
We study slow-roll accelerating cosmologies arising from geometric
compactifications of type IIA string theory on
. With the aid of a genetic
algorithm, we are able to find quasi-de Sitter backgrounds with both slow-roll
parameters of order . Furthermore, we study their evolution by numerically
solving the corresponding time-dependent equations of motion, and we show that
they actually display a few e-folds of accelerated expansion. Finally, we
comment on their perturbative reliability.Comment: 22 pages, 3 figures and 5 table
Loop corrections to the antibrane potential
Antibranes provide some of the most generic ways to uplift Anti-de Sitter
flux compactifications to de Sitter, and there is a growing body of evidence
that antibranes placed in long warped throats such as the Klebanov-Strassler
warped deformed conifold solution have a brane-brane-repelling tachyon. This
tachyon was first found in the regime of parameters in which the backreaction
of the antibranes is large, and its existence was inferred from a highly
nontrivial cancellation of certain terms in the inter-brane potential. We use a
brane effective action approach, similar to that proposed by Michel, Mintun,
Polchinski, Puhm and Saad in arXiv:1412.5702, to analyze antibranes in
Klebanov-Strassler when their backreaction is small, and find a regime of
parameters where all perturbative contributions to the action can be computed
explicitly. We find that the cancellation found at strong coupling is also
present in the weak-coupling regime, and we establish its existence to all
loops. Our calculation indicates that the spectrum of the antibrane worldvolume
theory is not gapped, and may generically have a tachyon. Hence uplifting
mechanisms involving antibranes remain questionable even when backreaction is
small.Comment: 27 pages, 5 figures, v2: Added clarification of statements, version
accepted for publication in JHE
BPS domain walls from backreacted orientifolds
Compactifications with D-brane and orientifold sources lead to standard
gauged supergravity theories if the sources are smeared over the internal
directions. It is therefore of interest to find how the solutions described by
the gauged supergravity are altered by properly localising the sources. In this
paper we analyse this for BPS domain wall solutions in the seven-dimensional
gauged supergravity obtained from an O6 toroidal orientifold compactification
in massive IIA supergravity. This is one of the simplest no-scale
supergravities that can be constructed and analysed in full detail. We find and
discuss the BPS domain walls both when the O6 planes are smeared and localised.
When the O6 planes are localised the domain wall solutions live in a warped
compactification. In order to get explicit expressions we also consider the
non-compact versions of the solutions for which the O6 planes have been traded
for D6 branes. Through T-duality we obtain partially localised solutions for
compactifications to four dimensions using O3 planes with 3-form fluxes.Comment: 23 pages, 1 figur
de Sitter vacua from nonperturbative flux compactifications
We present stable de Sitter solutions of supergravity in a
geometric type IIB duality frame with the addition of non-perturbative
contributions. Contrary to the standard approach, we retain the moduli
dependence of both the tree level superpotential and its non-perturbative
contribution. This provides the possibility for a single-step stabilisation of
all moduli simultaneously in a de Sitter vacuum. Using a genetic algorithm we
find explicit solutions with different features.Comment: 8 pages, 2 figures, 2 tables. v2: 5 pages, 1 figure, 2 tables.
Careful rephrasing of motivation and approach, added flux-quantisation
example, corrected error in Table 1.. Version accepted for publication in PR
(Anti-)Brane backreaction beyond perturbation theory
We improve on the understanding of the backreaction of anti-D6-branes in a
flux background that is mutually BPS with D6-branes. This setup is analogous to
the study of the backreaction of anti-D3-branes inserted in the KS throat, but
does not require us to smear the anti-branes or do a perturbative analysis
around the BPS background. We solve the full equations of motion near the
anti-D6-branes and show that only two boundary conditions are consistent with
the equations of motion. Upon invoking a topological argument we eliminate the
boundary condition with regular H flux since it cannot lead to a solution that
approaches the right kind of flux away from the anti-D6-brane. This leaves us
with a boundary condition which has singular, but integrable, H flux energy
density.Comment: 12 pages + appendices, 1 figure; v2: minor changes, version published
in JHE
The problematic backreaction of SUSY-breaking branes
In this paper we investigate the localisation of SUSY-breaking branes which,
in the smeared approximation, support specific non-BPS vacua. We show, for a
wide class of boundary conditions, that there is no flux vacuum when the branes
are described by a genuine delta-function. Even more, we find that the smeared
solution is the unique solution with a regular brane profile. Our setup
consists of a non-BPS AdS_7 solution in massive IIA supergravity with smeared
anti-D6-branes and fluxes T-dual to ISD fluxes in IIB supergravity.Comment: 27 pages, Latex2e, 5 figure
Smeared versus localised sources in flux compactifications
We investigate whether vacuum solutions in flux compactifications that are
obtained with smeared sources (orientifolds or D-branes) still survive when the
sources are localised. This seems to rely on whether the solutions are BPS or
not. First we consider two sets of BPS solutions that both relate to the GKP
solution through T-dualities: (p+1)-dimensional solutions from
spacetime-filling Op-planes with a conformally Ricci-flat internal space, and
p-dimensional solutions with Op-planes that wrap a 1-cycle inside an everywhere
negatively curved twisted torus. The relation between the solution with smeared
orientifolds and the localised version is worked out in detail. We then
demonstrate that a class of non-BPS AdS_4 solutions that exist for IASD fluxes
and with smeared D3-branes (or analogously for ISD fluxes with anti-D3-branes)
does not survive the localisation of the (anti) D3-branes. This casts doubts on
the stringy consistency of non-BPS solutions that are obtained in the limit of
smeared sources.Comment: 23 pages; v2: minor corrections, added references, version published
in JHE