17 research outputs found
A second look at N=1 supersymmetric AdS_4 vacua of type IIA supergravity
We show that a class of type IIA vacua recently found within the N=4
effective approach corresponds to compactification on Ads_4 \times S^3 \times
S^3/Z_2^3. The results obtained using the effective method completely match the
general ten-dimensional analysis for the existence of N=1 warped
compactifications on Ads_4 \times M_6. In particular, we verify that the
internal metric is nearly-Kahler and that for specific values of the parameters
the Bianchi identity of the RR 2-form is fulfilled without sources. For another
range of parameters, including the massless case, the Bianchi identity is
satisfied when D6-branes are introduced. Solving the tadpole cancellation
conditions in D=4 we are able to find examples of appropriate sets of branes.
In the second part of this paper we describe how an example with internal space
CP^3 but with non nearly-Kahler metric fits into the general analysis of flux
vacua.Comment: Latex file, 35 pages, no figures. Reference added, minor corrections
adde
Flux-induced SUSY-breaking soft terms on D7-D3 brane systems
We study the effect of RR and NSNS 3-form fluxes on the effective action of
the worldvolume fields of Type IIB D7/D3-brane configurations. The D7-branes
wrap 4-cycles on a local Calabi-Yau geometry. This is an extension of previous
work on hep-th/0311241, where a similar analysis was applied to the case of
D3-branes. Our present analysis is based on the D7- and D3-brane
Dirac-Born-Infeld and Chern-Simons actions, and makes full use of the
R-symmetries of the system, which allow us to compute explicitly results for
the fields lying at the D3-D7 intersections. A number of interesting new
properties appear as compared to the simpler case of configurations with only
D3-branes. As a general result one finds that fluxes stabilize some or all of
the D7-brane moduli. We argue that this is important for the problem of
stabilizing Kahler moduli through non-perturbative effects in KKLT-like vacua.
We also show that (0,3) imaginary self-dual fluxes, which lead to
compactifications with zero vacuum energy, give rise to SUSY-breaking soft
terms including gaugino and scalar masses, and trilinear terms. Particular
examples of chiral MSSM-like models of this class of vacua, based on D3-D7
brane systems at orbifold singularities are presented.Comment: 58 pages, no figures; v2: numerical factor in section 7.2 correcte
Non-geometric flux vacua, S-duality and algebraic geometry
The four dimensional gauged supergravities descending from non-geometric
string compactifications involve a wide class of flux objects which are needed
to make the theory invariant under duality transformations at the effective
level. Additionally, complex algebraic conditions involving these fluxes arise
from Bianchi identities and tadpole cancellations in the effective theory. In
this work we study a simple T and S-duality invariant gauged supergravity, that
of a type IIB string compactified on a orientifold with
O3/O7-planes. We build upon the results of recent works and develop a
systematic method for solving all the flux constraints based on the algebra
structure underlying the fluxes. Starting with the T-duality invariant
supergravity, we find that the fluxes needed to restore S-duality can be simply
implemented as linear deformations of the gauge subalgebra by an element of its
second cohomology class. Algebraic geometry techniques are extensively used to
solve these constraints and supersymmetric vacua, centering our attention on
Minkowski solutions, become systematically computable and are also provided to
clarify the methods.Comment: 47 pages, 10 tables, typos corrected, Accepted for Publication in
Journal of High Energy Physic
Open string wavefunctions in flux compactifications
We consider compactifications of type I supergravity on manifolds with SU(3)
structure, in the presence of RR fluxes and magnetized D9-branes, and analyze
the generalized Dirac and Laplace-Beltrami operators associated to the D9-brane
worldvolume fields. These compactifications are T-dual to standard type IIB
toroidal orientifolds with NSNS and RR 3-form fluxes and D3/D7 branes. By using
techniques of representation theory and harmonic analysis, the spectrum of open
string wavefunctions can be computed for Lie groups and their quotients, as we
illustrate with explicit twisted tori examples. We find a correspondence
between irreducible unitary representations of the Kaloper-Myers algebra and
families of Kaluza-Klein excitations. We perform the computation of 2- and
3-point couplings for matter fields in the above flux compactifications, and
compare our results with those of 4d effective supergravity.Comment: 89 pages, 4 figures. v3: more typos corrected, version published in
JHE
No-scale supersymmetry breaking vacua and soft terms with torsion
We analyze the conditions to have no-scale supersymmetry breaking solutions
of type IIA and IIB supergravity compactified on manifolds of SU(3)-structure.
The supersymmetry is spontaneously broken by the intrinsic torsion of the
internal space. For type IIB orientifolds with O9 and O5-planes the mass of the
gravitino is governed by the torsion class W_1, and the breaking is mediated
through F-terms associated to descendants of the original N=2 hypermultiplets.
For type IIA orientifolds with O6-planes we find two families of solutions,
depending on whether the breaking is mediated exclusively by hypermultiplets or
by a mixture of hypermultiplets and vector multiplets, the latter case
corresponding to a class of Scherk-Schwarz compactifications not dual to any
geometric IIB setup. We compute the geometrically induced mu-terms for D5, D6
and D9-branes on twisted tori, and discuss the patterns of soft-terms which
arise for pure moduli mediation in each type of breaking. As for D3 and
D7-branes in presence of 3-form fluxes, the effective scalar potential turns
out to possess interesting phenomenological properties.Comment: 44 pages; several minor corrections and added reference
Warped Supersymmetry Breaking
We address the size of supersymmetry-breaking effects within
higher-dimensional settings where the observable sector resides deep within a
strongly warped region, with supersymmetry breaking not necessarily localized
in that region. Our particular interest is in how the supersymmetry-breaking
scale seen by the observable sector depends on this warping. We obtain this
dependence in two ways: by computing within the microscopic (string) theory
supersymmetry-breaking masses in supermultiplets; and by investigating how
warping gets encoded into masses within the low-energy 4D effective theory. We
find that the lightest gravitino mode can have mass much less than the
straightforward estimate from the mass shift of the unwarped zero mode. This
lightest Kaluza-Klein excitation plays the role of the supersymmetric partner
of the graviton and has a warped mass m_{3/2} proportional to e^A, with e^A the
warp factor, and controls the size of the soft SUSY breaking terms. We
formulate the conditions required for the existence of a description in terms
of a 4D SUGRA formulation, or in terms of 4D SUGRA together with soft-breaking
terms, and describe in particular situations where neither exist for some
non-supersymmetric compactifications. We suggest that some effects of warping
are captured by a linear dependence in the Kahler potential. We outline
some implications of our results for the KKLT scenario of moduli stabilization
with broken SUSY.Comment: 34 pages, 1 figure. v2 Further discussion of dual interpretation and
gravitino mas
Realistic D-Brane Models on Warped Throats: Fluxes, Hierarchies and Moduli Stabilization
We describe the construction of string theory models with semirealistic
spectrum in a sector of (anti) D3-branes located at an orbifold singularity at
the bottom of a highly warped throat geometry, which is a generalisation of the
Klebanov-Strassler deformed conifold. These models realise the Randall-Sundrum
proposal to naturally generate the Planck/electroweak hierarchy in a concrete
string theory embedding, and yielding interesting chiral open string spectra.
We describe examples with Standard Model gauge group (or left-right symmetric
extensions) and three families of SM fermions, with correct quantum numbers
including hypercharge. The dilaton and complex structure moduli of the geometry
are stabilised by the 3-form fluxes required to build the throat. We describe
diverse issues concerning the stabilisation of geometric Kahler moduli, like
blow-up modes of the orbifold singularities, via D term potentials and gauge
theory non-perturbative effects, like gaugino condensation. This local
geometry, once embedded in a full compactification, could give rise to models
with all moduli stabilised, and with the potential to lead to de Sitter vacua.
Issues of gauge unification, proton stability, supersymmetry breaking and
Yukawa couplings are also discussed.Comment: 46 pages, 13 figures (figures 3 and 13 corrected
D6-branes and torsion
The D6-brane spectrum of type IIA vacua based on twisted tori and RR
background fluxes is analyzed. In particular, we compute the torsion factors of
the (co)homology groups H_n and describe the effect that they have on D6-brane
physics. For instance, the fact that H_3 contains Z_N subgroups explains why RR
tadpole conditions are affected by geometric fluxes. In addition, the presence
of torsional (co)homology shows why some D6-brane moduli are lifted, and it
suggests how the D-brane discretum appears in type IIA flux compactifications.
Finally, we give a clear, geometrical understanding of the Freed-Witten anomaly
in the present type IIA setup, and discuss its consequences for the
construction of semi-realistic flux vacua.Comment: 35 pages, 1 figure. One reference adde
Branes on Generalized Calibrated Submanifolds
We extend previous results on generalized calibrations to describe
supersymmetric branes in supergravity backgrounds with diverse fields turned
on, and provide several new classes of examples. As an important application,
we show that supersymmetric D-branes in compactifications with field strength
fluxes, and on SU(3)-structure spaces, wrap generalized calibrated
submanifolds, defined by simple conditions in terms of the underlying globally
defined, but non-closed, 2- and 3-forms. We provide examples where the
geometric moduli of D-branes (for instance D7-branes in 3-form flux
configurations) are lifted by the generalized calibration condition. In
addition, we describe supersymmetric D6-branes on generalized calibrated
3-submanifolds of half-flat manifolds, which provide the mirror of B-type
D-branes in IIB CY compactifications with 3-form fluxes. Supersymmetric sets of
such D-branes carrying no homology charges are mirror to supersymmetric sets of
D-branes which are homologically non-trivial, but trivial in K-theory. As an
additional application, we describe models with chiral gauge sectors, realized
in terms of generalized calibrated brane box configurations of NS- and
D5-branes, which are supersymmetric but carry no charges, so that no
orientifold planes are required in the compactification.Comment: 40 pages, 3 figures, references adde
D-branes on AdS flux compactifications
We study D-branes in N=1 flux compactifications to AdS_4. We derive their
supersymmetry conditions and express them in terms of background generalized
calibrations. Basically because AdS has a boundary, the analysis of stability
is more subtle and qualitatively different from the usual case of Minkowski
compactifications. For instance, stable D-branes filling AdS_4 may wrap trivial
internal cycles. Our analysis gives a geometric realization of the
four-dimensional field theory approach of Freedman and collaborators.
Furthermore, the one-to-one correspondence between the supersymmetry conditions
of the background and the existence of generalized calibrations for D-branes is
clarified and extended to any supersymmetric flux background that admits a
time-like Killing vector and for which all fields are time-independent with
respect to the associated time. As explicit examples, we discuss supersymmetric
D-branes on IIA nearly Kaehler AdS_4 flux compactifications.Comment: 43 pages, 2 pictures, 1 table; v2: added references, color to figure
and corrected typo in (6.21b