25 research outputs found
Higher order dilaton gravity: brane equations of motion in the covariant formulation
Dilaton gravity with general brane localized interactions is investigated.
Models with corrections up to arbitrary order in field derivatives are
considered. Effective gravitational equations of motion at the brane are
derived in the covariant approach. Dependence of such brane equations on the
bulk quantities is discussed. It is shown that the number of the bulk
independent brane equations of motion depends strongly on the symmetries
assumed for the model and for the background. Examples with two and four
derivatives of the fields are presented in more detail.Comment: 32 pages, references added, discussion extended, typos corrected,
version to be publishe
Quantum equivalence in Poisson-Lie T-duality
We prove that, general \s-models related by Poisson-Lie T-duality are
quantum equivalent under one-loop renormalization group flow. We reveal general
properties of the flows, we study the associated generalized coset models and
provide explicit examples.Comment: 16 page
Ricci flows and expansion in axion-dilaton cosmology
We study renormalization-group flows by deforming a class of conformal
sigma-models. We consider overall scale factor perturbation of Einstein spaces
as well as more general anisotropic deformations of three-spheres. At leading
order in alpha, renormalization-group equations turn out to be Ricci flows. In
the three-sphere background, the latter is the Halphen system, which is exactly
solvable in terms of modular forms. We also analyze time-dependent deformations
of these systems supplemented with an extra time coordinate and time-dependent
dilaton. In some regimes time evolution is identified with
renormalization-group flow and time coordinate can appear as Liouville field.
The resulting space-time interpretation is that of a homogeneous isotropic
Friedmann-Robertson-Walker universe in axion-dilaton cosmology. We find as
general behaviour the superposition of a big-bang (polynomial) expansion with a
finite number of oscillations at early times. Any initial anisotropy disappears
during the evolution.Comment: 22 page
Nearly K\"ahler heterotic compactifications with fermion condensates
We revisit AdS_4 heterotic compactifications on nearly K\"ahler manifolds in
the presence of H-flux and certain fermion condensates. Unlike previous
studies, we do not assume the vanishing of the supersymmetry variations.
Instead we determine the full equations of motion originating from the
ten-dimensional action, and subsequently we provide explicit solutions to them
on nearly K\"ahler manifolds at first order in alpha'. The Bianchi identity is
also taken into account in order to guarantee the absence of all anomalies. In
the presence of H-flux, which is identified with the torsion of the internal
space, as well as of fermion condensates in the gaugino and dilatino sectors,
new solutions are determined. These solutions provide a full classification of
consistent backgrounds of heterotic supergravity under our assumptions. All the
new solutions are non-supersymmetric, while previously known supersymmetric
ones are recovered too. Our results indicate that fully consistent
(supersymmetric or not) heterotic vacua on nearly K\"ahler manifolds are
scarce, even on AdS_4, and they can be completely classified.Comment: 1+17 pages, 1 figure; v2: remark and two references added, published
versio
Bundles over Nearly-Kahler Homogeneous Spaces in Heterotic String Theory
We construct heterotic vacua based on six-dimensional nearly-Kahler
homogeneous manifolds and non-trivial vector bundles thereon. Our examples are
based on three specific group coset spaces. It is shown how to construct line
bundles over these spaces, compute their properties and build up vector bundles
consistent with supersymmetry and anomaly cancelation. It turns out that the
most interesting coset is . This space supports a large number of
vector bundles which lead to consistent heterotic vacua, some of them with
three chiral families.Comment: 32 pages, reference adde
A supersymmetric consistent truncation for conifold solutions
We establish a supersymmetric consistent truncation of type IIB supergravity
on the T^{1,1} coset space, based on extending the Papadopoulos-Tseytlin ansatz
to the full set of SU(2)xSU(2) invariant Kaluza-Klein modes. The
five-dimensional model is a gauged N=4 supergravity with three vector
multiplets, which incorporates various conifold solutions and is suitable for
the study of their dynamics. By analysing the scalar potential we find a family
of new non-supersymmetric AdS_5 extrema interpolating between a solution
obtained long ago by Romans and a solution employing an Einstein metric on
T^{1,1} different from the standard one. Finally, we discuss some simple
consistent subtruncations preserving N=2 supersymmetry. One of them still
contains the Klebanov-Strassler solution, and is compatible with the inclusion
of smeared D7-branes.Comment: 34 pages, 1 figure; v2: minor changes, references added, appendix C
revised; v3: journal versio
Non-abelian T-duality, Ramond Fields and Coset Geometries
We extend previous work on non-abelian T-duality in the presence of Ramond
fluxes to cases in which the duality group acts with isotropy such as in
backgrounds containing coset spaces. In the process we generate new
supergravity solutions related to D-brane configurations and to standard
supergravity compactifications.Comment: 35 pages, Late
Dimensional Reduction of the Heterotic String over nearly-Kaehler manifolds
Our aim is to derive the effective action in four dimensions resulting by
reducing dimensionally the ten-dimensional heterotic supergravity
coupled to super Yang-Mills over manifolds admitting a
nearly-K\"{a}hler structure. Given the fact that all six-dimensional
nearly-K\"{a}hler manifolds are included in the class of the corresponding
non-symmetric coset spaces plus a group manifold, our procedure amounts in
applying the Coset Space Dimensional Reduction scheme using these coset spaces
as internal manifolds. In our examination firstly the rules of the reduction of
the theory over a general six-dimensional non-symmetric manifold are stated and
subsequently a detailed case by case analysis is performed for all the three
non-symmetric coset spaces. For each case the four-dimensional scalar potential
is derived and the corresponding nearly-K\"{a}hler limit is obtained. Finally,
we determine the corresponding supergravity description of the four-dimensional
theory employing the heterotic Gukov-Vafa-Witten formula and results of the
special K\"{a}hler geometry.Comment: version published in JHEP, minor corrections, added reference
The Worldvolume Action of Kink Solitons in AdS Spacetime
A formalism is presented for computing the higher-order corrections to the
worldvolume action of co-dimension one solitons. By modifying its potential, an
explicit "kink" solution of a real scalar field in AdS spacetime is found. The
formalism is then applied to explicitly compute the kink worldvolume action to
quadratic order in two expansion parameters--associated with the hypersurface
fluctuation length and the radius of AdS spacetime respectively. Two
alternative methods are given for doing this. The results are expressed in
terms of the trace of the extrinsic curvature and the intrinsic scalar
curvature. In addition to conformal Galileon interactions, we find a
non-Galileon term which is never sub-dominant. This method can be extended to
any conformally flat bulk spacetime.Comment: 32 pages, 3 figures, typos corrected and additional comments adde
Heterotic domain wall solutions and SU(3) structure manifolds
We examine compactifications of heterotic string theory on manifolds with
SU(3) structure. In particular, we study N = 1/2 domain wall solutions which
correspond to the perturbative vacua of the 4D, N =1 supersymmetric theories
associated to these compactifications. We extend work which has appeared
previously in the literature in two important regards. Firstly, we include two
additional fluxes which have been, heretofore, omitted in the general analysis
of this situation. This allows for solutions with more general torsion classes
than have previously been found. Secondly, we provide explicit solutions for
the fluxes as a function of the torsion classes. These solutions are
particularly useful in deciding whether equations such as the Bianchi
identities can be solved, in addition to the Killing spinor equations
themselves. Our work can be used to straightforwardly decide whether any given
SU(3) structure on a six-dimensional manifold is associated with a solution to
heterotic string theory. To illustrate how to use these results, we discuss a
number of examples taken from the literature.Comment: 34 pages, minor corrections in second versio