40,231 research outputs found
On Lagrangians and Gaugings of Maximal Supergravities
A consistent gauging of maximal supergravity requires that the T-tensor
transforms according to a specific representation of the duality group. The
analysis of viable gaugings is thus amenable to group-theoretical analysis,
which we explain and exploit for a large variety of gaugings. We discuss the
subtleties in four spacetime dimensions, where the ungauged Lagrangians are not
unique and encoded in an E_7(7)\Sp(56,R)/GL(28) matrix. Here we define the
T-tensor and derive all relevant identities in full generality. We present a
large number of examples in d=4,5 spacetime dimensions which include
non-semisimple gaugings of the type arising in (multiple) Scherk-Schwarz
reductions. We also present some general background material on the latter as
well as some group-theoretical results which are necessary for using computer
algebra.Comment: 39 pages, LaTeX2
The Superconformal Gaugings in Three Dimensions
We show how three-dimensional superconformal theories for any number N <= 8
of supersymmetries can be obtained by taking a conformal limit of the
corresponding three-dimensional gauged supergravity models. The superconformal
theories are characterized by an embedding tensor that satisfies a linear and
quadratic constraint. We analyze these constraints and give the general
solutions for all cases. We find new N = 4,5 superconformal theories based on
the exceptional Lie superalgebras F(4), G(3) and D(2|1;\alpha). Using the
supergravity connection we discuss which massive deformations to expect. As an
example we work out the details for the case of N = 6 supersymmetry.Comment: 22 pages; v2: refs. added, minor corrections, version published in
JHE
Exceptional Flux Compactifications
We consider type II (non-)geometric flux backgrounds in the absence of brane
sources, and construct their explicit embedding into maximal gauged D=4
supergravity. This enables one to investigate the critical points, mass spectra
and gauge groups of such backgrounds. We focus on a class of type IIA geometric
vacua and find a novel, non-supersymmetric and stable AdS vacuum in maximal
supergravity with a non-semisimple gauge group. Our construction relies on a
non-trivial mapping between SL(2) x SO(6,6) fluxes, SU(8) mass spectra and
gaugings of E7(7) subgroups.Comment: 51 pages, 2 figures and 4 tables. v3: change of SO(6,6) spinorial
conventions, published versio
Lectures on Gauged Supergravity and Flux Compactifications
The low-energy effective theories describing string compactifications in the
presence of fluxes are so-called gauged supergravities: deformations of the
standard abelian supergravity theories. The deformation parameters can be
identified with the various possible (geometric and non-geometric) flux
components. In these lecture notes we review the construction of gauged
supergravities in a manifestly duality covariant way and illustrate the
construction in several examples.Comment: 48 pages, lectures given at the RTN Winter School on Strings,
Supergravity and Gauge Theories, CERN, January 200
Dyonic ISO(7) supergravity and the duality hierarchy
Motivated by its well defined higher dimensional origin, a detailed study of
supergravity with a dyonically gauged gauge group is performed. We write down
the Lagrangian and describe the tensor and duality hierarchies, focusing on an
interesting subsector with closed field equations and supersymmetry
transformations. We then truncate the theory to some smaller
sectors with and supersymmetry and SU(3),
and SO(4) bosonic symmetry. Canonical and superpotential
formulations for these sectors are given, and their vacuum structure and
spectra is analysed. Unlike the purely electric ISO(7) gauging, the dyonic
gauging displays a rich structure of vacua, all of them AdS. We recover all
previously known ones and find a new vacuum with SU(3) symmetry
and various non-supersymmetric vacua, all of them stable within the full
theory.Comment: 52 pages, 4 tables. v2: Section 2.4 on critical points added. v3:
Version published in JHE
N=8 Supergravity with Local Scaling Symmetry
We construct maximal supergravity in four dimensions with local scaling
symmetry as deformation of the original Cremmer-Julia theory. The different
theories which include the standard gaugings are parametrized by an embedding
tensor carrying 56+912 parameters. We determine the form of the possible gauge
groups and work out the complete set of field equations. As a result we obtain
the most general couplings compatible with N=8 supersymmetry in four
dimensions. A particular feature of these theories is the absence of an action
and an additional positive contribution to the effective cosmological constant.
Moreover, these gaugings are generically dyonic, i.e. involve simultaneously
electric and magnetic vector fields.Comment: 39 page
Gravity and compactified branes in matrix models
A mechanism for emergent gravity on brane solutions in Yang-Mills matrix
models is exhibited. Newtonian gravity and a partial relation between the
Einstein tensor and the energy-momentum tensor can arise from the basic matrix
model action, without invoking an Einstein-Hilbert-type term. The key
requirements are compactified extra dimensions with extrinsic curvature M^4 x K
\subset R^D and split noncommutativity, with a Poisson tensor \theta^{ab}
linking the compact with the noncompact directions. The moduli of the
compactification provide the dominant degrees of freedom for gravity, which are
transmitted to the 4 noncompact directions via the Poisson tensor. The
effective Newton constant is determined by the scale of noncommutativity and
the compactification. This gravity theory is well suited for quantization, and
argued to be perturbatively finite for the IKKT model. Since no
compactification of the target space is needed, it might provide a way to avoid
the landscape problem in string theory.Comment: 35 pages. V2: substantially revised and improved, conclusion
weakened. V3: some clarifications, published version. V4: minor correctio
The maximal D=7 supergravities
The general seven-dimensional maximal supergravity is presented. Its
universal Lagrangian is described in terms of an embedding tensor which can be
characterized group-theoretically. The theory generically combines vector,
two-form and three-form tensor fields that transform into each other under an
intricate set of nonabelian gauge transformations. The embedding tensor encodes
the proper distribution of the degrees of freedom among these fields. In
addition to the kinetic terms the vector and tensor fields contribute to the
Lagrangian with a unique gauge invariant Chern-Simons term. This new
formulation encompasses all possible gaugings. Examples include the sphere
reductions of M theory and of the type IIA/IIB theories with gauge groups
SO(5), CSO(4,1), and SO(4), respectively.Comment: 42 page
Axial anomaly in the reduced model: Higher representations
The axial anomaly arising from the fermion sector of \U(N) or \SU(N)
reduced model is studied under a certain restriction of gauge field
configurations (the ``\U(1) embedding'' with ). We use the
overlap-Dirac operator and consider how the anomaly changes as a function of a
gauge-group representation of the fermion. A simple argument shows that the
anomaly vanishes for an irreducible representation expressed by a Young tableau
whose number of boxes is a multiple of (such as the adjoint
representation) and for a tensor-product of them. We also evaluate the anomaly
for general gauge-group representations in the large limit. The large
limit exhibits expected algebraic properties as the axial anomaly.
Nevertheless, when the gauge group is \SU(N), it does not have a structure
such as the trace of a product of traceless gauge-group generators which is
expected from the corresponding gauge field theory.Comment: 21 pages, uses JHEP.cls and amsfonts.sty, the final version to appear
in JHE
Emergent Geometry and Gravity from Matrix Models: an Introduction
A introductory review to emergent noncommutative gravity within Yang-Mills
Matrix models is presented. Space-time is described as a noncommutative brane
solution of the matrix model, i.e. as submanifold of \R^D. Fields and matter on
the brane arise as fluctuations of the bosonic resp. fermionic matrices around
such a background, and couple to an effective metric interpreted in terms of
gravity. Suitable tools are provided for the description of the effective
geometry in the semi-classical limit. The relation to noncommutative gauge
theory and the role of UV/IR mixing is explained. Several types of geometries
are identified, in particular "harmonic" and "Einstein" type of solutions. The
physics of the harmonic branch is discussed in some detail, emphasizing the
non-standard role of vacuum energy. This may provide new approach to some of
the big puzzles in this context. The IKKT model with D=10 and close relatives
are singled out as promising candidates for a quantum theory of fundamental
interactions including gravity.Comment: Invited topical review for Classical and Quantum Gravity. 57 pages, 5
figures. V2,V3: minor corrections and improvements. V4,V5: some improvements,
refs adde
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