401 research outputs found
Supersymmetry in gauge theories with extra dimensions
We show that a quantum-mechanical N=2 supersymmetry is hidden in 4d mass
spectrum of any gauge invariant theories with extra dimensions. The N=2
supercharges are explicitly constructed in terms of differential forms. The
analysis can be extended to extra dimensions with boundaries, and for a single
extra dimension we clarify a possible set of boundary conditions consistent
with 5d gauge invariance, although some of the boundary conditions break 4d
gauge symmetries.Comment: 18 page
Flavor Symmetry Breaking and Vacuum Alignment on Orbifolds
Flavor symmetry has been widely studied for figuring out the masses and
mixing angles of standard-model fermions. In this paper we present a framework
for handling flavor symmetry breaking where the symmetry breaking is triggered
by boundary conditions of scalar fields in extra-dimensional space. The
alignment of scalar expectation values is achieved without referring to any
details of scalar potential and its minimization procedure. As applications to
non-abelian discrete flavor symmetries, illustrative lepton mass models are
constructed where the S3 and A4 flavor symmetries are broken down to the
directions leading to the tri-bimaximal form of lepton mixing and realistic
mass patterns.Comment: 21 page
Non-local symmetry breaking in Kaluza-Klein theories
Scherk-Schwarz gauge symmetry breaking of a D-dimensional field theory model
compactified on a circle is analyzed. It is explicitly shown that forbidden
couplings in the unbroken theory appear in the one-loop effective action only
in a non-local way, implying that they are finite at all orders in perturbation
theory. This result can be understood as a consequence of the local gauge
symmetry, but it holds true also in the global limit.Comment: v2: Wilson loop contributions and generalization to SU(N) included;
references added. v3: version to appear in Phys. Rev. Let
Eleven-Dimensional Supergravity in Light-Cone Superspace
We show that Supergravity in eleven dimensions can be described in terms of a
constrained superfield on the light-cone, without the use of auxiliary fields.
We build its action to first order in the gravitational coupling constant
\kappa, by "oxidizing" (N=8,d=4) Supergravity. This is simply achieved, as for
N=4 Yang-Mills, by extending the transverse derivatives into superspace. The
eleven-dimensional SuperPoincare algebra is constructed and a fourth order
interaction is conjectured.Comment: 18 page
Potential and mass-matrix in gauged N=4 supergravity
We discuss the potential and mass-matrix of gauged N=4 matter coupled
supergravity for the case of six matter multiplets, extending previous work by
considering the dependence on all scalars. We consider all semi-simple gauge
groups and analyse the potential and its first and second derivatives in the
origin of the scalar manifold. Although we find in a number of cases an
extremum with a positive cosmological constant, these are not stable under
fluctuations of all scalar fields.Comment: 28 pages, LaTe
T-duality of NSR superstring: The worldsheet perspective
We formulate target space duality symmetry of NSR superstring from the
perspectives of worldsheet. The worldsheet action is presented in the
superspace formalism in the presence of massless backgrounds. We start from a
-dimensional target space worldsheet action and compactify the theory
on a d-dimensional torus, . It is assumed that the backgrounds are
independent of compact (super)coordinates. We adopt the formalism of our
earlier work to introduce dual supercoordinates along compact directions and
introduce the corresponding dual backgrounds. It is demonstrated that combined
equations of motion of the two sets of coordinates can be expressed in a
manifestly covariant form analogous to the equations of motions for
closed bosonic string derived by us. Furthermore, we show that the vertex
operators associated with excited massive levels of NSR string can be expressed
in an invariant form generalizing earlier result for closed bosonic
string.Comment: 21 page
Testing the equivalence principle: why and how?
Part of the theoretical motivation for improving the present level of testing
of the equivalence principle is reviewed. The general rationale for optimizing
the choice of pairs of materials to be tested is presented. One introduces a
simplified rationale based on a trichotomy of competing classes of theoretical
models.Comment: 11 pages, Latex, uses ioplppt.sty, submitted to Class. Quantum Gra
Asymmetric Orbifolds, Non-Geometric Fluxes and Non-Commutativity in Closed String Theory
In this paper we consider a class of exactly solvable closed string flux
backgrounds that exhibit non-commutativity in the closed string coordinates.
They are realized in terms of freely-acting asymmetric Z_N-orbifolds, which are
themselves close relatives of twisted torus fibrations with elliptic
Z_N-monodromy (elliptic T-folds). We explicitly construct the modular invariant
partition function of the models and derive the non-commutative algebra in the
string coordinates, which is exact to all orders in {\alpha}'. Finally, we
relate these asymmetric orbifold spaces to inherently stringy Scherk-Schwarz
backgrounds and non-geometric fluxes.Comment: 30 page
A Geometry for Non-Geometric String Backgrounds
A geometric string solution has background fields in overlapping coordinate
patches related by diffeomorphisms and gauge transformations, while for a
non-geometric background this is generalised to allow transition functions
involving duality transformations. Non-geometric string backgrounds arise from
T-duals and mirrors of flux compactifications, from reductions with duality
twists and from asymmetric orbifolds. Strings in ` T-fold' backgrounds with a
local -torus fibration and T-duality transition functions in are
formulated in an enlarged space with a fibration which is geometric,
with spacetime emerging locally from a choice of a submanifold of each
fibre, so that it is a subspace or brane embedded in the enlarged
space. T-duality acts by changing to a different subspace of .
For a geometric background, the local choices of fit together to give a
spacetime which is a bundle, while for non-geometric string backgrounds
they do not fit together to form a manifold. In such cases spacetime geometry
only makes sense locally, and the global structure involves the doubled
geometry. For open strings, generalised D-branes wrap a subspace of each
fibre and the physical D-brane is the part of the part of the physical
space lying in the generalised D-brane subspace.Comment: 28 Pages. Minor change
On Slow-roll Moduli Inflation in Massive IIA Supergravity with Metric Fluxes
We derive several no-go theorems in the context of massive type IIA string
theory compactified to four dimensions in a way that, in the absence of fluxes,
preserves N=1 supersymmetry. Our derivation is based on the dilaton, Kaehler
and complex structure moduli dependence of the potential of the
four-dimensional effective field theory, that is generated by the presence of
D6-branes, O6-planes, RR-fluxes, NSNS 3-form flux, and geometric fluxes. To
demonstrate the usefulness of our theorems, we apply them to the most commonly
studied class of toroidal orientifolds. We show that for all but two of the
models in this class the slow-roll parameter \epsilon is bounded from below by
numbers of order unity as long as the fluxes satisfy the Bianchi identities,
ruling out slow-roll inflation and even the existence of de Sitter extrema in
these models. For the two cases that avoid the no-go theorems, we provide some
details of our numerical studies, demonstrating that small \epsilon can indeed
be achieved. We stress that there seems to be an \eta-problem, however,
suggesting that none of the models in this class are viable from a cosmological
point of view at least at large volume, small string coupling, and leading
order in the \alpha'-expansion.Comment: 34 pages, v3: summary table added, comments added, accepted for
publication in PR
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