300 research outputs found
Supersymmetric codimension-two branes and U(1)_R mediation in 6D gauged supergravity
We construct a consistent supersymmetric action for brane chiral and vector
multiplets in a six-dimensional chiral gauged supergravity. A nonzero brane
tension can be accommodated by allowing for a brane-localized Fayet-Iliopoulos
term proportional to the brane tension. When the brane chiral multiplet is
charged under the bulk U(1)_R, we obtain a nontrivial coupling to the extra
component of the U(1)_R gauge field strength as well as a singular scalar
self-interaction term. Dimensionally reducing to 4D on a football
supersymmetric solution, we discuss the implication of such interactions for
obtaining the U(1)_R D-term in the 4D effective supergravity. By assuming the
bulk gaugino condensates and nonzero brane F- and/or D-term for the uplifting
potential, we have all the moduli stabilized with a vanishing cosmological
constant. The brane scalar with nonzero R charge then gets a soft mass of order
the gravitino mass. The overall sign of the soft mass squared depends on the
sign of the R charge as well as whether the brane F- or D-term dominates.Comment: 28 pages, no figures, version to appear in JHE
Volume stabilization in a warped flux compactification model
We investigate the stability of the extra dimensions in a warped, codimension
two braneworld that is based upon an Einstein-Maxwell-dilaton theory with a
non-vanishing scalar field potential. The braneworld solution has two 3-branes,
which are located at the positions of the conical singularities. For this type
of brane solution the relative positions of the branes (the shape modulus) is
determined via the tension-deficit relations, if the brane tensions are fixed.
However, the volume of the extra dimensions (the volume modulus) is not fixed
in the context of the classical theory, implying we should take quantum
corrections into account. Hence, we discuss the one-loop effective potential of
the volume modulus for a massless, minimally coupled scalar field.Comment: 25 pages, 8 figures, typos correcte
General Axisymmetric Solutions and Self-Tuning in 6D Chiral Gauged Supergravity
We re-examine the properties of the axially-symmetric solutions to chiral
gauged 6D supergravity, recently found in refs. hep-th/0307238 and
hep-th/0308064. Ref. hep-th/0307238 finds the most general solutions having two
singularities which are maximally-symmetric in the large 4 dimensions and which
are axially-symmetric in the internal dimensions. We show that not all of these
solutions have purely conical singularities at the brane positions, and that
not all singularities can be interpreted as being the bulk geometry sourced by
neutral 3-branes. The subset of solutions for which the metric singularities
are conical precisely agree with the solutions of ref. hep-th/0308064.
Establishing this connection between the solutions of these two references
resolves a minor conflict concerning whether or not the tensions of the
resulting branes must be negative. The tensions can be both negative and
positive depending on the choice of parameters. We discuss the physical
interpretation of the non-conical solutions, including their significance for
the proposal for using 6-dimensional self-tuning to understand the small size
of the observed vacuum energy. In passing we briefly comment on a recent paper
by Garriga and Porrati which criticizes the realization of self-tuning in 6D
supergravity.Comment: 27 pages, 1 figure; JHEP3 style; Some references added, and
discussion of tension constraints and unwarped solutions made more explici
Supersymmetric codimension-two branes in six-dimensional gauged supergravity
We consider the six-dimensional Salam-Sezgin supergravity in the presence of
codimension-2 branes. In the case that the branes carry only tension, we
provide a way to supersymmetrise them by adding appropriate localised
Fayet-Iliopoulos terms and localised corrections to the Chern-Simons term and
modifying accordingly the fermionic supersymmetry transformations. The
resulting brane action has N=1 supersymmetry (SUSY). We find the axisymmetric
vacua of the system and show that one has unwarped background solutions with
"football"-shaped extra dimensions which always respect N=1 SUSY for any value
of the equal brane tensions, in contrast with the non-supersymmetric brane
action background. Finally, we generically find multiple zero modes of the
gravitino in this background and discuss how one could obtain a single chiral
zero mode present in the low energy spectrum.Comment: 21 pages, no figures, A sign error in the gauge potential at the
lower brane corrected and its consequent effect discusse
3-Form Flux Compactification of Salam-Sezgin Supergravity
The compactification of 6 dimensional Salam-Sezgin model in the presence of
3-form flux H is investigated. We find a torus topology for this
compactification with two cusps which are the places of branes, while at the
limit of large size L of the compact direction we also obtain sphere topology.
This resembles the Randall-Sundrum I,II model. The branes at one of the cusps
can be chosen to be 3- and 4-branes which fill our 4-dimensional space together
with the fact that H=0 at this position restores the Lorentz symmetry. This
compactification also provides an example for the so-called `time warp'
solution, [0812.5107 [hep-th]]. According to a no-go theorem in , the
time warp compactification violates the null energy condition. While the
theorem is quiet for d=6, our model gives a time warp compactification which
satisfies the null energy condition. We also derive the four dimensional
effective Planck mass which is not obvious due to the time warp nature of the
solution.Comment: 19 pages, 5 fig
4d-Flat Compactifications With Brane Vorticities
We present solutions in six-dimensional gravity coupled to a sigma model, in
the presence of three-brane sources. The space transverse to the branes is a
compact non-singular manifold. The example of O(3) sigma model in the presence
of two three-branes is worked out in detail. We show that the four-dimensional
flatness is obtained with a single condition involving the brane tensions,
which are in general different and may be both positive, and another
characteristic of the branes, vorticity. We speculate that the adjustment of
the effective four-dimensional cosmological constant may occur through the
exchange of vorticity between the branes. We then give exact instanton type
solutions for sigma models targeted on a general K\"ahler manifold, and
elaborate in this framework on multi-instantons of the O(3) sigma model. The
latter have branes, possibly with vorticities, at the instanton positions, thus
generalizing our two-brane solution.Comment: 8 pages. New references added and minor typos are correcte
Flux Stabilization in 6 Dimensions: D-terms and Loop Corrections
We analyse D-terms induced by gauge theory fluxes in the context of
6-dimensional supergravity models. On the one hand, this is arguably the
simplest concrete setting in which the controversial idea of `D-term uplifts'
can be investigated. On the other hand, it is a very plausible intermediate
step on the way from a 10d string theory model to 4d phenomenology. Our
specific results include the flux-induced one-loop correction to the scalar
potential coming from charged hypermultiplets. Furthermore, we comment on the
interplay of gauge theory fluxes and gaugino condensation in the present
context, demonstrate explicitly how the D-term arises from the gauging of one
of the compactification moduli, and briefly discuss further ingredients that
may be required for the construction of a phenomenologically viable model. In
particular, we show how the 6d dilaton and volume moduli can be simultaneously
stabilized, in the spirit of KKLT, by the combination of an R symmetry twist, a
gaugino condensate, and a flux-induced D-term.Comment: 24 pages, 1 figure v2:minor correction
Gravity on codimension 2 brane worlds
We compute the matching conditions for a general thick codimension 2 brane, a
necessary previous step towards the investigation of gravitational phenomena in
codimension 2 braneworlds. We show that, provided the brane is weakly curved,
they are specified by the integral in the extra dimensions of the brane
energy-momentum, independently of its detailed internal structure. These
general matching conditions can then be used as boundary conditions for the
bulk solution. By evaluating Einstein equations at the brane boundary we are
able to write an evolution equation for the induced metric on the brane
depending only on physical brane parameters and the bulk energy-momentum
tensor. We particularise to a cosmological metric and show that a realistic
cosmology can be obtained in the simplest case of having just a non-zero
cosmological constant in the bulk. We point out several parallelisms between
this case and the codimension 1 brane worlds in an AdS space.Comment: 24 page
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