487 research outputs found
Supergravity Inspired Warped Compactifications and Effective Cosmological Constants
We propose a supergravity inspired derivation of a Randall-Sundrum's type
action as an effective description of the dynamics of a brane coupled to the
bulk through gravity only. The cosmological constants in the bulk and on the
brane appear at the classical level when solving the equations of motion
describing the bosonic sector of supergravities in ten and eleven dimensions
coupled to the brane. They are related to physical quantities like the brane
electric charge and thus inherit some of their physical properties. The most
appealing property is their quantization: in d_\perp extra dimensions,
Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical
origin also explains the apparent fine-tuning required in the Randall-Sundrum
scenario. In our approach, the cosmological constants are derived parameters
and cannot be chosen arbitrarily; instead they are determined by the underlying
Lagrangian. Some of the branes we construct that support cosmological constant
in the bulk have supersymmetric properties: D3-branes of type IIB superstring
theory provide an explicit example.Comment: 17 pages, LaTeX, 1 figure. v2: references added and a comment about
D-8 brane of massive IIA sugra included v3: improved argument on the
effective cosmological constants quantization and clarified discussion on the
supersymmetric issue of the solutions constructed. Final version to appear in
NP
Composite Higgs under LHC Experimental Scrutiny
The LHC has been built to understand the dynamics at the origin of the
breaking of the electroweak symmetry. Weakly coupled models with a fundamental
Higgs boson have focused most of the attention of the experimental searches. We
will discuss here how to reinterpret these searches in the context of strongly
coupled models where the Higgs boson emerges as a composite particle. In
particular, we use LHC data to constrain the compositeness scale. We also
briefly review the prospects to observe other bosonic and fermionic resonances
of the strong sector.Comment: 6 pages. Contribution to the proceedings of Hadron Collider Physics
Symposium 2011, Paris Nov. 14-1
First Glimpses at Higgs' face
The 8 TeV LHC Higgs search data just released indicates the existence of a
scalar resonance with mass ~ 125 GeV. We examine the implications of the data
reported by ATLAS, CMS and the Tevatron collaborations on understanding the
properties of this scalar by performing joint fits on its couplings to other
Standard Model particles. We discuss and characterize to what degree this
resonance has the properties of the Standard Model (SM) Higgs, and consider
what implications can be extracted for New Physics in a (mostly)
model-independent fashion. We find that, if the Higgs couplings to fermions and
weak vector bosons are allowed to differ from their standard values, the SM is
~ 2 sigma from the best fit point to current data. Fitting to a possible
invisible decay branching ratio, we find BR_{inv} = 0.05\pm 0.32\ (95% C.L.) We
also discuss and develop some ways of using the data in order to bound or rule
out models which modify significantly the properties of this scalar resonance
and apply these techniques to the global current data set.Comment: 26 pages, 7 figures, v2 post ICHEP data updat
Inflating Intersecting Branes and Remarks on the Hierarchy Problem
We generalize solutions of Einstein's equations for intersecting branes in
higher dimensional spacetimes to the nonstatic case, modeling an expanding
universe. The relation between the Hubble rate, the brane tensions, and the
bulk cosmological constant is similar to the case of a single 3-brane in a
5-dimensional spacetime. However, because the bulk inflates as well as the
branes, this class of solutions suffers from Newton's constant tending toward
zero on the TeV brane, where the Randall-Sundrum mechanism should solve the
weak scale hierarchy problem. The strength of gravity remains constant on the
Planck brane, however.Comment: 10 pages, LaTeX. v2:Misprint in eq. (23) corrected; citations fixed
and clarified relationship of our work to hep-th/9909053 and hep-th/9909076
v3: final version to appear in PLB. Corrected discussion of the time
dependance of the 4-D Planck mass on the TeV brane. Some references added to
earlier works on warped Kaluza-Klein compactification
General Properties of the Self-tuning Domain Wall Approach to the Cosmological Constant Problem
We study the dynamics of brane worlds coupled to a scalar field and gravity,
and find that self-tuning of the cosmological constant is generic in theories
with at most two branes or a single brane with orbifold boundary conditions. We
demonstrate that singularities are generic in the self-tuned solutions
compatible with localized gravity on the brane: we show that localized gravity
with an infinitely large extra dimension is only consistent with particular
fine-tuned values of the brane tension. The number of allowed brane tension
values is related to the number of negative stationary points of the scalar
bulk potential and, in the case of an oscillatory potential, the brane tension
for which gravity is localized without singularities is quantized. We also
examine a resolution of the singularities, and find that fine-tuning is
generically re-introduced at the singularities in order to retain a static
solution. However, we speculate that the presence of additional fields may
restore self-tuning.Comment: 26 pages, LaTeX, 8 figures included. V2: references added. To appear
in NP
Field theory on multithroat backgrounds
We consider extra dimensional field theory descriptions of backgrounds with N different throats where one of the extra dimensions in each throat is much larger than the others. Such backgrounds can be described by field theory on N 5D warped spaces which intersect on a ultraviolet (UV) brane. Given a field that propagates in all N throats there are N boundary conditions on the UV brane (which are determined by the effective Lagrangian on the UV brane) in addition to the boundary conditions on the N infrared branes. We derive a general set of UV boundary conditions and give examples of how they are applied to particular situations. Three simple example applications are given: in the first the number of families is determined by the number of throats and the SUSY flavor problem is solved via an S3 symmetry of the throats; in the second we embed this scenario in a SUSY GUT with a solution of the doublet-triplet splitting problem based on the product group approach; while in the final example we show a simple geometric implementation of a SUSY trinification model on three throats
Top and Bottom: a Brane of Their Own
We consider extra dimensional descriptions of models where there are two
separate strongly interacting sectors contributing to electroweak symmetry
breaking (``topcolor'' type models). In the extra dimensional picture there
would be two separate (anti-de Sitter) bulks meeting on the Planck brane, with
each bulk having its own corresponding IR (TeV) brane. Sources for electroweak
symmetry breaking can then be localized on both of these IR branes, while the
different generations of fermions may be separated from each other. We describe
the modes propagating in such a setup, and consider the cases where the
electroweak symmetry breaking on either of the two IR branes come either from a
higgsless scenario (via boundary conditions) or a (top-)Higgs. We show that the
tension that exists between obtaining a large top quark mass and the correct
value of the Zb\bar{b} couplings in ordinary higgsless models can be largely
relieved in the higgsless--top-Higgs versions of the two IR brane models. This
may also be true in the purely higgsless--higgsless case, however since that
model is necessarily in the strongly coupled regime the tree-level results for
the properties of the third generation may get large corrections. A necessary
consequence of such models is the appearance of additional pseudo-Goldstone
bosons (``top-pions''), which would be strongly coupled to the third
generation.Comment: 34 pages, LaTeX, 6 figures. v2: figure 2 fixed, footnote, comments
and references adde
Field Theory on Multi-throat Backgrounds
We consider extra dimensional field theory descriptions of backgrounds with N different throats where one of the extra dimensions in each throat is much larger than the others. Such backgrounds can be described by field theory on N 5D warped spaces which intersect on a ultraviolet (UV) brane. Given a field that propagates in all N throats there are N boundary conditions on the UV brane (which are determined by the effective Lagrangian on the UV brane) in addition to the boundary conditions on the N infrared branes. We derive a general set of UV boundary conditions and give examples of how they are applied to particular situations. Three simple example applications are given: in the first the number of families is determined by the number of throats and the SUSY flavor problem is solved via an S_3 symmetry of the throats; in the second we embed this scenario in a SUSY GUT with a solution of the doublet-triplet splitting problem based on the product group approach; while in the final example we show a simple geometric implementation of a SUSY trinification model on three throats
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