790 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
New physics in top production
In theories that provide a mechanism for mass generation, we expect new physics to have a large coupling to the top quark. It is therefore natural to use top quark observables to test the mechanism responsible for electroweak symmetry
breaking. In the first part of this paper, I discuss the production and decay of top partners at the LHC, stressing the theoretical motivations in the context of composite Higgs models. I then present an effective field theory approach to opposite and same sign top quark pair production and discuss the general model-independent
constraints that can be obtained at the LHC on the restricted number of dimensionsix operators affecting tÂŻt and tt production
Dark Matter at Colliders: a Model-Independent Approach
Assuming that cosmological dark matter consists of weakly interacting massive
particles, we use the recent precise measurement of cosmological parameters to
predict the guaranteed rates of production of such particles in association
with photons at electron-positron colliders. Our approach is based on general
physical principles such as detailed balancing and soft/collinear
factorization. It leads to predictions that are valid across a broad range of
models containing WIMPs, including supersymmetry, universal extra dimensions,
and many others. We also discuss the discovery prospects for the predicted
experimental signatures.Comment: 5 pages, 3 figure
Constraints on UED KK-neutrino dark matter from magnetic dipole moments
Generically, universal extra dimension (UED) extensions of the standard model
predict the stability of the lightest Kaluza-Klein (KK) particle and hence
provide a dark matter candidate. For UED scenarios with one extra dimension, we
model-independently determine the size of the induced dimension-five magnetic
dipole moment of the KK-neutrino, . We show that current
observational bounds on the interactions of dipole dark matter place
constraints on UED models with KK-neutrino dark matter.Comment: References added, figures altered, discussion of results revised and
expande
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
Four-top production and tt + missing energy events at multi TeV e+eâ colliders
Four-top production and top pair production in association with missing energy at e+eâ colliders are sensitive probes of beyond-the-Standard-Model physics. We consider Standard Model extensions containing a new U(1)' which couples preferably to the most massive states of the SMsuch as the top quark or Dark Matter but has suppressed couplings to all the light states of the SM, as inspired by
Randall-Sundrumâlike setups or theories of partial fermion compositeness. These simple models are poorly constrained by experimental data but lead to striking new signatures at colliders. In this paper we consider Z' ïżœproduction in association with a top quark pair in 3TeV e+eâ collisions at CLIC, leading to interesting four-top final states and tt + Emiss events
First-Order Electroweak Phase Transition in the Standard Model with a Low Cutoff
We study the possibility of a first-order electroweak phase transition (EWPT)
due to a dimension-six operator in the effective Higgs potential. In contrast
with previous attempts to make the EWPT strongly first-order as required by
electroweak baryogenesis, we do not rely on large one-loop thermally generated
cubic Higgs interactions. Instead, we augment the Standard Model (SM) effective
theory with a dimension-six Higgs operator. This addition enables a strong
first-order phase transition to develop even with a Higgs boson mass well above
the current direct limit of 114 GeV. The phi^6 term can be generated for
instance by strong dynamics at the TeV scale or by integrating out heavy
particles like an additional singlet scalar field. We discuss conditions to
comply with electroweak precision constraints, and point out how future
experimental measurements of the Higgs self couplings could test the idea.Comment: 5 pages, 4 figures. v2: corrected typos, improved discussion of the
case lambda<0 and added references. To be published in PR
Chiral Compactification on a Square
We study quantum field theory in six dimensions with two of them compactified
on a square. A simple boundary condition is the identification of two pairs of
adjacent sides of the square such that the values of a field at two identified
points differ by an arbitrary phase. This allows a chiral fermion content for
the four-dimensional theory obtained after integrating over the square. We find
that nontrivial solutions for the field equations exist only when the phase is
a multiple of \pi/2, so that this compactification turns out to be equivalent
to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are
either periodic or anti-periodic. The equality of the Lagrangian densities at
the identified points in conjunction with six-dimensional Lorentz invariance
leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the
stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in
section 2. Minor corrections made in section
- âŠ