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 t¯t 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, $\nu^{(1)}$. 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+e− colliders

Four-top production and top pair production in association with missing energy at e+e− 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-Sundrum–like 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' �production in association with a top quark pair in 3TeV e+e− 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