A comparison of ultraviolet sensitivities in universal, nonuniversal, and split extra dimensional models

We discuss the origin of ultraviolet sensitivity in extra dimensional theories, and compare and contrast the cutoff dependences in universal, nonuniversal and split five dimensional models. While the gauge bosons and scalars are in the five dimensional bulk in all scenarios, the locations of the fermions are different in different cases. In the universal model all fermions can travel in the bulk, in the nonuniversal case they are all confined at the brane, while in the split scenario some are in the bulk and some are in the brane. A possible cure from such divergences is also discussed.Comment: 9 pages, Latex, no figure, v2: further clarifications and references added, accepted for publication in Phys. Rev.

Effects of Universal Extra Dimensions on Higgs signals at LHC

A major focus at the Large Hadron Collider (LHC) will be Higgs boson studies and it would be an interesting prospect to simultaneously probe for physics beyond the Standard Model (SM) in the Higgs signals. In this work we show as to what extent, the effects of Universal Extra Dimension (UED) can be isolated at the LHC through the Higgs signals. By doing a detailed study of the different uncertainties involved in the measurement of the rates for the process pp --> h --> gamma gamma we estimate the extent to which these uncertainties can mask the effects of the contributions coming from UED.Comment: 13 pages, LateX, Title changed, text and figures modified. Version to appear in IJMP

Identifying the contributions of Universal Extra Dimensions in the Higgs sector at linear e+ e- colliders

We study the dilepton-dijet signal in the dominant Higgs production channel at a linear e+ e- collider. We estimate the effects of Universal Extra Dimension (UED) by a simple analysis of the cross-sections. The heavy Kaluza-Klein excitations of the Standard Model fields in UED can significantly alter the decay properties of the Higgs boson to loop-driven final states. We show that by taking a simple ratio between cross-sections of two different final states this difference can be very easily highlighted.Comment: Some parts of the text modified. 1 figure added. Version to appear in IJMP

Singlet Fermionic Dark Matter explains DAMA signal

It has been suggested that, considering channeling effect, the order of a few GeV dark matters which are elastically scattered from detector nuclei might be plausible candidates reconciling the DAMA annual modulation signal with the results of other null experiments. We show that Singlet Fermionic Dark Matter can be such a dark matter candidate, simultaneously providing the correct thermal relic density which is consistent with the WMAP data.Comment: 9 pages, 3 figure

Non-Commutativity and Unitarity Violation in Gauge Boson Scattering

We examine the unitarity properties of spontaneously broken non-commutative gauge theories. We find that the symmetry breaking mechanism in the non-commutative Standard Model of Chaichian et al. leads to an unavoidable violation of tree-level unitarity in gauge boson scattering at high energies. We then study a variety of simplified spontaneously broken non-commutative theories and isolate the source of this unitarity violation. Given the group theoretic restrictions endemic to non-commutative model building, we conclude that it is difficult to build a non-commutative Standard Model under the Weyl-Moyal approach that preserves unitarity.Comment: 31 page

Finite Gluon Fusion Amplitude in the Gauge-Higgs Unification

We show that the gluon fusion amplitude in the gauge-Higgs unification scenario is finite in any dimension regardless of its nonrenormalizability. This result is supported by the fact that the local operator describing the gluon fusion process is forbidden by the higher dimensional gauge invariance. We explicitly calculate the gluon fusion amplitude in an arbitrary dimensional gauge-Higgs unification model and indeed obtain the finite result.Comment: 15 pages, final version to appear in MPL

A Simple Explanation for DAMA with Moderate Channeling

We consider the possibility that the DAMA signal arises from channeled events in simple models where the dark matter interaction with nuclei is suppressed at small momenta. As with the standard WIMP, these models have two parameters (the dark matter mass and the size of the cross-section), without the need to introduce an additional energy threshold type of parameter. We find that they can be consistent with channeling fractions as low as about ~ 15%, so long as at least ~70% of the nuclear recoil energy for channeled events is deposited electronically. Given that there are reasons not to expect very large channeling fractions, these scenarios make the channeling explanation of DAMA much more compelling.Comment: 6 pages, 2 figure

Precision Measurements and Fermion Geography in the Randall-Sundrum Model Revisited

We re-examine the implications of allowing fermion fields to propagate in the five-dimensional bulk of the Randall-Sundrum (RS) localized gravity model. We find that mixing between the Standard Model top quark and its Kaluza Klein excitations generates large contributions to the rho parameter and consequently restricts the fundamental RS scale to lie above 100 TeV. To circumvent this bound we propose a `mixed' scenario which localizes the third generation fermions on the TeV brane and allows the lighter generations to propagate in the full five-dimensional bulk. We show that this construction naturally reproduces the observed m_c / m_t and m_s / m_b hierarchies. We explore the signatures of this scenario in precision measurements and future high energy collider experiments. We find that the region of parameter space that addresses the hierarchies of fermion Yukawa couplings permits a Higgs boson with a mass of 500 GeV and remains otherwise invisible at the LHC. However, the entire parameter region consistent with electroweak precision data is testable at future linear colliders. We briefly discuss possible constraints on this scenario arising from flavor changing neutral currents.Comment: 44 pages, 20 ps files; VII, typos fixed and refs adde