Collider Implications of Models with Extra Dimensions

We discuss the collider signals of large extra dimensions in which gravity as well as the SM particles propagate into the extra dimensions. These signals arise either from the production of Kaluza-Klein excitations of the SM particles and their subsequent decay, or from their off-shell exchanges. Depending on the scenario, the dominant signals are two high p_T jets + missing energy, two high p_T photons + missing energy and soft leptons, or a combination of photon + jet and missing energy. For the scenario in which only the gauge bosons propagate into the extra dimensions, Tevatron Run II (LHC) can observe such signals up to a compactification scale of about 2 TeV (7 TeV), while for the case of universal extra dimensions, the corresponding limits are about 600 GeV (3 TeV) respectively.Comment: 3 pages; invited talk presented by S. Nandi at the ICHEP 2002, Amsterdam, The Netherlands, July 24-31, 200

Monojet and Single Photon Signals from Universal Extra Dimensions

The usual universal extra dimensions scenario does not allow for single production of first level Kaluza-Klein (KK) excitations of matter due to the KK number conservation. However, if the matter fields are localized on a fat brane embedded in a higher dimensional space, matter-gravitation interactions violate KK number, and the production of single KK excitations becomes possible. In this paper we analyze the production of a single KK matter excitation together with a graviton in the final state, and study the potential for discovery at the Tevatron and Large Hadron Collider.Comment: 15 pages, 5 figure

Gluon Radiation in Top Quark Production and Decay at an e^+ e^- Collider

We study the effects of gluon radiation on top production and decay processes at an $e^+e^-$ collider.The matrix elements are computed without any approximations, using spinor techniques. We use a Monte Carlo event generator which takes into account the infrared singularity due to soft gluons and differences in kinematics associated with radiation in the production versus decay process. The calculation is illustrated for several strategies of top mass reconstruction.Comment: 9 pages, LaTeX, 6 postscript figures, uses aipproc.sty; presented at the 20th annual MRST meeting on High-Energy Physics, Montreal, Canada, 13-15 May 199

Neutrino Masses and Mixings in a Minimal SO(10) Model

We consider a minimal formulation of SO(10) Grand Unified Theory wherein all the fermion masses arise from Yukawa couplings involving one 126 and one 10 of Higgs multiplets. It has recently been recognized that such theories can explain, via the type-II seesaw mechanism, the large \nu_\mu - \nu_\tau mixing as a consequence of b-tau unification at the GUT scale. In this picture, however, the CKM phase \delta lies preferentially in the second quadrant, in contradiction with experimental measurements. We revisit this minimal model and show that the conventional type-I seesaw mechanism generates phenomenologically viable neutrino masses and mixings, while being consistent with CKM CP violation. We also present improved fits in the type-II seesaw scenario and suggest fully consistent fits in a mixed scenario.Comment: 27 pages, 13 eps figures, revtex4; references added, some minor correction

Lepton - Chargino Mixing and R-Parity Violating SUSY

We present a study of charged lepton mass matrix diagonalization in R-parity violating SUSY. The case in which the bilinear couplings $\mu_i$ have large values is given special attention.Comment: 7 pages, LaTeX, 1 postscript figure, uses aipproc.sty; presented at the 21th annual MRST meeting on High-Energy Physics, Ottawa, Canada, 10-12 May 199

Gravity and Matter in Extra Dimensions

In this paper, we derive from the viewpoint of the effective 4D theory the interaction terms between linearized gravity propagating in N>= 2 large extra dimensions and matter propagating into one extra dimension. This generalizes known results for the interactions between gravity and 4D matter in ADD-type models. Although we assume that matter is described by an Universal Extra Dimensions (UED) scenario (with all fields propagating into the fifth dimension), we present our results in a general form that can be easily adapted to various other scenarios of matter distribution. We then apply our results to the UED model on a fat brane and consider some phenomenological applications. Among these are the computation of the gravitational decay widths of the matter KK excitations and the effect the width of the brane has on the interactions of gravity with Standard Model particles. We also estimate the cross-section for producing single KK excitations at colliders through KK number-violating gravitational interaction.Comment: 21 pages, 6 figures, Late