M(atrix) String Theory on K3

We conjecture that M-theory compactified on an ALE space (or K3) is described by 0-branes moving on the ALE space. We give evidence for this by showing that if we compactify another circle, we recover string theory on the ALE space. This guarantees that in the large N limit, the matrix model correctly describes the force law between gravitons moving in an ALE background. We also show the appearance in M(atrix) theory of the duality of M-theory on K3 with the heterotic string on a three-torus.Comment: 11 pages, late

Multigraviton Scattering in the Matrix Model

We consider scattering processes in the matrix model with three incoming and three outgoing gravitons. We find a discrepancy between the amplitude calculated from the matrix model and the supergravity prediction. Possible sources for this discrepancy are discussed.Comment: 11 pages, latex, references adde

Orientifold Points in M Theory

We identify the lift to M theory of the four types of orientifold points, and show that they involve a chiral fermion on an orbifold fixed circle. From this lift, we compute the number of normalizable ground states for the SO(N) and $Sp(N)$ supersymmetric quantum mechanics with sixteen supercharges. The results agree with known results obtained by the mass deformation method. The mass of the orientifold is identified with the Casimir energy.Comment: 11 pages, Latex, references adde

Near Horizon Superspace

The adS_{p+2} x S^{d-p-2} geometry of the near horizon branes is promoted to a supergeometry: the solution of the supergravity constraints for the vielbein, connection and form superfields are found. This supergeometry can be used for the construction of new superconformal theories. We also discuss the Green-Schwarz action for a type IIB string on adS_5 x S_5.Comment: 11 pages, LaTe

Stability analysis for soliton solutions in a gauged CP(1) theory

We analyze the stability of soliton solutions in a Chern-Simons-CP(1) model. We show a condition for which the soliton solutions are stable. Finally we verified this result numerically.Comment: 13 pages, numerical analysis is added. To be published in Mod. Phys. Lett.

Tevatron Discovery Potential for Fourth Generation Neutrinos: Dirac, Majorana and Everything in Between

We analyze the power of the Tevatron dataset to exclude or discover fourth generation neutrinos. In a general framework, one can have mixed left- and right-handed neutrinos, with Dirac and Majorana neutrinos as extreme cases. We demonstrate that a single Tevatron experiment can make powerful statements across the entire mixing space, extending LEP's mass limits of 60-80 GeV up to 150-175 GeV, depending on the mixing.Comment: 4 pages, pdflate

Models and Phenomenology of Maximal Flavor Violation

We consider models of maximal flavor violation (MxFV), in which a new scalar mediates large q_3 q_1 or q_3 q_2 flavor changing transitions (q_i is an i'th generation quark), while q_3 q_3 transitions are suppressed, e.g., \xi_{31}, \xi_{13} ~ V_{tb} and \xi_{33} ~ V_{td}, where \xi_{ij} are the new scalar couplings to quarks and V is the CKM matrix. We show that, contrary to the conventional viewpoint, such models are not ruled out by the existing low energy data on K^0, B^0 and D^0 oscillations and rare K and B-decays. We also show that these models of MxFV can have surprising new signatures at the LHC and the Tevatron.Comment: Latex, 4 pages, 1 figure. Version as publishe

Revisiting Constraints on Fourth Generation Neutrino Masses

We revisit the current experimental bounds on fourth-generation Majorana neutrino masses, including the effects of right handed neutrinos. Current bounds from LEPII are significantly altered by a global analysis. We show that the current bounds on fourth generation neutrinos decaying to eW and mu W can be reduced to about 80 GeV (from the current bound of 90 GeV), while a neutrino decaying to tau W can be as light as 62.1 GeV. The weakened bound opens up a neutrino decay channel for intermediate mass Higgs, and interesting multi-particle final states for Higgs and fourth generation lepton decays.Comment: 7 pages 1 fi