SUSY Thresholds at a Muon Collider

One of the useful features of muon colliders is the naturally narrow spread in beam energies. Measurements of threshold cross sections then become a prime candidate for precision measurements of particle masses, widths, and couplings as well as determining particle spin. We describe the potential for measuring cross sections near threshold in supersymmetric theories.Comment: 6 pages, To appear in the Proceedings of the 5th International Conference on Physics Potential and Development of $\mu^+\mu^-$ Colliders (MuMu99), San Francisco, CA, 15-17 December 199

Superfield Realizations of Lorentz Violation

Lorentz-violating extensions of the Wess-Zumino model have been formulated in superspace. The models respect a supersymmetry algebra and can be understood as arising from suitably modified superspace transformations.Comment: 7 page

Abelian family symmetries and Leptogenesis

We study the impact of a set of horizontal symmetries on the requirements for producing the baryon asymmetry of the universe via leptogenesis. We find that Abelian horizontal symmetries lead to a simple description of the parameters describing leptogenesis in terms of the small expansion parameter that arises from spontaneous symmetry breaking. If the family symmetry is made discrete, then an enhancement in the amount of leptogenesis can result.Comment: 11 pages, 2 figures, version to appear in Physical Review

Precision W-Boson and Higgs Boson Mass Determinations at Muon Colliders

Precise determinations of the masses of the $W$ boson and of the top quark could stringently test the radiative structure of the Standard Model (SM) or provide evidence for new physics. We analyze the excellent prospects at a muon collider for measuring $M_W$ and $m_t$ in the $W^+W^-$ and $ZH$ threshold regions. With an integrated luminosity of 10 (100) fb$^{-1}$, the W-boson mass could be measured to a precision of 20 (6) MeV, provided that theoretical and experimental systematics are understood. A measurement of $\Delta M_W=6$ MeV would constrain the mass of a $\sim 100$ GeV Higgs to about $\pm 10$ GeV. We demonstrate that a measurement at future colliders of the Bjorken process. With an integrated luminosity of 100\fbi it is possible to measure the Standard Model Higgs mass to within 45\mev at a $\mu^+\mu^-$ collider for \mh=100\gev.Comment: 6 pages, 4 figure

Muon Collider Physics at Very High Energies

Muon colliders might greatly extend the energy frontier of collider physics. One can contemplate circular colliders with center-of-mass energies in excess of 10 TeV. Some physics issues that might be relevant at such a machine are discussed.Comment: 6 page

Anomaly-Free Flavor Symmetry and Neutrino Anarchy

We show that one can describe the quark and lepton masses with a single anomaly-free U(1) flavor symmetry provided a single order one parameter is enhanced by roughly 4-5. The flavor symmetry can be seen to arise from inside the $E_6$ symmetry group in such a way that it commutes with the SU(5) grand unified gauge group. The scenario does not distinguish between the left-handed lepton doublets and hence is a model of neutrino anarchy. It can therefore account for the large mixing observed in atmospheric neutrino experiments and predicts that the solar neutrino oscillation data is consistent with the large mixing angle solution of matter-enhanced oscillations.Comment: 5 pages, 1 figur

Threshold cross section measurements

Accurate measurements of particles masses, couplings and widths are possible by measuring production cross sections near threshold. We discuss the prospects for performing such measurements at a high luminosity muon collider.Comment: 7 pages, 1 figure, Presented at the Fourth International Conference on the Physics Potential and Development of $\mu ^+\mu^-$ Collider