Theoretical Study of the Electroweak Interaction -- Present and Future

There have been several important recent developments in precision electroweak tests. These include: the new LEP energy scan during the 1993 run; the first high-precision results on the left-right asymmetry from the SLD Collaboration at SLAC; the probable discovery of the top quark by the CDF Collaboration at Fermilab and the determination of its mass. I will discuss the implications of these and earlier results for testing the standard model; for the standard model parameters, including the top quark mass, the Higgs mass, the weak mixing angle, and the strong coupling constant, $\alpha_s$; and the search for new physics. In particular, given the CDF direct determination of $m_t$ it is now possible to severely constrain certain types of new physics by separating the contribution from new physics from the dependence on $m_t$.Comment: 22nd INS SYMPOSIUM ON PHYSICS WITH HIGH ENERGY COLLIDERS, Tokyo, March, 1994; 27 pages, Latex, 9 figures, not included; postscript file with embedded figures by anonymous ftp at dept.physics.upenn.edu; UPR-0624

Precision Experiments, Grand Unification, and Compositeness

Precision electroweak data allow one to test the standard model, constrain its parameters, and search for the effects of some kinds of new physics. The results of the most recent data from LEP, SLC, and elsewhere are described, as are their predictions for $m_t$, $M_H$, and $\alpha_s$. The implications for the two major classes of extensions of the standard model, supersymmetry/unification and compositeness, are described.Comment: Invited talk presented at {\it SUSY-95}, Palaiseau, France, May 1995. 19 pages, Latex, 6 figures, not included; postscript file with embedded figures by anonymous ftp at ftp://dept.physics.upenn.edu/pub/Langacker/paris.p

Implications of Solar and Atmospheric Neutrinos

The implications of the deficit of solar neutrinos are discussed. If all of the experiments are taken literally the relative suppressions render an astrophysical explanation unlikely. Allowing MSW conversions, the data simultaneously determine the temperature of the core of the sun to within five percent. The implications of the atmospheric $\nu_\mu/\nu_e$ ratio are briefly discussed.Comment: Latex, DPF92, 4 pages, 1 figure (available on request), UPR-0548

TeV Physics from the Top Down

Concrete semi-realistic string/M theory constructions often predict the existence of new physics at the TeV scale, which may be different in character from the bottom-up ideas that are motivated by specific problems of the standard model. I describe two examples, heterotic and open string, of such constructions. The latter has a particularly interesting strongly-coupled quasi-hidden sector, which may lead to composite states at low energy and dynamical supersymmetry breaking. General issues, such as grand unification versus direct compactification, additional U(1)' gauge symmetries and other exotics, and flat directions are discussed.Comment: 13 pages, invited talk presented at SUGRA20, Northeastern University, March, 200

Neutrino Oscillation Workshop 2000: Conference Summary

The NOW2000 Workshop summarized the present status and future possibilities for all aspects of neutrino physics and astrophysics. Neutrino oscillation physics has truly come of age in the last few years. It is now data driven (analogous to cosmology and much of high energy physics in general). Experimental techniques and the theoretical interpretation have developed dramatically. An example of the latter includes the more realistic analysis of neutrino oscillations in the framework of 3 or more mass eigenstates. The phenomenological emphasis has shifted from degenerate to hierarchical neutrino spectra.Comment: Summary talk for Neutrino Oscillation Workshop (NOW2000), Otranto, Italy, September 2000. 19 pages, 1 figur

Status and Phenomenology of the Standard Model

The status of the new standard model is briefly surveyed, with emphasis on experimental tests, unique features, theoretical problems, necessary extensions, and possible TeV signatures of Planck scale physics.Comment: 14 pages, 7 figures, invited talk presented at Physics at the LHC, Vienna, 2004; typos correction and one reference adde

The Physics of New U(1)' Gauge Bosons

Additional Z' gauge bosons are predicted by a wide variety of extensions of the standard model (SM). Possibilities include TeV-scale bosons with electroweak coupling, very light bosons which nearly decouple from the standard model particles, and bosons which communicate with a quasi-hidden sector. A broad survey is given of the theoretical possibilities and of the physics implications for particle physics and cosmology. Several novel examples, including light Z's suggested by PAMELA, Stueckelberg Z's, and Z's associated with the mediation of supersymmetry breaking, are described.Comment: 10 pages, 2 figures. Invited talk presented at SUSY09. References added and minor revision

NEUTRINO PHYSICS

The theoretical motivations, experimental searches/hints, and implications of neutrino mass are surveyed.Comment: Invited talk presented at Beyond the Standard Model IV, Lake Tahoe, CA, December, 1994. 16 pages, Latex, 2 figures, not included; postscript file with embedded figures by anonymous ftp at ftp://dept.physics.upenn.edu/pub/Langacker/bsmiv.p

Precision Tests of the Standard Model

The implications of recent precision $Z$-pole, $W$ mass, and weak neutral current data for testing the standard electroweak model, constraining the $t$ quark and Higgs masses, \alsz, and grand unification are discussed. A fit to all data yields \siz = 0.2328 \pm 0.0007 (\msb) or \sinn \equiv 1 - \mw^2/\mz^2 = 0.2267 \pm 0.0024 (on-shell), where the uncertainties are mainly from \mt. In the standard model one predicts \mt = 150^{+19 + 15}_{-24 - 20} GeV, where the central value assumes \mh = 300 GeV and the second uncertainty is for \mh \ra 60 GeV ($-$) or 1 TeV (+). In the minimal supersymmetric extension of the standard model (MSSM) one predicts \mt = 134^{+23}_{-28} \pm 5 GeV, where the difference is due the light Higgs scalar expected in the MSSM. There is no significant constraint on \mh \ until \mt \ is known independently.Comment: Lectures presented at {\it TASI-92}, Boulder, June 1992, 22 Pages, Latex, 9 figures, available on request, UPR-0555

Beyond the MSSM

Specific quasi-realistic superstring constructions often predict the existence of new TeV-scale physics which may be different in character from bottom-up motivated constructions. I describe examples of such beyond the MSSM physics, with special emphasis on heavy Z' gauge bosons and associated exotic particles. Implications of an extra U(1)' include a viable scienario for electroweak baryogenesis, a highly non-standard light Higgs sector, and Z'-mediated contributions to rare B decays.Comment: 9 pages, 2 figures, Talk presented at SUSY 2003: Supersymmetry in the Desert, held at the University of Arizona,Tucson, AZ, June 5-10, 2003. To appear in the Proceeding