Supersymmetric Unification

The measured value of the weak mixing angle is, at present, the only precise experimental indication for physics beyond the Standard Model. It points in the direction of Unified Theories with Supersymmetric particles at accessible energies. We recall the ideas that led to the construction of these theories in 1981.Comment: 21 pages, latex, two figures available by snail-mail upon e-mail request; Talk presented at the International Conference on the History of Original Ideas and Basic Discoveries in Particle Physics held at Ettore Majorana Centre for Scientific Culture, Erice, Sicily, July 29-Aug.4, 199

Beyond the Standard Model

A few topics beyond the standard model are reviewed.Comment: 10 pages, ichep.st

Soft Supersymmetry Breaking and the Supersymmetric Standard Model

We recall how the idea of Softly Broken Supersymmetry led to the construction of the Supersymmetric Standard Model in 1981. Its first prediction, the supersymmetric unification of gauge couplings, was conclusively verified by the LEP and SLC experiments 10 years later. Its other predictions include: the existence of superparticles at the electroweak scale; a stable lightest superparticle (LSP) with a mass of $\sim 100$ GeV, anticipated to be a neutral electroweak gaugino; the universality of scalar and gaugino masses at the unification scale. The original motivation for the model, solving the hierarchy problem, indicates that the superparticles should be discovered at the LHC or the TeVatron.Comment: Invited talk presented at the "Thirty Years of Supersymmetry" Symposium, University of Minnesota, October 13-15, 200

The Supersymmetric Flavor Problem

The supersymmetric $SU(3)\times SU(2)\times U(1)$ theory with minimal particle content and general soft supersymmetry breaking terms has 110 physical parameters in its flavor sector: 30 masses, 39 real mixing angles and 41 phases. The absence of an experimental indication for the plethora of new parameters places severe constraints on theories posessing Planck or GUT-mass particles and suggests that theories of flavor conflict with naturalness. We illustrate the problem by studying the processes $\mu \rightarrow e + \gamma$ and $K^0 - \bar{K}^0$ mixing which are very sensitive probes of Planckian physics: a single Planck mass particle coupled to the electron or the muon with a Yukawa coupling comparable to the gauge coupling typically leads to a rate for $\mu \rightarrow e + \gamma$ exceeding the present experimental limits. A possible solution is that the messengers which transmit supersymmetry breaking to the ordinary particles are much lighter than $M_{\rm Planck}$.Comment: 17 pages, Latex + epsf macros, 5 postscript figures uuencoded and attached at botto

The Hierarchy Problem and New Dimensions at a Millimeter

We propose a new framework for solving the hierarchy problem which does not rely on either supersymmetry or technicolor. In this framework, the gravitational and gauge interactions become united at the weak scale, which we take as the only fundamental short distance scale in nature. The observed weakness of gravity on distances \gsim 1 mm is due to the existence of $n \geq 2$ new compact spatial dimensions large compared to the weak scale. The Planck scale $M_{Pl} \sim G_N^{-1/2}$ is not a fundamental scale; its enormity is simply a consequence of the large size of the new dimensions. While gravitons can freely propagate in the new dimensions, at sub-weak energies the Standard Model (SM) fields must be localized to a 4-dimensional manifold of weak scale "thickness" in the extra dimensions. This picture leads to a number of striking signals for accelerator and laboratory experiments. For the case of $n=2$ new dimensions, planned sub-millimeter measurements of gravity may observe the transition from $1/r^2 \to 1/r^4$ Newtonian gravitation. For any number of new dimensions, the LHC and NLC could observe strong quantum gravitational interactions. Furthermore, SM particles can be kicked off our 4 dimensional manifold into the new dimensions, carrying away energy, and leading to an abrupt decrease in events with high transverse momentum p_T \gsim TeV. For certain compact manifolds, such particles will keep circling in the extra dimensions, periodically returning, colliding with and depositing energy to our four dimensional vacuum with frequencies of $\sim 10^{12}$ Hz or larger. As a concrete illustration, we construct a model with SM fields localised on the 4-dimensional throat of a vortex in 6 dimensions, with a Pati-Salam gauge symmetry $SU(4) \times SU(2) \times SU(2)$ in the bulk.Comment: 16 pages, latex, no figure

Towards a theory of quark and lepton masses

Has any progress been made on understanding and predicting the 13 parameters which describe the observed masses and mixing angles of the quarks and leptons? Arguments are given in favor of pursuing schemes in which grand unified and family symmetries provide many relations among these 13 parameters. A sequence of simple assumptions leads to a supersymmetric SO(10) theory with 8 predictions: $\tan \beta, m_t, V_{cb}, m_s, m_s/m_d$, $m_u/m_d, V_{ub}$ and the amount of CP violation $J$. These predictions are presented, together with experiments which will test them.Comment: (Talk given at Texas/Pascos Symposium), 18 page

Multi-Messenger Theories of Gauge-Mediated Supersymmetry Breaking

We study gauge-mediated theories containing several messengers with the most general SU(5)-invariant mass and supersymmetry-breaking parameters. We show that these theories are predictive, containing only two relevant parameters more than the minimal gauge-mediated model. Hypercharge D-terms can contribute significantly to the right-handed charged sleptons and bring them closer in mass to the left-handed sleptons. The messenger masses must be invariant under either SU(5) or a ``messenger parity" to avoid spontaneous breaking of charge conservation.Comment: 13 pages, 2 figure

Relic density in nonuniversal gaugino mass models with SO(10) GUT symmetry

Non-universal boundary conditions in grand unified theories can lead to nonuniversal gaugino masses at the unification scale. In R-parity preserving theories the lightest supersymmetric particle is a natural candidate for the dark matter. The composition of the lightest neutralino and the identity of the next-to-lightest supersymmetric particle are studied, when nonuniversal gaugino masses come from representations of SO(10). In these cases, the thermal relic density compatible with the Wilkinson Microwave Anisotropy Probe observations is found. Relic densities are compared with the universal case. Mass spectra in the studied cases are discussed.Comment: 7 pages, 13 figures, revtex4, two-column. V2: Typos corrected and references adde

K* vector and tensor couplings from Nf = 2 tmQCD

The mass m_K* and vector coupling f_K* of the K*-meson, as well as the ratio of the tensor to vector couplings fT/fV|_K*, are computed in lattice QCD. Our simulations are performed in a partially quenched setup, with two dynamical (sea) Wilson quark flavours, having a maximally twisted mass term. Valence quarks are either of the standard or the Osterwalder-Seiler maximally twisted variety. Results obtained at three values of the lattice spacing are extrapolated to the continuum, giving m_K* = 981(33) MeV, f_K* = 240(18) MeV and fT(2 GeV)/fV|_K* = 0.704(41).Comment: 1+11 page