Search

In supersymmetric (SUSY) models the misalignment between fermion and sfermion families introduces unsuppressed flavor-changing processes. Even if the mass parameters are chosen to give no flavor violation, family dependent radiative corrections make this adjustment not stable. We analyze the rate of l --> l' gamma in SUSY-GUT models with three quasi-degenerate neutrinos and universal scalar masses at the Planck scale. We pay special attention to a recently proposed scenario where the low-energy neutrino mixings are generated from identical quark and lepton mixings at large scales. We show that: (i) To take universal slepton masses at the GUT scale is a very poor approximation, even in no-scale models. (ii) For large neutrino Yukawa couplings the decay mu --> e gamma would be observed in the planned experiment at PSI. (iii) For large values of tanbeta the tau coupling gives important corrections, pushing mu --> e gamma and tau --> mu gamma to accessible rates. In particular, the non-observation of these processes in the near future would exclude the scenario with unification of quark and lepton mixing angles. (iv) The absence of lepton flavor violating decays in upcoming experiments would imply a low value of tanbeta, small neutrino couplings, and large (>~ 250$ GeV) SUSY-breaking masses., 13 pages, 4 figures. v3: introduction and discussion improved and references added; version to appear in EPJC

We study the form factor f_+^H (H=D,B) involved in H-\pi transitions. We use data on D^0 \to \pi^- l^+ \nu to find f_+^D at low recoil. Then we use perturbative QCD methods to calculate at larger recoil the contributions to f_+^H that break heavy quark symmetry (HQS). Using HQS relations we obtain an estimate of f_+^B which includes first order corrections in 1/(2m_Q). Comparison with recent data on B^0 \to \pi^- l^+ \nu gives V_ub = 0.0025 \pm 0.0005^ex \pm 0.0004^th., Comment: 13 pages, 3 figures, corrected version

It was recently suggested that the reported anomalies in R{sub b} and R{sub c} can be interpreted as the effect of a heavy vector boson that couples to quarks and is universally decoupled from leptons. We examine how an extra gauge boson with this property can arise from superstring derived models. In a specific three generation model we show that the U(1){sub B-L} symmetry combines with the horizontal flavor symmetries to form a universal leptophobic U(1) symmetry. In our model there is an enhancement of the color gauge group from twisted sectors. The enhancement occurs after the breaking of the unifying gauge symmetry by ``Wilson lines.`` The leptophobic U(1) symmetry then becomes a generator of the color SU(4) gauge group. We examine how similar symmetries may appear in other string models without the enhancement. We propose that if the current LEP anomalies persist it may be evidence for a certain class of un-unified superstring models. 15 refs., 4 tabs.

Cosmogenic neutrinos reach the Earth with energies around 109 GeV, and their interactions with matter will be measured in upcoming experiments (Auger, IceCube). Models with extra dimensions and the fundamental scale at the TeV could imply signals in these experiments. In particular, besides the production of microscopic black holes by cosmogenic neutrinos, gravity‐mediated interactions at larger distances (that can be calculated in the eikonal approximation) can take place. In these processes a neutrino of energy Ev interacts elastically with a parton inside a nucleon, loses a small fraction y of its energy, and starts a hadronic shower of energy yEv ≪ Ev. We show that for the expected fluxes of cosmogenic neutrinos these elastic processes give a stronger signal than black hole production in neutrino telescopes and that the energy distribution of contained hadronic showers can help to distinguish between eikonal and black hole or Standard Model events. On the other hand, the absence of any signal at IceCu...