Search results for "Electroweak"
showing 10 items of 744 documents
SINGLE PHOTON DECAYS OF THE $Z^0$ AND SUSY WITH SPONTANEOUSLY BROKEN R-PARITY
1995
Spontaneous violation of R parity can induce rare single photon decays of the $Z^0$ involving the emission of (nearly) massless pseudoscalar Goldstone bosons, majorons, as well as massive CP even or CP odd spin zero bosons that arise in the electroweak breaking sector of these models. We show that the majoron emitting decays can have a sizeable branching ratio of $10^{-5}$ or so, without conflicting any experimental observation from neutrino physics or particle searches. These decays may lead to interesting structures for the single photon spectrum involving either mono chromatic photons as well as continuous spectra that grow with energy. They would easily account for an excess of single p…
Invisible Higgs decays and neutrino physics
1993
Abstract A wide class of neutrino physics motivated models are characterized by the spontaneous violation of a global U(1) lepton number symmetry at or below the electroweak scale by an SU(2)⊗U(1) singlet vacuum expectation value 〈 σ 〉 ≲ O(1) TeV. In all these models the main Higgs decay channel is likely to be “invisible”, e.g. h → JJ, where J denotes the associated weakly interacting pseudoscalar Goldstone boson — the majoron. This leads to events with large missing energy that could be observable at LEP and affect the Higgs mass bounds obtained, as well as lead to novel ways to search for Higgs bosons and high-energy supercolliders such as the LHC/SSC.
An effective field theory approach to the electroweak corrections at LEP energies
1999
In the framework of the effective field theory (EFT) we discuss the electroweak (EW) corrections at LEP energies. We obtain the effective Lagrangian in the large m_t limit, and reproduce analytically the dominant EW corrections to the LEP2 processes e+ e- --> gamma Z and e+ e- --> Z Z. To include effects of finite top-quark and Higgs masses, we use the effective Lagrangian at tree level and fit LEP1/SLD observables with four arbitrary parameters, plus alpha_s(m_Z). The EFT approach works remarkably well. Using the effective couplings determined from the fit, and tree-level EFT formulae, we predict the cross sections for e+ e- --> Z Z, gamma Z at a level better than 1%.
CP properties of the leptonic sector for majorana neutrinos
1983
Abstract The leptonic sector of the electroweak theory is analyzed for massive Majorana neutrinos. For n generations, the Majorana mass lagrangian is diagonalized using the polar reduction to guarantee physical positive masses independently of the CP properties or the choice of the phases of the fields. When CP invariance holds, the CP eigenvalues of the definite mass neutrino fields are determined without commitment to a particular phase choice. For charged current interactions, we find that the observable CP violating phases can be parametrized a la Kobayashi-Maskawa for the vertec. Extra ( n − 1) relative phases of the massive neutrino fields are significant. The extra phases are observa…
Neutral heavy leptons and electroweak baryogenesis
1996
We investigate the possibility that baryogenesis occurs during the weak phase transition in a minimal extension of the Standard Model which contains extra neutral leptons and conserves total lepton number. The necessary CP-violating phases appear in the leptonic Yukawa couplings. We compute the CP-asymmetries in both the neutral and the charged lepton fluxes reflected on the bubble wall. Using present experimental bounds on the mixing angles and Standard Model estimates for the parameters related to the scalar potential, we conclude that it seems unlikely to produce the observed baryon to entropy ratio within this type of models. We comment on the possibility that the constraints on the mix…
Sparticle Mass Spectra from SO(10) Grand Unified Models with Yukawa Coupling Unification
1999
We examine the spectrum of superparticles obtained from the minimal SO(10) grand unified model, where it is assumed the gauge symmetry breaking yields the Minimal Supersymmetric Standard Model (MSSM) as the effective theory at $M_{GUT}\sim 2\times 10^{16}$ GeV. In this model, unification of Yukawa couplings implies a value of $\tan\beta\sim 45-55$. At such high values of $\tan\beta$, assuming universality of scalar masses, the usual mechanism of radiative electroweak symmetry breaking breaks down. We show that a set of weak scale sparticle masses consistent with radiative electroweak symmetry breaking can be generated by imposing non-universal GUT scale scalar masses consistent with univers…
Bounds on the Tau Magnetic Moments: Standard Model and Beyond
2001
We obtain new bounds for the magnetic dipole moments of the tau lepton. These limits on the magnetic couplings of the tau to the electroweak gauge bosons (gamma, W, Z) are set in a model independent way using the most general effective Lagrangian with the SU(2)_L x U(1)_Y symmetry. Comparison with data from the most precise experiments at high energies shows that the present limits are more stringent than the previous published ones. For the anomalous magnetic moment the bounds are, for the first time, within one order of magnitude of the standard model prediction.
Search for high-mass states with one lepton plus missing transverse momentum in proton–proton collisions at s=7 TeV with the ATLAS detector
2011
The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W', W*) decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb-1. No excess beyond standard model expectations is observed. A W' with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W*(charged chiral boson) for masses below 1.47 TeV.
Dynamical Symmetry Breaking in Warped Compactifications
2001
We study dynamical electroweak symmetry breaking in the Randall-Sundrum scenario. We show that one extra dimension is enough to give the correct pattern of electroweak symmetry breaking in a simple model with gauge bosons and the right-handed top quark in the bulk. The top quark mass is also in agreement with experiment. Furthermore, we propose an extended scenario with all Standard Model gauge bosons and fermions propagating in the bulk, which naturally accommodates the fermion mass hierarchies. No new fields or interactions beyond the observed in the Standard Model are required.
Status and implications of neutrino masses: a brief panorama
2015
15 pages.- 10 figures