Unitarity of the Standard Model at the Higgs' Resonance

We compute a unitarity bound for higgs mass using one--loop corrected s--wave partial amplitude for $Z_L Z_L \rightarrow Z_L Z_L$ scattering. We use the equivalence theorem and show that the higgs mass has to be less than $\approx 600$ GeV in order to save the (perturbative) unitarity in the higgs' resonance region. We also discuss about the validity of perturbation expansion in the symmetry breaking sector.Comment: 6 pages, LaTeX, figures available upon request, TURKU-FL-P

Electroweak Radiative Corrections To Polarized M{\o}ller Scattering Asymmetries

One loop electroweak radiative corrections to left-right parity violating M{\o}ller scattering ($e^-e^-\to e^-e^-$) asymmetries are presented. They reduce the standard model (tree level) prediction by 40$\pm 3$ \% where the main shift and uncertainty stem from hadronic vacuum polarization loops. A similar reduction also occurs for the electron-electron atomic parity violating interaction. That effect can be attributed to an increase of $\sin^2\theta_W(q^2)$ by $3\%$ in running from $q^2=m_Z^2$ to 0. The sensitivity of the asymmetry to ``new physics'' is also discussed.Comment: 14 pages, Revtex, postscript file including figures is available at ftp://ttpux2.physik.uni-karlsruhe.de/ttp95-14/ttp95-14.ps or via WWW at http://ttpux2.physik.uni-karlsruhe.de/cgi-bin/preprints/ (129.13.102.139

"Dark" Z implications for Parity Violation, Rare Meson Decays, and Higgs Physics

General consequences of mass mixing between the ordinary Z boson and a relatively light Z_d boson, the "dark" Z, arising from a U(1)_d gauge symmetry, associated with a hidden sector such as dark matter, are examined. New effects beyond kinetic mixing are emphasized. Z-Z_d mixing introduces a new source of low energy parity violation well explored by possible future atomic parity violation and planned polarized electron scattering experiments. Rare K (B) meson decays into pi (K) l^+ l^- (l = e, mu) and pi (K) nu anti-nu are found to already place tight constraints on the size of Z-Z_d mixing. Those sensitivities can be further improved with future dedicated searches at K and B factories as well as binned studies of existing data. Z-Z_d mixing can also lead to the Higgs decay H -> Z Z_d, followed by Z -> l_1^+ l_1^- and Z_d -> l_2^+ l_2^- or "missing energy", providing a potential hidden sector discovery channel at the LHC. An illustrative realization of these effects in a 2 Higgs doublet model is presented.Comment: Version to appear in PR

Polarized Moller Scattering Asymmetries

The utility of polarized electron beams for precision electroweak studies is described. Parity violating Moller scattering asymmetries in e-e- --> e-e- are discussed. Effects of electroweak radiative corrections and the running sin^2(theta_W(Q^2)) are reviewed. The sensitivity of E158 (a fixed target e-e- experiment at SLAC) and future e-e- collider studies to ``new physics'' is briefly outlined.Comment: Updated Fig.

Michel decay spectrum for a muon bound to a nucleus

The spectrum of electrons from muons decaying in an atomic bound state is significantly modified by their interaction with the nucleus. Somewhat unexpectedly, its first measurement, at the Canadian laboratory TRIUMF, differed from basic theory. We show, using a combination of techniques developed in atomic, nuclear, and high-energy physics, that radiative corrections eliminate the discrepancy. In addition to solving that outstanding problem, our more precise predictions are potentially useful for interpreting future high-statistics muon experiments that aim to search for exotic interactions at $10^{-16}$ sensitivity.Comment: 6 pages, 4 figures, Alberta Thy 7-14 v2: Expanded discussion. Journal versio

SUSY-QCD Corrections to W±H∓W^{\pm}H^{\mp} Associated Production at the CERN Large Hadron Collider

We calculate the SUSY-QCD corrections to the inclusive total cross sections of the associated production processes $pp\to W^{\pm}H^{\mp}+X$ in the Minimal Supersymmetric Standard Model(MSSM) at the CERN Large Hadron Collider(LHC). The SUSY-QCD corrections can increase and decrease the total cross sections depending on the choice of the SUSY parameters. When $\mu<0$ the SUSY-QCD corrections increase the leading-order (LO) total cross sections significantly for large tan$\beta$ ($\sim 40$), which can exceed 10% and have the opposite sign with respect to the QCD and the SUSY-EW corrections, and thus cancel with them to some extent. Moreover, we also investigate the effects of the SUSY-QCD on the differential distribution of cross sections in transverse momentum $p_T$ and rapidity Y of W-boson, and the invariant mass $M_{W^+H^-}$.Comment: 24 pages, 10 figures; minor changes in references; two figures and the corresponding disccusions added; a version to appear in PR

Production of (τ+τ−)b(\tau^+\tau^-)_b in electron positron collisions

$(\tau^+\tau^-)_b$ is an atom of simple hydrogenlike structure similar to positronium $(e^+e^-)_b$ and $(\mu^+\mu^-)_b$. In this paper energy levels and decay widths of different decay channels of $(\tau^+\tau^-)_b$ are given. Cross section of production of this atomic system in $e^+e^-$ annihilation taking into account radiative corrections is calculated. According to our estimates 886 $(\tau^+\tau^-)_b$ atoms may be produced at BEPCII and 29 $(\tau^+\tau^-)_b$ atoms are produced at VEPP-4M under the present experimental conditions.Comment: 5 pages, submitted to Int. Jour. Mod. Phys.

Fermi Constants and ``New Physics''

Various precision determinations of the Fermi constant are compared. Included are muon and (leptonic) tau decays as well as indirect prescriptions employing \alpha, m_Z, m_W, \ssthwmzms, \Gamma(Z\to\ell^+\ell^-), and $\Gamma(Z \to \nu\bar \nu)$ as input. Their good agreement tests the standard model at the $\pm 0.1$ level and provides stringent constraints on new physics. That utility is illustrated for: heavy neutrino mixing, 2 Higgs doublet models, S, T, and U parameters and excited $W^{\ast^\pm}$ bosons (Kaluza-Klein excitations). For the last of those examples, m_{W^\ast}\gsims 2.9 TeV is found.Comment: 14 page

Dimuon production by laser-wakefield accelerated electrons

We analyze $\mu^+\mu^-$ pair production generated by high-energy electrons emerging from a laser-wakefield accelerator. The $\mu^+\mu^-$ pairs are created in a solid thick high-$Z$ target, following the electron accelerating plasma region. Numerical estimates are presented for electron beams obtained presently in the LBL TW laser experiment \cite{C2} and possible future developments. Reactions induced by the secondary bremsstrahlung photons dominate the dimuon production. According to our estimates, a 20 pC electron bunch with energy of 1 (10) GeV may create about 200 (6000) muon pairs. The produced $\mu^\pm$ can be used in studying various aspects of muon-related physics in table top installations. This may be considered as an important step towards the investigation of more complicated elementary processes induced by laser driven electrons.Comment: 14 pages, 5 figure

Muon decay in orbit spectra for muon-electron conversion experiments

We have determined in detail the electron spectrum in the decay of bound muons. These results are especially relevant for the upcoming muon-electron conversion experiments.Comment: submitted to Proceedings of the International Conference on Exotic Atoms and Related Topics (EXA 2011