2,019 research outputs found
Recent developments in rare kaon decays
We discuss issues in rare and radiative kaon decays. The interest is to
extract useful short-distance information and uncover underlying dynamics. We
emphasize channels where either we can understand non-perturbative aspects of
QCD or there is a chance to test the Standard Model.Comment: Invited minireview for Modern Physics Letters A (MPLA), 15 pages, 9
figures, usepackages epsf,colo
Electroweak Radiative Corrections To Polarized M{\o}ller Scattering Asymmetries
One loop electroweak radiative corrections to left-right parity violating
M{\o}ller scattering () asymmetries are presented. They
reduce the standard model (tree level) prediction by 40 \% 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
by in running from 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
Rare kaon decays in SUSY with non-universal A terms
We study the rare kaon decays in the framework of general SUSY models. Unlike
the results in the literature, we find the contributions from the gluino
exchange to the branching ratio of can reach the
central value () of the new E787 data while the
predicted value of standard model is less than . We also find that
the same effects also enhance the decays of ,
and .Comment: 9 pages, references added, revised version to appear in J. Phys.
K_L \ra \mu^\pm e^\mp \nu \overline{\nu} as background to K_L \ra \mu^\pm e^\mp
We consider the process K_L \ra \mu^\pm e^\mp \nu \overline{\nu} at next to
leading order in chiral perturbation theory. This process occurs in the
standard model at second order in the weak interaction and constitutes a
potential background in searches for new physics through the modes K_L \ra
\mu^\pm e^\mp. We find that the same cut, ~MeV, used to remove
the sequential decays K_{l3}\ra \pi_{l2} pushes the B(K_L \ra \mu^\pm e^\mp
\nu \overline{\nu}) to the level, effectively removing it as a
background.Comment: 8 pages, LaTeX, 1 figure appended as postscript file after
\end{document}. Fermilab-Pub-93/024-
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 as input. Their good agreement tests the standard model at the
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 bosons (Kaluza-Klein
excitations). For the last of those examples, m_{W^\ast}\gsims 2.9 TeV is
found.Comment: 14 page
Model-dependent radiative corrections to tau- -> pi- pi0 nu revisited
The long-distance electromagnetic radiative corrections to tau- -> pi- pi0 nu
are re-evaluated. A meson dominance model is used to describe the emission of
real photons in this decay. Results obtained for the hadronic spectrum and the
decay rate in photon inclusive reactions are compared with previous
calculations based on the chiral resonance theory. Independent tests in tau ->
pi pi nu gamma that can help to validate the predictions of one of the two
models are briefly discussed.Comment: 5 pages, 4 figures, talk given by GLC at the 9th International
Workshop on Tau Lepton Physics, Pisa (Italy), september 200
Electroweak higher-order effects and theoretical uncertainties in deep-inelastic neutrino scattering
A previous calculation of electroweak O(alpha) corrections to deep-inelastic
neutrino scattering, as e.g. measured by NuTeV and NOMAD, is supplemented by
higher-order effects. In detail, we take into account universal two-loop
effects from \Delta\alpha and \Delta\rho as well as higher-order final-state
photon radiation off muons in the structure function approach. Moreover, we
make use of the recently released O(alpha)-improved parton distributions
MRST2004QED and identify the relevant QED factorization scheme, which is DIS
like. As a technical byproduct, we describe slicing and subtraction techniques
for an efficient calculation of a new type of real corrections that are induced
by the generated photon distribution. A numerical discussion of the
higher-order effects suggests that the remaining theoretical uncertainty from
unknown electroweak corrections is dominated by non-universal two-loop effects
and is of the order 0.0003 when translated into a shift in
sin^2\theta_W=1-MW^2/MZ^2. The O(alpha) corrections implicitly included in the
parton distributions lead to a shift of about 0.0004.Comment: 25 pages, latex, 8 postscript figure
Evidence for Bosonic Electroweak Corrections in the Standard Model
We present strong indirect evidence for the contribution of bosonic
electroweak corrections in the Standard Model. Although important conceptually,
these corrections give subleading contributions in current high energy
experiments, and it was previously thought that they are difficult to detect.
We also discuss the separate contribution of the Higgs boson.Comment: 9 pages (LaTeX + 3 PS figures, needs psfig
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