1,542 research outputs found
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
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
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
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-
Dimuon production by laser-wakefield accelerated electrons
We analyze pair production generated by high-energy electrons
emerging from a laser-wakefield accelerator. The pairs are created
in a solid thick high- 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 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
Flavour Mixing, Gauge Invariance and Wave-function Renormalisation
We clarify some aspects of the LSZ formalism and wave function
renormalisation for unstable particles in the presence of electroweak
interactions when mixing and CP violation are considered. We also analyse the
renormalisation of the CKM mixing matrix which is closely related to wave
function renormalisation. We critically review earlier attempts to define a set
of "on-shell" wave function renormalisation constants. With the aid of an
extensive use of the Nielsen identities complemented by explicit calculations
we corroborate that the counter term for the CKM mixing matrix must be
explicitly gauge independent and demonstrate that the commonly used
prescription for the wave function renormalisation constants leads to gauge
parameter dependent amplitudes, even if the CKM counter term is gauge invariant
as required. We show that a proper LSZ-compliant prescription leads to gauge
independent amplitudes. The resulting wave function renormalisation constants
necessarily possess absorptive parts, but we verify that they comply with the
expected requirements concerning CP and CPT. The results obtained using this
prescription are different (even at the level of the modulus squared of the
amplitude) from the ones neglecting the absorptive parts in the case of top
decay. The difference is numerically relevant.Comment: 19 pages, plain latex, one ps figur
Electroweak radiative corrections to deep-inelastic neutrino scattering - implications for NuTeV ?
We calculate the O(alpha) electroweak corrections to charged- and
neutral-current deep-inelastic neutrino scattering off an isoscalar target. The
full one-loop-corrected cross sections, including hard photonic corrections,
are evaluated and compared to an earlier result which was used in the NuTeV
analysis. In particular, we compare results that differ in input-parameter
scheme, treatment of real photon radiation and factorization scheme. The
associated shifts in the theoretical prediction for the ratio of neutral- and
charged-current cross sections can be larger than the experimental accuracy of
the NuTeV result.Comment: 19 pages late
The Hidden Quantum Groups Symmetry of Super-renormalizable Gravity
In this paper we consider the relation between the super-renormalizable
theories of quantum gravity (SRQG) studied in [arXiv:1110.5249v2,
arXiv:1202.0008] and an underlying non-commutativity of spacetime. For one
particular super-renormalizable theory we show that at linear level (quadratic
in the Lagrangian) the propagator of the theory is the same we obtain starting
from a theory of gravity endowed with {\theta}-Poincar\'e quantum groups of
symmetry. Such a theory is over the so called {\theta}-Minkowski non-commuative
spacetime. We shed new light on this link and show that among the theories
considered in [arXiv:1110.5249v2, arXiv:1202.0008], there exist only one
non-local and Lorentz invariant super-renormalizable theory of quantum gravity
that can be described in terms of a quantum group symmetry structure. We also
emphasize contact with pre-existent works in the literature and discuss
preservation of the equivalence principle in our framework.Comment: 10 page
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
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