1,165 research outputs found
Topics in Electroweak Physics
We briefly discuss five topics in Precision Electroweak Physics: i) the
recently proposed Effective Scheme of Renormalization, ii) evidence for
electroweak bosonic corrections derived from the radiative correction
Delta_r_eff, iii) an approach to estimate the scale of new physics in a
hypothetical Higgs-less scenario, iv) simple and accurate formulae for s^2_eff,
M_W, Gamma_l, and their physical applications, v) a recent proposal concerning
the field renormalization constant for unstable particles.Comment: 5 pages, talk presented at the International Symposium Radcor 2002,
September 8-13, Kloster Banz, German
The electroweak form factor \hat{\kappa}(q^2) and the running of \sin^2 \hat{\theta}_W
Gauge independent form factors \rho^(e; e) and \hat{\kappa}^(e; e)(q^2) for
Moller scattering at s << m_W^2 are derived. It is pointed out that
\hat{\kappa}^(e; e) is very different from its counterparts in other processes.
The relation between the effective parameter \hat{\kappa}^(e; e)(q^2,\mu)
\sin^2 \hat{\theta}_W(\mu) and \sin^2 \theta_eff is derived in a
scale-independent manner. A gauge and process-independent running parameter
\sin^2 \hat{\theta}_W (q^2), based on the pinch-technique self-energy a_{\gamma
Z} (q^2), is discussed for all q^2 values. At q^2=0 it absorbs very accurately
the Czarnecki-Marciano calculation of the Moller scattering asymmetry at low s
values, and at q^2 = m^2_Z it is rather close to \sin^2 \theta_eff. The q^2
dependence of \sin^2 \hat{\theta}_W (q^2) is displayed in the space and
time-like domains.Comment: A new paragraph has been inserted at the beginning of the discussion
in Section
Two-loop electroweak top corrections: are they under control?
The assumption that two-loop top corrections are well approximated by the
contribution is investigated. It is shown that in the case of
the ratio neutral-to-charged current amplitudes at zero momentum transfer the
terms are numerically comparable to the
contribution for realistic values of the top mass. An estimate of the
theoretical error due to unknown two-loop top effect is presented for a few
observables of LEP interest.Comment: 13 pages, LaTeX using equations, doublespace, cite macros. Hard
copies of the paper including one figure are available from
[email protected]
Production of Long-Lived Sleptons at LHC
We analyse the MSSM parameter space and discuss the narrow band near the
so-called co-annihilation region where sleptons may be long-lived particles.
This region is consistent with the WMAP restrictions on the Dark matter and
depends on the value of . In this region staus are long-lived and
may go through the detector. Due to a relatively small mass (150 850
GeV) their production cross-section at LHC may reach a few % pb.Comment: LaTex, 8 pages, 6 eps figure
Fermion Virtual Effects in Cross Section
We analyse the contribution of new heavy virtual fermions to the cross section. We find that there exists a relevant
interplay between trilinear and bilinear oblique corrections. The result
strongly depends on the chiral or vector--like nature of the new fermions. As
for the chiral case we consider sequential fermions: one obtains substantial
deviation from the Standard model prediction, making the effect possibly
detectable at or GeV linear colliders. As an example for
the vector--like case we take a SUSY extension with heavy charginos and
neutralinos: due to cancellation, the final effect turns out to be negligible.Comment: uuencoded, gz-compressed, tar-ed file. 8 pages, 4 EPS figures, uses
EPSFIG.ST
The Indirect Limit on the Standard Model Higgs Boson Mass from the Precision FERMILAB, LEP and SLD Data
Standard Model fits are performed on the most recent leptonic and b quark Z
decay data from LEP and SLD, and FERMILAB data on top quark production, to
obtain and . Poor fits are obtained, with confidence levels
2%. Removing the b quark data improves markedly the quality of the fits and
reduces the 95% CL upper limit on by 50 GeV.Comment: 6 pages 3 tables i figur
On the NLO QCD corrections to the production of the heaviest neutral Higgs scalar in the MSSM
We present a calculation of the two-loop top-stop-gluino contributions to
Higgs production via gluon fusion in the MSSM. By means of an asymptotic
expansion in the heavy particle masses, we obtain explicit and compact analytic
formulae that are valid when the Higgs and the top quark are lighter than stops
and gluino, without assuming a specific hierarchy between the Higgs mass and
the top mass. Being applicable to the heaviest Higgs scalar in a significant
region of the MSSM parameter space, our results complement earlier ones
obtained with a Taylor expansion in the Higgs mass, and can be easily
implemented in computer codes to provide an efficient and accurate
determination of the Higgs production cross section.Comment: 18 pages, 4 figure
Corrections to Quark Asymmetries at LEP
The most precise measurement of the weak mixing angle sin^2(theta) at LEP is
from the forward-backward asymmetry e+e- --> bbbar at the Z-pole. In this note
the QED and electroweak radiative corrections to obtain the pole asymmetry from
the measured asymmetry for b- and c-quarks have been calculated using ZFITTER,
which has been amended to allow a consistent treatment of partial two-loop
corrections for the b-quark final asymmetries.
A total correction of dAfbb=0.0019+/-0.0002 and dAfbc=0.0064+/-0.0001 has
been found, where the remaining theoretical uncertainty is much too small to
explain the apparent discrepancy between sin^2(theta) obtained from Afbb and
from the left-right asymmetry at SLD
On the connection between the pinch technique and the background field method
The connection between the pinch technique and the background field method is
further explored. We show by explicit calculations that the application of the
pinch technique in the framework of the background field method gives rise to
exactly the same results as in the linear renormalizable gauges. The general
method for extending the pinch technique to the case of Green's functions with
off-shell fermions as incoming particles is presented. As an example, the
one-loop gauge independent quark self-energy is constructed. We briefly discuss
the possibility that the gluonic Green's functions, obtained by either method,
correspond to physical quantities.Comment: 13 pages and 3 figures, all included in a uuencoded file, to appear
in Physical Review
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