1,131 research outputs found
B -> X_s gamma in supersymmetry: large contributions beyond the leading order
We discuss possible large contributions to B -> X_s gamma, which can occur at
the next-to-leading order in supersymmetric models. They can originate from
terms enhanced by tan(beta) factors, when the ratio between the two Higgs
vacuum expectation values is large, or by logarithm of M_{susy}/M_W, when the
supersymmetric particles are considerably heavier than the W boson. We give
compact formulae which include all potentially large higher-order
contributions. We find that tan(beta) terms at the next-to-leading order do not
only appear from the Hall-Rattazzi-Sarid effect (the modified relation between
the bottom mass and Yukawa coupling), but also from an analogous effect in the
top-quark Yukawa coupling. Finally, we show how next-to-leading order
corrections, in the large tan(beta) region, can significantly reduce the limit
on the charged-Higgs mass, even if supersymmetric particles are very heavy.Comment: 18 pages, 5 figs, extended discussion of light stop case, notational
improvement
QCD Corrections to Radiative B Decays in the MSSM with Minimal Flavor Violation
We compute the complete supersymmetric QCD corrections to the Wilson
coefficients of the magnetic and chromomagnetic operators, relevant in the
calculation of b -> s gamma decays, in the MSSM with Minimal Flavor Violation.
We investigate the numerical impact of the new results for different choices of
the MSSM parameters and of the scale where the quark and squark mass matrices
are assumed to be aligned. We find that the corrections can be important when
the superpartners are relatively light, and that they depend sizeably on the
scale of alignment. Finally, we discuss how our calculation can be employed
when the scale of alignment is far from the weak scale.Comment: 16 pages, 5 figures; v2: version to appear in Phys. Lett.
UV asymptotically free QED as a broken YM theory in the unitary gauge
We compute the -function of a YM theory, broken to , by
evaluating the coupling constant renormalization in the broken phase. We
perform the calculation in the unitary gauge where only physical particles
appear and the theory looks like a version of QED containing massive charged
spin 1 particles. We consider an on-shell scattering process and after
verifying that the non-renormalizable divergences which appear in the Green's
functions cancel in the expression of the amplitude, we show that the coupling
constant renormalization is entirely due to the photon self-energy as in QED.
However we get the expected asymptotic freedom and the physical charge
decreases logarithmically as a function of the symmetry breaking scale.Comment: 8 page
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
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
Constraints on the Higgs Boson Mass from Direct Searches and Precision Measurements
We combine, within the framework of the Standard Model, the results of Higgs
search experiments with the information coming from accurate theoretical
calculation and precision measurements to provide a probability density
function for the Higgs mass, from which all numbers of interest can be derived.
The expected value is 170 GeV, with an expectation uncertainty, quantified by
the standard deviation of the distribution, of about 80 GeV. The median of the
distribution is 150 GeV, while 75 % of the probability is concentrated in the
region GeV. The 95 % probability upper limit comes out to be
around 300 GeV.Comment: 32 pages, 5 figure
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
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