1,721,045 research outputs found
CURRENT-ALGEBRA APPROACH TO HEAVY TOP EFFECTS IN Z-]B+(B)OVER-BAR
No full textThe O(alpham(t)2/m(W)2) and O(alpha(s)m(t)2/m(W)2) corrections to the partial decay width GAMMA(Z --> b + bBAR) are computed using the cur-rent algebra formulation of radiative corrections. This framework allows one to easily enforce the relevant Ward identity that greatly simplifies the calculations. As a result, the one-loop O(alpham(t)2/m(W)2) contribution is computed through the investigation of only two convergent diagrams. The computation of the QCD corrections to the one-loop O(alpham(t)2/m(W)2) term involves fewer diagrams than in the standard approach. In particular, the number of infrared divergent contributions is reduced. The calculation is performed in the dimensional regularization scheme and no term more divergent than 1/(n - 4) is found. Our result confirms the screening of the one-loop top mass effect recently found by Fleischer et al
Where is the Higgs?
No full textI discuss the theoretical uncertainties in the indirect Higgs mass determination. I present the probability density function for the Higgs mass obtained by combining the information from precision measurements with the results from the direct search experiments carried out at LEP. The probability that the Higgs weights less than 116 GeV comes out to be around 35% while the 95% upper limit is located around 210-230 GeV
Accurate prediction of electroweak observables and impact on the Higgs mass bound
No full textI discuss the importance of the O(g(4)m(t)(2)/M-w(2)) corrections to the effective electroweak angle and M-w in the indirect determination of the Higgs mass. I emphasize the role of a very precise M-w measurement on the M-H estimate
Two-loop electroweak top corrections
No full textThe importance of two-loop top corrections of \gmud\
is discussed. It is shown that in the case
of the ratio neutral-to-charged current amplitudes at zero momentum transfer
these terms are numerically comparable to the
\gmuq\ contribution. An estimate of the theoretical error due to
unknown two-loop top effect for few LEP observable is derived through
a na\"\i ve extrapolation of this result
Two-loop electroweak corrections to Higgs production at hadron colliders
No full textWe compute the two-loop electroweak corrections due to the top quark to the gluon fusion production cross section of an intermediate-mass Higgs boson. This result, together with the previously known contribution due to the light fermions, allows a complete determination of the two-loop electroweak corrections to this production cross section. For Higgs mass values above 120 GeV the top corrections have opposite sign of the light fermlions contribution, however they are always smaller in size reaching at most 15% of the latter. The total electroweak corrections to the gluon fusion production cross section for 115 GeV less than or similar to m(H) less than or similar to 2m(W) range from 5% to 8% of the lowest order term. (C) 2004 Published by Elsevier B.V
Final Meeting of the Network Particle Physics Phenomenology at High Energy Colliders
No full textWork on electroweak precision calculations and event generators for electroweak physics studies at current and future colliders is summarize
Two-loop renormalization of the electric charge in the standard model
No full textWe discuss the renormalization of the electric charge at the two-loop level in the Standard Model of the electroweak interactions. We explicitly calculate the expression of the complete on-shell two-loop counterterm using the Background Field Method and discuss the advantages of this computational approach. We consider the related quantity , defined in the \ms renormalization scheme and present numerical results for different values of the scale . We find that the full 2-loop electroweak corrections contribute more than 10 parts in units to the \Delta \hat\alpha (\mz^2) parameter, obtaining \hat\alpha^{-1}(\mz)= 128.12 \pm 0.05 for \Delta\alpha_{had}(\mz^2) =0.027572 \pm 0.000359
COMPARATIVE-ANALYSIS OF ELECTROWEAK CORRECTIONS TO E++E--]F+FBAR IN ON-SHELL AND MSBAR FRAMEWORKS
No full textA novel analysis of the electroweak radiative corrections to e+ + e- --> f + fBAR, carried out in three different schemes, is presented. The first parametrizes the corrections in terms of G-mu, m(Z) and sin2-theta-W = 1 - m(W)2/m(Z)2 and employs recently proposed renormalized self-energies satisfying simple renormalization conditions. The second is parametrized in terms of m(Z) and the MSBAR couplings e2(m(Z)) and sin2-theta-W(m(Z)). The third introduces an effective gauge-invariant angle sin2-theta-W(eff). Compact formulae to evaluate the differential cross sections, partial widths and asymmetries are given. A numerical comparison is made of various predictions obtained on the basis of the first two schemes as well as on Hollik's formulation
GAUGE-INVARIANT SELF-ENERGIES AND VERTEX PARTS OF THE STANDARD MODEL IN THE PINCH TECHNIQUE FRAMEWORK
No full textThe pinch technique (PT) is applied to obtain one-loop gauge-invariant self-energies, vertex and box diagrams in the electroweak sector of the standard model. Describing the interaction of vector bosons with fermions in terms of current correlation functions, we propose to directly identify the pinch parts with the contributions of equal-time commutators in the relevant Ward identities. We argue that this procedure isolates the parts of vertex and box diagrams that are independent of strong interaction dynamics. The formalism promptly leads us to very simple gauge-invariant transverse self-energies, as well as vertex and box diagrams relevant to four-fermion processes mediated by charged and neutral currents. They automatically possess very desirable theoretical properties. We then apply the PT to e+e----> W+W- and explicitly demonstrate that the propagatorlike pinch parts are absorbed in the same self-energies encountered in the four-fermion case. The PT self-energies and vertex corrections are compared with those obtained in other formulations. A number of applications are discussed, including the possibility of a gauge-invariant on-shell definition of the vector-boson mass
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