708 research outputs found
Two-loop electroweak corrections at high energies
We discuss two-loop leading and angular-dependent next-to-leading logarithmic
electroweak virtual corrections to arbitrary processes at energies above the
electroweak scale. The relevant Feynman diagrams involving soft-collinear gauge
bosons gamma, Z, W, have been evaluated in eikonal approximation. We present
results obtained from the analytic evaluation of massive loop integrals. To
isolate mass singularities we used the Sudakov method and alternatively the
sector decomposition method in the Feynman-parameter representation.Comment: 5 pages. Talk presented by S.P. at the International Symposium on
Radiative Corrections RADCOR 2002, September 8-13, Kloster Banz, Germany. To
appear in the proceeding
Logarithmic electroweak corrections to hadronic Z+1 jet production at large transverse momentum
We consider hadronic production of a Z boson in association with a jet and
study one- and two-loop electroweak logarithmic corrections in the region of
high Z-boson transverse momentum, p_T >> M_Z, including leading and
next-to-leading logarithms. Numerical results for the LHC and Tevatron
colliders are presented. At the LHC these corrections amount to tens of per
cent and will be important for interpretation of the measurements.Comment: 10 pages, 4 figures; one reference added; minor improvements.
Accepted for publication in Phys. Lett.
Two-loop electroweak angular-dependent logarithms at high energies
We present results on the two-loop leading and angular-dependent
next-to-leading logarithmic virtual corrections to arbitrary processes at
energies above the electroweak scale. In the `t Hooft-Feynman gauge the
relevant Feynman diagrams involving soft and collinear gauge bosons \gamma, Z,
W^\pm coupling to external legs are evaluated in the eikonal approximation in
the region where all kinematical invariants are much larger than the
electroweak scale. The logarithmic mass singularities are extracted from
massive multi-scale loop integrals using the Sudakov method and alternatively
the sector-decomposition method in the Feynman-parameter representation. The
derivations are performed within the spontaneously broken phase of the
electroweak theory, and the two-loop results are in agreement with the
exponentiation prescriptions that have been proposed in the literature based on
a symmetric SU(2) x U(1) theory matched with QED at the electroweak scale.Comment: 31 pages, LaTe
Next-to-leading mass singularities in two-loop electroweak singlet form factors
We consider virtual electroweak corrections to the form factors for massless
chiral fermions coupling to an SU(2)xU(1) singlet gauge boson in the asymptotic
region , where the invariant mass of the external gauge boson
is much higher than the weak-boson mass scale. Using the sector-decomposition
method we compute mass singularities, which arise as logarithms of
and poles in dimensions, to one- and two-loop
next-to-leading logarithmic accuracy. In this approximation we include all
contributions of order , with
and . We find that the electroweak two-loop leading- and
next-to-leading-logarithmic mass singularities can be written in a form that
corresponds to a generalization of Catani's formula for massless QCD.Comment: 38 pages. Minor modifications. Version published in Nucl.Phys.
An algorithm for the high-energy expansion of multi-loop diagrams to next-to-leading logarithmic accuracy
We present an algorithm to compute arbitrary multi-loop massive Feynman
diagrams in the region where the typical energy scale \sqrt{s} is much larger
than the typical mass scale M, i.e. s>>M^2, while various different energy and
mass parameters may be present. In this region we perform an asymptotic
expansion and, using sector decomposition, we extract the leading contributions
resulting from ultraviolet and mass singularities, which consist of large
logarithms log(s/M^2) and 1/\epsilon poles in D=4-2\epsilon dimensions. To
next-to-leading accuracy, at L loops all terms of the form \alpha^L
\epsilon^{-k} log^j(s/M^2) with j+k=2L and j+k=2L-1 are taken into account.
This algorithm permits, in particular, to compute higher-order next-to-leading
logarithmic electroweak corrections for processes involving various kinematical
invariants of the order of hundreds of GeV and masses M_W \sim M_Z \sim M_H
\sim M_t of the order of the electroweak scale, in the approximation where the
masses of the light fermions are neglected.Comment: 30 pages, LaTeX. The complete paper is also available via the www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints
Exact Differential O(alpha**2) Results for Hard Bremsstrahlung in e+e- Annihilation to 2f At and Beyond LEP2 Energies
We present the exact O(alpha) correction to the process e+ e- -> f f-bar +
gamma, f neq e, for ISR oplus FSR at and beyond LEP2 energies. We give explicit
formulas for the completely differential cross section. As an important
application, we compute the size of the respective sub-leading corrections of
O(alpha L) to the f f-bar cross section, where L is the respective big
logarithm in the renormalization group sense so that it is identifiable as L =
ln |s|/m_e^2 when s is the squared e+e- cms energy. Comparisons are made with
the available literature. We show explicitly that our results have the correct
infrared limit, as a cross-check. Some comments are made about the
implementation of our results in the framework of the Monte Carlo event
generator KK MC.Comment: 26 pages, 5 figs.;improved discussion, figs. and
definitions;corrected misprint
Light Higgs production at the Compton Collider
We have studied the production of a light Higgs boson with a mass of 120 GeV
in photon-photon collisions at a Compton collider. The event generator for the
backgrounds to a Higgs signal due to bbbar and ccbar heavy quark pair
production in polarized gamma-gamma collisions is based on a complete
next-to-leading order (NLO) perturbative QCD calculation. For J_z=0 the large
double-logarithmic corrections up to four loops are also included. It is shown
that the two-photon width of the Higgs boson can be measured with high
statistical accuracy of about 2 % for integrated gamma-gamma luminosity in the
hard part of the spectrum of 40 fb**-1. As a result the total Higgs boson width
can be calculated in a model independent way to an accuracy of about 14 %Comment: submitted to the proceedings of the International Workshop on Linear
Colliders (LCWS99) at Sitges, Spain, 28 April - 5 May 199
Two-loop electroweak next-to-leading logarithmic corrections to massless fermionic processes
We consider two-loop leading and next-to-leading logarithmic virtual
corrections to arbitrary processes with external massless fermions in the
electroweak Standard Model at energies well above the electroweak scale. Using
the sector-decomposition method and alternatively the strategy of regions we
calculate the mass singularities that arise as logarithms of Q^2/MW^2, where Q
is the energy scale of the considered process, and 1/\epsilon poles in
D=4-2\epsilon dimensions, to one- and two-loop next-to-leading logarithmic
accuracy. The derivations are performed within the complete electroweak theory
with spontaneous symmetry breaking. Our results indicate a close analogy
between the form of two-loop electroweak logarithmic corrections and the
singular structure of scattering amplitudes in massless QCD. We find agreement
with the resummation prescriptions that have been proposed in the literature
based on a symmetric SU(2) \times U(1) theory matched with QED at the
electroweak scale and provide new next-to-leading contributions proportional to
ln(MZ^2/MW^2).Comment: 63 pages, LaTeX, references updated, some typos corrected, version to
appear in Nucl. Phys.
Charged Higgs Production in the 1 TeV Domain as a Probe of Supersymmetric Models
We consider the production, at future lepton colliders, of charged Higgs
pairs in supersymmetric models. Assuming a relatively light SUSY scenario, and
working in the MSSM, we show that, for c.m. energies in the one TeV range, a
one-loop logarithmic Sudakov expansion that includes an "effective" next-to
subleading order term is adequate to the expected level of experimental
accuracy. We consider then the coefficient of the linear (subleading) SUSY
Sudakov logarithm and the SUSY next to subleading term of the expansion and
show that their dependence on the supersymmetric parameters of the model is
drastically different. In particular the coefficient of the SUSY logarithm is
only dependent on while the next to subleading term depends on a
larger set of SUSY parameters. This would allow to extract from the data
separate informations and tests of the model.Comment: 18 pages and 13 figures e-mail: [email protected]
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