982 research outputs found
Supersymmetric Sudakov corrections
For superpartner masses not much heavier than the weak scale ,
large logarithmic corrections of the Sudakov type arise at TeV energies. In
this paper we discuss the general structure of electroweak supersymmetric
(susy) Sudakov corrections in the framework of the infrared evolution equation
method. We discuss Yukawa sector Ward-identities which lead to the
exponentiation of the subleading (SL) logarithmic Yukawa enhanced Sudakov
corrections in both the Standard Model (SM) as well as in softly broken
supersymmetric extensions. The results are given to SL accuracy to all orders
in perturbation theory for arbitrary external lines in the ``light'' susy-mass
scenario. The susy-QCD limit for virtual corrections is presented.
Phenomenological applications regarding the precise determination of the
important parameter through virtual corrections are discussed
which are independent of the soft susy breaking mechanism to sub-subleading
accuracy to all orders.Comment: 5 pages, 2 figures, contribution to RADCOR02/Loops and Legs 200
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
Reliability of a high energy one-loop expansion of e+e- --> W+W- in the SM and in the MSSM
We compare the logarithmic Sudakov expansions of the process e+e- --> W+W- in
the one-loop approximation and in the resummed version, to subleading order
accuracy, in the SM case and in a light SUSY scenario for the MSSM. We show
that the two expansions are essentially identical below 1 TeV, but differ
drastically at higher (2,3 TeV) center of mass energies. Starting from these
conclusions, we argue that a complete one-loop calculation in the energy region
below 1 TeV does not seem to need extra two-loop corrections, in spite of the
relatively large size of the one-loop effects.Comment: 15 pages, 1 Encapsulated PostScript figur
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]
SUSY Scalar Production in the Electroweak Sudakov Regime of Lepton Colliders
We consider the production of SUSY scalar pairs at lepton colliders, for c.m.
energies much larger than the mass of the heaviest SUSY (real or virtual)
particle involved in the process. In that energy regime, we derive the leading
and subleading terms of the electroweak Sudakov logarithms in the MSSM, first
working at one loop with physical states and then resumming to all orders with
asymptotic expansions. We show that the first order of the resummed expression
reproduces the physical one loop approximation, and compute systematically the
possible effects on various observables both at one loop and to all orders. We
discuss the regimes and the processes where the one loop approximation can or
cannot be trusted, working in an energy range between 1 TeV and 4 TeV under a
"light" SUSY mass assumption. As a byproduct of our analysis, we propose a
determination of the MSSM parameter tan(beta) showing how a relative accuracy
of about 25 percent can be easily achieved in the region tan(beta)>14, under
reasonable experimental assumptions.Comment: 35 pages and 15 figures e-mail: [email protected]
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
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