158 research outputs found
Renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking
The renormalization of supersymmetric Yang-Mills theories with soft
supersymmetry breaking is presented using spurion fields for introducing the
breaking terms. It is proven that renormalization of the fields and parameters
in the classical action yields precisely the correct counterterms to cancel all
divergences. In the course of the construction of higher orders additional
independent parameters appear, but they can be shown to be irrelevant in
physics respects. Thus, the only parameters with influence on physical
amplitudes are the supersymmetric and the well-known soft breaking parameters.Comment: 29 pages, published in The European Physical Journal
One-loop MSSM Contribution to the Weak Magnetic Dipole Moments of Heavy Fermions
The MSSM predictions at the one-loop level for the weak-magnetic dipole
moments of the lepton and the quark are analysed. The entire
supersymmetric parameter space is scannedwith the usual GUT constraint and
common squark and slepton mass parameters. The real part of is
dominated by the chargino contribution, being the same order as the SM one or
even larger in the high region whereas the imaginary part, due to
Higgs boson diagrams, is negligible comparedto the SM value. The real part
of is controlled mainly by charginos andalso by gluinos, when the mixing
in the bottom squark sector is large, to yield, for high , a
contribution one order of magnitude largerthan the pure electroweak SM value
but a factor five smaller than the standard QCD contribution. The imaginary
part of is the same order as in the SM.Comment: 14 pages, Latex, 4 eps and 1 ps figure, needs epsfig.sty. Minor
changes, new references added. To be published in Phys. Lett.
Computation of in FDH and DRED: renormalization, operator mixing, and explicit two-loop results
The amplitude relevant for Higgs production via gluon fusion is
computed in the four-dimensional helicity scheme (FDH) and in dimensional
reduction (DRED) at the two-loop level. The required renormalization is
developed and described in detail, including the treatment of evanescent
-scalar contributions. In FDH and DRED there are additional
dimension-5 operators generating the vertices, where can either be
a gluon or an -scalar. An appropriate operator basis is given and the
operator mixing through renormalization is described. The results of the
present paper provide building blocks for further computations, and they allow
to complete the study of the infrared divergence structure of two-loop
amplitudes in FDH and DRED
SCET approach to regularization-scheme dependence of QCD amplitudes
We investigate the regularization-scheme dependence of scattering amplitudes
in massless QCD and find that the four-dimensional helicity scheme (FDH) and
dimensional reduction (DRED) are consistent at least up to NNLO in the
perturbative expansion if renormalization is done appropriately. Scheme
dependence is shown to be deeply linked to the structure of UV and IR
singularities. We use jet and soft functions defined in soft-collinear
effective theory (SCET) to efficiently extract the relevant anomalous
dimensions in the different schemes. This result allows us to construct
transition rules for scattering amplitudes between different schemes (CDR, HV,
FDH, DRED) up to NNLO in massless QCD. We also show by explicit calculation
that the hard, soft and jet functions in SCET are regularization-scheme
independent.Comment: 46 pages, 6 figure
Factorization and regularization by dimensional reduction
Since an old observation by Beenakker et al., the evaluation of QCD processes in dimensional reduction has repeatedly led to terms that seem to violate the QCD factorization theorem. We reconsider the example of the process and show that the factorization problem can be completely resolved. A natural interpretation of the seemingly non-factorizing terms is found, and they are rewritten in a systematic and factorized form. The key to the solution is that the D- and (4−D)-dimensional parts of the 4-dimensional gluon have to be regarded as independent partons
Photonic SUSY Two-Loop Corrections to the Muon Magnetic Moment
Photonic SUSY two-loop corrections to the muon magnetic moment are
contributions from diagrams where an additional photon loop is attached to a
SUSY one-loop diagram. These photonic corrections are evaluated exactly,
extending a leading-log calculation by Degrassi and Giudice. Compact analytical
expressions are provided and the numerical behaviour is discussed. The photonic
corrections reduce the SUSY one-loop result by 7...9%. The new terms are
typically around ten times smaller than the leading logarithms, but they can be
larger and have either sign in cases with large SUSY mass splittings. We also
provide details on renormalization and regularization and on how to incorporate
the photonic corrections into a full SUSY two-loop calculation.Comment: 25 page
Status of the Fermilab Muon (g-2) Experiment
The New Muon Collaboration at Fermilab has proposed to measure the
anomalous magnetic moment of the muon, , a factor of four better than
was done in E821 at the Brookhaven AGS, which obtained ppm. The last digit of is changed
from the published value owing to a new value of the ratio of the
muon-to-proton magnetic moment that has become available. At present there
appears to be a difference between the Standard-Model value and the measured
value, at the standard deviation level when electron-positron
annihilation data are used to determine the lowest-order hadronic piece of the
Standard Model contribution. The improved experiment, along with further
advances in the determination of the hadronic contribution, should clarify this
difference. Because of its ability to constrain the interpretation of
discoveries made at the LHC, the improved measurement will be of significant
value, whatever discoveries may come from the LHC.Comment: Proceedings of the PhiPsi09, Oct. 13-16, 2009, Beijing, China, 4
pages 2 figures. Version 2 includes Fermilab report number, minor corrections
and one additional referenc
Precision Observables in the MSSM: W mass and the muon magnetic moment
The precision observables M_W and g-2 of the muon are discussed in the
framework of the MSSM. Recent progress in the evaluation of the theoretical
predictions is described, and the MSSM predictions are compared with the SM
predictions and the experimental values.Comment: 4 pages, 2 figures. To appear in Proceedings of SUSY06, the 14th
International Conference on Supersymmetry and the Unification of Fundamental
Interactions, UC Irvine, California, 12-17 June 200
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