We present a study of the effective action approach to incorporate higher-order effects in
e
+
e
−→
n fermions. In its minimal version, the effective action approach is found to exhibit problems with ...unitarity and high-energy behaviour. We identify the origin of these problems by investigating the zero-mode solutions of the Ward identities. A numerical analysis of the importance of the zero-mode solutions is presented for four-fermion production processes.
A fully massive Monte Carlo program to compute all four-fermion processes in
e
+e
−
collisions, including Higgs boson production, is presented. Leading higher order effects are discussed and included.
In this paper, we compute the Standard Model polarized amplitudes and cross sections of the processes
γν → γγν, γγ → γν
ν
and
ν
ν → γγγ
, for centre-of-mass energies ω within the range of validity of ...the Fermi theory. By using a large electron-mass expansion of the exact result, we also derive the first correction term to the effective, low-energy (
ω <
m
e
) formula for
γν →
γγν. Finally, we discuss possible astrophysical implications of our results and provide simple fits to the exact expressions.
We give an introduction to several regularization schemes that deal with ultraviolet and infrared singularities appearing in higher-order computations in quantum field theories. Comparing the ...computation of simple quantities in the various schemes, we point out similarities and differences between them.
We investigate in this work the leading contributions of the MSSM with
R-parity violation and of Left–Right models to the low-energy five-leg photon–neutrino processes. We discuss the results and ...compare them to the Standard Model ones.
A study is made of the feasibility of maximum likelihood fits to determine
M
W
and triple gauge boson couplings using only those experimental kinematical variables that are well measured. A ...computational tool to calculate theoretical probabilities for those kinematical variables is discussed and then applied to samples of unweighted events produced by an event generator. Detailed results on the
M
W
determination for semileptonic final states in
W-pair production show the feasibility of the method. For TGCs one result is presented as an illustration.
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