816 research outputs found
Next-to-leading order corrections to Bhabha scattering in renormalization group approach (I). Soft and virtual photonic contributions
Soft and virtual loop photonic contributions to the second order
next-to-leading QED radiative corrections to Bhabha scattering are calculated
with help of the renormalization group approach. The results are in agreement
with earlier calculations, where other methods were used. Scale dependence and
the present theoretical accuracy of Bhabha cross section description are
discussed.Comment: 12 pages, 10 Figures, elsart.cl
Observations on the radiative corrections to pion beta-decay
We find that, in the local V-A theory, the radiative corrections to pion
beta-decay involving the weak vector current, when evaluated in the current
algebra (CA) formulation in which quarks are the fundamental underlying fields,
show a small difference with the more elementary calculations based directly on
the pion fields. We show that this difference arises from a specific
short-distance effect that depends on the algebra satisfied by the weak and
electromagnetic currents. On the other hand, we present a simple theoretical
argument that concludes that this difference does not occur when the CA
formulation is compared with the chiral perturbation theory (chiPT) approach.
Comparisons with previous studies, and with a more recent calculation based on
chiPT, are included. We also briefly review the important differences between
the results in the local V-A theory and the Standard Model.Comment: 5 pages, 1 figure. V2: two paragraphs have been added in Section III.
Final version on PR
Analytic Invariant Charge in QCD
This paper gives an overview of recently developed model for the QCD analytic
invariant charge. Its underlying idea is to bring the analyticity condition,
which follows from the general principles of local Quantum Field Theory, in
perturbative approach to renormalization group (RG) method. The concrete
realization of the latter consists in explicit imposition of analyticity
requirement on the perturbative expansion of function for the strong
running coupling, with subsequent solution of the corresponding RG equation. In
turn, this allows one to avoid the known difficulties originated in
perturbative approximation of the RG functions. Ultimately, the proposed
approach results in qualitatively new properties of the QCD invariant charge.
The latter enables one to describe a wide range of the strong interaction
processes both of perturbative and intrinsically nonperturbative nature.Comment: Invited review article; 46 pages, 14 EPS figure
Virtual and Soft Pair Corrections to Polarized Muon Decay Spectrum
Radiative corrections to the muon decay spectrum due to soft and virtual
electron--positron pairs are calculated.Comment: 10pp, 2 PS figs, details of calculations are adde
Two-Loop Bhabha Scattering in QED
In the context of pure QED, we obtain analytic expressions for the
contributions to the Bhabha scattering differential cross section at order
alpha^4 which originate from the interference of two-loop photonic vertices
with tree-level diagrams and from the interference of one-loop photonic
diagrams amongst themselves. The ultraviolet renormalization is carried out.
The IR-divergent soft-photon emission corrections are evaluated and added to
the virtual cross section. The cross section obtained in this manner is valid
for on-shell electrons and positrons of finite mass, and for arbitrary values
of the center of mass energy and momentum transfer. We provide the expansion of
our results in powers of the electron mass, and we compare them with the
corresponding expansion of the complete order alpha^4 photonic cross section,
recently obtained in hep-ph/0501120. As a by-product, we obtain the
contribution to the Bhabha scattering differential cross section of the
interference of the two-loop photonic boxes with the tree-level diagrams, up to
terms suppressed by positive powers of the electron mass. We evaluate
numerically the various contributions to the cross section, paying particular
attention to the comparison between exact and expanded results.Comment: 35 pages, 18 figure
On relativization of the Sommerfeld-Gamow-Sakharov factor
The Sommerfeld-Gamow-Sakharov factor is considered for the general case of
arbitrary masses and energies. It is shown that the scalar triangular one-loop
diagram gives the Coulomb singularity in radiative corrections at the
threshold. The singular part of the correction is factorized at the complete
Born cross section regardless of its partial wave decomposition. Different
approaches to generalize the factor are discussed.Comment: 9 pages, 4 figures; references and discussion are extende
O(\alpha^2 \ln(m_\mu/m_e)) Corrections to Electron Energy Spectrum in Muon Decay
O(\alpha^2 \ln(m_\mu/m_e)) corrections to electron energy spectrum in muon
decay are computed using perturbative fragmentation function approach. The
magnitude of these corrections is comparable to anticipated precision of the
TWIST experiment at TRIUMF where Michel parameters will be extracted from the
measurement of the electron energy spectrum in muon decay.Comment: 8 pages, LaTeX, revtex4.cls, 1 PostScript figur
SANC integrator in the progress: QCD and EW contributions
Modules and packages for the one-loop calculations at partonic level
represent the first level of SANC output computer product. The next level
represents Monte Carlo integrator mcsanc, realizing fully differential hadron
level calculations (convolution with PDF) for the HEP processes at LHC. In this
paper we describe the implementation into the framework mcsanc first set of
processes: DY NC, DY CC, ff->HW(Z) and single top production. Both EW and QCD
NLO corrections are taken into account. A comparison of SANC results with those
existing in the world literature is given
Inverse bremsstrahlung contributions to Drell-Yan like processes
The contribution of the sub-process in
hadron-hadron interactions is considered. It is a part of one-loop electroweak
radiative corrections for the Drell-Yan production of lepton pairs at hadron
colliders. It is shown that this contribution should be taken into account
aiming at the 1% accuracy of the Drell-Yan process theoretical description.
Both the neutral and charged current cases are evaluated. Numerical results are
presented for typical conditions of LHC experiments.Comment: 11 pages, 8 figure
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