819 research outputs found
Spontaneous generation of the Nambu --Jona-Lazinio interaction in quantum chromodynamics with two light quarks
In QCD with two light quarks with application of Bogolubov quasi-averages
approach a possibility of spontaneous generation of an effective interaction,
leading to the Nambu -- Jona-Lazinio model, is studied. Compensation equations
for form-factor of the interaction is shown to have the non-trivial solution
leading to theory with two parameters: average low-energy value of
and dimensional parameter . All other parameters: the current and the
constituent quark masses, the quark condensate, mass of meson, mass of
meson and its width are expressed in terms of the two initial
parameters in satisfactory correspondence to experimental phenomenology. The
results being obtained allow to state an applicability of the approach in the
low-energy hadron physics and promising possibilities of its applications to
other problems.Comment: 16 pages, 1 table, 3 figure
Pair Production in Small-Angle Bhabha Scattering
Radiative corrections due to the production of virtual as well as real soft
and hard pairs in small-angle Bhabha scattering are calculated analytically.
Both the collinear and the semi-collinear kinematical regions of hard pair
production are considered. The calculation, within the leading and
next-to-leading logarithmic approximation, provides an accuracy of O(0.1%).
Numerical results show that the effects of pair production have to be taken
into account for a luminosity determination accurate to O(0.1%) at LEP.Comment: Latex. 20 page
Hadronic Cross Sections in Electron-Positron Annihilation with Tagged Photon
Events with tagged photons in the process of electron-positron annihilation
into hadrons are considered. The initial state radiation is suggested to scan
the hadronic cross section with the energy. QED radiative corrections are taken
into account. The results for the total and exclusive cross sections are given
in an analytic form. Some numerical estimates are presented.Comment: 12 pages, 2PS figures, the final journal versio
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
Planar box diagram for the (N_F = 1) 2-loop QED virtual corrections to Bhabha scattering
In this paper we present the master integrals necessary for the analytic
calculation of the box diagrams with one electron loop (N_{F}=1) entering in
the 2-loop (\alpha^3) QED virtual corrections to the Bhabha scattering
amplitude of the electron. We consider on-shell electrons and positrons of
finite mass m, arbitrary squared c.m. energy s, and momentum transfer t; both
UV and soft IR divergences are regulated within the continuous D-dimensional
regularization scheme. After a brief overview of the method employed in the
calculation, we give the results, for s and t in the Euclidean region, in terms
of 1- and 2-dimensional harmonic polylogarithms, of maximum weight 3. The
corresponding results in the physical region can be recovered by analytical
continuation. For completeness, we also provide the analytic expression of the
1-loop scalar box diagram including the first order in (D-4).Comment: Misprints in Eqs. (36), (38), (39), and (B.9) have been corrected.
The results are now available at http://pheno.physik.uni-freiburg.de/~bhabha,
as FORM input file
Two-Loop N_F =1 QED Bhabha Scattering: Soft Emission and Numerical Evaluation of the Differential Cross-section
Recently, we evaluated the virtual cross-section for Bhabha scattering in
pure QED, up to corrections of order alpha^4 (N_F =1). This calculation is
valid for arbitrary values of the squared center of mass energy s and momentum
transfer t; the electron and positron mass m was considered a finite, non
vanishing quantity. In the present work, we supplement the previous calculation
by considering the contribution of the soft photon emission diagrams to the
differential cross-section, up to and including terms of order alpha^4 (N_F=1).
Adding the contribution of the real corrections to the renormalized virtual
ones, we obtain an UV and IR finite differential cross-section; we evaluate
this quantity numerically for a significant set of values of the squared center
of mass energy s.Comment: 24 pages, 15 figures. Formulas in Appendix B corrected, changes in
Section 3, references adde
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