Four quark processes at LEP 200

In this paper I investigate the production of four quarks at LEP 200 energies. Effects due to initial state QED corrections and background diagrams, including QCD contributions, are studied and examples of results obtained with an event generator presented.Comment: 9 pages, INLO-PUB-8/9

Inelastic photon-neutrino interactions using an effective Lagrangian

We justify the feasibility of substituting a photon leg by a neutrino current in the Euler-Heisenberg Lagrangian to obtain an effective Lagrangian for the process $\gamma\nu\to\gamma\gamma \nu$ and its crossed reactions. We establish the link between these processes and the four-photon scattering in both the Standard Model and the effective theory. As an application, we compute the processes $\gamma\nu\to\gamma\gamma\nu$ and $\gamma\gamma\to\gamma{\nu}\bar\nu$, give their polarized cross sections, and show how to use the $\gamma\gamma\to\gamma\gamma$ results as a check. We settle the question about the disagreement between two computations in the literature concerning the reaction $\gamma\gamma\to \gamma \nu\bar\nu$.Comment: 14 pages, RevTeX, axodraw, 3 figures, comment adde

Five-leg photon-neutrino interactions

In a first part, we justify the feasibility of substituting a photon leg by a neutrino current in the Euler-Heisenberg Lagrangian to obtain an effective Lagrangian for the process $\gamma\nu\to\gamma\gamma \nu$ and its crossed reactions. We establish the link between these processes and the four-photon scattering in both the Standard Model and the effective theory. As an application, we compute in this effective theory the processes $\gamma\nu\to\gamma\gamma\nu$ and $\gamma\gamma\to\gamma{\nu}\bar\nu$ and show how to use the $\gamma\gamma\to\gamma\gamma$ results as a check. We settle the question of the disagreement between two computations in the literature concerning the reaction $\gamma\gamma\to \gamma \nu\bar\nu$. In the second part, we present results of the direct computation of the photon-neutrino five-leg processes in the Standard Model, discuss possible astrophysical implications of our results, and provide simple fits to the exact expressions.Comment: 6 pages, axodraw, ltwol2e, 5 figures, contributed paper to the 29th International Conference on High Energy Physics (Vancouver

A simple method for multi-leg loop calculations 2: a general algorithm

The method introduced in a previous paper to simplify the tensorial reduction in multi-leg loop calculations is extended to generic one-loop integrals, with arbitrary internal masses and external momenta.Comment: 7 pages, latex, no figure

QCD corrections to forward-backward charge asymmetries in l- l+ j production at hadron colliders

The large cross sections for gauge boson production at the Fermilab Tevatron and the CERN Large Hadron Collider (LHC) might give a chance to determine the electroweak parameters with high precision. We calculated two different forward-backward charge asymmetries (A^CS_FB and A^j_FB) of lepton pairs in events with a large transverse momentum jet p p (pbar) -> Z, gamma* + j -> e- e+ j at next-to-leading order (NLO), O(alpha_s) corrections, making use of the Monte Carlo programs MCFM and ALPGEN. These observables could provide a new determination of the weak mixing angle sin^2 theta^lept_eff (M_Z^2) with a statistical precision for each lepton flavour of 10^{-3} (7 x 10^{-3}) at LHC (Tevatron). If b jets are identified, a new asymmetry with respect to the b quark (A^b_FB) can also be measured with a statistical precision of 2 x 10^{-3} (4 x 10^{-2}) at LHC (Tevatron). Finally, we comment on the dependence of our results on various sources of uncertainties and compare, in the case of A^b_FB, the exact result with an approximation that might be more suitable when performing a realistic experimental analysis.Comment: 5 pages, 1 figure, talk presentad by R. Pittau at the International Europhysics Conference on High Energy Physics, July 21st - 27th 2005, Lisbon, Portuga

QCD: Recent theoretical developments and results

present recent developments and results in theoretical, perturbative QCD