Ritorno radiativo per la misura di R: come e perche

The measurement of the pion form factor and, more generally, of the cross section for electron--positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the $\Phi$- or $B$-meson factories. This quantity is crucial for predictions of the hadronic contributions to $(g-2)_\mu$, the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling. But the radiative return opens also the possibility of many other physical applications. The physics potential of this method at high luminosity meson factories is discussed and recent results are reviewed.Comment: Talk given in italian at Incontri sulla Fisica delle Alte Energie, Lecce, Italy, Apr 2003; 4 page

Radiative return at NLO and the measurement of the hadronic cross-section

The measurement of the hadronic cross-section in $e^+ e^-$ annihilation at high luminosity factories using the radiative return method is motivated and discussed. A Monte Carlo generator which simulates the radiative process $e^+ e^- \to \gamma+hadrons$ at the next-to-leading order accuracy is presented. The analysis is then extended to the description of events with hard photons radiated at very small angle.Comment: 12 pages, 6 figures. To appear in Acta Physica Polonica B. Presented at the XXV International Conference on Theoretical Physics ``Particle Physics and Astrophysics in the Standard Model and Beyond'', Ustron, Poland, 9-16 September 200

Heavy Quark Impact Factor at Next-to-leading Level

We further analyze the definition and the calculation of the heavy quark impact factor at next-to-leading (NL) log(s) level, and we provide its analytical expression in a previously proposed k-factorization scheme. Our results indicate that k-factorization holds at NL level with a properly chosen energy scale, and with the same gluonic Green's function previously found in the massless probe case.Comment: LaTeX2e, 17pp, 2 figures, uses JHEP.cls. The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp00/ttp00-06, or via www at http://www-ttp.physik.uni-karlsruhe.de/Preprints

Charge asymmetry: a theory appraisal

The most recent measurements at Tevatron of the charge asymmetry in top-antitop quark pair production reduce the discrepancy with the Standard Model from 2sigma to 1.7sigma, and open a little window, at 95% C.L., for negative contributions to the charge asymmetry beyond the SM. We update our analysis for colour octet gauge bosons or axigluons in flavour universal and flavour non universal scenarios. We review other possible models and make an educated guess on their parameter space allowed by the new measurements. Finally, we comment on the prospects to measure the charge asymmetry at the LHC.Comment: Presented at 3rd International Workshop on Top Quark Physics (TOP 2010), Bruges, Belgium, 31 May - 4 Jun 2010. 8 page

Resummed jet rates for heavy quark production in electron-positron annihilation

Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.Comment: Talk given by German Rodrigo at EPS2003 - Aachen, Germany, July 2003; 3 pages, 2 figure

Universal dual amplitudes and asymptotic expansions for gg→Hgg\to H and H→γγH\to \gamma\gamma in four dimensions

Though the one-loop amplitudes of the Higgs boson to massless gauge bosons are finite because there is no direct interaction at tree-level in the Standard Model, a well-defined regularization scheme is still required for their correct evaluation. We reanalyze these amplitudes in the framework of the four-dimensional unsubtraction and the loop-tree duality (FDU/LTD), and show how a local renormalization solves potential regularization ambiguities. The Higgs boson interactions are also used to illustrate new additional advantages of this formalism. We show that LTD naturally leads to very compact integrand expressions in four space-time dimensions of the one-loop amplitude with virtual electroweak gauge bosons. They exhibit the same functional form as the amplitudes with top quarks and charged scalars, thus opening further possibilities for simplifications in higher-order computations. Another outstanding application is the straightforward implementation of asymptotic expansions by using dual amplitudes. One of the main benefits of the LTD representation is that it is supported in a Euclidean space. This characteristic feature naturally leads to simpler asymptotic expansions.Comment: 11 pages, no figures. Minor modifications, discussion improved. Final version published in EPJ

QED corrections to the Altarelli-Parisi splitting functions

We discuss the combined effect of QED and QCD corrections to the evolution of parton distributions. We extend the available knowledge of the Altarelli-Parisi splitting functions to one order higher in QED, and provide explicit expressions for the splitting kernels up to ${\cal O}(\alpha \, \alpha_{\mathrm{S}})$. The results presented in this article allow to perform a parton distribution function analysis reaching full NLO QCD-QED combined precision.Comment: 11 pages, 1 figure. References added, improved discussion. Final version published in EPJC. Typo corrected in Eq. (22