Leading Logarithms in Field Theory

We consider the Sudakov form factor in effective theories and we show that one can derive correctly the double logarithms of the original, high-energy, theory. We show that in effective theories it is possible to separate explicitely soft and hard dynamics being these two regimes related to velocity conserving and to velocity changing operators respectively. A new effective theory is sketched which extracts the leading collinear singularities of the full theory amplitudes. Finally, we show how all leading logarithmic effects in field theory can be obtained by means of simple effective theories, where they correspond to a renormalization effect.Comment: Latex file, 20 pages, no figures, corrected some typo

A new approach to evaluate the leading hadronic corrections to the muon g-2

We propose a novel approach to determine the leading hadronic corrections to the muon g-2. It consists in a measurement of the effective electromagnetic coupling in the space-like region extracted from Bhabha scattering data. We argue that this new method may become feasible at flavor factories, resulting in an alternative determination potentially competitive with the accuracy of the present results obtained with the dispersive approach via time-like data.Comment: 7 pages, 3 figures. Version accepted for publication in Phys. Lett.

Flavor Changing Fermion-Graviton Vertices

We study the flavor-changing quark-graviton vertex that is induced at the one-loop level when gravitational interactions are coupled to the standard model. Because of the conservation of the energy-momentum tensor the corresponding form factors turn out to be finite and gauge-invariant. Analytical expressions of the form factors are provided at leading order in the external masses. We show that flavor-changing interactions in gravity are local if the graviton is strictly massless while if the graviton has a small mass long-range interactions inducing a flavor-changing contribution in the Newton potential appear. Flavor-changing processes with massive spin-2 particles are also briefly discussed. These results can be generalized to the case of the lepton-graviton coupling.Comment: 21 pages, 2 figures. New results and two references added. To be published in PR

Resummed Mass Distribution for Jets Initiated by Massive Quarks

We resum to all orders of perturbation theory the invariant mass distribution of jets initiated by massive quarks. We find that the inclusion of mass terms, in the N-moment space, results in the universal factor delta_N(Q^2;m^2), taking into account dead-cone effects in gluon emission, which multiplies the massless jet distribution function J_N(Q^2). The variable N is rescaled by the mass correction parameter r = m^2/Q^2 c l nu decay spectra or the inclusion of beauty mass effects in t --> b W decays, are briefly sketched

Radiative Corrections to the Hadronic Cross-Section Measurement at DAPHNE

The hadronic invariant mass distribution for the process of electron-positron annihilation into a pair of charged pions accompanied by a photon radiated from the initial state has been studied for the region of DA$\Phi$NE energies. The Born cross-section and the electromagnetic radiative corrections to it are calculated for realistic conditions of the KLOE detector. The dependence on the physical parameters which define the event selection is obtained.Comment: 15 pages, Latex, 21 references, no figure

Minimal prescription corrected spectra in heavy quark decays

The Minimal Prescription procedure is applied to tame the Landau pole singularities of resummed formulae for heavy quark decays. Effects of the final quark mass are taken into account. Explicit expressions are obtained for the t->b and b->c transitions for both the frozen coupling approximation and in the QCD running coupling case.Comment: Text revised, as accepted by Phys Rev D. Same content, formulas and conclusions. Title changed, one figure and appendix added. 24 pages, 10 figure

Scanning of the e+e- to pi+pi- cross--section below 1 GeV by radiative events with untagged photon

We discuss an inclusive approach to the measurement of the e+e- --> pi+ pi- cross--section by the radiative return method without photon tagging. The essential part of this approach is the choice of rules for event selection which provide rejection of events with 3 (or more) pions and decrease the final--state radiation background. The radiative corrections to the initial--state radiation process are computed for DAPhNE conditions, using the quasi--real electron approximation for both, the cross--section and the underlying kinematics. The two cases of restricted and unrestricted pion phase space are considered. Some numerical calculations illustrate our analytical results.Comment: 25 pages, 4 figures, late

Comment on Resummation of Mass Distribution for Jets Initiated by Massive Quarks

We compute in the heavy quark effective theory the soft coefficient D_2 entering the resummation of next-to-next-to-leading threshold logarithms for jets initiated by a quark with a small mass compared to the hard scale of the process. We find complete agreement with a previous computation in full QCD. Contrary to our previous guess, this coefficient turns out to be different from that one entering heavy flavor decay or heavy flavor fragmentation.Comment: 5 pages, no figures; minor changes, references added, version accepted in Phys.Lett.

Fracture functions from cut vertices

Using a generalized cut vertex expansion we introduce the concept of an extended fracture function for the description of semi-inclusive deep inelastic processes in the target fragmentation region. Extended fracture functions are shown to obey a standard homogeneous DGLAP-type equation which, upon integration over t, becomes the usual inhomogeneous evolution equation for ordinary fracture functions.Comment: latex, 15 pages including 7 postscript figure