Giulia Ricciardi

D-D mixing in heavy quark effective field theory; the sequel

Abstract We perform a quantitative analysis of D- D mixing in heavy quark effective field theory (HQEFT) including leading order QCD corrections. We find an enhancement of the short-distance contribution by a factor of two or three.

QCD corrections to electroweak processes in an unconventional scheme: application to the b → sγ decay

Abstract In this work we give a detailed description of a method for the calculation of QCD corrections to electroweak processes in dimensional regularization that does not require any definition of the γ 5 matrix in d dimensions. This method appears particularly convenient to limit the algebraic complexity of higher order calculations. As an example, we compute the leading logarithmic corrections to the b → sγ decay.

The structure function of semi-inclusive heavy flavour decays in field theory

Abstract We consider the decay of a heavy flavour into an inclusive hadronic state X of invariant mass m X small with respect to its energy E X , m X ≪E X . The electron spectrum and the hadronic mass distribution in semileptonic b→u decays, or the photon spectrum in b→sγ decays, all require, close to their endpoints, a control over this region. This region is affected both by non-perturbative phenomena related to the Fermi motion of the heavy quark and by perturbative soft gluon radiation in the final state (Sudakov form factor). Fermi motion can be described by the shape function f(m ∗ ) , which represents the distribution of the effective mass m ∗ of the heavy quark at disintegration time. We perform a factorization with a simple technique in order to consistently separate perturbative from non-perturbative effects. We find that the shape function, contrary to naive expectations, is not a physical distribution, as it is affected by substantial regularization scheme effects, controlling even the leading, double-logarithmic term. It factorizes, however, the bulk of non-perturbative effects in lattice-like regularizations. Some non-perturbative effects are present in the coefficient function even at leading twist, but they are expected to be suppressed on physical grounds. Finally, we clarify a controversial factor of 2 in the evolution kernel of the shape function.

QCD nonleading corrections to weak decays in the dimensional scheme

We compute the next-to-leading-order QCD corrections to weak four-fermion interactions, introducing a scheme that does not require an explicit definition of

Short and long distance interplay in inclusive B → Xdγ decay

{\ensuremath{\gamma}}_{5}

LIGHT MASSES IN SHORT DISTANCE PENGUIN LOOPS

in

The b→sγ decay revisited

d

THRESHOLD RESUMMED SPECTRA IN B → Xulν DECAYS IN NLO (I)

dimensions. This scheme greatly reduces the difficulties in calculating the two-loop anomalous dimensions; we recover results obtained in the literature.

NNLO THRESHOLD RESUMMATION IN HEAVY FLAVOUR DECAYS

Abstract We analyze the short and long distance contributions to inclusive B → Xdγ decay, paying particular attention to the dependence on the Cabibbo-Kobayashi-Maskawa parameter Vtd. We discuss penguin diagrams with internal u and c quarks in the framework of the effective field theory. We also estimate the size of possible long range contributions by using vector meson dominance.

THRESHOLD RESUMMED SPECTRA IN B → XulDECAYS IN NLO (II)

Abstract Penguin diagrams for decays such as b →( s , d ) γ involve virtual loops of u or other light quarks. Logarithms of the virtual quark mass could, in principle, influence the phenomenological analysis of the decay. It is thus important to study these logarithms to all orders in QCD perturbation theory. In this paper we show that, at arbitrary order, the matrix elements of operators in the effective hamiltonian contributing to b → sγ are finite for the limit of m u →0 in penguin loops.