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Pietro Santorelli

Publications and source records attributed to Pietro Santorelli.

At least 55 records · Page 3Linked to original sources
arXiv2009

On the phase-integral method for the radial Dirac equation

In the application of potential models, the use of the Dirac equation in central potentials remains of phenomenological interest. The associated set of decoupled second-order ordinary differential equations is here studied by exploiting the phase-integral technique, following the work of Froman and Froman that provides a powerful tool in ordinary quantum mechanics. For various choices of the scalar and vector parts of the potential, the phase-integral formulae are derived and discussed, jointly with formulae for the evaluation of Stokes and anti-Stokes lines. A criterion for choosing the base function in the phase-integral method is also obtained, and tested numerically. The case of scalar confinement is then found to be more tractable.

hep-ph↗
arXiv2008

Final state interaction effects on the eta(b) => J/psi J/psi decay

We study the effects of final state interactions on the eta(b) => J/psi J/psi decay. In particular, we discuss the effects of the annihilation of eta(b) into two charmed meson and their rescattering into J/psi J/psi. We find that the inclusion of this contribution may enhance the short-distance branching ratio up to about 2 orders of magnitude.

hep-ph↗
arXiv2008

Long distance contributions to the eta_b => Jpsi Jpsi decay

It was argued long ago that eta_b could be observed through the eta_b => Jpsi(=> mu+ mu-) Jpsi(=> mu+ mu-) decay chain. Recent calculations indicate that the width of eta_b into two Jpsi is almost 3 orders of magnitude smaller than the one into the D bar D*. We study the effects of final-state interactions due to the D bar D* intermediate state on the Jpsi Jpsi final state. We find that the inclusion of this contribution may enhance the short-distance branching ratio up to about 2 orders of magnitude.

hep-ph↗
arXiv2007

On the eta(b) => J/psi J/psi decay

It has been argued long ago that eta(b) could be observed through the eta(b) => J/psi(=> mu+ mu-) J/psi(=> mu+ mu-) decay chain. Recent calculations indicate that the width of eta(b) into two J/psi is almost three order of magnitude smaller than the one into the D D*. We study the effects of final state interactions due to the D D* intermediate state on the J/psi J/psi final state. We find that the inclusion of this contribution may enhance the short distance branching ratio of about two orders of magnitude.

hep-ph↗
arXiv2006

Semileptonic and nonleptonic decays of Bc

Using our relativistic constituent quark model we present results on the exclusive nonleptonic and semileptonic decays of the Bc-meson. The nonleptonic decays are studied in the framework of the factorization approximation. We calculate the branching ratios for a large set of exclusive nonleptonic and semileptonic decays of the Bc-meson and compare our results with the results of other models.

hep-ph↗
arXiv2006

Exclusive semileptonic and nonleptonic decays of the Bc meson

We study exclusive nonleptonic and semileptonic decays of the Bc-meson within a relativistic constituent quark model previously developed by us. For the nonleptonic decays we use the factorizing approximation. We update our model parameters by using new experimental data for the mass and the lifetime of the Bc meson and the leptonic decay constants of the D-meson. We calculate the branching ratios for a large set of exclusive nonleptonic and semileptonic decays of the $B_c$ meson and compare our results with the results of other studies. As a guide for further experimental exploration we provide explicit formulas for the full angular decay distributions in the cascade decays Bc^- => J/psi(=> l^+l^-) + rho^-(=> pi^- pi^0) and Bc^- => J/psi(=> l^+l^-) + W^-(off-shell)(=> l^- + nubar).

hep-ph↗
arXiv2005

Role of final state interactions in the B meson decay into two pions

We estimate final state interactions in the B-meson decays into two pions by the Regge model. We consider Pomeron exchange and the leading Regge trajectories that can relate intermediate particles to the final state. In some cases, most notably B => pi^0 pi^0 and B => pi^+ pi^-, the effect is relevant and produces a better agreement between theory and experiment.

hep-ph↗
arXiv2005

Semileptonic decays of Bc mesons into charmonium states in a relativistic quark model

We use the framework of a relativistic constituent quark model to study the semileptonic transitions of the Bc meson into CCbar charmonium states where CCbar = etaC (1S0), J/psi (3S1), chiC0 (3P0), chiC1 (3P1), hc (1P1), chiC2 (3P2), psi (3D2). We compute the q^2-dependence of all relevant form factors and give predictions for their semileptonic Bc decay modes including also their tau-modes. We derive a formula for the polar angle distribution of the charged lepton in the (l nu) c.m. frame and compute the partial helicity rates that multiply the angular factors in the decay distribution. For the discovery channel [B_c => J/psi (=> mu+ mu-) l nu] we compute the transverse/longitudinal composition of the J/psi which can be determined by an angular analysis of the decay J/psi => mu+ mu-. We compare our results with the results of other calculations.

hep-ph↗
arXiv2004

B => D(*) transitions in a quark model

We propose a constituent quark model to evaluate heavy decay constants and form factors relevant for B=>D(*) semileptonic transitions. We show that the model reproduces the scaling laws dictated by the spin-flavour symmetry in the heavy quark limit and describes quite well the experimental data.

hep-ph↗
arXiv2004

Final state interactions for B => VV charmless decays

We estimate final state interactions in the B-meson decays into two light vector mesons by the Regge model. We consider Pomeron exchange and charmed Regge trajectories that can relate intermediate charmed particles to the final state. The Regge poles have various helicity-flip residues, which allows a change from the longitudinal to transverse polarization. In this way a significant reduction of the longitudinal polarization fraction can be produced. In the factorization approximation we find agreement with recent data from the BaBar and Belle collaborations in the B => K* phi decay channel, as a result of an appropriate choice of semileptonic form factors and Regge exchanges. On the other hand, data for the K* rho decay channels appear more elusive. The soft effects discussed in the present paper are based on a model of Regge trajectories that is shown to reproduce correctly in the non-charmed case the Regge phenomenology of light mesons.

hep-ph↗
arXiv2004

J/ψdissociation cross sections in a relativistic quark model

We calculate the amplitudes and the cross sections of the charm dissociation processes J/ψπ=> D \bar D, D* \bar D, D \bar D*, D* \bar D* within a relativistic constituent quark model. We consistently account for the contributions coming from both the box and triangle diagrams that contribute to the dissociation processes. The cross section is dominated by the D* \bar D and D* \bar D* channels. When summing up the four channels we find a maximum total cross section of about 2.3 mb at sqrt(s) \approx 4.1 GeV. We compare our results to the results of other model calculations.

hep-ph↗
arXiv1999

A Semianalytical Method to Solve Altarelli-Parisi Evolution Equations

We discuss a new method to solve in a semianalytical way the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations at NLO order in the x-space. The method allows to construct an evolution operator expressed in form of a rapidly convergent series of matrices, depending only on the splitting functions. This operator, acting on a generic initial distribution, provides a very accurate solution in a short computer time (only a few hundredth of second). As an example, we apply the method, useful to solve a wide class of systems of integrodifferential equations, to the polarized parton distributions

hep-ph↗
arXiv1999

Qualitative Properties of the Dirac Equation in a Central Potential

The Dirac equation for a massive spin-1/2 field in a central potential V in three dimensions is studied without fixing a priori the functional form of V. The second-order equations for the radial parts of the spinor wave function are shown to involve a squared Dirac operator for the free case, whose essential self-adjointness is proved by using the Weyl limit point-limit circle criterion, and a `perturbation' resulting from the potential. One then finds that a potential of Coulomb type in the Dirac equation leads to a potential term in the above second-order equations which is not even infinitesimally form-bounded with respect to the free operator. Moreover, the conditions ensuring essential self-adjointness of the second-order operators in the interacting case are changed with respect to the free case, i.e. they are expressed by a majorization involving the parameter in the Coulomb potential and the angular momentum quantum number. The same methods are applied to the analysis of coupled eigenvalue equations when the anomalous magnetic moment of the electron is not neglected.

hep-th↗
arXiv1999

A Semianalytical Method to Evolve Parton Distributions

We present a new method to solve in a semianalytical way the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations at NLO order in the x-space. The method allows to construct an evolution operator expressed in form of a rapidly convergent series of matrices, depending only on the splitting functions. This operator, acting on a generic initial distribution, provides a very accurate solution in a short computer time (only a few hundredth of second). As an example, we apply the method, useful to solve a wide class of systems of integrodifferential equations, to the polarized parton distributions.

hep-ph↗
arXiv1997

QCD Sum Rule Analysis of B \to (K,K^*) (\ell^+\ell^-,ν\barν) Decays

We use three-point QCD sum rules to calculate the form factors governing the rare exclusive decays B \to (K,K^*) \ell^+ \ell^-, B \to (K,K^*) ν\barν. We predict the branching ratios, the invariant mass distributions of the lepton pair for B \to (K,K^*) \ell^+ \ell^-, and the spectra of missing energy for B \to (K,K^*) ν\barν. The forward-backward asymmetry in B \to K^* \ell^+ \ell^- provides us with interesting tests of the Standard Model and its extensions.

hep-ph↗
arXiv1996

A Geometric Picture For Fermion Masses

We describe a geometric picture for the pattern of fermion masses of the three generations which is invariant with respect to the renormalization group below the electroweak scale. Moreover, we predict the upper limit for the ratio between the Dirac masses of the $μ$ and $τ$ neutrinos, $m_{ν_μ}/ m_{ν_τ} < (9.6 \pm 0.6) 10^{-3}$.

hep-ph↗
arXiv1995

Coleman-Weinberg SO(10) GUT Theories as Inflationary Models

The flat-space limit of the one-loop effective potential for SO(10) GUT theories in spatially flat Friedmann-Robertson-Walker cosmologies is applied to study the dynamics of the early universe. The numerical integration of the corresponding field equations shows that, for such grand unified theories, a sufficiently long inflationary stage is achieved for suitable choices of the initial conditions. However, a severe fine tuning of these initial conditions is necessary to obtain a large $e$-fold number. In the direction with residual symmetry $SU(4)_{PS} \otimes SU(2)_{L} \otimes SU(2)_{R}$, one eventually finds parametric resonance for suitable choices of the free parameters of the classical potential. This phenomenon leads in turn to the end of inflation.

gr-qc↗