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G. Ossola

Publications and source records attributed to G. Ossola.

30 records · Page 2Linked to original sources
arXiv2010

Complete (O_7,O_8) contribution to B -> X_s gamma at order alpha_s^2

We calculate the set of O(alpha_s^2) corrections to the branching ratio and to the photon energy spectrum of the decay process B -> X_s gamma originating from the interference of diagrams involving the electromagnetic dipole operator O_7 with diagrams involving the chromomagnetic dipole operator O_8. The corrections evaluated here are one of the elements needed to complete the calculations of the B -> X_s gamma branching ratio at next-to-next-to-leading order in QCD. We conclude that this set of corrections does not change the central value of the Standard Model prediction for Br(B -> X_s gamma) by more than 1 %.

hep-ph↗
arXiv2008

NLO QCD corrections to tri-boson production

We present a calculation of the NLO QCD corrections for the production of three vector bosons at the LHC, namely Z Z Z, W+ W- Z, W+ Z Z, and W+ W- W+ production. The virtual corrections are computed using the recently proposed method of reduction at the integrand level (OPP reduction). Concerning the contributions coming from real emission we used the dipole subtraction to treat the soft and collinear divergences. We find that the QCD corrections for these electroweak processes are in the range between 70 and 100 percent. As such they have to be considered in experimental studies of triple vector boson production at the LHC.

hep-ph↗
arXiv2008

Optimizing the Reduction of One-Loop Amplitudes

We present an optimization of the reduction algorithm of one-loop amplitudes in terms of master integrals. It is based on the exploitation of the polynomial structure of the integrand when evaluated at values of the loop-momentum fulfilling multiple cut-conditions, as emerged in the OPP-method. The reconstruction of the polynomials, needed for the complete reduction, is rended very versatile by using a projection-technique based on the Discrete Fourier Transform. The novel implementation is applied in the context of the NLO QCD corrections to u d-bar --> W+ W- W+.

hep-ph↗
arXiv2007

Inclusive semileptonic B decays and the determination of |V_ub|

We study the triple differential distribution of B-> Xu l nu, consistently including all perturbative and non-perturbative effects through O(alphas^2 beta_0) and O(1/mb^3). The Fermi motion is parameterized in terms of a single light-cone function for each structure function and for any value of q^2, accounting for all subleading effects. We discuss the problems and uncertainties related to the high-q^2 tail and to Weak Annihilation effects. We work in the kinetic scheme, a framework characterized by a Wilsonian treatment with a hard cutoff mu ~ 1GeV. Our method is illustrated with the extraction of |V_ub| from some of the latest experimental data, providing a detailed estimate of the theoretical uncertainty.

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arXiv2004

Bounds on the Higgs Boson Mass from M_W

Recent experimental and theoretical progress in the M_H estimates from M_W and Sin^2_eff_lept is reviewed, with particular emphasis on the role played by M_t. Assuming that the SM is correct and taking into account the lower bound on M_H from direct searches, we derive restrictive bounds on M_W and M_t. We also discuss a representative ``benchmark'' scenario for the possible future evolution of these parameters. Amusingly, this benchmark scenario suggested some time ago a value for M_t that turned out to be in very close agreement with its most recent experimental determination.

hep-ph↗
arXiv2004

Bounds on M_W, M_t, Sin^2 theta_eff^lept

Assuming that the Standard Model is correct and taking into account the lower bound on M_H from direct searches, we discuss bounds on M_W, M_top, and Sin^2 theta_eff_lept at various confidence levels. This permits to identify theoretically favored ranges for these important parameters in the Standard Model framework, regardless of other observables. As an illustration of possible future developments, a hypothetical benchmark scenario, involving shifts less then 1 sigma in the experimental central values, is discussed.

hep-ph↗
arXiv2004

The electroweak form factor \hatκ(q^2) and the running of \sin^2 \hatθ_W

Gauge independent form factors ρ^(e; e) and \hatκ^(e; e)(q^2) for Moller scattering at s << m_W^2 are derived. It is pointed out that \hatκ^(e; e) is very different from its counterparts in other processes. The relation between the effective parameter \hatκ^(e; e)(q^2,μ) \sin^2 \hatθ_W(μ) and \sin^2 θ_eff is derived in a scale-independent manner. A gauge and process-independent running parameter \sin^2 \hatθ_W (q^2), based on the pinch-technique self-energy a_{γZ} (q^2), is discussed for all q^2 values. At q^2=0 it absorbs very accurately the Czarnecki-Marciano calculation of the Moller scattering asymmetry at low s values, and at q^2 = m^2_Z it is rather close to \sin^2 θ_eff. The q^2 dependence of \sin^2 \hatθ_W (q^2) is displayed in the space and time-like domains.

hep-ph↗
arXiv2002

Simple Formulae for Sin^2 theta_eff^lept, M_W, Gamma_l, and their Physical Applications

The calculation of the partial widths of the Z boson in the effective scheme is discussed. Simple formulae for Sin^2 theta_eff^lept, M_W, and Gamma_l in the on-shell, MS, and effective renormalization schemes are presented. Their domain of validity extends to low M_H values probed by current experiments, and to the range of Delta alpha_hadr results from recent calculations. Physical applications of these formulae are illustrated. A comparative analysis of the above mentioned schemes is presented. The paper includes a discussion of the discrepancy of the Sin^2 theta_eff^lept values derived from the leptonic and hadronic sectors and of the shortcomings of theoretical error estimates of Sin^2 theta_eff^lept based solely on those affecting M_W.

hep-ph↗
arXiv2001

Novel Approach to Renormalize the Electroweak Sector of the Standard Model

We discuss a novel approach to renormalize the Electroweak Sector of the Standard Model, in which \sin^2θ_{eff}, measured at the Z^0 peak, is identified with the basic renormalized electroweak mixing parameter. This approach shares the desirable convergence properties of the MS scheme and provides a framework for calculations that are strictly independent of the electroweak scale in finite orders of perturbation theory. We illustrate the method with updated precise calculations of \sin^2θ_{eff} and M_W, as functions of M_H, and comment on the implications of these calculations for the Higgs boson search and the theoretical prediction of M_W.

hep-ph↗
arXiv2001

Scale-Independent Calculation of $\sin^2 θ_{eff}^{lept}$

We present a calculation of the electroweak mixing parameter $\sin^2 θ_{eff}^{lept}$ that incorporates known higher order effects, shares the desirable convergence properties of the $\bar{MS}$ scheme, and has the important theoretical advantage of being strictly independent of the electroweak scale in finite orders of perturbation theory . We also show how this formulation can be extended to the calculation of the W mass $M_W$. The results provide accurate, scale-independent evaluations of these important parameters, as functions of the Higgs boson mass $M_H$, and are compared with previous calculations in order to analyze the scheme and scale dependence of the electroweak corrections.

hep-ph↗
arXiv1999

Considerations Concerning the Radiative Corrections to Muon Decay in the Fermi and Standard Theories

The FAC, PMS, and BLM optimization methods are applied to the QED corrections to the muon lifetime in the Fermi V-A theory. The FAC and PMS scales are close to m_e, while the BLM scale nearly concides with the geometric average \sqrt{m_e m_μ}. The optimized expressions are employed to estimate the third order coefficient in the α(m_μ) expansion and the theoretical error of the perturbative series. Using arguments based on effective field theory and a simple examination of Feynman diagrams, it is shown that, if contributions of O(αm_μ^2/M_W^2) are neglected, the corrections to muon decay in the SM factorize into the QED correction of the Fermi V-A theory and the electroweak amplitude g^2/(1-Δr), both of which are strictly scale-independent. We use the results to clarify how the QED corrections to muon decay and the Fermi constant G_F should be used in the SM, and what is the natural choice of scales if running couplings are employed.

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