Enrico Lunghi

Possible indications of new physics in Bd-mixing and in sin(2β) determinations

Abstract Using the hadronic matrix elements from the lattice, B K and ξ s , involving only the 4-quark operators for Δ flavor = 2 Hamiltonian relevant for K – K ¯ , B d – B ¯ d and B s – B ¯ s mixing, along with V c b , we deduce a non-trivial constraint on the SM, sin ( 2 β ) = 0.87 ± 0.09 . This deviates from direct experimental measurements via the tree process, b → c c ¯ s as well as the one via the penguin-loop b → s decays by around 2.1 and 2.7σ respectively. If these deviations are confirmed they would imply the presence of new physics rather pervasively in both B d – B ¯ d (i.e. very likely in b → d ) as well as in b → s transitions requiring a beyond the SM CP-odd phase. Consequently, improvements in the relevant lattice calculations should be given a high priority.

Electromagnetic logarithms in B¯→Xsℓ+ℓ−

Abstract The B ¯ → X s l + l − decay rate is known at the next-to-next-to-leading order in QCD. It is proportional to α em ( μ ) 2 and has a ± 4 % scale uncertainty before including the O ( α em ln ( M W 2 / m b 2 ) ) electromagnetic corrections. We evaluate these corrections and confirm the earlier findings of Bobeth et al. Furthermore, we complete the calculation of logarithmically enhanced electromagnetic effects by including also QED corrections to the matrix elements of four-fermion operators. Such corrections contain a collinear logarithm ln ( m b 2 / m l 2 ) that survives integration over the low dilepton invariant mass region 1 GeV 2 m l l 2 6 GeV 2 and enhances the integrated decay rate in this domain. For the low- m l l 2 integrated branching ratio in the muonic case, we find B ( B → X s μ + μ − ) = ( 1.59 ± 0.11 ) × 10 −6 , where the error includes the parametric and perturbative uncertainties only. For B ( B → X s e + e − ) , in the current BaBar and Belle setups, the logarithm of the lepton mass gets replaced by angular cut parameters and the integrated branching ratio for the electrons is expected to be close to that for the muons.

Logarithmically enhanced corrections to the decay rate and forward–backward asymmetry in B¯→Xsℓ+ℓ−

Abstract We study logarithmically enhanced electromagnetic corrections to the decay rate in the high dilepton invariant mass region as well as corrections to the forward–backward asymmetry (FBA) of the inclusive rare decay B ¯ → X s l + l − . As expected, the relative effect of these corrections in the high dilepton mass region is around −8% for the muonic final state and therefore much larger than in the low dilepton mass region. We also present a complete phenomenological analysis, to improved NNLO accuracy, of the dilepton mass spectrum and the FBA integrated in the low dilepton mass region, including a new approach to the zero of the FBA. The latter represents one of the most precise predictions in flavour physics with a theoretical uncertainty of order 5%. We find ( q 0 2 ) μ μ = ( 3.50 ± 0.12 ) GeV 2 . For the high dilepton invariant mass region, we have B ( B ¯ → X s μ μ ) high = ( 2.40 −0.62 +0.69 ) × 10 −7 . The dominant uncertainty is due to the 1 / m b corrections and can be significantly reduced in the future. For the low dilepton invariant mass region, we confirm previous results up to small corrections.

Huge right-handed current effects in B → K ∗ (Kπ)ℓ + ℓ − in supersymmetry

Transverse asymmetries in the decay B → K ∗ (Kπ)l + l − are an extremely sensitive probe of right-handed flavour-changing neutral currents. We show how to include the contribution from the chiral partner of the electromagnetic operator on the transverse asymmetries at NLO in QCD factorization. We then consider supersymmetric models with non-minimal flavour violation in the down-squark sector. We include all the relevant experimental constraints and present a numerical formula for B → Xsγ that takes into account the most recent NNLO calculations. We show that the flavour-changing parameters of these models are poorly constrained by present data and allow for large effects on the transverse asymmetries that we consider.

Analysis of enhanced tan(beta) corrections in MFV GUT scenarios

Long-range forces between macroscopic objects are mediated by light particles that interact with the electrons or nucleons, and include spin-dependent static components as well as spin- and velocity-dependent components. We parametrize the long-range potential between two fermions assuming rotational invariance, and find 16 different components. Applying this result to electrically neutral objects, we show that the macroscopic potential depends on 72 measurable parameters. We then derive the potential induced by the exchange of a new gauge boson or spinless particle, and compare the limits set by measurements of macroscopic forces to the astrophysical limits on the couplings of these particles.

Light charged Higgs at the beginning of the LHC era

The terascale will be explored with the start of the LHC. One of the most fundamental questions which we expect to be answered is the root of electroweak symmetry breaking and whether the Higgs mechanism is realized in nature or not. In this context we pose the question if existing experimental data still allow for a light non-minimal Higgs sector. We tackle this question first in the context of the two Higgs doublet model and then we concentrate in two supersymmetric models, the constrained MSSM and the MSSM with non-universal Higgs masses. In both supersymmetric scenarios, light pseudoscalar and light charged-Higgs bosons are still viable provided tan β is large. In this regime, we emphasize the importance of the constraints provided by the decay B → τν mediated by the charged-Higgs at tree-level. In addition we comment on generic predictions for hadronic colliders and indirect searches in such scenarios.

Kinetic corrections to bar B ? Xc?bar nu at one loop

We evaluate the one-loop corrections to the Wilson coefficient of the kinetic operator in the operator product expansion of the differential B -> X_c l nu decay rate. With a moderate cut on the lepton energy, the one-loop terms change the kinetic operator contributions to spectral moments by about 20%. This amounts to a small correction for leptonic and hadronic moments, except for those which vanish at the lowest order, where the effect can be sizable. Together with a two-loop calculation of the leading-power rate and an evaluation of the one-loop corrections to the Wilson coefficient of the chromo-magnetic operator, our results will allow for a high-precision determination of |V_cb| and the b- and c-quark masses.

Kinetic corrections to B̄ → Xcℓν̄ at one loop

We evaluate the one-loop corrections to the Wilson coefficient of the kinetic operator in the operator product expansion of the differential B -> X_c l nu decay rate. With a moderate cut on the lepton energy, the one-loop terms change the kinetic operator contributions to spectral moments by about 20%. This amounts to a small correction for leptonic and hadronic moments, except for those which vanish at the lowest order, where the effect can be sizable. Together with a two-loop calculation of the leading-power rate and an evaluation of the one-loop corrections to the Wilson coefficient of the chromo-magnetic operator, our results will allow for a high-precision determination of |V_cb| and the b- and c-quark masses.