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We investigate the leading power corrections to the decay rates and distributions in the decay B→X s l ϩ l Ϫ in the standard model ͑SM͒ using heavy quark expansion ͑HQE͒ in (1/m b ) and a phenomenological model implementing the Fermi motion effects of the b quark bound in the B hadron. In the HQE method, we find that including the leading power corrections the decay width ⌫(B→X s l ϩ l Ϫ ) decreases by about 4% and the branching ratio B(B→X s l ϩ l Ϫ ) by about 1.5% from their ͑respective͒ parton model values.The dilepton invariant mass spectrum is found to be stable against power corrections over a good part of this spectrum. However, near the high-mass end point this distribution becomes negative with the current value of the nonperturbative parameter 2 ͑the 1 -dependent corrections are found to be innocuous͒, implying the breakdown of the HQE method in this region. Our results are at variance with the existing ones in the literature in both the decay rate and the invariant dilepton mass distribution calculated in the HQE approach. As an alternative, we implement the nonperturbative effects in the decay B→X s l ϩ l Ϫ using a phenomenologically motivated Gaussian Fermi motion model. We find small corrections to the branching ratio, but the nonperturbative effects are perceptible in both the dilepton mass distribution and the forward-backward asymmetry in the high dilepton mass region. Using this model for estimating the nonperturbative effects, modeling the dominant long distance contributions from the decays B→X s ϩ(J/,Ј, . . . )→X s l ϩ l Ϫ , and taking into account the next-to-leading order perturbative QCD corrections in b→sl ϩ l Ϫ , we present the decay rates and distributions for the inclusive process B→X s l ϩ l Ϫ in the SM. ͓S0556-2821͑97͒00107-0͔

We discuss the possibility of relating the size and sign of the observed baryon asymmetry of the universe to CP violation observable at low energies, in a framework where the observed baryon asymmetry is produced by leptogenesis through the out of the equilibrium decay of heavy Majorana neutrinos. We identify the CP violating phases entering in leptogenesis as well as those relevant for CP violation at low energies in the minimal seesaw model. We show that although in general there is no relation between these two sets of phases, there are specific frameworks in which such a connection may be established and we give a specific grand unification inspired example where such a connection does exist. We construct weak-basis invariants related to CP violation responsible for leptogenesis, as well as those relevant for CP violation at low energies. * gbranco@thwgs.cern.ch and

In the leptogenesis scenario, decays of heavy Majorana neutrinos generate lepton family asymmetries, Y e , Y µ and Y τ . These asymmetries are sensitive to CP violating phases in seesaw models. The time evolution of the lepton family asymmetries is derived by solving Boltzmann equations. Considering a minimal seesaw model, we show how each family asymmetry varies with one particular CP violating phase. For instance, we find the case in which the lepton asymmetry is dominated by Y µ or Y τ , depending on the choice of the CP violating phase. We also find the case in which the signs of the lepton family asymmetries Y µ and Y τ are opposite. Their absolute values can be larger than the total lepton asymmetry, and baryon asymmetry may result from the cancellation of the lepton family asymmetries. * ) by guest on April 9, 2015 http://ptp.oxfordjournals.org/ Downloaded from where i = 1, 2, 3 and k = 1, 2, · · · , N. Here, L i are SU (2) lepton doublet fields, N R k are the heavy Majorana right-handed neutrinos, and l R i are the right-handed charged leptons. M N R is the N ×N Majorana mass matrix of the right-handed neutrinos, and it is diagonal, i.e., M N R = diag.(M 1 , M 2 , · · · , M N ). y i l are the Yukawa terms for charged leptons. We can choose the basis in which both M N R and y i l are real and diagonal, without loss of generality. In this basis, flavor violating processes occur through off-diagonal elements of the 3×N Yukawa matrix y ν . In the broken phase, the Higgs field has the vacuum expectation value v = 246 GeV, and a Dirac mass term is generated as m D = v √ 2 y ν . The minimal seesaw model, which is compatible with the present neutrino oscil-by guest on April 9, 2015 http://ptp.oxfordjournals.org/ Downloaded from by guest on April 9, 2015 http://ptp.oxfordjournals.org/ Downloaded from

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