Takuya Morozumi

A bridge between CP violation at low energies and leptogenesis

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.

Primordial lepton family asymmetries in seesaw model

In the leptogenesis scenario, decays of heavy Majorana neutrinos generate lepton family asymmetries, Ye ,Y µ and Yτ. 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 Yµ or Yτ, depending on the choice of the CP violating phase. We also find the case in which the signs of the lepton family asymmetries Yµ and Yτ 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.

CP violation in neutrino oscillation and leptogenesis

We study the correlation between CP violation in neutrino oscillations and leptogenesis in the framework with two heavy Majorana neutrinos and three light neutrinos. Among three unremovable CP phases, a heavy Majorana phase contributes to leptogenesis. We show how the heavy Majorana phase contributes to Jarlskog determinant J as well as neutrinoless double beta decay by identifying a low energy CP-violating phase which signals the CP-violating phase for leptogenesis. For some specific cases of the Dirac mass term of neutrinos, a direct relation between lepton number asymmetry and J is obtained. We also study the effect coming from the phases which are not related to leptogenesis.

Model-independent analysis of the rare B decay B → X s l + l −

The most general model-independent analysis of the rare B decay

Quantum correction to tiny vacuum expectation value in two Higgs doublet model for Dirac neutrino mass

\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}

Leptogenesis and low-energy CP violation: A Link

is presented. There are ten independent local four-Fermi interactions which may contribute to this process. The branching ratio, the forward-backward asymmetry, and the double differential rate are written as functions of the Wilson coefficients of the ten operators. We also study the correlation between the branching ratio and the forward-backward asymmetry by changing each coefficient. This procedure tells us which types of operator contribute to the process, and it will be very useful to pin down new physics systematically, once we have the experimental data with high statistics and the deviation from the standard model is found.

B{r_arrow}X{sub q}l{sup +}l{sup {minus}}(q=d,s) and determination of {vert_bar}V{sub td}/V{sub ts}{vert_bar}

We study a Dirac neutrino mass model of Davidson and Logan. In the model, the smallness of the neutrino mass is originated from the small vacuum expectation value of the second Higgs of two Higgs doublets. We study the one loop effective potential of the Higgs sector and examine how the small vacuum expectation is stable under the radiative correction. By deriving formulae of the radiative correction, we numerically study how large the one loop correction is and show how it depends on the quadratic mass terms and quartic couplings of the Higgs potential. The correction changes depending on the various scenarios for extra Higgs mass spectrum.

Azimuthal angle distribution in B → K * ( → K π ) l + l − in the low invariant m l + l − region

How is CP violation of low energy related to CP violation required from baryon number asymmetry ? We give an example which shows a direct link between CP violation of neutrino oscillation and baryogenesis through leptogenesis.

Effects of large threshold corrections in supersymmetric type-I seesaw model

We propose a new method to extract |Vtd/Vts| from the ratio of the decay distributions dR/ds = dB(B->Xdl+l-)/ds/dB(B->Xsl+l-)/ds. This ratio depends only on the KM ratio |Vtd/Vts| with 15% theoretical uncertainties, if dilepton invariant mass-squared s is away from the peaks of the possible resonance states, J/psi, psiprime, and etc. We also give a detailed analytical and numerical analysis on dB(B-Xql+l-)/ds (q=d,s) and dR/ds.

Quantum correction to the tiny vacuum expectation value in the two-Higgs-doublet-model for the Dirac neutrino mass

We present the angular distribution of the rare B decay,