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T. Morozumi

Publications and source records attributed to T. Morozumi.

27 records · Page 2Linked to original sources
arXiv1998

Quark Mass Hierarchy, FCNC and CP violation in a Seesaw model

The seesaw model of quark masses is studied systematically, focusing on its developments. A framework allowing the top quark mass to be of the order of the electroweak symmetry breaking scale, while the remaining light quarks have much smaller masses, due to the seesaw mechanism, is presented. The violation of the GIM mechanism is shown to be small and the tree level FCNC are suppressed naturally. In this model, there are many particles which could contribute to the FCNC in the one-loop level. Parameters of the model are constrained by using the experimental data on K^0-\bar{K}^0 mixing and ε_K. The rare K meson decays K_{L,S} -> π^0 ν\barν and K^+ -> π^+ ν\barν are also investigated in the model. In these processes the scalar operators (\bar{s}d)(\barν_τν_τ), which are derived from box diagrams in the model, play an important role due to an enhancement factor M_K/m_s in the matrix element <π|\bar{s}d|K>. It is emphasized that the K_L decay process through the scalar operator is not the CP violating mode, so B(K_L -> π^0 ν\barν) remains non-zero even in the CP conserved limit. The pion energy spectra for these processes are predicted.

hep-ph↗
arXiv1998

A Model Independent Analysis of the Rare B Decay B -> X_s l^+ l^-

The most general model-independent analysis of the rare $B$ decay, $\Bsll$, 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.

hep-ph↗
arXiv1998

Rare Decay of K Meson

We investigate the rare decay processes of the K mesons, K_{L,S} -> π^0 ν\barν and K^{+} -> π^+ ν\barν in LR model with lepton family number being well conserved. In these processes, scalar operators (\bar{s}d)(\barν_τν_τ), which are derived from box diagram in LR model, play an important role due to an enhancement factor M_{K}/m_{s} in the matrix element $<π|\bar{s}d|K>$. It is emphasized that the K_{L} decay process through the scalar operator is not the CP violating mode, so the B(K_L -> π^{0} ν\barν) remains non-zero even in the CP conserved limit. We present the pion energy spectrum for these processes and discuss the effects of LR model.

hep-ph↗
arXiv1997

B->Xq l+ l- (q=d,s) and Determination of |Vtd/Vts|

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.

hep-ph↗
arXiv1997

The top quark mass and flavor mixing in a Seesaw model of Quark Masses

The top quark mass and the flavor mixing are studied in the context of a Seesaw model of Quark Masses based on the gauge group $SU(2)_L \times SU(2)_R \times U(1)$. Six isosinglet quarks are introduced to give rise to the mass hierarchy of ordinary quarks. In this scheme, we reexamine a mechanism for the generation of the top quark mass. It is shown that, in order to prevent the Seesaw mechanism to act for the top quark, the mass parameter of its isosinglet partner must be much smaller than the breaking scale of $SU(2)_R$. As a result the fourth lightest up quark must have a mass of the order of the breaking scale of $SU(2)_R$, and a large mixing between the right-handed top quark and its singlet partner occurs. We also show that this mechanism is compatible with the mass spectrum of light quarks and their flavor mixing.

hep-ph↗
arXiv1997

Power Corrections in the Decay Rate and Distributions in $B \to X_s \ell^+ \ell^- $ in the Standard Model

We investigate the leading power corrections to the decay rates and distributions in the decay $B \rightarrow X_s \ell^+ \ell^- $ in the standard model (SM) using heavy quark expansion (HQE) 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 decreases by about 4% and the branching ratio by about 1.5% from their (respective) 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 non-perturbative parameter $λ_2$ (the $λ_1$-dependent corrections are found to be inoccouos), 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 non-perturbative effects in the decay $B \rightarrow X_s \ell^+ \ell^- $ using a phenomenologically motivated Gaussian Fermi motion model. We find small corrections to the branching ratio, but the non-perturbative 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 non-perturbative effects, we present the decay rates and distributions for the inclusive process $B \rightarrow X_s \ell^+ \ell^- $ in the SM.

hep-ph↗
arXiv1995

Effect of the Flavor Changing Neutral Current on Rare $B$ decays

We study the effect of the FCNC on rare $B$ decays in the beyond standard model with vector like singlet quarks. It has been shown that $b \rightarrow s γ$ does not receive sizable contribution compared with that of the standard model while $b \rightarrow d γ$, $b \rightarrow s(d) l^+ l^-$, can be changed from the predictions of the standard model.

hep-ph↗
arXiv1994

Effective Lagrangian for a Technicolor Model without Exact Custodial Symmetry

Effective Lagrangian including technimesons is constructed for a realistic one-family Technicolor model without exact custodial symmetry. Tree level contribution to oblique correction parameters $S$ and $U$ due to spin 1 technimesons are computed with the effective Lagrangian. An isospin breaking term which is associated with technilepton vector mesons gives a negative contribution to the electroweak radiative correction parameter $S$ due to mixing between $I=0$ and $I=1$ vector mesons. $U$ receives non-zero contribution due to exotic left-handed charged vector mesons and its sign can be both negative and positive.

hep-ph↗