Phys.Lett.B660:508-514,2008 In an economical system with only two heavy right handed neutrinos, we
postulate a new texture for $3 \times 2$ Dirac mass matrix $m_D$. This model
implies one massless ...light neutrino and thus displays only two patterns of mass
spectrum for light neutrinos, namely hierarchical or inverse-hierarchical. Both
the cases can correctly reproduce all the current neutrino oscillation data
with a unique prediction $m_{\nu_e \nu_e} = \frac{\sqrt{\Delta
m^2_{solar}}}{3}$ and $\sqrt{\Delta m^2_{atm}}$ for the hierarchical and the
inverse-hierarchica cases, respectively, which can be tested in next generation
neutrino-less double beta decay experiments. Introducing a single physical CP
phase in $m_D$, we examine baryon asymmetry through leptogenesis.
Interestingly, through the CP phase there are correlations between the amount
of baryon asymmetry and neutrino oscillation parameters. We find that for a
fixed CP phase, the hierarchical case also succeeds in generating the observed
baryon asymmetry in our universe, plus a non-vanishing $U_{e3}$ which is
accessible in future baseline neutrino oscillation experiments.
We investigate the phenomenology of a model based on the \(SU(3)_c\times SU(3)_L\times U(1)_X\) gauge theory, the so-called 331 model. In particular, we focus on the Higgs sector of the model which ...is composed of three \(SU(3)_L\) triplet Higgs fields, and this corresponds to the minimal form to realize phenomenologically acceptable scenario. After the spontaneous symmetry breaking \(SU(3)_L\times U(1)_X\to SU(2)_L\times U(1)_Y\), our Higgs sector effectively becomes that with two \(SU(2)_L\) doublet scalar fields, in which the first and the second generation quarks couple to the different Higgs doublet from that couples to the third generation quarks. This structure causes the flavour changing neutral current mediated by Higgs bosons at the tree level. By taking an alignment limit of the mass matrix for the CP-even Higgs bosons, which is naturally realized in the case with the breaking scale of \(SU(3)_L\times U(1)_X\) to be much larger than that of \(SU(2)_L\times U(1)_Y\), we can avoid current constraints from flavour experiments such as the \(B^0\)-\(\bar{B}^0\) mixing even for the Higgs bosons masses being \({\cal O}(100)\) GeV. In this allowed parameter space, we clarify that a characteristic deviation in quark Yukawa couplings of the standard model-like Higgs boson is predicted, which has a different pattern from that seen in two Higgs doublet models with a softly-broken \(Z_2\) symmetry. We also find that the flavour violating decay modes of the extra Higgs boson, e.g., \(H/A \to tc\) and \(H^\pm \to ts\) can be dominant, and they yield the important signature to distinguish our model from the two Higgs doublet models.
In the presence of non-minimal gravitational coupling \( \xi H^\dagger H {\cal R}\) between the standard model (SM) Higgs doublet \(H\) and the curvature scalar \({\cal R}\), the effective ...ultraviolet cutoff scale is given by \(\Lambda_{\rm cut}\approx m_P/\xi\), where \(m_P\) is the reduced Planck mass, and \(\xi \gtrsim 1\) is a dimensionless coupling constant. In type I and type III seesaw extended SM, which can naturally explain the observed solar and atmospheric neutrino oscillations, we investigate the implications of this non-minimal gravitational coupling for the SM Higgs boson mass bounds based on vacuum stability and perturbativity arguments. A lower bound on the Higgs boson mass close to 120 GeV is realized with type III seesaw and \(\xi \sim 10-10^3\).
Phys.Lett.B669:34-38,2008 There are lots of new physics models which predict an extra neutral gauge
boson, referred as Z'-boson. In a certain class of these new physics models,
the Z'-boson has ...flavor-dependent couplings with the fermions in the Standard
Model (SM). Based on a simple model in which couplings of the SM fermions in
the third generation with the Z'-boson are different from those of the
corresponding fermions in the first two generations, we study the signatures of
Z'-boson at the Large Hadron Collider (LHC) and the International Linear
Collider (ILC). We show that at the LHC, the Z'-boson with mass around 1 TeV
can be produced through the Drell-Yan processes and its dilepton decay modes
provide us clean signatures not only for the resonant production of Z'-boson
but also for flavor-dependences of the production cross sections. We also study
fermion pair productions at the ILC involving the virtual Z'-boson exchange.
Even though the center-of-energy of the ILC is much lower than a Z'-boson mass,
the angular distributions and the forward-backward asymmetries of fermion pair
productions show not only sizable deviations from the SM predictions but also
significant flavor-dependences.
We examine the leading order noncommutative corrections to the differential and total cross sections for e+ e- --> q q-bar. After averaging over the earth's rotation, the results depend on the ...latitude for the collider, as well as the direction of the incoming beam. They also depend on scale and direction of the noncommutativity. Using data from LEP, we exclude regions in the parameter space spanned by the noncommutative scale and angle relative to the earth's axis. We also investigate possible implications for phenomenology at the future International Linear Collider.
Prog.Theor.Phys.116:757-769,2007 The gauge coupling unification is one of main motivations in the split-SUSY
scenario, and the existence of the grand unified theories (GUTs) is assumed. We
examine ...how to realize split-SUSY mass spectrum in the context of GUTs and find
that the construction of split-SUSY GUTs is by no means straightforward. With
R-symmetry breaking sources in the GUT sector,
GUT particles play a role of the messengers in the gauge mediation scenario
and their contributions to gaugino masses can be sizable. We find the upper
bound on soft scalar masses of
O(10^{10}) GeV from consistency for constructing the split-SUSY GUT. Also, we
discuss the attempt to construct R-symmetric GUT models.
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