arXiv subjects

Naoyuki Haba

Publications and source records attributed to Naoyuki Haba.

151 records · Page 9Linked to original sources

arXiv1996

Large Majorana Mass from the Anomalous U(1) Gauge Symmetry

We show a new and simple model which induces large Majorana masses of right-handed neutrinos. It is based on U(1)_X anomalous gauge symmetry, which is cancelled by the Green-Schwarz mechanism. These Majorana masses can solve the solar neutrino problem by the vacuum oscillation mechanism. The superpotential of this model is scale invariant. The field contents are simple extensions of the MSSM, which have four standard gauge singlet fields, two extra vector-like fields, and right-handed neutrinos in addition to the MSSM.

hep-ph↗

arXiv1996

Can the Higgs Sector Trigger CP Violation in the MSSM?

We reanalyze the possibility of CP violation in the Higgs sector of the minimal supersymmetric standard model (MSSM). Contrary to the result of previous analysis, spontaneous CP violation can not occur by only chargino and neutralino radiative corrections since the vacuum does not stable. Top and stop radiative corrections are crucially needed. However even with this correction there is no experimentally allowed region in \tan β\geq 1. This situation is not remedied even if the stop left-right mixing is included. We also analyze explicit CP violation in the Higgs sector of the MSSM and show that the effect is too small to influence the phenomenology. We thus show that the Higgs sector can not, by itself, trigger CP violation in the MSSM.

hep-ph↗

arXiv1996

Explicit CP Violation in the Higgs Sector of the Next-to-Minimal Supersymmetric Standard Model

We analyze explicit CP violation in the Higgs sector of the next-to-minimal supersymmetric standard model which contains an additional gauge singlet field N. It is shown that there is no mixing among scalar and pseudoscalar Higgs fields in the two Higgs doublets, and scalar-pseudoscalar mixings could exist between two Higgs doublets and the singlet N, and between N itself. CP symmetry is conserved in the extreme limits of < N > >> v, < N > << v, and tan beta >> 1. In the region of < N > = O(v) and tan beta = O(1), large scalar-pseudoscalar mixings are realized, and this effect can reduce the lightest Higgs mass. The mass difference between no mixing and mixing case is about 10 - 30 GeV. The neutron electric dipole moment in this model is consistent with the present experimental upper limit provided that squark and gaugino masses are heavy enough of O(1) TeV.

hep-ph↗

arXiv1996

Higgs Masses and $CP$ Violation in SUSY Models

Though the mass of Higgs particle is the parameter determined by the experiment in the standard model (SM), SUSY models have rather predictive power for the lightest Higgs mass, and its upper bound in some SUSY models are close to the observable region in LEP2. The upper bound of the lightest Higgs mass is analysed systematically on the basis of the $CP$ violation in the minimal and the next minimal supersymmetric standard model (MSSM and NMSSM). In the explicit $CP$ violation case, the mass bound is large around $130 \sim 160$ GeV in both models. In the spontaneous $CP$ violation case induced by the radiative effects, the lightest Higgs mass upper bound is about $52$ GeV and sum of two light neutral Higgs should be around $O$(100 GeV) in the NMSSM in contrast to the one in the MSSM which implies about 6 GeV. This model gives the interesting predictions for the neutron electric dipole moment.

hep-ph↗

arXiv1995

Quark-Lepton Masses and the Ckm Matrix in a String Inspired Model

In the context of the Calabi-Yau string model we discuss the origin of characteristic pattern of quark-lepton masses and the CKM matrix. The discrete $R$-symmetry $Z_{2k+1} \times Z_2$ is introduced and the $Z_2$ is assigned to the $R$-parity. The gauge symmetry at the string scale is broken into the standard model gauge group at an intermediate energy scale. At energies below the intermediate scale down-type quarks and also leptons are mixed with unobserved heavy states, respectively. On the other hand, there are no such mixings for up-type quarks. The large mixings between light states and heavy ones cause different mass pattern of leptons and down-type quarks from that of up-type quarks and yield a nontrivial CKM matrix for quarks but a trivial one for leptons. The mixing mechanism is illustrated using a two-generation toy model.

hep-ph↗

arXiv1994

The Aligned $SU(5) \times U(1)^2$ Model

In Calabi-Yau string compactification, it is pointed out that there exists a new type of $SU(5) \times U(1)^2$ model (the aligned $SU(5) \times U(1)^2$ model) in which the $SU(5)$ differs from the standard $SU(5)$ and also from the flipped $SU(5)$. With the aid of the discrete symmetry suggested from Gepner model, we construct a simple and phenomenologically interesting three-generation model with the aligned $SU(5) \times U(1)^2$ gauge symmetry. The triplet-doublet splitting problem can be solved. It is also found that there is a realistic solution for solar neutrino problem and for the $μ$-problem. At low energies this model is in accord with the minimal supersymmetric standard model except for the existence of singlet fields with masses of $O(1)$TeV.

hep-ph↗

arXiv1993

A Large Majorana-Mass From Calabi-Yau Superstring Models

In Calabi-Yau superstring models it is found that two large intermediate energy scales of symmetry breaking can be induced for special types of the nonrenormalizable interactions. In the models one set of $SO(10)$-singlet, right-handed neutrino and their mirror chiral superfields is needed. Through the study of the minimization of the scalarpotential, the conditions for the presence of two large intermediate scales are obtained. In this scheme a Majorana-mass possibly amounts to $O(10^{9 \sim 10}\gev)$. This large Majorana-mass solves the solar neutrino problem and also is compatible with the cosmological bound for stable light neutrinos.

hep-ph↗