Probing Models of Neutrino Masses via the Flavor Structure of the Mass Matrix

We discuss what kinds of combinations of Yukawa interactions can generate the Majorana neutrino mass matrix. We concentrate on the flavor structure of the neutrino mass matrix because it does not depend on details of the models except for Yukawa interactions while determination of the overall scale of the mass matrix requires to specify also the scalar potential and masses of new particles. Thus, models to generate Majorana neutrino mass matrix can be efficiently classified according to the combination of Yukawa interactions. We first investigate the case where Yukawa interactions with only leptons are utilized. Next, we consider the case with Yukawa interactions between leptons and gauge singlet fermions, which have the odd parity under the unbroken Z_2 symmetry. We show that combinations of Yukawa interactions for these cases can be classified into only three groups. Our classification would be useful for the efficient discrimination of models via experimental tests for not each model but just three groups of models.Comment: 14 pages, 9 eps files, references adde

Loop Suppression of Dirac Neutrino Mass in the Neutrinophilic Two Higgs Doublet Model

We extend the scalar sector of the neutrinophilic two Higgs doublet model, where small masses of Dirac neutrinos are obtained via a small vacuum expectation value v_nu of the neutrinophilic SU(2)_L-doublet scalar field which has a Yukawa interaction with only right-handed neutrinos. A global U(1)_X symmetry is used for the neutrinophilic nature of the second SU(2)_L-doublet scalar field and also for eliminating Majorana mass terms of neutrinos. By virtue of an appropriate assignment of the U(1)_X-charges to new particles, our model has an unbroken Z_2 symmetry, under which the lightest Z_2-odd scalar boson can be a dark matter candidate. In our model, v_nu is generated by the one-loop diagram to which Z_2-odd particles contribute. We briefly discuss a possible signature of our model at the LHC.Comment: 15 pages, 2 figures, published in Physics Letters

Probing Models of Dirac Neutrino Masses via the Flavor Structure of the Mass Matrix

We classify models of the Dirac neutrino mass by concentrating on flavor structures of the mass matrix. The advantage of our classification is that we do not need to specify detail of models except for Yukawa interactions because flavor structures can be given only by products of Yukawa matrices. All possible Yukawa interactions between leptons (including the right-handed neutrino) are taken into account by introducing appropriate scalar fields. We also take into account the case with Yukawa interactions of leptons with the dark matter candidate. Then, we see that flavor structures can be classified into seven groups. The result is useful for the efficient test of models of the neutrino mass. One of seven groups can be tested by measuring the absolute neutrino mass. Other two can be tested by probing the violation of the lepton universality in $\ell \to \ell^\prime \nu \overline{\nu}$. In order to test the other four groups, we can rely on searches for new scalar particles at collider experiments.Comment: 21 pages, 20 eps files, published in PL

Japan's Export Trade, 1859-1899, With Special Reference to Silk, Tea and Coal.

My intention is to contribute to an understanding of Japan's economic development in the context of changes in the world economic structure during the second half of the nineteenth century, and to clarify the role of exports of primary products in industrialization. I focus on Japan's export trade with reference to her three main export articles of raw silk, tea and coal, which played a strategic role as the main source of finance for her industrialization. I have reviewed the interrelationship between the overseas market and the development of these export industries, in both its quantitative and qualitative aspects, examining in particular the question of international competitiveness. Exports of raw silk and tea, which were products of traditional industries, developed in connection with the European and American markets, where they competed with Chinese products; coal was developed as a modern industry by the Zaibatsu for the Asian market, and sold in competition with exports from Britain and Australia. The development of these industries was encouraged by various forms of institutional support from the Meiji government. I conclude that success in exporting depended on the degree to which exports could compete in the overseas market. This in turn basically depended on factors of quality, supply and price. In the case of silk and coal, Japan was able to increase exports through adjustment to overseas demand, mainly adjustments in production costs and technology. She was aided by favourable international economic factors such as the depreciation in the value of silver. Tea provides a contrasting example of a case where Japan failed to maintain competitiveness, due to unfavourable market conditions. Primary material has come mainly from British and United States consular reports, the Jardine Matheson Archive, papers in the Public Record Office, Japanese and Chinese records, and official statistics

New model for radiatively generated Dirac neutrino masses and lepton flavor violating decays of the Higgs boson

We propose a new mechanism to explain neutrino masses with lepton number conservation, in which the Dirac neutrino masses are generated at the two-loop level involving a dark matter candidate. In this model, branching ratios of lepton flavor violating decays of the Higgs boson can be much larger than those of lepton flavor violating decays of charged leptons. If lepton flavor violating decays of the Higgs boson are observed at future collider experiments without detecting lepton flavor violating decays of charged leptons, most of the models previously proposed for tiny neutrino masses are excluded while our model can still survive. We show that the model can be viable under constraints from current data for neutrino experiments, searches for lepton flavor violating decays of charged leptons and dark matter experiments.Comment: 26 pages, 9 eps file

Testing neutrino mass generation mechanisms from the lepton flavor violating decay of the Higgs boson

We investigate how observations of the lepton flavor violating decay of the Higgs boson ($h \to \ell\ell^\prime$) can narrow down models of neutrino mass generation mechanisms, which were systematically studied in Refs. [1,2] by focusing on the combination of new Yukawa coupling matrices with leptons. We find that a wide class of models for neutrino masses can be excluded if evidence for $h \to \ell\ell^\prime$ is really obtained in the current or future collider experiments. In particular, simple models of Majorana neutrino masses cannot be compatible with the observation of $h \to \ell\ell^\prime$. It is also found that some of the simple models to generate masses of Dirac neutrinos radiatively can be compatible with a significant rate of the $h \to \ell\ell^\prime$ process.Comment: 16 pages, 7 eps files, published in PL

Compton Spectrum from Poynting Flux Accelerated e+e- Plasma

We report the Compton scattering emission from the Poynting flux acceleration of electron- positron plasma simulated by the 2-1/2 dimensional particle-in-cell(PIC) code. We show these and other remarkable properties of Poynting flux acceleration and Compton spectral output, and discuss the agreement with the observed spectra of GRBs and XRFs.Comment: 4 pages, 4 figures, submitted to Swift GRB Workshop Proceedings 2006 (in press