Electron/Muon Specific Two Higgs Doublet Model

We discuss two Higgs doublet models with a softly-broken discrete $\mathbb{S}_3$ symmery, where the mass matrix for charged-leptons is predicted as the diagonal form in the weak eigenbasis of lepton fields. Similar to an introduction of $\mathbb{Z}_2$ symmetry, the tree level flavor changing neutral current can be forbidden by imposing the $\mathbb{S}_3$ symmetry to the model. Under the $\mathbb{S}_3$ symmetry, there are four types of Yukawa interactions depending on the $\mathbb{S}_3$ charge assignment to right-handed fermions. We find that extra Higgs bosons can be muon and electron specific in one of four types of the Yukawa interaction. This property does not appear in any other two Higgs doublet models with a softly-broken ${\mathbb Z}_2$ symmetry. We discuss the phenomenology of the muon and electron specific Higgs bosons at the Large Hadron Collider; namely we evaluate allowed parameter regions from the current Higgs boson search data and discovery potential of such a Higgs boson at the 14 TeV run.Comment: 17 pages, 5 figures, 6 tables; version published in Nuclear Physics

Light Dark Matter Candidate in B-L Gauged Radiative Inverse Seesaw

We study a radiative inverse seesaw model with local B-L symmetry, in which we extend the neutrino mass structure that is generated through a kind of inverse seesaw framework to the more generic one than our previous work. We focus on a real part of bosonic particle as a dark matter and investigate the features in O(1-80) GeV mass range, reported by the experiments such as CoGeNT and XENON (2012).Comment: 10 pages, 1 table, 3 figures; version accepted for publication in European Physical Journal

A Comment on Nishimura, Nakajima, and Kiyota's "Does the natural selection mechanism still work in severe recessions? Examination of the Japanese economy in the 1990s"

Nishimura et al. (2005) analyze the entry/exit behavior of Japanese firms during the 1990s and find that relatively efficient firms exited while relatively inefficient firms survived during the banking-crisis period of 1996-97. They conclude that the natural selection mechanism (NSM) apparently malfunctions during severe recessions, but we offer a more plausible interpretation: NSM continued to function effectively even during this period, but aberrant banking practices caused a shift in the type of natural selection from directional to disruptive selection, with the most efficient as well as the least efficient firms being favored and firms of intermediate efficiency being selected against.

A Comment on Nishimura, Nakajima, and Kiyota's "Does the Natural Selection Mechanism Still Work in Severe Recessions? Examination of the Japanese Economy in the 1990s"

Nishimura, Nakajima, and Kiyota (2005) analyze the entry/exit behavior patterns of Japanese firms during the 1990s and find that relatively efficient (high total factor productivity (TFP)) firms exited while relatively inefficient (low TFP) firms survived during the banking-crisis period of 1996-97. They conclude from this finding that the natural selection mechanism (NSM) apparently malfunctions during severe recessions, but we offer a much more plausible interpretation: the NSM continued to function effectively even during this period, but aberrant banking practices (in particular, "forbearance lending" ("evergreening") and the "forcible withdrawal of loans" and/or the "reluctance to lend") caused a shift in the type of natural selection from "directional selection" to "disruptive selection," with the most efficient (highest TFP) firms as well as the least efficient (lowest TFP) firms being favored and firms of intermediate efficiency and TFP being selected against.