Muon specific two-Higgs-doublet model

We investigate a new type of a two-Higgs-doublet model as a solution of the muon $g-2$ anomaly. We impose a softly-broken $Z_4$ symmetry to forbid tree level flavor changing neutral currents in a natural way. This $Z_4$ symmetry restricts the structure of Yukawa couplings. As a result, extra Higgs boson couplings to muons are enhanced by a factor of $\tan\beta$, while their couplings to all the other standard model fermions are suppressed by $\cot\beta$. Thanks to this coupling property, we can avoid the constraint from leptonic $\tau$ decays in contrast to the lepton specific two-Higgs-doublet model, which can explain the muon $g-2$ within the 2$\sigma$ level but cannot within the $1\sigma$ level due to this constraint. We find that the model can explain the muon $g-2$ within the 1$\sigma$ level satisfying constraints from perturbative unitarity, vacuum stability, electroweak precision measurements, and current LHC data.Comment: 24 pages, 3 figure

Changing Wealth Inequality in Japan

The 13th Next-Generation Global Workshop第13回次世代グローバルワークショップテーマ: New Risks and Resilience in Asian Societies and the World 日程: 21-23 November, 2020 開催場所: ベトナム社会科学院(ハノイ)/Vietnam Academy of Social Sciences(No. 1 Lieu Giai street, Ba Dinh, Hanoi, Vietnam) ※Due to the COVID-19, the workshop will be held at ONLINE for overseas participants(not from Vietnam)/ONSITE for Vietnamese participants

Gravitational Wave Background from Population III Stars

We estimate the gravitational wave (GW) background from Population III (Pop III) stars using the results from our hydrodynamic simulations (Suwa et al. 2007). We calculate gravitational waveforms from matter motions and anisotropic neutrino emissions for single Pop III stars. We find that the GW amplitudes from matter motions are dominant until just after bounce, but those from neutrinos dominate later on at frequencies below $\sim 10$ Hz in the GW spectrum. Computing the overall signal produced by the ensemble of such Pop III stars, we find that the resultant density parameter of the GW background peaks at the amplitude of $\Omega_\mathrm{GW}\sim 10^{-10}$ in the frequency interval $\sim 1-10$ Hz. We show that such signals, depending on the formation rate of Pop III stars, can be within the detection limits of future planned interferometers such as DECIGO and BBO in the frequency interval of $\sim 0.1-1$ Hz. Our results suggest that the detection of the GW background from Pop III stars can be an important tool to supply the information about the star formation history in the early universe.Comment: 4 pages, 3 figures, accepted for publication in ApJ

Quantum Nucleation of Two-Flavor Quark Matter in Neutron Stars

Rates for nucleation of two-flavor quark matter in a neutron star core, originally composed of nuclear matter in $\beta$ equilibrium, are calculated at zero temperature by a quantum tunneling analysis incorporating the electrostatic energy. We find that a nucleated droplet would develop into bulk matter due to electron screening effects.Comment: 8 pages (LaTeX, PTP style), 4 Postscript figures, to be published in Prog. Theor. Phys. (Letters