Masaki Yamada

6-Amino-2,2′-bipyridine as a new fluorescent organic compound

6,6′-Diamino-2,2′-bipyridine (1a) has been found to exhibit a strong fluorescence in the near-UV region. Some amino and/or chloro substituted bipyridines (bpys) have been synthesized and studied to show that only 6-amino-substituted derivatives exhibited a strong emission. The emission of 6-amino-6′-chloro-bpy (3a) was the strongest (λmax= 429.0 nm; Φ= 0.78 in ethanol) among them. On the other hand, little or no emission was observed for monochloro-, dichloro- and 4-amino- derivatives.

Dark Matter Production in Late Time Reheating

We estimate dark matter density for the Universe with a reheating temperature smaller than the mass of dark matter, assuming dark matter to be a weakly interacting massive particle. During the reheating process, an inaton decays and releases high energy particles, which are scattered inelastically by the thermal plasma and emit many particles. Dark matters are produced through these inelastic scattering processes and pair creation processes by high energy particles. We properly take account of the Landau-Pomeranchuk-Migdal eect on inelastic processes and show that the resultant energy density of dark matter is much larger than that estimated in the literature and can be consistent with that observed when the mass of dark matter is larger than O(100) GeV.

A comprehensive quantification method for eicosanoids and related compounds by using liquid chromatography/mass spectrometry with high speed continuous ionization polarity switching

Fatty acids and related metabolites, comprising several hundreds of molecular species, are an important target in disease metabolomics, as they are involved in various mammalian pathologies and physiologies. Selected reaction monitoring (SRM) analysis, which is capable of monitoring hundreds of compounds in a single run, has been widely used for comprehensive quantification. However, it is difficult to monitor a large number of compounds with different ionization polarity, as polarity switching requires a sub-second period per cycle in classical mass spectrometers. In the present study, we developed and evaluated a comprehensive quantification method for eicosanoids and related compounds by using LC/MS with high-speed continuous ionization polarity switching. The new method employs a fast (30ms/cycle) continuous ionization polarity switching, and differentiates 137 targets either by chromatography or by SRM transition. Polarity switching did not affect the lower limits of quantification, which ranged similarly from 0.5 to 200pg on column. Lipid extracts from mouse tissues were analyzed by this method, and 65 targets were quantitatively detected in the brain, including 6 compounds analyzed in the positive ion mode. We demonstrated that a fast continuous ionization polarity switching enables the quantification of a wide variety of lipid mediator species without compromising the sensitivity and reliability.

Metamagnetic properties of MnSi near the critical pressure

The magnetization of MnSi has been measured at low temperatures down to 1.4 K under high pressures up to P=1.7 GPa and magnetic fields up to B=9 T. The magnetic transition at TC is second-order for 0 GPa≤P 1.5 GPa, where a low magnetic field produces a metamagnetic transition from the nonmagnetic to a conical magnetic state at low temperatures. In the first-order region 1.2 GPa<P<1.5 GPa, a metamagnetic transition appears also just above TC. In the above three pressure regions, magnetic phase diagrams are determined in the B–T plane. Shapes of the phase diagrams are quite different from each other. This can be explained well by a theory of itinerant electron metamagnetism considering thermal spin fluctuations.

Influence of pressure on itinerant electron metamagnetic transition in La(FexSi1−x)13 compounds

The influence of pressure on the itinerant electron metamagnetic (IEM) transition has been investigated for a La(FexSi1−x)13 compound. The critical temperature T0 defined as the disappearance point of the IEM transition decreases with increasing hydrostatic pressure. Since the pressure dependence of T0 is smaller than that of TC, the temperature range for appearance of the IEM transition becomes wider with increasing hydrostatic pressure. These results are consistent with the theoretical model based on the Landau expansion of free energy including the influence of spin fluctuations and the magnetovolume effect. On applying pressure, the critical field Bc for the IEM transition increases proportionally with temperature in low pressures, whereas it exhibits a quadratic temperature dependence with lowering the Curie temperature in high pressures. The change in the temperature dependence of Bc is explained by a change in the thermal growth rate of spin fluctuations.

Thermalization Process after Inflation and Effective Potential of Scalar Field

We investigate the thermalization process of the Universe after inflation to determine the evolution of the effective temperature. The time scale of thermalization is found to be so long that it delays the evolution of the effective temperature, and the resulting maximal temperature of the Universe can be significantly lower than the one obtained in the literature. Our results clarify the finite density corrections to the effective potential of a scalar field and also processes of heavy particle production. In particular, we find that the maximum temperature of the Universe may be at most electroweak scale if the reheating temperature is as low as Script Oxa0(1) MeV, which implies that the electroweak symmetry may be marginally restored. In addition, it is noticeable that the dark matter may not be produced from thermal plasma in such a low reheating scenario, since the maximum temperature can be smaller than the conventional estimation by five orders of magnitude. We also give implications to the Peccei-Quinn mechanism and the Affleck-Dine baryogenesis.

Inflation in random Gaussian landscapes

We develop analytic and numerical techniques for studying the statistics of slow-roll inflation in random Gaussian landscapes. As an illustration of these techniques, we analyze small-field inflation in a one-dimensional landscape. We calculate the probability distributions for the maximal number of e-folds and for the spectral index of density fluctuations

Suppressing the QCD Axion Abundance by Hidden Monopoles

n_s

Realization of a micrometre-scale spin-wave interferometer

and its running

Revisiting the gravitino dark matter and baryon asymmetry from Q-ball decay in gauge mediation

alpha_s