Gauge Origin of Discrete Flavor Symmetries in Heterotic Orbifolds

We show that non-Abelian discrete symmetries in orbifold string models have a gauge origin. This can be understood when looking at the vicinity of a symmetry enhanced point in moduli space. At such an enhanced point, orbifold fixed points are characterized by an enhanced gauge symmetry. This gauge symmetry can be broken to a discrete subgroup by a nontrivial vacuum expectation value of the K\"ahler modulus $T$. Using this mechanism it is shown that the $\Delta(54)$ non-Abelian discrete symmetry group originates from a $SU(3)$ gauge symmetry, whereas the $D_4$ symmetry group is obtained from a $SU(2)$ gauge symmetry.Comment: 12 page

Three-generation Asymmetric Orbifold Models from Heterotic String Theory

Using Z3 asymmetric orbifolds in heterotic string theory, we construct N=1 SUSY three-generation models with the standard model gauge group SU(3)_C \times SU(2)_L \times U(1)_Y and the left-right symmetric group SU(3)_C \times SU(2)_L \times SU(2)_R \times U(1)_{B-L}. One of the models possesses a gauge flavor symmetry for the Z3 twisted matter.Comment: 24 page

Gauge extension of non-Abelian discrete flavor symmetry

We investigate a gauge theory realization of non-Abelian discrete flavor symmetries and apply the gauge enhancement mechanism in heterotic orbifold models to field-theoretical model building. Several phenomenologically interesting non-Abelian discrete symmetries are realized effectively from a $U(1)$ gauge theory with a permutation symmetry. We also construct a concrete model for the lepton sector based on a $U(1)^2 \rtimes S_3$ symmetry.Comment: 18 pages, 1 figur

O, Ne, Mg, and Fe abundances in hot X-ray emitting halos of galaxy clusters, groups, and giant early-type galaxies with XMM-Newton RGS spectroscopy

Chemical elements in the hot medium permeating early-type galaxies, groups, and clusters make them an excellent laboratory for studying metal enrichment and cycling processes in the largest scales of the Universe. Here, we report the XMM-Newton RGS analysis of 14 early-type galaxies, including the well-known brightest cluster galaxies of Perseus, for instance. The spatial distribution of the O/Fe, Ne/Fe, and Mg/Fe ratios is generally flat at the central 60 arcsecond regions of each object, irrespective of whether or not a central Fe abundance drop has been reported. Common profiles between noble gas and normal metal suggest that the dust depletion process does not work predominantly in these systems. Therefore, observed abundance drops are possibly attributed to other origins, like systematics in the atomic codes. Giant systems of high gas mass-to-luminosity ratio tend to hold a hot gas ($\sim$ 2 keV) yielding the solar N/Fe, O/Fe, Ne/Fe, Mg/Fe, and Ni/Fe ratios. Contrarily, light systems at a subkiloelectronvolt temperature regime, including isolated or group-centered galaxies, generally exhibit super-solar N/Fe, Ni/Fe, Ne/O, and Mg/O ratios. We find that the latest supernova nucleosynthesis models fail to reproduce such a super-solar abundance pattern. Possible systematic uncertainties contributing to these high abundance ratios of cool objects are also discussed in tandem with the crucial role of future X-ray missions.Comment: submitted to Ap

Affirmation of the effect of pH on shake-gel and shear thickening of a mixed suspension of polyethylene oxide and silica nanoparticles

The mixture of silica nanoparticles and polyethylene oxide (PEO) shows unique rheological behaviors, such as reversible gelation and shear thickening, when moderate shear is applied. These behaviors are attributed to the transient bridging network, which is formed via the simultaneous adsorption of a PEO chain onto multiple silica nanoparticles. The adsorption affinity depends on pH and thus, we expect that these behaviors change with pH. Nevertheless, the effect of pH on shake-gel behavior and shear thickening has not yet been systematically examined. In order to improve our understanding, we attempt to study the influence of pH and ionic strength on the relaxation time of the gel and the viscosity of the mixture. Our experimental results demonstrate that shake-gel and shear thickening can be observed in the pH range of 8.0–9.9. Moreover, the relaxation time required for the gel recovery to sol increases and the critical shear rate at which the viscosity begins to rise decreases as the pH decreases. Furthermore, we determined that irreversible shake-gels can be obtained in a narrow range of PEO concentrations at the pH of approximately 8.0. In conclusion, we determined that the relaxation time of gel is longer at low pH, and the critical shear rate decreases with the decrease in interparticle repulsion of silica

A lack of classical Cepheids in the inner part of the Galactic disk

Recent large-scale infrared surveys have been revealing stellar populations in the inner Galaxy seen through strong interstellar extinction in the disk. In particular, classical Cepheids with their period-luminosity and period-age relations are useful tracers of Galactic structure and evolution. Interesting groups of Cepheids reported recently include four Cepheids in the Nuclear Stellar Disk (NSD), about 200 pc around the Galactic Centre, found by Matsunaga et al. and those spread across the inner part of the disk reported by Dekany and collaborators. We here report our discovery of nearly thirty classical Cepheids towards the bulge region, some of which are common with Dekany et al., and discuss the large impact of the reddening correction on distance estimates for these objects. Assuming that the four Cepheids in the NSD are located at the distance of the Galactic Centre and that the near-infrared extinction law, i.e. wavelength dependency of the interstellar extinction, is not systematically different between the NSD and other bulge lines-of-sight, most of the other Cepheids presented here are located significantly further than the Galactic Centre. This suggests a lack of Cepheids in the inner 2.5 kpc region of the Galactic disk except the NSD. Recent radio observations show a similar distribution of star-forming regions.Comment: 8 pages, 4 figures, accepted for publication in MNRA

Cepheids and other short-period variables near the Galactic Centre

We report the result of our near-infrared survey of short-period variable stars (P<60d) in a field-of-view of 20'x30' towards the Galactic Centre. Forty-five variables are discovered and we classify the variables based on their light curve shapes and other evidence. In addition to 3 classical Cepheids reported previously, we find 16 type II Cepheids, 24 eclipsing binaries, one pulsating star with P=0.265d (RR Lyr or delta Sct) and one Cepheid-like variable whose nature is uncertain. Eclipsing binaries are separated into the foreground objects and those significantly obscured by interstellar extinction. One of the reddened binaries contains an O-type supergiant and its light curve indicates an eccentric orbit. We discuss the nature and distribution of type II Cepheids as well as the distance to the Galactic Centre based on these Cepheids and other distance indicators. The estimates of R0(GC) we obtained based on photometric data agree with previous results obtained with kinematics of objects around the GC. Furthermore, our result gives a support to the reddening law obtained by Nishiyama and collaborators, A(Ks)/E(H-Ks)=1.44, because a different reddening law would result in a rather different distance estimate.Comment: 13 pages, 10 figures, 7tables, accepted for publication in MNRA