Time-Reversal Symmetry-Breaking Nematic Insulators near Quantum Spin Hall Phase Transitions

We study the phase diagram of a model quantum spin Hall system as a function of band inversion and band-coupling strength, demonstrating that when band hybridization is weak, an interaction-induced nematic insulator state emerges over a wide range of band inversion. This property is a consequence of the long-range Coulomb interaction, which favors interband phase coherence that is weakly dependent on momentum and therefore frustrated by the single-particle Hamiltonian at the band inversion point. For weak band hybridization, interactions convert the continuous gap closing topological phase transition at inversion into a pair of continuous phase transitions bounding a state with broken time-reversal and rotational symmetries. At intermediate band hybridization, the topological phase transition proceeds instead via a quantum anomalous Hall insulator state, whereas at strong hybridization interactions play no role. We comment on the implications of our findings for InAs/GaSb and HgTe/CdTe quantum spin Hall systems.Comment: 5 pages, 3 figures plus 4 pages supplemental material, accepted for publication in Physical Review Letter

Geotechnical Aspects of Recent Japan Earthquakes

Recently middle class earthquakes have occurred and caused various geotechnical damages every year in Japan. Among them geotechnical damages during five earthquakes from 2004 to 2008 are introduced. The 2004 Niigataken-chuetsu earthquake caused failure of expressway embankments and uplift of sewage manholes. Liquefaction-induced damage to quay walls and tanks occurred in artificially reclaimed lands during the 2005 Fukuokaken-seiho-oki earthquake. Liquefiable area had been predicted about 17 years before the earthquake. Liquefied zones were fairly coincided with the predicted liquefiable zones. Very severe slide of highway embankments occurred at 11 sites during the 2007 Notohanto earthquake. During the 2007 Niigataken-chuetsu-oki earthquake, liquefaction induced in old river channels and on gentle slopes of sand dunes, and caused settlement of houses and breakage of low pressure gas pipes. However, some houses, sewage manholes, gas pipes were survived. Huge landslides and serious debris flows occurred along the slopes of Kurikoma Volcano during the 2008 Iwate-Miyagi-nairiku earthquake. Many landslides and debris flows occurred

Experimental T33-stress Formulation of Test Specimen Thickness Effect on Fracture Toughness in the Transition Temperature Region

This paper describes a study of the test specimen thickness effect on fracture toughness of a material, in the transition temperature region, for CT specimens. In addition we studied the specimen thickness effect on the T33-stress (the out-of-plane non-singular term in the series of elastic crack-tip stress fields), expecting that T33-stress affected the crack-tip triaxiality and thus constraint in the out-of-plane direction. Finally, an experimental expression for the thickness effect on the fracture toughness using T33-stress is proposed for 0.55% carbon steel S55C. In addition to the fact that T33 (which was negative) seemed to show an upper bound for large B/W, these results indicate the possibility of improving the existing methods for correlating fracture toughness obtained by test specimen with the toughness of actual cracks found in the structure, using T33–stress

Simultaneous flood risk analysis and its future change among all the 109 class-A river basins in Japan using a large ensemble climate simulation database d4PDF

This study investigated simultaneous flood risk among all the 109 class-A river basins over Japan using the big data of (over 1000 years) annual maximum hourly flow simulated from a large ensemble climate simulation database for policy decision making for future climate change, and proposed a novel approach in its geospatial analysis by applying two informatics techniques: the association rule analysis and graph theory. Frequency analysis of the number of rivers with the annual maximum flow over the flow capacity in the same year (defined as simultaneous flooding here) indicated that simultaneous flood risk will increase in the future climate under 4-degree rise scenarios in Japan, whose increment is larger than the variation of sea surface temperature projections. As the result, the return period of simultaneous flooding in eight river basins (the same number as in a severe storm in western Japan, 2018, causing the second worst economic damage since 1962) is estimated at 400 years in the historical experiment, 25 years in the 4-degree rise experiment. The association rule and graph theory analyses for the big data of annual maximum flows in the future climate scenarios indicated that simultaneous flood occurrence is dominated by spatial distance at a national scale as well as by the spatial relation between mountainous ridges and typhoon courses at a regional scale. Large ensemble climate simulation data combined with the informatics technology is a powerful approach to simultaneous flood risk analysis

SPADExp: A photoemission angular distribution simulator directly linked to first-principles calculations

We develop a software package SPADExp (simulator of photoemission angular distribution for experiments) to calculate the photoemission angular distribution (PAD), which is the momentum dependence of spectrum intensity in angle-resolved photoemission spectroscopy (ARPES). The software can directly load the output of the first-principles software package OpenMX, so users do not need to construct tight-binding models as previous studies did for PAD calculations. As a result, we can calculate the PADs of large systems such as quasicrystals and slab systems. We calculate the PADs of sublattice systems (graphene and graphite) to reproduce characteristic intensity distributions, which ARPES has experimentally observed. After that, we investigate twisted bilayer graphene, a quasicrystal showing 12-fold rotational symmetric spectra in ARPES, and the surface states of the topological insulator $\mathrm{Bi}_2\mathrm{Se}_3$. Our calculations show good agreement with previous ARPES measurements, showing the correctness of our calculation software and further potential to investigate the photoemission spectra of novel quantum materials.Comment: 19 pages, 5 figures, Software has been developed in https://github.com/Hiroaki-Tanaka-0606/SPADEx

Drell-Yan Production of Z' in the Three-Site Higgsless Model at the LHC

In the Higgsless models, there are extra gauge bosons which keep the perturbative unitarity of a longitudinally polarized gauge boson. The three-site Higgsless model is a minimal Higgsless model and contains three extra gauge bosons, $W^{\prime \pm}$ and Z'. In this paper, we report the discovery potential of the Z' gauge boson via Drell-Yan production with Z'(mass=380, 500, 600 GeV) $\rightarrow WW \rightarrow \ell\nu qq$ ($\ell=e$, $\mu$) at the LHC ($\sqrt{s}$=14 TeV).Comment: 7 pages, 5 figures included. References revise

Naked singularities and quantum gravity

There are known models of spherical gravitational collapse in which the collapse ends in a naked shell-focusing singularity for some initial data. If a massless scalar field is quantized on the classical background provided by such a star, it is found that the outgoing quantum flux of the scalar field diverges in the approach to the Cauchy horizon. We argue that the semiclassical approximation (i.e. quantum field theory on a classical curved background) used in these analyses ceases to be valid about one Planck time before the epoch of naked singularity formation, because by then the curvature in the central region of the star reaches Planck scale. It is shown that during the epoch in which the semiclassical approximation is valid, the total emitted energy is about one Planck unit, and is not divergent. We also argue that back reaction in this model does not become important so long as gravity can be treated classically. It follows that the further evolution of the star will be determined by quantum gravitational effects, and without invoking quantum gravity it is not possible to say whether the star radiates away on a short time scale or settles down into a black hole state.Comment: 16 pages, paper rewritten into sections, conclusions unchanged, 4 references added, to appear in Phys. Rev. D (Rapid Communication