Three large bathymetric highs (from north to south: the Amami Plateau, the Daito Ridge, and the Oki-Daito Ridge) originating from paleo-island arcs characterize the northwestern end of the Philippine Sea plate. We obtained 10 seismic refraction and multi-channel seismic reflection profiles across and along these bathymetric highs and obtained P wave velocity (Vp) models of the crust and the uppermost mantle. Although there are large variations in the crustal structure throughout this region, these bathymetric highs usually have a middle crust with Vp of 6.3 to 6.8 km/s, a lower crust with Vp of 6.8 to 7.2 km/s, a Pn velocity of 7.6 to 7.8 km/s, and a total crustal thickness of 15 to 25 km. These features are similar to those of the Izu-Ogasawara (Bonin)-Mariana island arc and the Kyushu-Palau Ridge, which are immature paleo-island arcs. However, the crust at the southwestern part of the Oki-Daito Ridge contains a relatively thin middle crust and a smaller total crustal thickness compared with other ridges in this region. In addition, we identified a deep reflector beneath the ridge, with these properties indicating a different origin, such as intraplate volcanism.
We acquired coincident wide-angle and multi-channel seismic reflection data along four profiles perpendicular to the Kyushu-Palau Ridge (KPR) between 15• N and 20• N on the Philippine Sea plate. The crustal thickness beneath the KPR, which is a remnant arc created in the Late Eocene, varies along the strike from 8 to approximately 20 km and is always thicker than the adjacent oceanic crust of the West Philippine Basin to the west and the Parece Vela Basin to the east. The thickest crust among the four profiles, which is primarily due to a thickening of the lower crust, is found where the KPR adjoins Oki-no-Tori-Shima Island. There is no clear evidence of the thick (>5 km) middle crustal layer with a P-wave velocity of 6.0-6.5 km/s that has been inferred beneath the conjugate rifted counterpart of the Izu-Ogasawara(Bonin)-Mariana Island-arc. Our results suggest that the crust of the KPR at 15-21• N represents a less mature island arc crust relative to that further north along the ridge where a mid-crustal layer of 6 km/s has been reported.
We investigate the explicit forms of the fermionic zeromodes in heterotic fivebrane backgrounds. By explicitly solving the fermionic field equations in the fivebrane backgrounds, two normalizable and physical fermionic zeromodes are obtained. Each of these zeromodes has a non-vanishing gravitino component. We propose a possible scenario for gravitino pair condensation. §1. IntroductionSupersymmetry is a very attractive symmetry, but we do not have any concrete experimental evidence which supports this symmetry at low energies. Therefore it must be broken spontaneously in some way. It is desirable for supersymmetry to be broken dynamically, and one interesting such scenario has been proposed. 1) In this scenario, local supersymmetry is broken due to the topological effect of gravity. As an explicit realization of this scenario, four-dimensional supersymmetry breaking in the background of the Eguchi-Hanson metric is well-known. 2) In this special background, there are non-trivial gravitino zeromodes, and these zeromodes induce the gravitino condensation, i.e. ψ ab ψ ab = 0, which implies the breaking of supersymmetry through the Konishi anomaly relation.It is an interesting question whether this scenario is possible in string theory, because string theory can be considered a consistent theory of quantum gravity. The heterotic fivebranes, or the Callan-Harvey-Strominger (CHS) solitons, are known as exact solutions of the heterotic string theory. 3) These solitons possess just half of the supersymmetry of the heterotic string theory. The background field configuration, which is similar to that of the heterotic fivebrane, was studied, and the existence of gravitino zeromodes that can contribute to the gravitino condensation was explicitly shown. 4) Therefore, we can expect the existence of gravitino zeromodes also in the heterotic fivebrane background.It should be remarked that no relation like the Konishi anomaly relation is known to exist in heterotic string theory. Therefore, the dynamical breaking of supersymmetry does not follow directly from the presence of gravitino zeromodes. However, it would be interesting to study the dynamics of fermions in string theory that could exhibit these interesting phenomena as a first step.In this paper, we find explicit forms of two fermionic zeromodes in the heterotic fivebrane background by explicitly solving the field equations of fermions. They can be considered well-defined physical zeromodes that can contribute to gravitino * )
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