A Problem in Virtual Graviton exchanges in Flat Large Extra Dimensions

It is pointed out in a class of models with large extra dimensions that the cross section of processes with virtual Kaluza-Klein graviton exchanges becomes either much smaller or much larger by many orders of magnitude than what is expected from that of the on-shell production of the Kaluza-Klein gravitons. We demonstrate how the problem arises using a toy model. The cause of this new problem lies in the fact that we do not have momentum conservation in the extra dimensions. To search for the signal of the large extra dimensions with high energy collider experiments, we need more care in interpreting the earlier results on the cross sections of these processes.Comment: 12 pages, no figur

Japan\u27s Missile Defense

For some years, Japan has pursued its own missile defense system in cooperation with the United States. The Japanese government claims that the missile defense (JMD) program is purely defensive and will not pose a threat to other countries. JMD may seem justified by North Korea\u27s development of ballistic missiles and nuclear weapons. However, neighboring states regarded it as a sign of military ambition and revival of Japan\u27s prewar militarism. The development and deployment of JMD could have grave implications for regional and global security. This dissertation focuses on these implications, domestic and international political considerations and the future direction of Japan\u27s defense and security policy. After the Cold War, when the superpowers maintained strategic stability with massive offensive nuclear arsenals (mutual assured destruction--MAD), new threats from rogue states and terrorists have forced us to rethink the credibility of MAD. But attempts to build shields against nuclear ballistic missiles could trigger a new phase of the arms race pitting offensive vs. defensive capabilities. The author argues that defense must be emphasized in order to achieve stability and security (mutual defense emphasis--MDE). Characterization of JMD as truly defensive or not depends on theoretical and strategic viewpoints. The key is the distinction between defense and offense, and whether Japan will emphasize defense, and convince other states that its strategic intentions are really defensive. For the Japanese, with their dual realist and pacifist identities, JMD can be a tool of either realist military strategy or pacifist arms control. Japan should choose defensive realism, including MDE arms control, as a middle way that may eventually open a pacifist route to disarmament. With the world\u27s most sophisticated technology and a tradition of pacifism, Japan is in a unique and advantageous position to promote arms control. In pursuit of JMD, the Japanese government should not only promote arms control and MDE--building missile shields against rogue and terrorist missile attacks or accidental or unauthorized launches, but also advance offensive arms reduction among major states. Japan can and must become a leader in such a shift toward a less dangerous world

Unoccupied topological surface state in Bi2_{2}Te2_{2}Se

Bias voltage dependent scattering of the topological surface state is studied by scanning tunneling microscopy/spectroscopy for a clean surface of the topological insulator Bi$_2$Te$_2$Se. A strong warping of constant energy contours in the unoccupied part of the spectrum is found to lead to a spin-selective scattering. The topological surface state persists to higher energies in the unoccupied range far beyond the Dirac point, where it coexists with the bulk conduction band. This finding sheds light on the spin and charge dynamics over the wide energy range and opens a way to designing opto-spintronic devices.Comment: 5 pages, 4 figure

The linkage between financial market and real economy : the analysis with an agent based simulation

Financial markets are driven by the real economy and in turn also has a profound effect on the financial economy. Understanding the feedback between these two sectors leads to a deeper understanding of the stability, robustness and efficiency of the economic system. In this paper, we investigate the effect of credit linkages on the macroeconomic activity by developing an agent-based model, which allows us to explain some key elements occurred during the recent economic and financial crisis. In particular, we study the linkage dependence among agents (firms and banks) at the micro-level and to estimate their impact on the macro activities such as the GDP growth rate, the size and growth rate distributions of agents

Electronic Structure of Charge- and Spin-controlled Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3}

We present the electronic structure of Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3} investigated by high-resolution photoemission spectroscopy. In the vicinity of Fermi level, it was found that the electronic structure were composed of a Cr 3d local state with the t_{2g}^{3} configuration and a Ti 3d itinerant state. The energy levels of these Cr and Ti 3d states are well interpreted by the difference of the charge-transfer energy of both ions. The spectral weight of the Cr 3d state is completely proportional to the spin concentration x irrespective of the carrier concentration y, indicating that the spin density can be controlled by x as desired. In contrast, the spectral weight of the Ti 3d state is not proportional to y, depending on the amount of Cr doping.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let

Anomalous momentum dependence of the multiband electronic structure of FeSe_1-xTe_x superconductors induced by atomic disorder

When periodicity of crystal is disturbed by atomic disorder, its electronic state becomes inhomogeneous and band dispersion is obscured. In case of Fe-based superconductors, disorder of chalcogen/pnictogen height causes disorder of Fe 3d level splitting. Here, we report an angle-resolved photoemission spectroscopy study on FeSe_1-xTe_x with the chalcogen height disorder, showing that the disorder affects the Fe 3d band dispersions in an orbital-selective way instead of simple obscuring effect. The reverse of the Fe 3d level splitting due to the chalcogen height difference causes the splitting of the hole band with Fe 3d x^2-y^2 character around the Gamma point.Comment: 5 pages, 4 figure

Orbital Degeneracy and Peierls Instability in Triangular Lattice Superconductor Ir1−x_{1-x}Ptx_xTe2_2

We have studied electronic structure of triangular lattice Ir$_{1-x}$Pt$_x$Te$_2$ superconductor using photoemission spectroscopy and model calculations. Ir $4f$ core-level photoemission spectra show that Ir $5d$ $t_{2g}$ charge modulation established in the low temperature phase of IrTe$_2$ is suppressed by Pt doping. This observation indicates that the suppression of charge modulation is related to the emergence of superconductivity. Valence-band photoemission spectra of IrTe$_2$ suggest that the Ir $5d$ charge modulation is accompanied by Ir $5d$ orbital reconstruction. Based on the photoemission results and model calculations, we argue that the orbitally-induced Peierls effect governs the charge and orbital instability in the Ir$_{1-x}$Pt$_x$Te$_2$.Comment: 5 pages,4 figure