Smearing effect due to the spread of a probe-particle on the Brownian motion near a perfectly reflecting boundary

Quantum fluctuations of electromagnetic vacuum are investigated in a half-space bounded by a perfectly reflecting plate by introducing a probe described by a charged wave-packet distribution in time-direction. The wave-packet distribution of the probe enables one to investigate the smearing effect upon the measured vacuum fluctuations caused by the quantum nature of the probe particle. It is shown that the wave-packet spread of the probe particle significantly influences the measured velocity dispersion of the probe. In particular, the asymptotic late-time behavior of its $z$-component, $$, for the wave-packet case is quite different from the test point-particle case ($z$ is the coordinate normal to the plate). The result for the wave-packet is \sim 1/\t^2 in the late time (\t is the measuring time), in stead of the reported late-time behavior $\sim 1/z^2$ for a point-particle probe. This result can be quite significant for further investigations on the measurement of vacuum fluctuations.Comment: 8 page

Holographic Confining Gauge theory and Response to Electric Field

We study the response of confining gauge theory to the external electric field by using holographic Yang-Mills theories in the large $N_c$ limit. Although the theories are in the confinement phase, we find a transition from the insulator to the conductor phase when the electric field exceeds its critical value. Then, the baryon number current is generated in the conductor phase. At the same time, in this phase, the meson melting is observed through the quasi-normal modes of meson spectrum. Possible ideas are given for the string state corresponding to the melted mesons, and they lead to the idea that the source of this current may be identified with the quarks and anti-quarks supplied by the melted mesons. We also discuss about other possible carriers. Furthermore, from the analysis of the massless quark, chiral symmetry restoration is observed at the insulator-conductor transition point by studying a confining theory in which the chiral symmetry is broken.Comment: 27 pages, 14 figure

Effects of Fermi surface and superconducting gap structure in the field-rotational experiments: A possible explanation of the cusp-like singularity in YNi2_2B2_2C

We have studied the field-orientational dependence of zero-energy density of states (FODOS) for a series of systems with different Fermi surface and superconducting gap structures. Instead of phenomenological Doppler-shift method, we use an approximate analytical solution of Eilenberger equation together with self-consistent determination of order parameter and a variational treatment of vortex lattice. First, we compare zero-energy density of states (ZEDOS) when a magnetic field is applied in the nodal direction ($\nu_{node}(0)$) and in the antinodal direction ($\nu_{anti}(0)$), by taking account of the field-angle dependence of order parameter. As a result, we found that there exists a crossover magnetic field $H^*$ so that $\nu_{anti}(0) > \nu_{node}(0)$ for $H \nu_{anti}(0)$ for $H > H^*$, consistent with our previous analyses. Next, we showed that $H^*$ and the shape of FODOS are determined by contribution from the small part of Fermi surface where Fermi velocity is parallel to field-rotational plane. In particular, we found that $H^*$ is lowered and FODOS has broader minima, when a superconducting gap has point nodes, in contrast to the result of the Doppler-shift method. We also studied the effects of in-plane anisotropy of Fermi surface. We found that in-plane anisotropy of quasi-two dimensional Fermi surface sometimes becomes larger than the effects of Doppler-shift and can destroy the Doppler-shift predominant region. In particular, this tendency is strong in a multi-band system where superconducting coherence lengths are isotropic. Finally, we addressed the problem of cusp-like singularity in YNi$_2$B$_2$C and present a possible explanation of this phenomenon.Comment: 13pages, 23figure

Spectral-Function Sum Rules in Supersymmetry Breaking Models

The technique of Weinberg's spectral-function sum rule is a powerful tool for a study of models in which global symmetry is dynamically broken. It enables us to convert information on the short-distance behavior of a theory to relations among physical quantities which appear in the low-energy picture of the theory. We apply such technique to general supersymmetry breaking models to derive new sum rules.Comment: 18 pages, 1 figur

Possible solution to the 7^7Li problem by the long lived stau

Modification of standard big-bang nucleosynthesis is considered in the minimal supersymmetric standard model to resolve the excessive theoretical prediction of the abundance of primordial lithium 7. We focus on the stau as a next-lightest superparticle, which is long lived due to its small mass difference with the lightest superparticle. It provides a number of additional decay processes of $\mathrm{^{7}Li}$ and $\mathrm{^{7}Be}$. A particularly important process is the internal conversion in the stau-nucleus bound state, which destroys the $\mathrm{^{7}Li}$ and $\mathrm{^{7}Be}$ effectively. We show that the modification can lead to a prediction consistent with the observed abundance of $\mathrm{^{7}Li}$.Comment: 6 pages, 5 figure

Land of the Falling “Poison Pill : Understanding Defensive Measures in Japan on Their Own Terms

Embraced by United States (“U.S.”) managers in the 1980s as a lifeline in a sea of hostile takeovers, the poison pill fundamentally altered the trajectory of American corporate governance. When a hostile takeover wave seemed imminent in Japan in the mid-2000s, Japanese boards appeared to embrace this American invention with equal enthusiasm. Japan's experience should have been a ringing endorsement for the utility of American corporate governance solutions in foreign jurisdictions-but it was not to be. Japan's unique interpretation of the “poison pill” that was so eagerly adopted by Japanese companies in the mid-to-late 2000s has turned out to be nothing like their potent American namesakes-and, in fact, the opposite of what would be expected by leading U.S. academics who have built a cottage industry publishing on the U.S. poison pill. Based on hand collected empirical data, we provide the first in-depth analysis of why Japan’s “poison pill” (defensive measures) is heading towards extinction—a watershed reversal that is unexplained in the Japanese literature and has almost entirely escaped the English language literature. By drawing on our hand-collected data, case studies, and Japanese jurisprudence, we illuminate the unique and untold story of how one of the most discussed mechanisms of corporate governance in the U.S. has worked almost entirely differently when transplanted to Japanese soil—the importance of which is heightened as Japan is by far the largest economy in which the poison pill has been tested outside of the United States. Additionally, our analysis sheds light on the unexpected importance of Japan’s recently implemented corporate governance code and stewardship code—two Western legal transplants that have garnered considerable attention in the English language literature, but which have yet to be evaluated in light of their impact on defensive measures in Japan.Published versionThis work was financially supported by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid JP18K01336 and by the Centre for Asian Legal Studies at NUS Law

Switching effect upon the quantum Brownian motion near a reflecting boundary

The quantum Brownian motion of a charged particle in the electromagnetic vacuum fluctuations is investigated near a perfectly reflecting flat boundary, taking into account the smooth switching process in the measurement. Constructing a smooth switching function by gluing together a plateau and the Lorentzian switching tails, it is shown that the switching tails have a great influence on the measurement of the Brownian motion in the quantum vacuum. Indeed, it turns out that the result with a smooth switching function and the one with a sudden switching function are qualitatively quite different. It is also shown that anti-correlations between the switching tails and the main measuring part plays an essential role in this switching effect. The switching function can also be interpreted as a prototype of an non-equilibrium process in a realistic measurement, so that the switching effect found here is expected to be significant in actual applications in vacuum physics.Comment: 12 pages, 2 figures This version is just to correct the author-lis

Evolution of the discrepancy between a universe and its model

We study a fundamental issue in cosmology: Whether we can rely on a cosmological model to understand the real history of the Universe. This fundamental, still unresolved issue is often called the ``model-fitting problem (or averaging problem) in cosmology''. Here we analyze this issue with the help of the spectral scheme prepared in the preceding studies. Choosing two specific spatial geometries that are very close to each other, we investigate explicitly the time evolution of the spectral distance between them; as two spatial geometries, we choose a flat 3-torus and a perturbed geometry around it, mimicking the relation of a ``model universe'' and the ``real Universe''. Then we estimate the spectral distance between them and investigate its time evolution explicitly. This analysis is done efficiently by making use of the basic results of the standard linear structure-formation theory. We observe that, as far as the linear perturbation of geometry is valid, the spectral distance does not increase with time prominently,rather it shows the tendency to decrease. This result is compatible with the general belief in the reliability of describing the Universe by means of a model, and calls for more detailed studies along the same line including the investigation of wider class of spacetimes and the analysis beyond the linear regime.Comment: To be published in Classical and Quantum Gravit