Taishi Katsuragawa

Stability and antievaporation of the Schwarzschild–de Sitter black holes in bigravity

We study the stability under the perturbation and the related antievaporation of the Nariai space-time in bigravity. If we impose a specific condition for the solutions and parameters, we obtain asymptotically de Sitter space-time, and show the existence of the Nariai space-time as a background solution. Considering the perturbation around the Nariai space-time up to the first order, we investigate the behavior of the black hole horizon. We show that the antievaporation does not occur on the classical level in the bigravity.

Readout technologies for directional WIMP Dark Matter detection

The measurement of the direction of WIMP-induced nuclear recoils is a compelling but technologically challenging strategy to provide an unambiguous signature of the detection of Galactic dark matter. Most directional detectors aim to reconstruct the dark-matter-induced nuclear recoil tracks, either in gas or solid targets. The main challenge with directional detection is the need for high spatial resolution over large volumes, which puts strong requirements on the readout technologies. In this paper we review the various detector readout technologies used by directional detectors. In particular, we summarize the challenges, advantages and drawbacks of each approach, and discuss future prospects for these technologies.

Relativistic stars in de Rham-Gabadadze-Tolley massive gravity

Taishi Katsuragawa, Shin’ichi Nojiri, Sergei D. Odintsov, Masashi Yamazaki 1) Department of Physics, Nagoya University, Nagoya 464-8602, Japan 2) Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602, Japan 3) Institut de Ciencies de lEspai (IEEC-CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Cerdanyola del Valles, Barcelona, Spain 4) ICREA, Passeig LluAs Companys, 23, 08010 Barcelona, Spain 5) Tomsk State Pedagogical University, 634061 Tomsk, Russia

NEWS: Nuclear Emulsions for WIMP Search

Nowadays there is compelling evidence for the existence of dark matter in the Universe. A general consensus has been expressed on the need for a directional sensitive detector to confirm, with a complementary approach, the candidates found in conventional searches and to finally extend their sensitivity beyond the limit of neutrino-induced background. We propose here the use of a detector based on nuclear emulsions to measure the direction of WIMP-induced nuclear recoils. The production of nuclear emulsion films with nanometric grains is established. Several measurement campaigns have demonstrated the capability of detecting sub-micrometric tracks left by low energy ions in such emulsion films. Innovative analysis technologies with fully automated optical microscopes have made it possible to achieve the track reconstruction for path lengths down to one hundred nanometers and there are good prospects to further exceed this limit. The detector concept we propose foresees the use of a bulk of nuclear emulsion films surrounded by a shield from environmental radioactivity, to be placed on an equatorial telescope in order to cancel out the effect of the Earth rotation, thus keeping the detector at a fixed orientation toward the expected direction of galactic WIMPs. We report the schedule and cost estimate for a one-kilogram mass pilot experiment, aiming at delivering the first results on the time scale of six years.

Dark matter in modified gravity

We explore a new horizon of modified gravity from the viewpoint of the particle physics. As a concrete example, we take the F (R) gravity to raise a question: can a scalar particle (“scalaron”) derived from the F (R) gravity be a dark matter candidate? We place the limit on the parameter in a class of F (R) gravity model from the constraint on the scalaron as a dark matter. The role of the screening mechanism and compatibility with the dark energy problem are addressed.

Properties of bigravity solutions in a solvable class

We consider the properties of solutions in the bigravity theory for general models, which are parametrized by two parameters

Noether current from surface term, Virasoro algebra and black hole entropy in bigravity

\alpha_{3}

Status and analysis system of directional dark matter search with nuclear emulsion

and

Palatini-Born-Infeld gravity and black hole formation

\alpha_{4}

Discovery potential for directional Dark Matter detection with nuclear emulsions

. Assuming that two metric tensors