28204727
Present status of large-scale cryogenic gravitational wave telescope
The large-scale cryogenic gravitational wave telescope (LCGT) is the future project of the Japanese gravitational wave group. Two sets of 3 km arm length laser interferometric gravitational wave detectors will be built in a tunnel of Kamioka mine in Japan. LCGT will detect chirp waves from binary neutron star coalescence at 240 Mpc away with a S/N of 10. The expected number of detectable events in a year is two or three. To achieve the required sensitivity, several advanced techniques will be employed such as a low-frequency vibration-isolation system, a suspension point interferometer, cryogenic mirrors, a resonant side band extraction method, a high-power laser system and so on. We hope that the beginning of the project will be in 2005 and the observations will start in 2009.
67813587
Screening of cosmological constant in non-local cosmology
We consider a model of non-local gravity with a large bare cosmological constant, Λ, and study its cosmological solutions. The model is characterized by a function f(ψ) = f0eαψ, where ψ = □-1R and α is a real dimensionless parameter. In the absence of matter, we find an expanding universe solution a ∝ tn with n αcr ≈ 0.17. This is quite a weak condition. We argue that the solution is stable against the inclusion of matter fields. Thus our solution opens up new possibilities for solution to the cosmological constant problem.
119040664
Wronskian Formulation of the Spectrum of Curvature Perturbations
We present a new formulation for the evaluation of the primordial spectrum of curvature perturbations generated during inflation, using the fact that the Wronskian of the scalar field perturbation equation is constant. In the literature, there are many works on the same issue focusing on a few specific aspects or effects. Here we deal with the general multi-component scalar field, and show that our new formalism gives a method for evaluating the final amplitude of the curvature perturbation systematically and economically. The advantage of the new method is that one only has to solve a single mode of the scalar field perturbation equation backwards in time from the end of inflation to the stage at which the perturbation is within the Hubble horizon, at which the initial values of the scalar field perturbations are given. We also clarify the relation of the new method with the new, recently developed δN formalism.
122629397
Large Scale Quantum Fluctuations in the Inflationary Universe
On evalue les fluctuations quantiques d'un champ scalaire gouvernant l'inflation d'une facon manifestement independante du choix des conditions de jauge en coordonnee. On donne une representation du degre de liberte dynamique du champ fluctuant
119276954
Squeezed primordial bispectrum from a general vacuum state
We study the general relation between the power spectrum and the squeezed limit of the bispectrum of the comoving curvature perturbation produced during single-field slow-roll inflation when the initial state is a general vacuum. Assuming the scale invariance of the power spectrum, we derive a formula for the squeezed limit of the bispectrum, represented by the parameter fNL, which is not slow-roll suppressed and is found to contain a single free parameter for a given amplitude of the power spectrum. Then, we derive the conditions for achieving a scale-invariant fNL and discuss a few examples.
17177650
Dynamical D4-D8 and D3-D7 branes in supergravity
We present a class of dynamical solutions for intersecting D4-D8 and D3-D7 brane systems in ten-dimensional type IIA and IIB supergravity. We discuss if these solutions can be recovered in lower-dimensional effective theories for the warped compactification of a general p-brane system. It is found that an effective p+1-dimensional description is not possible in general due to the entanglement of the transverse coordinates and the p+1-dimensional coordinates in the metric components. For the D4-D8 brane system, the dynamical solutions reduces to a static warped AdS{sub 6}xS{sup 4} geometry in a certain spacetime region. For the D3-D7 brane system, we find a dynamical solution whose metric form is similar to that of a D3-brane solution. The main difference is the existence of a nontrivial dilaton configuration in the D3-D7 solution. Then we discuss cosmology of these solutions. We find that they behave like a Kasner-type cosmological solution at {tau}{yields}{infinity}, while it reduces to a warped static solution at {tau}{yields}0, where {tau} is the cosmic time.
16363947
Detecting very high energy neutrinos by the telescope array
Abstract We present the cosmic neutrino detecting potential of the telescope array (TA) for quasi-horizontally downward and upward air showers initiated by very high energy neutrinos penetrating the air and the Earth respectively. We adopted model predictions for extraterrestrial neutrino fluxes from active galactic nuclei, gamma-ray bursts, Greisen photo production, the collapse of topological defects, and Z-bursts. The TA, using a large array of bright and wide field-of-view fluorescence telescopes, can explore these very high energy cosmic neutrino sources.
21928235
Development of a 16-inch UV-ray image intensifier tube
We have developed a 16-inch ultraviolet-ray image intensifier (UVII) tube to form the spherical focal surface of the All-sky Survey High Resolution Air-shower Detector (Ashra) telescope, a new air fluorescence and Cerenkov detector to observe TeV gamma rays, very high energy neutrinos, and extremely high energy cosmic rays. The UVII has a very large effective photocathode area of 16-inch diameter and reduces an image size to 1-inch diameter using the electric lens effect. This enables us to use a solid-state imager to take focal surface images in the Ashra telescope. Thus, UVII is a key technology for the Ashra experiment to realize a much lower pixel cost in comparison with other experiments using photomultiplier arrays at the focal surface. The UVII achieves a high resolution of 3.4 Lp/mm at the input window. The output screen of the UVII is made of a fiber optic plate (FOP) with a concave shape to optimize the electric lens configuration under the fixed curvature of input window. This results in an almost uniform resolution over the whole sensitive area. We have adopted a P47 phosphor screen with a 10% decay time of /spl sim/100 ns and have obtained an amplification factor of about 100. In this paper we present the design, construction, and performance of the 16-inch UVII.
120440980
All-sky survey high resolution air-shower detector (Ashra)
119251015
Performance of a 20-in. photoelectric lens image intensifier tube
Abstract We have evaluated a 20-in. photoelectric lens image intensifier tube (PLI) to be mounted on the spherical focal surface of the Ashra light collectors, where Ashra stands for All-sky Survey High Resolution Air-shower Detector, an unconventional optical collector complex that images air showers produced by very high energy cosmic-ray particles in a 42°-diameter field of view with a resolution of a few arcminutes. The PLI, the worlds largest image intensifier, has a very large effective photocathode area of 20-in. diameter and reduces an image size to less than 1-in. diameter using the electric lens effect. This enables us to use a solid-state imager to take focal surface images in the Ashra light collector. Thus, PLI is a key technology for the Ashra experiment to realize a much lower pixel cost in comparison with other experiments using photomultiplier arrays at the focal surface. In this paper we present the design and performance of the 20-in. PLI.