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.
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.
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.
120440980
All-sky survey high resolution air-shower detector (Ashra)
119650047
Gradient Expansion Approach to Nonlinear Superhorizon Perturbations. II — A Single Scalar Field —
We formulate nonlinear perturbations of a scalar field dominated universe on super-horizon scales. We consider the case of a single scalar field. We take the gradient expansion approach. We adopt the uniform Hubble slicing and derive the general solution valid to $O(\epsilon^2)$, where $\epsilon$ is the expansion parameter associated with a spatial derivative, which includes both the scalar and tensor modes. In particular, the $O(\epsilon^2)$ correction terms to the nonlinear curvature perturbation, which become important in models with a non-slowroll stage during inflation, are explicitly obtained.
119335363
Massive scalar states localized on a de Sitter brane
We consider a brane scenario with a massive scalar field in the five-dimensional bulk. We study the scalar states that are localized on the brane, which is assumed to be a de Sitter brane. These localized scalar modes are massive in general, their effective four-dimensional mass depending on the mass of the five-dimensional scalar field, on the Hubble parameter in the brane and on the coupling between the brane tension and the bulk scalar field. We then introduce a purely four-dimensional approach based on an effective potential for the projection of the scalar field in the brane, and discuss its regime of validity. Finally, we explore the quasilocalized scalar states, which have a nonzero width that quantifies their probability of tunneling from the brane into the bulk.
118688649
Waterfall field in hybrid inflation and curvature perturbation
We study carefully the contribution of the waterfall field to the curvature perturbation at the end of hybrid inflation. In particular we clarify the parameter dependence analytically under reasonable assumptions on the model parameters. After calculating the mode function of the waterfall field, we use the δN formalism and confirm the previously obtained result that the power spectrum is very blue with the index 4 and is absolutely negligible on large scales. However, we also find that the resulting curvature perturbation is highly non-Gaussian and hence we calculate the bispectrum. We find that the bispectrum is at leading order independent of momentum and exhibits its peak at the equilateral limit, though it is unobservably small on large scales. We also present the one-point probability distribution function of the curvature perturbation.
119232600
Lorentz-violating vs. ghost gravitons: the example of Weyl gravity
A bstractWe show that the ghost degrees of freedom of Einstein gravity with a Weyl term can be tamed by a simple mechanism that invokes local Lorentz symmetry breaking. We demonstrate how the mechanism works in a cosmological setting. The presence of the Weyl term forces a redefinition of the quantum vacuum state of the tensor perturbations. As a consequence the amplitude of their spectrum blows up when the Lorentz-violating scale becomes comparable to the Hubble radius. Such a behaviour is in sharp contrast to what happens in standard Weyl gravity where the gravitational ghosts smoothly damp out the spectrum of primordial gravitational waves.