7,239 research outputs found
Experimental study of partitioning of trace elements and rare earth elements between immiscible silicate liquids-titanite-zircon at the atmospheric pressure
第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日(木) 国立極地研究所 2階大会議室前フロ
The oxygen-II luminosity density of the Universe
Equivalent widths of [OII] 3727 A lines are measured in 375 faint galaxy
spectra taken as part of the Caltech Faint Galaxy Redshift Survey centered on
the Hubble Deep Field. The sensitivity of the survey spectra to the [OII] line
is computed as a function of magnitude, color and redshift. The luminosity
function of galaxies in the [OII] line and the integrated luminosity density of
the Universe in the [OII] line are computed as a function of redshift. It is
found that the luminosity density in the [OII] line was a factor of ~10 higher
at redshifts z~1 than it is at the present day. The simplest interpretation is
that the star formation rate density of the Universe has declined dramatically
since z~1.Comment: accepted for publication in Ap
Quantum-Gravitational Diffusion and Stochastic Fluctuations in the Velocity of Light
We argue that quantum-gravitational fluctuations in the space-time background
give the vacuum non-trivial optical properties that include diffusion and
consequent uncertainties in the arrival times of photons, causing stochastic
fluctuations in the velocity of light ``in vacuo''. Our proposal is motivated
within a Liouville string formulation of quantum gravity that also suggests a
frequency-dependent refractive index of the particle vacuum. We construct an
explicit realization by treating photon propagation through quantum excitations
of -brane fluctuations in the space-time foam. These are described by
higher-genus string effects, that lead to stochastic fluctuations in couplings,
and hence in the velocity of light. We discuss the possibilities of
constraining or measuring photon diffusion ``in vacuo'' via -ray
observations of distant astrophysical sources.Comment: 17 pages LATEX, uses axodraw style fil
Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity
It has recently been pointed out that generic models of quantum gravity must
contend with severe phenomenological constraints imposed by gravitational
Cerenkov radiation, neutrino oscillations and the cosmic microwave background
radiation. We show how the non-critical Liouville-string model of quantum
gravity we have proposed escapes these constraints. It gives energetic
particles subluminal velocities, obviating the danger of gravitational Cerenkov
radiation. The effect on neutrino propagation is naturally flavour-independent,
obviating any impact on oscillation phenomenology. Deviations from the expected
black-body spectrum and the effects of time delays and stochastic fluctuations
in the propagation of cosmic microwave background photons are negligible, as
are their effects on observable spectral lines from high-redshift astrophysical
objects.Comment: 15 pages LaTeX, 2 eps figures include
Caltech Faint Galaxy Redshift Survey VII: Data Analysis Techniques and Redshifts in the Field J0053+1234
We present the techniques used to determine redshifts and to characterize the
spectra of objects in the Caltech Faint Galaxy Redshift Survey in terms of
spectral classes and redshift quality classes. These are then applied to
spectra from an investigation of a complete sample of objects with mag
in a 2 by 7.3 arcmin^2 field at J005325+1234. Redshifts were successfully
obtained for 163 of the 195 objects in the sample; these redshifts lie in the
range [0.173, 1.44] and have a median of 0.58 (excluding 24 Galactic stars).
The sample includes two broad lined AGNs and one QSO.Comment: 20 pages, Latex, 3 figures, accepted for publication in the ApJ
Supplement
Detecting a Lorentz-Violating Field in Cosmology
We consider cosmology in the Einstein-aether theory (the generally covariant
theory of gravitation coupled to a dynamical timelike Lorentz-violating vector
field) with a linear aether-Lagrangian. The 3+1 spacetime splitting approach is
used to derive covariant and gauge invariant perturbation equations which are
valid for a general class of Lagrangians. Restricting attention to the
parameter space of these theories which is consistent with local gravity
experiments, we show that there are tracking behaviors for the aether field,
both in the background cosmology and at linear perturbation level. The
primordial power-spectrum of scalar perturbations in this model is shown to be
the same that predicted by standard general relativity. However, the
power-spectrum of tensor perturbation is different from that in general
relativity, but has a smaller amplitude and so cannot be detected at present.
We also study the implications for late-time cosmology and find that the
evolution of photon and neutrino anisotropic stresses can source the aether
field perturbation during the radiation and matter dominated epochs, and as a
result the CMB and matter power spectra are modified. However these effects are
degenerate with respect to other cosmological parameters, such as neutrino
masses and the bias parameter in the observed galaxy spectrum.Comment: 13 pages, 3 figures; modified version to appear in Physical Review
Dynamical Formation of Horizons in Recoiling D Branes
A toy calculation of string/D-particle interactions within a world-sheet
approach indicates that quantum recoil effects - reflecting the gravitational
back-reaction on space-time foam due to the propagation of energetic particles
- induces the appearance of a microscopic event horizon, or `bubble', inside
which stable matter can exist. The scattering event causes this horizon to
expand, but we expect quantum effects to cause it to contract again, in a
`bounce' solution. Within such `bubbles', massless matter propagates with an
effective velocity that is less than the velocity of light in vacuo, which may
lead to observable violations of Lorentz symmetry that may be tested
experimentally. The conformal invariance conditions in the interior geometry of
the bubbles select preferentially three for the number of the spatial
dimensions, corresponding to a consistent formulation of the interaction of D3
branes with recoiling D particles, which are allowed to fluctuate independently
only on the D3-brane hypersurface.Comment: 25 pages LaTeX, 4 eps figures include
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