42,483 research outputs found
Supernova Constraints and Systematic Uncertainties from the First Three Years of the Supernova Legacy Survey
We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = â0.91^(+0.16)_(â0.20)(stat)^(+0.07)_(â0.14)(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems
Neutrino Oscillations Induced by Gravitational Recoil Effects
Quantum gravitational fluctuations of the space-time background, described by
virtual D branes, may induce neutrino oscillations if a tiny violation of the
Lorentz invariance (or a violation of the equivalence principle) is imposed. In
this framework, the oscillation length of massless neutrinos turns out to be
proportional to M/E^2, where E is the neutrino energy and M is the mass scale
characterizing the topological fluctuations in the vacuum. Such a functional
dependence on the energy is the same obtained in the framework of loop quantum
gravity.Comment: 5 pages, LaTex fil
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
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Tryptophan metabolism and its relationship with immune activation, depression, and neurocognitive impairment among HIV-infected individuals
Birkhoff Theorem and Matter
Birkhoff's theorem for spherically symmetric vacuum spacetimes is a key
theorem in studying local systems in general relativity theory. However
realistic local systems are only approximately spherically symmetric and only
approximately vacuum. In a previous paper, we showed the theorem remains
approximately true in an approximately spherically symmetric vacuum space time.
In this paper we prove the converse case: the theorem remains approximately
true in a spherically symmetric, approximately vacuum space time.Comment: 7 pages, Revtex
Effect of field of view and monocular viewing on angular size judgements in an outdoor scene
Observers typically overestimate the angular size of distant objects. Significantly, overestimations are greater in outdoor settings than in aircraft visual-scene simulators. The effect of field of view and monocular and binocular viewing conditions on angular size estimation in an outdoor field was examined. Subjects adjusted the size of a variable triangle to match the angular size of a standard triangle set at three greater distances. Goggles were used to vary the field of view from 11.5 deg to 90 deg for both monocular and binocular viewing. In addition, an unrestricted monocular and binocular viewing condition was used. It is concluded that neither restricted fields of view similar to those present in visual simulators nor the restriction of monocular viewing causes a significant loss in depth perception in outdoor settings. Thus, neither factor should significantly affect the depth realism of visual simulators
Magneto-optical determination of the electron-solid phase-boundary
We have obtained a two-dimensional electron-solid phase diagram in the extreme magnetic quantum limit by studying the temperature dependence of the radiative recombination of electrons in a GaAs/AlxGa1-xAs heterojunction with holes bound to a delta-layer, 250 A away in the GaAs, of Be acceptors. The low-energy shoulder to the luminescence line, indicating the presence of the electron solid, is seen to disappear at a filling-factor-dependent critical temperature. We observe no shoulder above a filling factor of 0.25, and the critical temperature falls to below 0.4 K at filling factors 1/5 and 1/7
Environmental Effects in the Evolution of Galactic Bulges
We investigate possible environmental trends in the evolution of galactic
bulges over the redshift range 0<z<0.6. For this purpose, we construct the
Fundamental Plane (FP) for cluster and field samples at redshifts =0.4 and
=0.54 using surface photometry based on HST imaging and velocity dispersions
based on Keck spectroscopy. As a reference point for our study we include data
for pure ellipticals, which we model as single-component Sersic profiles;
whereas for multi-component galaxies we undertake decompositions using Sersic
and exponential models for the bulge and disk respectively. Although the FP for
both distant cluster and field samples are offset from the local relation,
consistent with evolutionary trends found in earlier studies, we detect
significant differences in the zero point of ~=0.2 dex between the field and
cluster samples at a given redshift. For both clusters, the
environmentally-dependent offset is in the sense expected for an accelerated
evolution of bulges in dense environments. By matching the mass range of our
samples, we confirm that this difference does not arise as a result of the
mass-dependent downsizing effects seen in larger field samples. Our result is
also consistent with the hypothesis that - at fixed mass and environment - the
star formation histories of galactic bulges and pure spheroids are
indistinguishable, and difficult to reconcile with the picture whereby the
majority of large bulges form primarily via secular processes within spiral
galaxies.Comment: 5 pages, 3 figures, accepted for publication in ApJ Letter
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