709 research outputs found
Constraining chameleon field theories using the GammeV afterglow experiments
The GammeV experiment has constrained the couplings of chameleon scalar
fields to matter and photons. Here we present a detailed calculation of the
chameleon afterglow rate underlying these constraints. The dependence of GammeV
constraints on various assumptions in the calculation is studied. We discuss
GammeV--CHASE, a second-generation GammeV experiment, which will improve upon
GammeV in several major ways. Using our calculation of the chameleon afterglow
rate, we forecast model-independent constraints achievable by GammeV--CHASE. We
then apply these constraints to a variety of chameleon models, including
quartic chameleons and chameleon dark energy models. The new experiment will be
able to probe a large region of parameter space that is beyond the reach of
current tests, such as fifth force searches, constraints on the dimming of
distant astrophysical objects, and bounds on the variation of the fine
structure constant.Comment: 17 pages, 12 figures, 2 table
Chameleon Dark Energy
Chameleons are scalar fields whose mass depends on the environment,
specifically on the ambient matter density. While nearly massless in the
cosmos, where the matter density is tiny, their mass is of order of an inverse
millimeter on Earth, where the density is high. In this note, we review how
chameleons can satisfy current experimental constraints on deviations from
General Relativity (GR). Moreover, we study the cosmological evolution with a
chameleon field and show the existence of an attractor solution, akin to the
tracker solution in quintessence models. We discuss how chameleons can
naturally drive the observed acceleration of the universeComment: 5 pages, 2 figures. To appear in the proceedings of the "Phi in the
Sky" conference, 8-10 July 2004, Porto, Portugua
Nuclear weapons spread and Australian policy
In this monograph Dr John J. Weltman examines the problems raised for Australian foreign and strategic policies by the prospect of further spread of nuclear weapons. Australia has had an extensive historical involvement with nuclear energy, an involvement which considerably antedates the contemporary domestic debate over the mining and export of Australian uranium ores
Molecular composition of particulate matter emissions from dung and brushwood burning household cookstoves in Haryana, India
Emissions of airborne particles from biomass burning are a significant source of black carbon (BC) and brown carbon (BrC) in rural areas of developing countries where biomass is the predominant energy source for cooking and heating. This study explores the molecular composition of organic aerosols from household cooking emissions with a focus on identifying fuel-specific compounds and BrC chromophores. Traditional meals were prepared by a local cook with dung and brushwood-fueled cookstoves in a village in Palwal district, Haryana, India. Cooking was done in a village kitchen while controlling for variables including stove type, fuel moisture, and meal. Fine particulate matter (PM2.5) emissions were collected on filters, and then analyzed via nanospray desorption electrospray ionization-high-resolution mass spectrometry (nano-DESI-HRMS) and high-performance liquid chromatography-photodiode array-high-resolution mass spectrometry (HPLC-PDA-HRMS) techniques. The nano-DESI-HRMS analysis provided an inventory of numerous compounds present in the particle phase. Although several compounds observed in this study have been previously characterized using gas chromatography methods a majority of the species in the nano-DESI spectra were newly observed biomass burning compounds. Both the stove (chulha or angithi) and the fuel (brushwood or dung) affected the composition of organic aerosols. The geometric mean of the PM2.5 emission factor and the observed molecular complexity increased in the following order: brushwood-chulha (7.3±1.8 g kg-1 dry fuel, 93 compounds), dung-chulha (21.1±4.2 g kg-1 dry fuel, 212 compounds), and dung-angithi (29.8±11.5 g kg-1 dry fuel, 262 compounds). The mass-normalized absorption coefficient (MACbulk) for the organic-solvent extractable material for brushwood PM2.5 was 3.7±1.5 and 1.9±0.8m2 g-1 at 360 and 405 nm, respectively, which was approximately a factor of two higher than that for dung PM2.5. The HPLC-PDA-HRMS analysis showed that, regardless of fuel type, the main chromophores were CxHyOz lignin fragments. The main chromophores accounting for the higher MACbulk values of brushwood PM2.5 were C8H10O3 (tentatively assigned to syringol), nitrophenols C8H9NO4, and C10H10O3 (tentatively assigned to methoxycinnamic acid)
Probing beyond-Horndeski gravity on ultra-large scales
The beyond-Horndeski gravity has recently been reformulated in the dark energy paradigm—which has been dubbed, Unified Dark Energy (UDE). The evolution equations for the given UDE appear to correspond to a non-conservative dark energy scenario, in which the total energy-momentum tensor is not conserved. We investigate both the background cosmology and, the large-scale imprint of the UDE by probing the angular power spectrum of galaxy number counts, on ultra-large scales; taking care to include the full relativistic corrections in the observed overdensity. The background evolution shows that only an effective mass smaller than the Planck mass is needed in the early universe in order for predictions in the given theory to match current observational constraints. We found that the effective mass-evolution-rate parameter, which drives the evolution of the UDE, acts to enhance the observed power spectrum and, hence, relativistic effects (on ultra-large scales) by enlarging the UDE sound horizon. Conversely, both the (beyond) Horndeski parameter and the kineticity act to diminish the observed power spectrum, by decreasing the UDE sound horizon. Our results show that, in a universe with UDE, a multi-tracer analysis will be needed to detect the relativistic effects in the large-scale structure. In the light of a multi-tracer analysis, the various relativistic effects hold the potential to distinguish different gravity models. Moreover, while the Doppler effect will remain significant at all epochs and, thus can not be ignored, the integrated Sachs-Wolfe, the time-delay and the potential (difference) effects, respectively, will only become significant at epochs near z = 3 and beyond, and may be neglected at late epochs. In the same vein, the Doppler effect alone can serve as an effective cosmological probe for the large-scale structure or gravity models, in the angular power spectrum—at all z
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