430 research outputs found
Dusty Universe Mapped by Herschel and CIB in arcminute-scale CMB (and TIME-Pilot to JCMT)
No full textCooray, Asantha. (2015). Dusty Universe Mapped by Herschel and CIB in arcminute-scale CMB (and TIME-Pilot to JCMT). Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/169641
The trispectrum of 21-cm background anisotropies as a probe of primordial non-Gaussianity
No full textThe 21-cm anisotropies from the neutral hydrogen distribution prior to the era of reionization are a sensitive probe of primordial non-Gaussianity. Unlike the case with cosmic microwave background, 21-cm anisotropies provide multi-redshift information with frequency selection and are not damped at arcminute angular scales. We discuss the angular trispectrum of the 21-cm background anisotropies and discuss how the trispectrum signal generated by the primordial non-Gaussianity can be measured with the three-to-one correlator and the corresponding angular power spectrum. We also discuss the separation of primordial non-Gaussian information in the trispectrum with that generated by the subsequent nonlinear gravitational evolution of the density field. While with the angular bispectrum of 21-cm anisotropies one can limit the second-order corrections to the primordial fluctuations below fNL~1, using the trispectrum information we suggest that the third-order coupling term, f2 or gNL, can be constrained to be around 10 with future 21-cm observations over the redshift interval of 50 to 100
Impact of point source clustering on cosmological parameters with CMB anisotropies
No full textThe faint radio point sources that are unresolved in cosmic microwave background (CMB) anisotropy maps are likely to be a biased tracer of the large-scale structure dark matter distribution. While the shot-noise contribution to the angular power spectrum of unresolved radio point sources is included either when optimally constructing the CMB angular power spectrum, as with WMAP data, or when extracting cosmological parameters, we suggest that clustering part of the point source power spectrum should also be included. This is especially necessary at high frequencies above 150 GHz, where the Clustering of far-IR sources is expected to dominate the shot-noise level of the angular power spectrum at tens of arcminute angular scales of both radio and sub-mm sources. We make an estimate of source clustering of unresolved radio sources in both WMAP and ACBAR, and marginalize over the amplitude of source clustering in each CMB data set when model fitting for cosmological parameters. For the combination of WMAP 5-year data and ACBAR, we find that the spectral index changes from the value of 0.963 +/- 0.014 to 0.959 +/- 0.014 (at 68% C.L.) when the clustering power spectrum of point sources is included in model fits. While we find that the differences are marginal with and without source clustering in current data, it may be necessary to account for source clustering with future data sets such as Planck, especially to properly model fit anisotropies at arcminute angular scales. If clustering is not accounted and point sources are modeled with a shot noise only out to l similar to 2000, the spectral index will be biased by about 1.5 sigma
Red Density Perturbations and Inflationary Gravitational Waves
No full textWe study the implications of recent indications for a red spectrum of primordial density perturbations for the detection of inflationary gravitational waves (IGWs) with forthcoming cosmic microwave background experiments. We find that if inflation occurs with a single field with an inflaton potential minimized at V=0, then Planck will be able to detect IGWs at better than 2 confidence level, unless the inflaton potential is a power law with a very weak power. The proposed satellite missions of the Cosmic Vision and Inflation Probe programs will be able to detect IGWs from all the models we have surveyed at better than 5 confidence level. We provide an example of what is required if the IGW background is to remain undetected even by these latter experiments.We study the implications of recent indications for a red spectrum of primordial density perturbations for the detection of inflationary gravitational waves (IGWs) with forthcoming cosmic microwave background experiments. We find that if inflation occurs with a single field with an inflaton potential minimized at V=0, then Planck will be able to detect IGWs at better than 2 confidence level, unless the inflaton potential is a power law with a very weak power. The proposed satellite missions of the Cosmic Vision and Inflation Probe programs will be able to detect IGWs from all the models we have surveyed at better than 5 confidence level. We provide an example of what is required if the IGW background is to remain undetected even by these latter experiments
WMAP-normalized inflationary model predictions and the search for primordial gravitational waves with direct detection experiments
No full textIn addition to density perturbations, inflationary models of the early Universe generally predict a stochastic background of gravitational waves or tensor fluctuations. By making use of the inflationary flow approach for single field models and fitting the models with Monte Carlo techniques to cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP), we discuss the expected properties of the gravitational wave background from inflation at scales corresponding to direct detection experiments with laser interferometers in space. We complement the Monte Carlo numerical calculations by including predictions expected under several classes of analytical inflationary models. We find that an improved version of big bang observer (BBO-grand) can be used to detect a gravitational wave background at 0.1 Hz with a corresponding CMB tensor-to-scalar ratio above 10(-4). Even if the CMB tensor-to-scalar ratio were to be above 10(-2), we suggest that BBO-grand will be useful to study inflationary models as the standard version of BBO, with a sensitivity to a stochastic gravitational wave background Omega(GW)h(2)> 10(-17), will only allow a marginal detection of the amplitude while leaving the tensor spectral index at 0.1 Hz unconstrained. Also, inflationary models with a large tensor-to-scalar ratio predict a substantial negative tensor spectral index such that the gravitational wave amplitude is damped at direct detection frequencies. We also discuss the extent to which CMB measurements can be used to predict the gravitational wave background amplitude in a direct detection experiment and how any measurement of the amplitude and the spectral tilt of the gravitational wave background at direct detection frequencies together with the CMB tensor-to-scalar ratio can be used to establish slow-roll inflation
Stellar occultation observations of Saturn's upper atmosphere
No full textThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997.Includes bibliographical references (leaves 74-79).by Asantha Roshan Cooray.M.S
Anisotropies in the cosmic neutrino background after Wilkinson Microwave Anisotropy Probe five-year data
No full textWe search for the presence of cosmological neutrino background ( CNB) anisotropies in recent Wilkinson Microwave Anisotropy Probe ( WMAP) five-year data using their signature imprinted on modi. cations to the cosmic microwave background ( CMB) anisotropy power spectrum. By parameterizing the neutrino background anisotropies with the speed viscosity parameter c(vis), we find that the WMAP five-year data alone provide only a weak indication for CNB anisotropies with c(vis)(2) > 0.06 at the 95% confidence level. When we combine CMB anisotropy data with measurements of galaxy clustering, the SN-Ia Hubble diagram, and other cosmological information, the detection increases to c(vis)(2) > 0.16 at the same 95% confidence level. Future data from Planck, combined with a weak lensing survey such as the one expected with DUNE from space, will be able to measure the CNB anisotropy parameter at about 10% accuracy. We discuss the degeneracy between neutrino background anisotropies and other cosmological parameters such as the number of effective neutrinos species and the dark energy equation of state
Large scale structure as a probe of gravitational slip
No full textA new time-dependent, scale-independent parameter, (omega) over bar, is employed in a phenomenological model of the deviation from general relativity in which the Newtonian and longitudinal gravitational potentials slip apart on cosmological scales as dark energy, assumed to be arising from a new theory of gravitation, appears to dominate the Universe. A comparison is presented between (omega) over bar and other parametrized post-Friedmannian models in the literature. The effect of (omega) over bar on the cosmic microwave background anisotropy spectrum, the growth of large-scale structure, the galaxy weak-lensing correlation function, and cross correlations of cosmic microwave background anisotropy with galaxy clustering are illustrated. Cosmological models with conventional maximum likelihood parameters are shown to find agreement with a narrow range of gravitational slip
A constraint on Planck-scale modifications to electrodynamics with CMB polarization data
No full textWe show that the Cosmic Microwave Background (CMB) polarization data gathered by the BOOMERanG 2003 flight and WMAP provide an opportunity to investigate in-vacuo birefringence, of a type expected in some quantum pictures of space-time, with a sensitivity that extends even beyond the desired Planck-scale energy. In order to render this constraint more transparent we rely on a well studied phenomenological model of quantum-gravity-induced birefringence, in which one easily establishes that effects introduced at the Planck scale would amount to values of a dimensionless parameter, denoted by., with respect to the Planck energy which are roughly of order 1. By combining BOOMERanG and WMAP data we estimate xi similar or equal to -0.110 +/- 0.075 at the 68% c.l. Moreover, we forecast on the sensitivity to. achievable by future CMB polarization experiments (PLANCK, Spider, EPIC), which, in the absence of systematics, will be at the 1-sigma confidence of 8.5 x 10(-4) (PLANCK), 6.1 x 10(-3) (Spider), and 1.0 x 10(-5) (EPIC) respectively. The cosmic variance-limited sensitivity from CMB is 6.1 x 10(-6)
CMB neutrino mass bounds and reionization
No full textCurrent cosmic microwave background bounds on the sum of the neutrino masses assume a sudden reionization scenario described by a single parameter that determines the onset of reionization. We investigate the bounds on the neutrino mass in a more general reionization scenario based on a principal component approach. We found the constraint on the sum of the neutrino masses from cosmic microwave background data can be relaxed by similar to 40% in a generalized reionization scenario. Moreover, the amplitude of the rms mass fluctuations sigma(8) is also considerably lower providing a better consistency with the low amplitude of the Sunyaev-Zel'dovich signal recently found by the South Pole Telescope
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