arXiv subjects

Joseph Smidt

Publications and source records attributed to Joseph Smidt.

48 records · Page 3Linked to original sources

arXiv2010

CMB Constraints on Primordial non-Gaussianity from the Bispectrum (f_{NL}) and Trispectrum (g_{NL} and τ_{NL}) and a New Consistency Test of Single-Field Inflation

We outline the expected constraints on non-Gaussianity from the cosmic microwave background (CMB) with current and future experiments, focusing on both the third (f_{NL}) and fourth-order (g_{NL} and τ_{NL}) amplitudes of the local configuration or non-Gaussianity. The experimental focus is the skewness (two-to-one) and kurtosis (two-to-two and three-to-one) power spectra from weighted maps. In adition to a measurement of τ_{NL} and g_{NL} with WMAP 5-year data, our study provides the first forecasts for future constraints on g_{NL}. We describe how these statistics can be corrected for the mask and cut-sky through a window function, bypassing the need to compute linear terms that were introduced for the previous-generation non-Gaussianity statistics, such as the skewness estimator. We discus the ratio A_{NL} = τ_{NL}/(6f_{NL}/5)^2 as an additional test of single-field inflationary models and discuss the physical significance of each statistic. Using these estimators with WMAP 5-Year V+W-band data out to l_{max}=600 we constrain the cubic order non-Gaussianity parameters τ_{NL}, and g_{NL} and find -7.4 < g_{NL}/10^5 < 8.2 and -0.6 < τ_{NL}/10^4 < 3.3 improving the previous COBE-based limit on τ_{NL} < 10^8 nearly four orders of magnitude with WMAP.

astro-ph.CO↗

arXiv2010

The Impact of Secondary non-Gaussianities in the CMB on Cosmological Parameter Estimation

We consider corrections to the underlying cosmology due to secondary contributions from weak gravitational lensing, the integrated Sachs-Wolfe effect, and the Sunyaev-Zel'dovich effect contained in the trispectrum. We incorporate these additional contributions to the covariance of a binned angular power spectrum of temperature anisotropies in the analysis of current and prospective data sets. Although recent experiments such as ACBAR and CBI are not particularly sensitive to these additional non-Gaussian effects, the interpretation of Planck and CMBPol anisotropy spectra will require an accounting of non-Gaussian covariance leading to a degradation in cosmological parameter estimates by up to 20% and 30%, respectively.

astro-ph.CO↗

arXiv2010

A Measurement of Cubic-Order Primordial Non-Gaussianity (g_{NL} and τ_{NL}) With WMAP 5-Year Data

We measure two higher-order power spectra involving weighted cubic and squared temperature anisotropy maps from WMAP 5-year data to study the trispectrum generated by primordial non-Gaussianity. Using these measurements combined with Gaussian and noise simulations, we constrain the cubic order non-Gaussianity parameters τ_{NL}, and g_{NL}. With V+W-band data out to l_{max}=600, we find -7.4 < g_{\rm NL}/10^5 < 8.2 and -0.6 < τ_{\rm NL}/10^4 < 3.3 improving the previous COBE-based limit on τ_{\rm NL} < 10^8 nearly four orders of magnitude with WMAP. We find that the ratio of trispectrum to bispectrum amplitude as captured by the ratio of τ_{\rm Nl}/(6f_{\rm NL}/5)^2 ranges from -3 to 21 at the 95% confidence level.

astro-ph.CO↗

arXiv2010

Higher-order Statistics of Weak Lensing Shear and Flexion

Owing to their more extensive sky coverage and tighter control on systematic errors, future deep weak lensing surveys should provide a better statistical picture of the dark matter clustering beyond the level of the power spectrum. In this context, the study of non-Gaussianity induced by gravity can help tighten constraints on the background cosmology by breaking parameter degeneracies, as well as throwing light on the nature of dark matter, dark energy or alternative gravity theories. Analysis of the shear or flexion properties of such maps is more complicated than the simpler case of the convergence due to the spinorial nature of the fields involved. Here we develop analytical tools for the study of higher-order statistics such as the bispectrum (or trispectrum) directly using such maps at different source redshift. The statistics we introduce can be constructed from cumulants of the shear or flexions, involving the cross-correlation of squared and cubic maps at different redshifts. Typically, the low signal-to-noise ratio prevents recovery of the bispectrum or trispectrum mode by mode. We define power spectra associated with each multi- spectra which compresses some of the available information of higher order multispectra. We show how these can be recovered from a noisy observational data even in the presence of arbitrary mask, which introduces mixing between Electric (E-type) and Magnetic (B-type) polarization, in an unbiased way. We also introduce higher order cross-correlators which can cross-correlate lensing shear with different tracers of large scale structures.

astro-ph.CO↗

arXiv2010

Primordial Non-Gaussianity from a Joint Analysis of Cosmic Microwave Background Temperature and Polarization

We explore a systematic approach to the analysis of primordial non-Gaussianity using fluctuations in temperature and polarization of the Cosmic Microwave Background (CMB). Following Munshi & Heavens (2009), we define a set of power-spectra as compressed forms of the bispectrum and trispectrum derived from CMB temperature and polarization maps; these spectra compress the information content of the corresponding full multispectra and can be useful in constraining early Universe theories. We generalize the standard pseudo-C_l estimators in such a way that they apply to these spectra involving both spin-0 and spin-2 fields, developing explicit expressions which can be used in the practical implementation of these estimators. While these estimators are suboptimal, they are nevertheless unbiased and robust hence can provide useful diagnostic tests at a relatively small computational cost. We next consider approximate inverse-covariance weighting of the data and construct a set of near-optimal estimators based on that approach. Instead of combining all available information from the entire set of mixed bi- or trispectra, i.e multispectra describing both temperature and polarization information, we provide analytical constructions for individual estimators, associated with particular multispectra. The bias and scatter of these estimators can be computed using Monte-Carlo techniques. Finally, we provide estimators which are completely optimal for arbitrary scan strategies and involve inverse covariance weighting; we present the results of an error analysis performed using a Fisher-matrix formalism at both the one-point and two-point level.

astro-ph.CO↗

arXiv2009

New Optimised Estimators for the Primordial Trispectrum

Cosmic microwave background studies of non-Gaussianity involving higher-order multispectra can distinguish between early universe theories that predict nearly identical power spectra. However, the recovery of higher-order multispectra is difficult from realistic data due to their complex response to inhomogeneous noise and partial sky coverage, which are often difficult to model analytically. A traditional alternative is to use one-point cumulants of various orders, which collapse the information present in a multispectrum to one number. The disadvantage of such a radical compression of the data is a loss of information as to the source of the statistical behaviour. A recent study by Munshi & Heavens (2009) has shown how to define the skew spectrum (the power spectra of a certain cubic field, related to the bispectrum) in an optimal way and how to estimate it from realistic data. The skew spectrum retains some of the information from the full configuration-dependence of the bispectrum, and can contain all the information on non-Gaussianity. In the present study, we extend the results of the skew spectrum to the case of two degenerate power-spectra related to the trispectrum. We also explore the relationship of these power-spectra and cumulant correlators previously used to study non-Gaussianity in projected galaxy surveys or weak lensing surveys. We construct nearly optimal estimators for quick tests and generalise them to estimators which can handle realistic data with all their complexity in a completely optimal manner. We show how these higher-order statistics and the related power spectra are related to the Taylor expansion coefficients of the potential in inflation models, and demonstrate how the trispectrum can constrain both the quadratic and cubic terms.

astro-ph.CO↗

arXiv2009

Non-Gaussianity in WMAP Data Due to the Correlation of CMB Lensing Potential with Secondary Anisotropies

We measure the skewness power spectrum of the Cosmic Microwave Background (CMB) anisotropies optimized for a detection of the secondary bispectrum generated by the correlation of the CMB lensing potential with integrated Sachs-Wolfe effect and the Sunyaev-Zel'dovich effect. The covariance of our measurements is generated by Monte-Carlo simulations of Gaussian CMB fields with noise properties consistent with Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data. When interpreting multi-frequency measurements we also take into account the confusion resulting from unresolved radio point sources. We analyze Q, V and W-band WMAP 5-year raw and foreground-cleaned maps using the KQ75 mask out to l_max=600. We find no significant evidence for a non-zero non-Gaussian signal from the lensing-secondary correlation in all three bands and we constrain the overall amplitude of the cross power spectrum between CMB lensing potential and the sum of SZ and ISW fluctuations to be 0.42 \pm 0.86 and 1.19 \pm 0.86 in combined V and W-band raw and foreground-cleaned maps provided by the WMAP team, respectively. The point source amplitude at the bispectrum level measured with this skewness power spectrum is higher than previous measurements of point source non-Gaussianity. We also consider an analysis where we also account for the primordial non-Gaussianity in addition to lensing-secondary bispectrum and point sources. The focus of this paper is on secondary anisotropies. Consequently the estimator is not optimised for primordial non-Gaussianity and the limit we find on local non-Gaussianity from the foreground-cleaned V+W maps is f_NL = -13 \pm 62, when marginalized over point sources and lensing-ISW/SZ constributions to the total bispectrum.

astro-ph.CO↗

arXiv2009

A Measurement of Primordial Non-Gaussianity Using WMAP 5-Year Temperature Skewness Power Spectrum

We constrain the primordial non-Gaussianity parameter of the local model f_{NL} using the skewness power spectrum associated with the two-to-one cumulant correlator of cosmic microwave background temperature anisotropies. This bispectrum-related power spectrum was constructed after weighting the temperature map with the appropriate window functions to form an estimator that probes the multipolar dependence of the underlying bispectrum associated with the primordial non-Gaussianity. We also estimate a separate skewness power spectrum sensitive more strongly to unresolved point sources. When compared to previous attempts at measuring the primordial non-Gaussianity with WMAP data, our estimators have the main advantage that we do not collapse information to a single number. When model fitting the two-to-one skewness power spectrum we make use of bispectra generated by the primordial non-Gaussianity, radio point sources, and lensing-secondary correlation. We analyze Q, V and W-band WMAP 5-year data using the KQ75 mask out to l_{max}=600. Using V and W-band data and marginalizing over model parameters related to point sources and lensing-secondary bispectrum, our overall and preferred constraint on f_{NL} is 11.0\pm23.7 at the 68% confidence level (-36.4 < f_{NL} < 58.4 at 95% confidence). We find no evidence for a non-zero value of f_{NL} even marginally at the 1σlevel.

astro-ph.CO↗

arXiv2009

Parameter Space of General Gauge Mediation

We study a subspace of General Gauge Mediation (GGM) models which generalize models of gauge mediation. We find superpartner spectra that are markedly different from those of typical gauge and gaugino mediation scenarios. While typical gauge mediation predictions of either a neutralino or stau next-to-lightest supersymmetric particle (NLSP) are easily reproducible with the GGM parameters, chargino and sneutrino NLSPs are generic for many reasonable choices of GGM parameters.

hep-ph↗

arXiv2009

Cosmological Radiative Transfer Comparison Project II: The Radiation-Hydrodynamic Tests

The development of radiation hydrodynamical methods that are able to follow gas dynamics and radiative transfer self-consistently is key to the solution of many problems in numerical astrophysics. Such fluid flows are highly complex, rarely allowing even for approximate analytical solutions against which numerical codes can be tested. An alternative validation procedure is to compare different methods against each other on common problems, in order to assess the robustness of the results and establish a range of validity for the methods. Previously, we presented such a comparison for a set of pure radiative transfer tests (i.e. for fixed, non-evolving density fields). This is the second paper of the Cosmological Radiative Transfer (RT) Comparison Project, in which we compare 9 independent RT codes directly coupled to gasdynamics on 3 relatively simple astrophysical hydrodynamics problems: (5) the expansion of an H II region in a uniform medium; (6) an ionization front (I-front) in a 1/r^2 density profile with a flat core, and (7), the photoevaporation of a uniform dense clump. Results show a broad agreement between the different methods and no big failures, indicating that the participating codes have reached a certain level of maturity and reliability. However, many details still do differ, and virtually every code has showed some shortcomings and has disagreed, in one respect or another, with the majority of the results. This underscores the fact that no method is universal and all require careful testing of the particular features which are most relevant to the specific problem at hand.

astro-ph.CO↗

arXiv2008

How the First Stars Regulated Local Star Formation I: Radiative Feedback

We present numerical simulations of how a 120 M$_\odot$ primordial star regulates star formation in nearby cosmological halos at $z \sim$ 20 by photoevaporation. Our models include nine-species primordial chemistry and self-consistent multifrequency conservative transfer of UV photons with all relevant radiative processes. Whether or not new stars form in halos clustered around a Population III star ultimately depends on their core densities and proximity to the star. Diffuse halos with central densities below 2 - 3 cm$^{-3}$ are completely ionized and evaporated anywhere in the cluster. Evolved halos with core densities above 2000 cm$^{-3}$ are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse as quickly as they would in its absence. Star formation in halos of intermediate density can be either promoted or suppressed depending on how the I-front remnant shock compresses, deforms and enriches the core with H$_2$. We find that the 120 M$_\odot$ star photodissociates H$_2$ in most halos in the cluster but that catalysis by H- restores it a few hundred kyr after the death of the star, with little effect on star formation. Our models exhibit significant departures from previous one-dimensional spherically-symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.

astro-ph↗

arXiv2007

Photoionization of Clustered Halos by the First Stars

We present numerical simulations of the photoevaporation of cosmological halos clustered around a 120 M$_\odot$ primordial star, confining our study to structures capable of hosting Population III star formation. The calculations include self-consistent multifrequency conservative transfer of UV photons together with nine-species primordial chemistry and all relevant radiative processes. The ultimate fates of these halos varies with central density and proximity to the central source but generally fall into one of four categories. Diffuse halos with central densities below 2 - 3 cm$^{-3}$ are completely ionized and evaporated by the central star anywhere in the cluster. More evolved halo cores at densities above 2000 cm$^{-3}$ are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse of their cores proceeds without delay. Radiative feedback in halos of intermediate density can be either positive or negative, depending on how the I-front remnant shock both compresses and deforms the core and enriches it with H$_2$. We find that the 120 M$_\odot$ star photodissociates H$_2$ in most halos within the cluster but that catalysis by H- rapidly restores molecular hydrogen within a few hundred Kyr after the death of the star, with little delay in star formation. Our models exhibit significant departures from previous one-dimensional spherically-symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.

astro-ph↗