arXiv subjects

Andrew H. Jaffe

Publications and source records attributed to Andrew H. Jaffe.

63 records · Page 4Linked to original sources

arXiv1999

The Angular Three-Point Correlation Function in the Quasilinear Regime

We calculate the normalized angular three-point correlation function (3PCF), $q$, as well as the normalized angular skewness, $s_3$, assuming the small-angle approximation, for a biased mass distribution in flat and open cold-dark-matter (CDM) models with Gaussian initial conditions. The leading-order perturbative results incorporate the explicit dependence on the cosmological parameters, the shape of the CDM transfer function, the linear evolution of the power spectrum, the form of redshift distribution function, and linear and nonlinear biasing, which may be evolving. Results are presented for different redshift distributions, including that appropriate for the APM Galaxy Survey, as well as for a survey with a mean redshift of $\bar{z} \simeq 1$ (such as the VLA FIRST Survey). Qualitatively, many of the results found for $s_3$ and $q$ are similar to those obtained in a related treatment of the spatial skewness and 3PCF (Buchalter & Kamionkowski 1999), such as a leading-order correction to the standard result for $s_3$ in the case of nonlinear bias (as defined for unsmoothed density fields), and the sensitivity of the configuration dependence of $q$ to both cosmological and biasing models. We show that since angular CFs are sensitive to clustering over a range of redshifts, the various evolutionary dependences included in our predictions imply that measurements of $q$ in a deep survey might better discriminate between models with different histories, such as evolving vs. non-evolving bias, that can have similar spatial CFs at low redshift. Our calculations employ a derived equation---valid for open, closed, and flat models---for obtaining the angular bispectrum from the spatial bispectrum in the small-angle approximation.

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arXiv1999

WOMBAT & FORECAST: Making Realistic Maps of the Microwave Sky

The Wavelength-Oriented Microwave Background Analysis Team (WOMBAT) is constructing microwave maps which will be more realistic than previous simulations. Our foreground models represent a considerable improvement: where spatial templates are available for a given foreground, we predict the flux and spectral index of that component at each place on the sky and estimate uncertainties. We will produce maps containing simulated CMB anisotropy combined with expected foregrounds. The simulated maps will be provided to the community as the WOMBAT Challenge, so such maps can be analyzed to extract cosmological parameters by scientists who are unaware of their input values. This will test the efficacy of foreground subtraction, power spectrum analysis, and parameter estimation techniques and help identify the areas most in need of progress. These maps are also part of the FORECAST project, which allows web-based access to the known foreground maps for the planning of CMB missions.

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arXiv1999

Computing challenges of the Cosmic Microwave Background

The Cosmic Microwave Background (CMB) encodes information on the origin and evolution of the universe, buried in a fractional anisotropy of one part in 100,000 on angular scales from arcminutes to tens of degrees. We await the coming onslaught of data from experiments measuring the microwave sky from the ground, from balloons and from space. However, we are faced with the harsh reality that current algorithms for extracting cosmological information cannot handle data sets of the size and complexity expected even in the next few years. Here we review the challenges involved in understanding this data: making maps from time-ordered data, removing the foreground contaminants, and finally estimating the power spectrum and cosmological parameters from the CMB map. If handled naively, the global nature of the analysis problem renders these tasks effectively impossible given the volume of the data. We discuss possible techniques for overcoming these issues and outline the many other challenges that wait to be addressed.

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arXiv1998

Constraining Large Scale Structure Theories with the Cosmic Background Radiation

We review the relevant 10+ parameters associated with inflation and matter content; the relation between LSS and primary and secondary CMB anisotropy probes; COBE constraints on energy injection; current anisotropy band-powers which strongly support the gravitational instability theory and suggest the universe could not have reionized too early. We use Bayesian analysis methods to determine what current CMB and CMB+LSS data imply for inflation-based Gaussian fluctuations in tilted $Λ$CDM, $Λ$hCDM and oCDM model sequences with age 11-15 Gyr, consisting of mixtures of baryons, cold (and possibly hot) dark matter, vacuum energy, and curvature energy in open cosmologies. For example, we find the slope of the initial spectrum is within about 5% of the (preferred) scale invariant form when just the CMB data is used, and for $Λ$CDM when LSS data is combined with CMB; with both, a nonzero value of $Ω_Λ$ is strongly preferred ($\approx 2/3$ for a 13 Gyr sequence, similar to the value from SNIa). The $o$CDM sequence prefers $Ω_{tot}<1 $, but is overall much less likely than the flat $Ω_Λ\ne 0$ sequence with CMB+LSS. We also review the rosy forecasts of angular power spectra and parameter estimates from future balloon and satellite experiments when foreground and systematic effects are ignored.

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arXiv1997

CMB Power Spectrum Estimation

We explore power spectrum estimation in the context of a Gaussian approximation to the likelihood function. Using the Saskatoon data, we estimate the power averaged through a set of ten filters designed to make the errors on the power estimates uncorrelated. We also present an improvement to using the window function, $W_l$, for calculating bandpower estimates.

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arXiv1996

Cosmic Parameter Estimation Combining Sub-Degree CMB Experiments with COBE

We describe the Bayesian-based signal-to-noise eigenmode method for cosmological parameter estimation, show how it can be used to optimally compress large CMB anisotropy data sets to manageable sizes, and apply it to the DMR 4-year, South Pole and Saskatchewan data, individually and in combination. A simple prior probability method is used to include large scale structure observations. Estimates of the Hubble parameter, vacuum energy density, baryon fraction and primordial spectral tilt derived from the combined data are given.

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arXiv1993

Quasi-Linear Evolution of Compensated Cosmological Perturbations: The Nonlinear Sigma Model

We consider the evolution of perturbations to a flat FRW universe that arise from a ``stiff source,'' such as a self-ordering cosmic field that forms in a global symmetry-breaking phase transition and evolves via the Kibble mechanism. Although the linear response of the normal matter to the source depends on the details of the source dynamics, we show that the higher-order non-linear perturbative equations reduce to a form identical to those of source-free Newtonian gravity in the small wavelength limit. Consequently, the resulting $n$-point correlation functions and their spectral counterparts will have a hierarchical contribution arising from this gravitational evolution (as in the source-free case) in addition to that possibly coming from non-Gaussian initial conditions. We apply this formalism to the $O(N)$ nonlinear sigma model at large $N$ and find that observable differences from the case of initially Gaussian perturbations and Newtonian gravity in the bispectrum and higher-order correlations are not expected on scales smaller than about $100\,h^{-1}{\rm Mpc}$.

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arXiv1993

Minimal Microwave Anisotropy from Perturbations Induced at Late Times

Aside from primordial gravitational instability of the cosmological fluid, various mechanisms have been proposed to generate large-scale structure at relatively late times, including, e.g., ``late-time'' cosmological phase transitions. In these scenarios, it is envisioned that the universe is nearly homogeneous at the time of last scattering and that perturbations grow rapidly sometime after the primordial plasma recombines. On this basis, it was suggested that large inhomogeneities could be generated while leaving relatively little imprint on the cosmic microwave background (MBR) anisotropy. In this paper, we calculate the minimal anisotropies possible in any ``late-time'' scenario for structure formation, given the level of inhomogeneity observed at present. Since the growth of the inhomogeneity involves time-varying gravitational fields, these scenarios inevitably generate significant MBR anisotropy via the Sachs-Wolfe effect. Moreover, we show that the large-angle MBR anisotropy produced by the rapid post-recombination growth of inhomogeneity is generally greater than that produced by the same inhomogeneity grown via gravitational instability. In ``realistic'' scenarios one can decrease the anisotropy compared to models with primordial adiabatic fluctuations, but only on very small angular scales. The value of any particular measure of the anisotropy can be made small in late-time models, but only by making the time-dependence of the gravitational field sufficiently ``pathological''.

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arXiv1992

Limits on Neutrino Radiative Decay from Sn1987a

We calculate limits on the properties of neutrinos using data from gamma-ray detectors on the Pioneer Venus Orbiter and Solar Max Mission satellites. A massive neutrino decaying in flight from the supernova would produce gamma rays detectable by these instruments. The lack of such a signal allows us to constrain the mass, radiative lifetime, and branching ratio to photons of a massive neutrino species produced in the supernova. Presented at Beyond The Standard Model III, June, 1992.

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