arXiv subjects

Arthur Kosowsky

Publications and source records attributed to Arthur Kosowsky.

At least 163 records · Page 9Linked to original sources

arXiv2002

Gravitational Radiation From Cosmological Turbulence

An injection of energy into the early Universe on a given characteristic length scale will result in turbulent motions of the primordial plasma. We calculate the stochastic background of gravitational radiation arising from a period of cosmological turbulence, using a simple model of isotropic Kolmogoroff turbulence produced in a cosmological phase transition. We also derive the gravitational radiation generated by magnetic fields arising from a dynamo operating during the period of turbulence. The resulting gravitational radiation background has a maximum amplitude comparable to the radiation background from the collision of bubbles in a first-order phase transition, but at a lower frequency, while the radiation from the induced magnetic fields is always subdominant to that from the turbulence itself. We briefly discuss the detectability of such a signal.

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arXiv2002

Efficient Cosmological Parameter Estimation from Microwave Background Anisotropies

We revisit the issue of cosmological parameter estimation in light of current and upcoming high-precision measurements of the cosmic microwave background power spectrum. Physical quantities which determine the power spectrum are reviewed, and their connection to familiar cosmological parameters is explicated. We present a set of physical parameters, analytic functions of the usual cosmological parameters, upon which the microwave background power spectrum depends linearly (or with some other simple dependence) over a wide range of parameter values. With such a set of parameters, microwave background power spectra can be estimated with high accuracy and negligible computational effort, vastly increasing the efficiency of cosmological parameter error determination. The techniques presented here allow calculation of microwave background power spectra $10^5$ times faster than comparably accurate direct codes (after precomputing a handful of power spectra). We discuss various issues of parameter estimation, including parameter degeneracies, numerical precision, mapping between physical and cosmological parameters, and systematic errors, and illustrate these considerations with an idealized model of the MAP experiment.

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arXiv2002

Microwave Background Signatures of a Primordial Stochastic Magnetic Field

A stochastic magnetic field in the early Universe will produce anisotropies in the temperature and polarization of the cosmic microwave background. We derive analytic expressions for the microwave background temperature and polarization power spectra induced by vector and tensor perturbations from a power-law magnetic field. For a scale-invariant stochastic magnetic field smoothed over a comoving scale of $1 {\rm Mpc}$, the MAP satellite has the potential to constrain the comoving mean-field amplitude to be no greater than approximately $2\times10^{-9}$ G. Limits improve as the power-law slope increases: for causally-generated power-law magnetic fields, the comoving mean-field amplitude has an upper bound of approximately $4\times10^{-13} {\rm G}$. Such constraints will surpass all current limits on galactic-scale primordial stochastic magnetic fields at decoupling.

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arXiv2001

The Cosmic Microwave Background

This set of lectures provides an overview of the basic theory and phenomenology of the cosmic microwave background. Topics include a brief historical review; the physics of temperature and polarization fluctuations; acoustic oscillations of the primordial plasma; the space of inflationary cosmological models; current and potential constraints on these models from the microwave background; and constraints on inflation.

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arXiv2001

Stochastic Gravitational Radiation from Phase Transitions

A stochastic background of gravitational radiation from cosmological processes in the very early Universe is potentially detectable. We review the gravitational radiation which may arise from cosmological phase transitions, covering both bubble collisions and turbulence as sources. Prospects for detecting a direct signal from the electroweak phase transition or other cosmological sources with a space-based laser interferometer are discussed.

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arXiv2000

CMB Signatures of a Primordial Magnetic Field

A primordial stochastic magnetic field will induce temperature and polarization fluctuations in the cosmic microwave background. We outline a calculation of the resulting fluctuation power spectra and present numerical results.

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arXiv1999

The Cosmic Microwave Background and Particle Physics

In forthcoming years, connections between cosmology and particle physics will be made increasingly important with the advent of a new generation of cosmic microwave background (CMB) experiments. Here, we review a number of these links. Our primary focus is on new CMB tests of inflation. We explain how the inflationary predictions for the geometry of the Universe and primordial density perturbations will be tested by CMB temperature fluctuations, and how the gravitational waves predicted by inflation can be pursued with the CMB polarization. The CMB signatures of topological defects and primordial magnetic fields from cosmological phase transitions are also discussed. Furthermore, we review current and future CMB constraints on various types of dark matter (e.g. massive neutrinos, weakly interacting massive particles, axions, vacuum energy), decaying particles, the baryon asymmetry of the Universe, ultra-high-energy cosmic rays, exotic cosmological topologies, and other new physics.

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arXiv1999

Introduction to Microwave Background Polarization

Microwave background polarization, though presently undetected, is a fundamental prediction of any viable cosmological model. These lectures review the theoretical description of polarization, its physical interpretation, and potentially interesting polarization signals.

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arXiv1998

Seeing Sound Waves in the Early Universe

Temperature and polarization power spectra of the cosmic microwave background can provide essentially incontrovertible evidence for coherent acoustic oscillations in the early universe. A simple model calculation demonstrates explicitly how polarization couples to velocities at the surface of last scatter and is nearly independent of gravitational or density perturbations. For coherent acoustic oscillations, peaks in the temperature and polarization power spectra are precisely interleaved. If observed, such a signal would provide strong support for initial density perturbations on scales larger than the horizon, and thus for inflation.

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arXiv1998

Efficient Computation of Hyperspherical Bessel Functions

Fast and accurate computations of the power spectrum of cosmic microwave background fluctuations are essential for comparing current and upcoming data sets with the large parameter space of viable cosmological models. The most efficient numerical algorithm for power spectrum calculation, recently implemented by Seljak and Zaldarriaga, involves integrating sources against spherical Bessel functions or, in the case of a non-flat universe, analogous hyperspherical Bessel functions. Evaluation of these special functions usually dominates the computation time in non-flat spatial geometries. This paper presents a highly accurate and very fast WKB approximation for computing hyperspherical Bessel functions which will greatly increase the speed of microwave background power spectrum computations in open and closed universes.

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arXiv1997

Minkowski Functional Description of Microwave Background Gaussianity

A Gaussian distribution of cosmic microwave background temperature fluctuations is a generic prediction of inflation. Upcoming high-resolution maps of the microwave background will allow detailed tests of Gaussianity down to small angular scales, providing a crucial test of inflation. We propose Minkowski functionals as a calculational tool for testing Gaussianity and characterizing deviations from it. We review the mathematical formalism of Minkowski functionals of random fields; for Gaussian fields the functionals can be calculated exactly. We then apply the results to pixelized maps, giving explicit expressions for calculating the functionals from maps as well as the Gaussian predictions, including corrections for map boundaries, pixel noise, and pixel size and shape. Variances of the functionals for Gaussian distributions are derived in terms of the map correlation function. Applications to microwave background maps are discussed.

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arXiv1997

Detectability of Inflationary Gravitational Waves with Microwave Background Polarization

Inflation predicts specific relations between the amplitudes and spectral indices of the primordial spectrum of density (scalar metric) perturbations and gravitational waves (tensor metric perturbations). Detection of a stochastic gravitational-wave background is essential for identifying this unmistakable signature. Polarization of the cosmic microwave background can isolate these tensor modes in a model-independent way and thereby circumvent the cosmic-variance limit to detecting a small tensor signal with only a temperature map. Here we assess the detectability of a gravity-wave background with a temperature and polarization map. For detector sensitivities better than $10-20 μK \sqrt{sec}$, the sensitivity to a tensor signal is always dominated by the polarization map. With a detector sensitivity of order $1 μK \sqrt{sec}$, polarization could improve on a temperature-map sensitivity to tensor modes by two to three orders of magnitude. Even a small amount of reionization substantially enhances tensor-mode detectability. We also argue that the sensitivity of the Planck Surveyor to tensor modes is significantly improved with polarization, even taking into account the resulting degradation of the intensity determination in the high-frequency channels.

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arXiv1996

Statistics of Cosmic Microwave Background Polarization

We present a formalism for analyzing a full-sky temperature and polarization map of the cosmic microwave background. Temperature maps are analyzed by expanding over the set of spherical harmonics to give multipole moments of the two-point correlation function. Polarization, which is described by a second-rank tensor, can be treated analogously by expanding in the appropriate tensor spherical harmonics. We provide expressions for the complete set of temperature and polarization multipole moments for scalar and tensor metric perturbations. Four sets of multipole moments completely describe isotropic temperature and polarization correlations; for scalar metric perturbations one set is identically zero, giving the possibility of a clean determination of the vector and tensor contributions. The variance with which the multipole moments can be measured in idealized experiments is evaluated, including the effects of detector noise, sky coverage, and beam width. Finally, we construct coordinate-independent polarization two-point correlation functions, express them in terms of the multipole moments, and derive small-angle limits.

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arXiv1996

A Probe of Primordial Gravity Waves and Vorticity

A formalism for describing an all-sky map of the polarization of the cosmic microwave background is presented. The polarization pattern on the sky can be decomposed into two geometrically distinct components. One of these components is not coupled to density inhomogeneities. A non-zero amplitude for this component of polarization can only be caused by tensor or vector metric perturbations. This allows unambiguous identification of long-wavelength gravity waves or large-scale vortical flows at the time of last scattering.

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arXiv1996

Determining Cosmological Parameters from the Microwave Background

Recently funded satellites will map the cosmic microwave background radiation with unprecedented sensitivities and angular resolutions. Assuming only primordial adiabatic scalar and tensor perturbations, we evaluate how accurately experiments of this type will measure the basic cosmological parameters $Ω$ (the total density of the Universe), $Ω_b$ (the baryon density), $h$ (the Hubble constant), and $Λ$ (the cosmological constant). The proposed experiments are capable of measuring these parameters at the few-percent level. We briefly discuss the generality of these estimates and complications arising in actual data analysis.

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arXiv1996

Cosmological-Parameter Determination with Microwave Background Maps

The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe ($Ω$), the baryon density, the Hubble constant ($h$), the cosmological constant ($Λ$), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with $0.5^\circ$ angular resolution and a noise level of 15 $μ$K per pixel can determine $Ω$, $h$, and $Λ$ with standard errors of $\pm0.1$ or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the the underlying cosmological model is discussed.

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arXiv1996

Faraday Rotation of Microwave Background Polarization by a Primordial Magnetic Field

The existence of a primordial magnetic field at the last scattering surface may induce a measurable Faraday rotation in the polarization of the cosmic microwave background. We calculate the magnitude of this effect by evolving the radiative transfer equations for the microwave background polarization through the epoch of last scatter, in the presence of a magnetic field. For a primordial field amplitude corresponding to a present value of $10^{-9}{\rm G}$ (which would account for the observed galactic field if it were frozen in the pre-galactic plasma), we find a rotation angle of around $1^\circ$ at a frequency of 30 GHz. The statistical detection of this signal is feasible with future maps of the microwave background.

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arXiv1996

Future Cosmic Microwave Background Constraints to the Baryon Density

We discuss what can be learned about the baryon density from an all-sky map of the cosmic microwave background (CMB) with sub-degree angular resolution. With only minimal assumptions about the primordial spectrum of density perturbations and the values of other cosmological parameters, such a CMB map should be able to distinguish between a Universe with a baryon density near 0.1 and a baryon-dominated Universe. With additional reasonable assumptions, it is conceivable that such measurements will constrain the baryon density to an accuracy similar to that obtained from BBN calculations.

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