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Edward W. Kolb

Publications and source records attributed to Edward W. Kolb.

98 records · Page 6Linked to original sources
arXiv1994

Large-amplitude isothermal fluctuations and high-density dark-matter clumps

Large-amplitude isothermal fluctuations in the dark matter energy density, parameterized by $Φ\equivδ\rhodm/\rhodm$, are studied within the framework of a spherical collapse model. For $Φ\ga 1$, a fluctuation collapses in the radiation-dominated epoch and produces a dense dark-matter object. The final density of the virialized object is found to be $ρ_F \approx 140\, Φ^3 (Φ+1) \rhoeq$, where $\rhoeq$ is the matter density at equal matter and radiation energy density. This expression is valid for the entire range of possible values of $Φ$, both for $Φ\gg 1$ and $Φ\ll 1$. Some astrophysical consequences of high-density dark-matter clumps are discussed.

astro-ph↗
arXiv1993

Non-Linear Axion Dynamics and Formation of Cosmological Pseudo-Solitons

The $(3+1)$-dimensional evolution of an inhomogeneous axion field configuration around the QCD epoch is studied numerically, including important non-linear effects due to the attractive self-interaction. It is found that axion perturbations on scales corresponding to causally disconnected regions at $T \sim 1 \, {\rm GeV}$ can lead to very dense pseudo-soliton configurations we call axitons. These configurations evolve to axion miniclusters with present density $ρ_a \ga 10^{-8}\,{\rm g \, cm^{-3}}$. This is high enough for the collisional $2a \rightarrow 2a$ process to lead to Bose--Einstein relaxation in the gravitationally bound clumps of axions, forming Bose stars.

astro-ph↗
arXiv1993

Reconstructing the Inflaton Potential---Perturbative Reconstruction to Second Order

One method to reconstruct the scalar field potential of inflation is a perturbative approach, where the values of the potential and its derivatives are calculated as an expansion in departures from the slow-roll approximation. They can then be expressed in terms of observable quantities, such as the square of the ratio of the gravitational wave amplitude to the density perturbation amplitude, the deviation of the spectral index from the Harrison--Zel'dovich value, etc. Here, we calculate complete expressions for the second-order contributions to the coefficients of the expansion by including for the first time corrections to the standard expressions for the perturbation spectra. As well as offering an improved result, these corrections indicate the expected accuracy of the reconstruction. Typically the corrections are only a few percent.

astro-ph↗
arXiv1993

Observing the Inflaton Potential

We show how observations of the density perturbation (scalar) spectrum and the gravitational wave (tensor) spectrum allow a reconstruction of the potential responsible for cosmological inflation. A complete functional reconstruction or a perturbative approximation about a single scale are possible; the suitability of each approach depends on the data available. Consistency equations between the scalar and tensor spectra are derived, which provide a powerful signal of inflation.

hep-ph↗
arXiv1993

Axion Miniclusters and Bose Stars

Evolution of inhomogeneities in the axion field around the QCD epoch is studied numerically, including for the first time important non-linear effects. It is found that perturbations on scales corresponding to causally disconnected regions at $T \sim 1 \, {\rm GeV}$ can lead to very dense axion clumps, with present density $ρ_a \ga 10^{-8}\,{\rm g \, cm^{-3}}$. This is high enough for the collisional $2a \rightarrow 2a$ process to lead to Bose--Einstein relaxation in the gravitationally bound clumps of axions, forming Bose stars.

hep-ph↗
arXiv1993

Reconstructing the Inflaton Potential---in Principle and in Practice

Generalizing the original work by Hodges and Blumenthal, we outline a formalism which allows one, in principle, to reconstruct the potential of the inflaton field from knowledge of the tensor gravitational wave spectrum or the scalar density fluctuation spectrum, with special emphasis on the importance of the tensor spectrum. We provide some illustrative examples of such reconstruction. We then discuss in some detail the question of whether one can use real observations to carry out this procedure. We conclude that in practice, a full reconstruction of the functional form of the potential will not be possible within the foreseeable future. However, with a knowledge of the dark matter components, it should soon be possible to combine intermediate-scale data with measurements of large-scale cosmic microwave background anisotropies to yield useful information regarding the potential.

hep-ph↗
arXiv1992

Critical Behavior in the Electroweak Phase Transition

We examine the behavior of the standard-model electroweak phase transition in the early Universe. We argue that close to the critical temperature it is possible to estimate the {\it effective} infrared corrections to the 1-loop potential using well known $\varepsilon$-expansion results from the theory of critical phenomena in 3 spatial dimensions. The theory with the $\varepsilon$-corrected potential exhibits much larger fluctuations in the spatial correlations of the order parameter, considerably weakening the strength of the transition.

hep-ph↗