On the abundance of extreme voids

Cosmic voids have been shown to be an effective probe of cosmology, complementary to galaxy clusters. In this work, we present a simple theoretical framework for predicting of the size of the largest voids expected within a given redshift and volume. Our model is based on the exact extreme-value statistics which has previously been successfully applied to massive galaxy clusters. We implement our formalism using the void-abundance models and compare the extreme-void predictions to simulations and observations. We find that the simplest void models can only explain the extreme-void abundance with ad hoc parameter adjustments. We argue that the prediction extreme-void distribution should be used as an additional test on theories of void abundance

The Lyman α forest as a tool for disentangling non-Gaussianities

© 2014 IOP Publishing Ltd and Sissa Medialab srl . Detection of primordial non-Gaussianity will give us an unprecedented detail of the physics of inflation. As observational probes are now exploring new expanses of the inflationary landscape, it is crucial to distinguish and disentangle effects of various non-Gaussianities beyond f NL . In this work, we calculate the effects of non-Gaussianities parametrized by f NL and the cubic-order g NL , on the Lyman α-forest flux measurements. We give the expressions of the bias due to f NL and g NL , which can be deduced from accurate measurements of the transmitted flux. We show how these two effects can be cleanly disentangled via a flux transformation, which also keeps the error in check

The Lyman-alpha Forest as a tool for disentangling non-Gaussianities

Detection of primordial non-Gaussianity will give us an unprecedented detail of the physics of inflation. As observational probes are now exploring new expanses of the inflationary landscape, it is crucial to distinguish and disentangle effects of various non-Gaussianities beyond f_NL. In this work, we calculate the effects of non-Gaussianities parametrized by f_NL and the cubic-order g_NL, on the Lyman-alpha-forest flux measurements. We give the expressions of the bias due to f_NL and g_NL, which can be deduced from accurate measurements of the transmitted flux. We show how these two effects can be cleanly disentangled via a flux transformation, which also keeps the error in check.Comment: 12 pages, 5 figures. Accepted for publication in JCA

Inflation model building with an accurate measure of e-folding

It has become standard practice to take the logarithmic growth of the scale factor as a measure of the amount of inflation, despite the well-known fact that this is only an approximation for the true amount of inflation required to solve the horizon and flatness problems. The aim of this work is to show how this approximation can be completely avoided using an alternative framework for inflation model building. We show that using the inverse Hubble radius, H=aH , as the key dynamical parameter, the correct number of e-folding arises naturally as a measure of inflation. As an application, we present an interesting model in which the entire inflationary dynamics can be solved analytically and exactly, and, in special cases, reduces to the familiar class of power-law models

Constraining isocurvature perturbations with the 21 cm emission from minihaloes

We investigate the effects of isocurvature perturbations on the 21 cm radiation from minihaloes (MHs) at high redshifts and examine constraints on the isocurvature amplitude and power spectrum using the next generation of radio telescopes such as the Square Kilometre Array. We find that there is a realistic prospect of observing the isocurvature imprints in the 21 cm emission from MHs, but only if the isocurvature spectral index is close to 3 (i.e. the spectrum is blue). When the isocurvature fraction increases beyond ∼10 per cent of the adiabatic component, we observe an unexpected decline in the 21 cm fluctuations from small-mass MHs, which can be explained by the incorporation small MHs into larger haloes. We perform a detailed Fisher-matrix analysis and conclude that the combination of future cosmic microwave background and 21 cm experiments (such as CMBPol and the Fast Fourier Transform Telescope) is ideal in constraining the isocurvature parameters, but will stop short of distinguishing between cold dark matter and baryon types of isocurvature perturbations, unless the isocurvature fraction is large and the spectrum is blue

A gauge-invariant approach to interactions in the dark sector

We outline a gauge-invariant framework to calculate cosmological perturbations in dark energy models consisting of a scalar field interacting with dark matter via energy and momentum exchanges. Focusing on three well-known models of quintessence and three common types of dark-sector interactions, we calculate the matter and dark energy power spectra as well as the Integrated Sachs-Wolfe (ISW) effect in these models. We show how the presence of dark-sector interactions can produce a large-scale enhancement in the matter power spectrum and a boost in the low multipoles of the cosmic microwave background anisotropies. Nevertheless, we find these enhancements to be much more subtle than those found by previous authors who model dark energy using simple ansatz for the equation of state. We also address issues of instabilities and emphasise the importance of momentum exchanges in the dark sector.Comment: 24 pages, 9 figures. Accepted for publication in JCA

Dynamics of the Inflationary Flow Equations

We present a dynamical analysis of the inflationary flow equations. Our technique uses the Hubble `jerk' parameter as a discriminant of stability of fixed points. The results of the analysis are used to explain qualitatively the distribution of various observable parameters (e.g. the tensor-scalar ratio, r, and scalar spectral index, n_s) seen in numerical solutions of the flow equations using stochastic initial conditions. Finally, we give a physical interpretation of the flow in phase-space in terms of slow-roll motion of the inflaton.Comment: 9 pages 4 figures. Accepted for publication in Physical Review