118481628
Dark matter on the smallest scales
Abstract This work investigates the dark matters structures that form on the smallest cosmological scales. We find that the types and abundances of structures which form at approximately Earth-mass scales are very sensitive to the nature of dark matter. We explore various candidates for dark matter and determine the corresponding properties of small-scale structure. In particular, we discuss possibilities for indirect detection of dark matter through small-scale structure, and comment on the potential of these methods for discriminating between dark matter candidates.
18713265
Galilean symmetry in the effective theory of inflation: new shapes of non-Gaussianity
We study the consequences of imposing an approximate Galilean symmetry on the Effective Theory of Inflation, the theory of small perturbations around the inflationary background. This approach allows us to study the effect of operators with two derivatives on each field, which can be the leading interactions due to non-renormalization properties of the Galilean Lagrangian. In this case cubic non-Gaussianities are given by three independent operators, containing up to six derivatives, two with a shape close to equilateral and one peaking on flattened isosceles triangles. The four-point function is larger than in models with small speed of sound and potentially observable with the Planck satellite.
15555516
Sachs-Wolfe at second order: the CMB bispectrum on large angular scales
It is a pleasure to thank Nicola Bartolo, Francis Bernardeau, Eiichiro Komatsu, Roy Maartens,Sabino Matarrese, Toni Riotto, Misao Sasaki, Uros Seljak, Leonardo Senatore and Matias Zaldarriaga for useful discussions. G.D’A. and P.C. thank the Institut de Physique Th´eorique at Saclay and 
F.V. thanks the ICTP for hospitality while working on this project. G.D’A., P.C., and F.V. thank the Galileo Galilei Institute, where part of this work was carried out during the workshop “New Horizons for Modern Cosmology”. Furthermore, F.V. thanks the Yukawa Institute for Theoretical Physics at Kyoto University, where part of this work was carried out during the GCOE/YITP workshop 
YITP-W-09-01 on “Non-linear cosmological perturbations” and the EU Marie Curie Research and Training network ”UniverseNet” (MRTN-CT-2006-035863) for support..
119276936
The (not so) squeezed limit of the primordial 3-point function
We prove that, in a generic single-field model, the consistency relation for the 3-point function in the squeezed limit receives corrections that vanish quadratically in the ratio of the momenta, i.e. as (k L/k S) 2. This implies that a detection of a bispectrum signal going as 1/k L 2 in the squeezed limit, that is suppressed only by one power of k L compared with the local shape, would rule out all single-field models. The absence of this kind of terms in the bispectrum holds also for multifield models, but only if all the fields have a mass much smaller than H. The detection of any scale dependence of the bias, for scales much larger than the size of the haloes, would disprove all single-field models. We comment on the regime of squeezing that can be probed by realistic surveys. © 2011 IOP Publishing Ltd and SISSA.
119268546
An improved calculation of the non-Gaussian halo mass function
The abundance of collapsed objects in the universe, or halo mass function, is an important theoretical tool in studying the effects of primordially generated non-Gaussianities on the large scale structure. The non-Gaussian mass function has been calculated by several authors in different ways, typically by exploiting the smallness of certain parameters which naturally appear in the calculation, to set up a perturbative expansion. We improve upon the existing results for the mass function by combining path integral methods and saddle point techniques (which have been separately applied in previous approaches). Additionally, we carefully account for the various scale dependent combinations of small parameters which appear. Some of these combinations in fact become of order unity for large mass scales and at high redshifts, and must therefore be treated non-perturbatively. Our approach allows us to do this, and also to account for multi-scale density correlations which appear in the calculation. We thus derive an accurate expression for the mass function which is based on approximations that are valid over a larger range of mass scales and redshifts than those of other authors. By tracking the terms ignored in the analysis, we estimate theoretical errors for our result and also for the results of others. We also discuss the complications introduced by the choice of smoothing filter function, which we take to be a top-hat in real space, and which leads to the dominant errors in our expression. Finally, we present a detailed comparison between the various expressions for the mass functions, exploring the accuracy and range of validity of each. © 2011 IOP Publishing Ltd and SISSA.
29642485
CMB temperature anisotropies from third-order gravitational perturbations
In this paper we present a complete computation of the cosmic microwave background (CMB) anisotropies up to third order from gravitational perturbations accounting for scalar, vector and tensor perturbations. We then specify our results to the large-scale limit, providing the evolution of the gravitational potentials in a flat universe filled with matter and cosmological constant which characterizes the integrated Sachs–Wolfe effect. As a by-product in the large scale approximation we are able to give non-perturbative solutions for the photon geodesic equations. Our results are the first step towards providing a complete theoretical prediction for cubic nonlinearities which are particularly relevant for characterizing the level of non-Gaussianity in the CMB through the detection of the four-point angular connected correlation function (trispectrum). For this purpose we also allow for generic initial conditions due to primordial non-Gaussianity.
119117453
First and second order semi-Markov chains for wind speed modeling
The increasing interest in renewable energy, particularly in wind, has given rise to the necessity of accurate models for the generation of good synthetic wind speed data. Markov chains are often used for this purpose but better models are needed to reproduce the statistical properties of wind speed data. We downloaded a database, freely available from the web, in which are included wind speed data taken from L.S.I. -Lastem station (Italy) and sampled every 10 min. With the aim of reproducing the statistical properties of this data we propose the use of three semi-Markov models. We generate synthetic time series for wind speed by means of Monte Carlo simulations. The time lagged autocorrelation is then used to compare statistical properties of the proposed models with those of real data and also with a synthetic time series generated through a simple Markov chain.