Engineering topics

Bonometto, Silvio A.

Publications and source records attributed to Bonometto, Silvio A..

7 records

DOE OSTI2017

Growth and dissolution of spherical density enhancements in SCDEW cosmologies

Strongly Coupled Dark Energy plus Warm dark matter (SCDEW) cosmologies are based on the finding of a conformally invariant (CI) attractor solution during the early radiative expansion, requiring then the stationary presence of ∼ 1 % of coupled-DM and DE, since inflationary reheating. In these models, coupled-DM fluctuations, even in the early radiative expansion, grow up to non-linearity, as shown in a previous associated paper. Such early non-linear stages are modelized here through the evolution of a top-hat density enhancement. As expected, its radius R increases up to a maximum and then starts to decrease. Virial balance is reached when the coupled-DM density contrast is just 25–26 and DM density enhancement is O(10 %) of total density. Moreover, we find that this is not an equilibrium configuration as, afterwards, coupling causes DM particle velocities to increase, so that the fluctuation gradually dissolves. We estimate the duration of the whole process, from horizon crossing to dissolution, and find z {sub horizon}/ z {sub erasing} ∼ 3 × 10{sup 4}. Therefore, only fluctuations entering the horizon at z ∼< 10{sup 9}–10{sup 10} are able to accrete WDM with mass ∼ 100 eV—as soon as it becomes non-relativistic—so avoiding full disruption. Accordingly, SCDEW cosmologies, whose WDM has mass ∼ 100 eV, can preserve primeval fluctuations down to stellar mass scale.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Sample variance in N-body simulations and impact on tomographic shear predictions

We study the effects of sample variance in N-body simulations as a function of the size of the simulation box, namely in connection with predictions on tomographic shear spectra. We make use of a set of eight ΛCDM simulations in boxes of 128, 256, and 512 h{sup −1} Mpc a side, for a total of 24, differing just by the initial seeds. Among the simulations with 128 and 512 h{sup −1} Mpc a side, we suitably select those closest and farthest from average. Numerical and linear spectra P(k,z) are suitably connected at low k to evaluate the effects of sample variance on shear spectra C{sub ij}(ℓ) for 5 or 10 tomographic bands. We find that shear spectra obtained by using 128 h{sup −1} Mpc simulations can vary up to ∼25%, just because of the seed. The sample variance lowers to ∼3.3% when using 512 h{sup −1} Mpc. These percentages could however slightly vary if other sets of the same number of realizations were considered. Accordingly, in order to match the ∼1% precision expected for the data, if still using eight boxes, we require a size of ∼1300–1700 h{sup −1} Mpc for them.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Fluctuations in strongly coupled cosmologies

In the early Universe, a dual component made of coupled CDM and a scalar field Φ, if their coupling β > (3){sup 1/2}/2, owns an attractor solution, making them a stationary fraction of cosmic energy during the radiation dominated era. Along the attractor, both such components expand ∝a{sup −4} and have early density parameters Ω{sub d} = 1/(4β{sup 2}) and Ω{sub c} = 2 Ω{sub d} (field and CDM, respectively). In a previous paper it was shown that, if a further component, expanding ∝a{sup −3}, breaks such stationary expansion at z ∼ 3–5 × 10{sup 3}, cosmic components gradually acquire densities consistent with observations. This paper, first of all, considers the case that this component is warm. However, its main topic is the analysis of fluctuation evolution: out of horizon modes are then determined; their entry into horizon is numerically evaluated as well as the dependence of Meszaros effect on the coupling β; finally, we compute: (i) transfer function and linear spectral function; (ii) CMB C{sub l} spectra. Both are close to standard ΛCDM models; in particular, the former one can be so down to a scale smaller than Milky Way, in spite of its main DM component being made of particles of mass < 1 keV. The previously coupled CDM component, whose present density parameter is O(10{sup −3}), exhibits wider fluctuations δρ/ρ, but approximately β-independent δρ values. We discuss how lower scale features of these cosmologies might ease quite a few problems that ΛCDM does not easily solve.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

Recovery of fluctuation spectrum evolution from tomographic shear spectra

Forthcoming large angle surveys are planned to obtain high precision tomographic shear data. In principle, they will allow us to recover the spectra of matter density fluctuation, at various redshift, through the inversion of the expressions yielding shear spectra from fluctuation spectra. This was discussed in previous work, where SVD techniques for matrix inversion were also shown to be the optimal tool to this aim. Here we show the significant improvements obtainable by using a 7 bin tomography, as allowed by future Euclid data, and discuss error propagation from shear to fluctuation spectra. We find that the technique is a promising tool, namely for the analysis of baryon physics through high–l shear spectra and to test the consistency between expansion rate and fluctuation growth.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Dark energy from dark radiation in strongly coupled cosmologies with no fine tuning

A dual component made of non-relativistic particles and a scalar field, exchanging energy, naturally falls onto an attractor solution, making them a (sub)dominant part of the cosmic energy during the radiation dominated era, provided that the constant β, measuring the coupling, is strong enough. The density parameters of both components are then constant, as they expand as a{sup −4}. If the field energy is then prevalently kinetic, as is expected, its energy is exactly half of the pressureless component; the dual component as a whole, then, has a density parameter Ω{sub cd} = 3/4β{sup 2} (e.g., for β ≅ 2.5, Ω{sub cd} ≅ 0.1, in accordance with Dark Radiation expectations). The stationary evolution can only be broken by the rising of other component(s), expanding as a{sup −3}. In a realistic scenario, this happens when z ∼ 3–5 × 10{sup 3}. When such extra component(s) become(s) dominant, the densities of the dual components also rise above radiation. The scalar field behavior can be easily tuned to fit Dark Energy data, while the coupled DM density parameter becomes O(10{sup −3}). This model however requires that, at present, two different DM components exist. The one responsible for the break of the stationary regime could be made, e.g., by thermally distributed particles with mass even >> 1–2 keV (or non-thermal particles with analogous average speed) so accounting for the size of observed galactic cores; in fact, a fair amount of small scale objects is however produced by fluctuation re-generated by the coupled DM component, in spite of its small density parameter, after the warm component has become non-relativistic.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Direct recovery of fluctuation spectra from tomographic shear spectra

Forthcoming experiments will enable us to determine high precision tomographic shear spectra. Matter density fluctuation spectra, at various z, should then be recovered from them, in order to constrain the model and determine the DE state equation. Available analytical expressions, however, do the opposite, enabling us to derive shear spectra from fluctuation spectra. Here we find the inverse expression, yielding density fluctuation spectra from observational tomographic shear spectra. The procedure involves SVD techniques for matrix inversion. We show in detail how the approach works and provide a few examples.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Non-linear weak lensing forecasts

We investigate the impact of non-linear corrections on dark energy parameter estimation from weak lensing probes. We find that using halofit expressions, suited to ΛCDM models, implies substantial discrepancies with respect to results directly obtained from N-body simulations, when w(z)≠−1. Discrepancies appear strong when using models with w'(z = 0) > 0, as fiducial models; they are however significant even in the neighborhood of ΛCDM, where neglecting the degrees of freedom associated with the DE state equation can lead to a misestimate of the matter density parameter Ω{sub m}.

79 ASTRONOMY AND ASTROPHYSICS↗