Weak lensing signal in Unified Dark Matter models

TL;DR

This paper compares weak lensing signals in standard b4CDM and Unified Dark Matter models, showing how the latter's parameters influence observable lensing effects, especially at low redshifts and small scales.

Contribution

It provides theoretical predictions for weak lensing power spectra in UDM models, highlighting the impact of the sound speed parameter c_ on observable signals.

Findings

UDM models' lensing spectra are more sensitive to c_ at low redshifts.

For c_ > 10^{-3}, lensing power spectrum is significantly suppressed at small scales.

Weak lensing signals can distinguish between b4CDM and UDM models based on c_ values.

Abstract

Weak gravitational lensing is a powerful tool for studying both the geometry and the dynamics of the Universe. Its power spectrum contains information on the sources emitting photons and on the large--scale structures that these hotons cross. We calculate the weak lensing cosmic convergence and shear power spectra, in linear theory and Limber's approximation, for two different classes of cosmological models: the standard \LambdaCDM and Unified Dark Matter (UDM) models. The latter models attempt to solve the problems of the dark matter in the dynamics of galaxies and galaxy clusters and of the late-time acceleration of the Universe expansion by introducing a scalar field that mimics both dark matter and dark energy. A crucial feature of the UDM models is the speed of sound c_\infty, that is the value of the sound speed at late times, on which structure formation depends. In this paper, we provide the predictions of the UDM models for the weak lensing signal,with various values of c_\infty. We consider both the Cosmic Microwave Background and background galaxies at different redshifts as sources for the weak lensing power spectra. We find that the power spectra in UDM models are more sensitive to the variations of c_\infty for sources located at low redshifts. Moreover, we find that for c_\infty>10^{-3} (in units of the speed of light), the UDM weak lensing convergence power spectrum C^{\kappa\kappa}(l) for background galaxies is strongly suppressed with respect to the \LambdaCDM spectrum, particularly at small angular scales l\gtrsim100.