Speaker
Description
Cosmological perturbation theory provides the fundamental framework for
describing the evolution of the matter-energy density field in an expanding Universe and serves as the basis for understanding the formation of large-scale structures within the ΛCDM paradigm. In this work, we present a semi-analytical approach to describe the evolution of fluctuations —small deviations from the mean density— in a mixed fluid composed of cold dark matter (CDM) and baryonic matter. Assuming that the Universe is governed by General Relativity (GR), we employ the Vlasov equation to derive the general equations of motion for this mixed cosmological fluid, incorporating baryonic effects through the stress tensor by considering only the contributions from baryonic pressure. We then introduce the Jeans Filtering Functions (JFF) as a biasing tool that allows us to describe baryonic fluctuations with CDM as a tracer, and obtain an semi-analytical description of the fluctuations —a novel and uncommon approach compared to the accepted computational advances currently available in this field. First- and second-order solutions are obtained using an semi-analytical method based on a single iteration of the equations of motion. These solutions can be evaluated at low computational cost to study the behavior of the filtering scale at second order relative to the linear case and its impact on the matter power spectrum, without computing it explicitly. Unlike previous works, which evaluate these effects at the level of the power spectrum, we rely solely on the fluctuation fields to quantify the impact of baryonic matter on the matter power spectrum. Specifically, we obtain semi-analytical expressions for baryonic fluctuations in the density and velocity fields, with our most significant result concerning to the velocity divergence field. These semi-analytical results represent a main contribution of this work, are readily evaluable, and provide valuable physical insight into the role of baryons in the large-scale structure (LSS) of the Universe. They also reveal how pressure effects shift the filtering scale and how the inclusion of this component could influence parameters such as the filtering mass and the temperature of pressure-supported components.