arXiv subjects

W. S. Hipólito-Ricaldi

Publications and source records attributed to W. S. Hipólito-Ricaldi.

11 recordsLinked to original sources

arXiv2025

Cosmological Remapping for Efficient Generation of 21 cm Intensity Mapping Mocks

We present a novel application of cosmological rescaling, or "remapping," to generate 21 cm intensity mapping mocks for different cosmologies. The remapping method allows for computationally efficient generation of N-body catalogs by rescaling existing simulations. In this work, we employ the remapping method to construct dark matter halo catalogs, starting from the Horizon Run 4 simulation with WMAP5 cosmology, and apply it to different target cosmologies, including WMAP7, Planck18 and Chevallier-Polarski-Linder (CPL) models. These catalogs are then used to simulate 21 cm intensity maps. We use the halo occupation distribution (HOD) method to populate halos with neutral hydrogen (HI) and derive 21 cm brightness temperature maps. Our results demonstrate the effectiveness of the remapping approach in generating cosmological simulations for large-scale structure studies, offering an alternative for testing observational data pipelines and performing cosmological parameter forecasts without the need for computationally expensive full N-body simulations. We also analyze the precision and limitations of the remapping, in light of the rescaling parameters $s$ and $s_m$, as well as the effects of the halo mass and box size thresholds.

astro-ph.CO↗

arXiv2024

Probing the statistical isotropy of the universe with Planck data of the cosmic microwave background

We study the angular distribution of temperature fluctuations in the cosmic microwave background (CMB) to probe the statistical isotropy of the universe by using precise full-sky CMB data with a model-independent approach. We investigated the temperature-temperature angular correlations in the four Planck foreground-cleaned CMB maps that were released recently. We performed a directional analysis on the CMB sphere to search directions in which the temperature-temperature angular correlations are extreme. Our analyses confirm a preferred axis in the CMB sphere, pointing in the direction $(l,b) \simeq (260^{\circ}, 130^{\circ})$, at the $98\% -99\%$ confidence level. In this direction, the CMB angular correlations exceed the antipodal direction most strongly. This preferred direction is unexpected in the $Λ$CDM cosmological model and represents a significant deviation from results obtained by applying the same procedure to simulated statistically isotropic CMB maps. This result confirms the north-south asymmetry in the most recent Planck data. This phenomenon is one of the previously reported CMB anomalies. We performed a robust detection of the north-south asymmetry in the temperature-temperature angular correlations, with a slightly different statistical significance, in the four Planck foreground-cleaned CMB maps. Moreover, we performed consistency tests by adding foreground and noise, both Planck data products, to the CMB map we studied, and we also investigated and discarded possible bias in our method. After these detailed analyses, we conclude that the north-south asymmetry phenomenon is present with a high statistical significance in the Planck CMB maps we studied. This result confirms previous reports in the literature in the past 20 years.

astro-ph.CO↗

arXiv2017

Does a generalized Chaplygin gas correctly describe the cosmological dark sector?

Yes, but only for a parameter value that makes it almost coincide with the standard model. We reconsider the cosmological dynamics of a generalized Chaplygin gas (gCg) which is split into a cold dark matter (CDM) part and a dark energy (DE) component with constant equation of state. This model, which implies a specific interaction between CDM and DE, has a $Λ$CDM limit and provides the basis for studying deviations from the latter. Including matter and radiation, we use the (modified) CLASS code \cite{class} to construct the CMB and matter power spectra in order to search for a gCg-based concordance model that is in agreement with the SNIa data from the JLA sample and with recent Planck data. The results reveal that the gCg parameter $α$ is restricted to $|α|\lesssim 0.05$, i.e., to values very close to the $Λ$CDM limit $α=0$. This excludes, in particular, models in which DE decays linearly with the Hubble rate.

astro-ph.CO↗

arXiv2017

CMB and matter power spectra with non-linear dark-sector interactions

An interaction between dark matter and dark energy, proportional to the product of their energy densities, results in a scaling behavior of the ratio of these densities with respect to the scale factor of the Robertson-Walker metric. This gives rise to a class of cosmological models which deviate from the standard model in an analytically tractable way. In particular, it becomes possible to quantify the role of potential dark-energy perturbations. We investigate the impact of this interaction on the structure formation process. Using the (modified) CAMB code we obtain the CMB spectrum as well as the linear matter power spectrum. It is shown that the strong degeneracy in the parameter space present in the background analysis is considerably reduced by considering \textit{Planck} data. Our analysis is compatible with the $Λ$CDM model at the $2σ$ confidence level with a slightly preferred direction of the energy flow from dark matter to dark energy.

astro-ph.CO↗

arXiv2016

A Jacobian generalization of the pseudo Nambu-Goldstone bosons potential

We enlarge the classes of inflaton and quintessence fields by generalizing the pseudo Nambu--Goldstone boson potential by means of elliptic Jacobian functions, which are characterized by a parameter $k$. We use such a generalization to implement an inflationary era and a late acceleration of the universe. As an inflationary model the Jacobian generalization leads us to a number of e-foldings and a primordial spectrum of perturbations compatible with the {\it Planck collaboration} 2015. As a quintessence model, a study of the evolution of its equation of state (EoS) and its $w'$--$w$ plane helps us to classify it as a thawing model. This allows us to consider analytical approximations for the EoS recently discovered for thawing quintessence. By using JLA Supernovae Ia and Hubble parameter $H(z)$ data sets, we perform an observational analysis of the viability of the model as quintessence.

gr-qc↗

arXiv2016

Matter Perturbations in Scaling Cosmology

A suitable nonlinear interaction between dark matter with an energy density $ρ_{M}$ and dark energy with an energy density $ρ_{X}$ is known to give rise to a non-canonical scaling $ρ_{M} \propto ρ_{X}a^{-ξ}$ where $ξ$ is a parameter which generally deviates from $ξ=3$. Here we present a covariant generalization of this class of models and investigate the corresponding perturbation dynamics. The resulting matter power spectrum for the special case of a time-varying Lambda model is compared with data from the SDSS DR9 catalogue. We find a best-fit value of $ξ= 3.25$ which corresponds to a decay of dark matter into the cosmological term. Our results are compatible with the $Λ$CDM model at the 2$σ$ confidence level.

astro-ph.CO↗

arXiv2014

Baryonic matter perturbations in decaying vacuum cosmology

We consider the perturbation dynamics for the cosmic baryon fluid and determine the corresponding power spectrum for a $Λ(t)$CDM model in which a cosmological term decays into dark matter linearly with the Hubble rate. The model is tested by a joint analysis of data from supernovae of type Ia (SNIa) (Constitution and Union 2.1), baryonic acoustic oscillation (BAO), the position of the first peak of the anisotropy spectrum of the cosmic microwave background (CMB) and large-scale-structure (LSS) data (SDSS DR7). While the homogeneous and isotropic background dynamics is only marginally influenced by the baryons, there are modifications on the perturbative level if a separately conserved baryon fluid is included. Considering the present baryon fraction as a free parameter, we reproduce the observed abundance of the order of $5\%$ independently of the dark-matter abundance which is of the order of $32\%$ for this model. Generally, the concordance between background and perturbation dynamics is improved if baryons are explicitly taken into account.

astro-ph.CO↗

arXiv2013

Interacting dark energy and transient accelerated expansion

We argue that interactions in the dark sector may have a crucial impact on the cosmological dynamics. In particular, the future cosmic evolution may be very different from that predicted by the LCDM model. An example is a scenario in which the currently observed accelerated expansion is an interaction-induced transient phenomenon. We discuss such type of behavior on the basis of a two-fluid toy model.

astro-ph.CO↗

arXiv2011

Viscous dark fluid Universe: a unified model of the dark sector?

The Universe is modeled as consisting of pressureless baryonic matter and a bulk viscous fluid which is supposed to represent a unified description of the dark sector. In the homogeneous and isotropic background the \textit{total} energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically nonadiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value of the deceleration parameter. Moreover, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis. A problem of simple bulk viscous models, however, is the behavior of the gravitational potential and the reproduction of the CMB power spectrum.

astro-ph.CO↗

arXiv2011

Non-adiabatic perturbations in decaying vacuum cosmology

We investigate a spatially flat Friedmann-Lemaître-Robertson-Walker cosmology in which a decaying vacuum term causes matter production at late times. Assuming a decay proportional to the Hubble rate, the ratio of the background energy densities of dark matter and dark energy changes with the cosmic scale factor as $a^{-3/2}$. The intrinsically non-adiabatic two-component perturbation dynamics of this model is reduced to a single second-order equation. Perturbations of the vacuum term are shown to be negligible on scales that are relevant for structure formation. On larger scales, dark-energy perturbations give a somewhat higher contribution but remain always smaller than the dark-matter perturbations.

astro-ph.CO↗

arXiv2010

Viscous dark fluid universe

We investigate the cosmological perturbation dynamics for a universe consisting of pressureless baryonic matter and a viscous fluid, the latter representing a unified model of the dark sector. In the homogeneous and isotropic background the \textit{total} energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically non-adiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value $q_0 \approx - 0.53$ of the deceleration parameter. Moreover, while previous descriptions on the basis of generalized Chaplygin gas models were incompatible with the matter power spectrum data since they required a much too large amount of pressureless matter, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis.

astro-ph.CO↗