We analyze the H0-tension problem in the context of models of the early universe that predict a blue tilted spectrum of primordial gravitational waves (GWs), which is a positive value of the tensor ...tilt nT. By considering the GW’s contribution, NeffGW, to the effective number of relativistic degrees of freedom, Neff, and assuming standard particle physics, we discuss the effects of NeffGW on the background expansion, especially the constraints on the Hubble parameter H0. We analyze three scenarios that take into account the contribution of NeffGW using recent data of cosmic microwave background, baryon acoustic oscillation, the latest measurement of the local expansion rate, along with the LIGO constraints on the tensor to scalar ratio, r, and the tensor index. For the models explored, we show that an additional contribution from the primordial GW’s background to Neff does not solve but alleviates the current H0-tension problem.
Currently, the standard cosmological model faces some tensions and discrepancies between observations at early and late cosmological time. One of them concerns the well-known H0-tension problem, ...i.e., a ∼4.4σ-difference between the early-time estimate and late-time measurements of the Hubble constant, H0. Another puzzling question rests in the cosmological lithium abundance, where again local measurements differ from the one predicted by Big Bang Nucleosynthesis (BBN). In this work, we show that a mechanism of light dark matter production might hold the answer for these questions. If dark matter particles are sufficiently light and a fraction of them were produced non-thermally in association with photons, this mechanism has precisely what is needed to destroy Lithium without spoiling other BBN predictions. Besides, it produces enough radiation that leads to a larger H0 value, reconciling early and late-time measurements of the Hubble expansion rate without leaving sizable spectral distortions in the Cosmic Microwave Background spectrum.
We perform a Bayesian analysis to study possible features in the primordial inflationary power spectrum of scalar perturbations. In particular, we analyze the possibility of detecting the imprint of ...these primordial features in the anisotropy temperature power spectrum of the cosmic microwave background (CMB) and also in the matter power spectrum P(k). We use the most recent CMB data provided by the Planck Collaboration and P(k) measurements from the 11th data release of the Sloan Digital Sky Survey. We focus our analysis on a class of potentials whose features are localized at different intervals of angular scales, corresponding to multipoles in the ranges 10<scriptl<60 (Oscill-1) and 150<scriptl<300 (Oscill-2). Our results show that one of the step potentials (Oscill-1) provides a better fit to the CMB data than does the featureless LambdaCDM scenario, with moderate Bayesian evidence in favor of the former. Adding the P(k) data to the analysis weakens the evidence of the Oscill-1 potential relative to the standard model and strengthens the evidence of this latter scenario with respect to the Oscill-2 model.
Is there evidence for a hotter Universe? Bengaly, Carlos A. P.; Gonzalez, Javier E.; Alcaniz, Jailson S.
The European physical journal. C, Particles and fields,
10/2020, Letnik:
80, Številka:
10
Journal Article
Recenzirano
Odprti dostop
The measurement of present-day temperature of the Cosmic Microwave Background (CMB),
T
0
=
2.72548
±
0.00057
K (1
σ
), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS) as recalibrated by ...the Wilkinson Microwave Anisotropy Probe (WMAP), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant,
H
0
, obtained from measurements of the CMB temperature fluctuations assuming the standard
Λ
CDM model exhibit a large (
4.1
σ
) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in
T
0
could alleviate or solve the
H
0
-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift
T
(
z
) measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of
≥
1.9
σ
from the
T
0
values required to solve the
H
0
tension. This result reinforces the idea that a solution of the
H
0
-tension problem in fact requires either a better understanding of the systematic errors on the
H
0
measurements or new physics.
A
bstract
In this work, we revisit the non-minimally coupled Higgs Inflation scenario and investigate its observational viability in light of the current Cosmic Microwave Background, Baryon Acoustic ...Oscillation and type Ia Supernovae data. We explore the effects of the Coleman-Weinberg approximation to the Higgs potential in the primordial universe, connecting the predictions for the Lagrangian parameters at inflationary scales to the electroweak observables through Renormalization Group methods at two-loop order. Initially, we find that electroweak scale measurements may be dissonant to the limits obtained from the cosmological data sets used in the analysis. Specifically, an ≈ 8
σ
-discrepancy between the inflationary parameters and the value of the Monte Carlo reconstructed top quark mass is found. However, considering the most recent results obtained by the CMS Collaboration from differential cross-section measurements of the top quark production a good agreement is obtained.
Fast Radio Bursts (FRBs) are millisecond-duration radio transients with an observed dispersion measure (
DM
) greater than the expected Milky Way contribution, which suggests that such events are of ...extragalactic origin. Although some models have been proposed to explain the physics of the pulse, the mechanism behind the FRBs emission is still unknown. From FRBs data with known host galaxies, the redshift is directly measured and can be combined with estimates of the
DM
to constrain the cosmological parameters, such as the baryon number density and the Hubble constant. However, the poor knowledge of the fraction of baryonic mass in the intergalactic medium (
f
IGM
) and its degeneracy with the cosmological parameters impose limits on the cosmological application of FRBs. In this work we present a cosmological model-independent method to determine the evolution of
f
IGM
combining the latest FRBs observations with localized host galaxy and current supernovae data. We consider constant and time-dependent
f
IGM
parameterizations and show, through a Bayesian model selection analysis, that a conclusive answer about the time-evolution of
f
IGM
depend strongly on the
DM
fluctuations due to the spatial variation in cosmic electron density (
δ
). In particular, our analysis show that the evidence varies from strong (in favor of a growing evolution of
f
IGM
with redshift) to inconclusive, as larger values of
δ
are considered.
The assumption of homogeneity and isotropy on large scales is one of the main hypotheses of the standard cosmological model. In this paper, we revisit a test of cosmological isotropy using type Ia ...supernova (SN Ia) distances provided by the latest SN Ia compilation available, namely, the Pantheon compilation. We perform a model-independent analysis by selecting low-redshift subsamples lying in two redshift intervals, i.e., z ≤ 0.10 and z ≤ 0.20. By mapping the directional asymmetry of cosmological parameters across the sky, we show that the current SN Ia data favor the hypothesis of cosmic isotropy, as the anisotropy found in the maps can be mostly ascribed to the nonuniform sky coverage of the data rather than an actual cosmological signal. These results confirm that there is null evidence against the cosmological principle in the low-redshift universe.
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