10 research outputs found
Cosmological constraints from low-redshift data
In this paper we summarise the constraints that low-redshift data --such as
supernovae Ia (SN Ia), baryon acoustic oscillations (BAO) and cosmic
chronometers (CC)-- are able to set on the concordance model and its
extensions, as well as on inhomogeneous but isotropic models. We provide a
broad overlook into these cosmological scenarios and several aspects of data
analysis. In particular, we review a number of systematic issues of SN Ia
analysis that include magnitude correction techniques, selection bias and their
influence on the inferred cosmological constraints. Furthermore, we examine the
isotropic and anisotropic components of the BAO data and their individual
relevance for cosmological model-fitting. We extend the discussion presented in
earlier works regarding the inferred dynamics of cosmic expansion and its
present rate from the low-redshift data. Specifically, we discuss the
cosmological constraints on the accelerated expansion and related
model-selections. In addition, we extensively talk about the Hubble constant
problem, then focus on the low-redshift data constraint on that is based
on CC. Finally, we present the way in which this result compares the two of
high-redshift estimate and local (redshift zero) measurements that are in
tension.Comment: 18 pages, 7 plots; prepared for proceedings of Lema\^{i}tre Workshop:
black holes, gravitational waves and spacetime singularitie
Isotropic vs. Anisotropic components of BAO data: a tool for model selection
We conduct a selective analysis of the isotropic () and anisotropic
() components of the most recent Baryon Acoustic Oscillations (BAO) data.
We find that these components provide significantly different constraints and
could provide strong diagnostics for model selection, also in view of more
precise data to arrive. For instance, in the CDM model, we find a mild
tension of for the estimates obtained using
and separately. Considering both and as free parameters, we
find that the concordance model is in tension with the best-fit values provided
by the BAO data alone at 2.2. We complemented the BAO data with the
Supernova Ia (SNIa) and Observational \textit{Hubble} datasets to perform a
joint analysis on the CDM model and its standard extensions. By
assuming CDM scenario, we find that these data provide \text{km/s Mpc} as the best-fit value for the present expansion
rate. In the CDM scenario we find that the evidence for acceleration
using the BAO data alone is more than , which increases to in our joint analysis.Comment: Accepted for publication in JCAP. References update
Strong evidence for an accelerating universe
A recent analysis of the Supernova Ia data claims a 'marginal'
() evidence for a cosmic acceleration. This result has been
complemented with a non-accelerating cosmology, which was presented
as a valid alternative to the CDM model. In this paper, we use the
same analysis to show that a non-marginal evidence for acceleration is actually
found. We compare the standard Friedmann models to the cosmology by
complementing SN Ia data with the Baryon Acoustic Oscillations, Gamma Ray
Bursts and Observational Hubble datasets. We also study the power-law model
which is a functional generalisation of . We find that the evidence
for late-time acceleration is beyond refutable at a 4.56 confidence
level from SN Ia data alone, and at an even stronger confidence level
() from our joint analysis. Also, the non-accelerating
model fails to statistically compare with the CDM having a
Exploring the evidence for a large local void with supernovae Ia data
In this work we utilise the most recent publicly available type Ia supernova
(SN Ia) compilations and implement a well formulated cosmological model based
on Lema\^{i}tre-Tolman-Bondi metric in presence of cosmological constant
(LTB) to test for signatures of large local inhomogeneities
at . Local underdensities in this redshift range have been
previously found based on luminosity density (LD) data and galaxy number
counts. Our main constraints on the possible local void using the Pantheon SN
Ia dataset are: redshift size of ;
density contrast of between
16th and 84th percentiles. Investigating the possibility to alleviate the
disagreement between measurements of present expansion rate
coming from calibrated local SN Ia and high- cosmic microwave background
data, we find large local void to be a very unlikely explanation alone,
consistently with previous studies. However, the level of matter inhomogeneity
at a scale of 100Mpc that is allowed by SN Ia data, although not expected
from cosmic variance calculations in standard model of cosmology, could be the
origin of additonal systematic error in distance ladder measurements based on
SN Ia. Fitting low-redshift Pantheon data with a cut to the
LTB model and to the Taylor expanded luminosity distance formula we
estimate that this systematic error amounts to towards the lower
value. A test for local anisotropy in Pantheon SN Ia data yields null evidence.
Analysis of LD data provides a constraint on contrast of large isotropic void
, which is in tension
with SN Ia results. More data are necessary to better constrain the local
matter density profile and understand the disagreement between SN and LD
samplesComment: Equivalent to version published in MNRAS, 12 pages, 7 figures, 1
table. Comments and questions are welcom