5 research outputs found
Inevitable manifestation of wiggles in the expansion of the late Universe
Using the fact that the comoving angular diameter distance to the last
scattering surface is strictly constrained almost model independently, we show
that, for any model agreeing with the standard CDM model on its
background dynamics at and size of the comoving sound horizon at last
scattering, the deviations of the Hubble radius from the one of the standard
CDM model must be a member of the set of admissible wavelets. The
family of models characterized by this framework also offers nontrivial
oscillatory behaviours in various functions that define the kinematics of the
Universe, even when the wavelets themselves are very simple. We also discuss
the consequences of attributing these kinematics to, first, dark energy, and
second, varying gravitational coupling strength. Utilizing some simplest
wavelets, we demonstrate the competence of this framework in describing the
baryon acoustic oscillation (BAO) data without any modifications to the
agreement with cosmic microwave background measurements. This framework also
provides a natural explanation for the bumps found in nonparametric
observational reconstructions of the Hubble parameter and dark energy density
as compensations of the dips suggested by some BAO data, and questions the
physical reality of their existence. We note that utilizing this framework on
top of the models that agree with both the cosmic microwave background and
local measurements but are held back by BAO data, one may resurrect these
models through the wiggly nature of wavelets that can naturally accommodate the
BAO data. Finally, we also suggest narrowing the plausible set of admissible
wavelets to further improve our framework by imposing conditions from expected
kinematics of a viable cosmological model or first principle fundamental
physics such as energy conditions.Comment: 16 pages, 4 figures; matches the version published in Physical Review
Relaxing cosmological tensions with a sign switching cosmological constant: Improved results with Planck, BAO, and Pantheon data
We present a further observational analysis of the CDM model
proposed in Akarsu et al. [Phys. Rev. D 104, 123512 (2021)]. This model is
based on the recent conjecture suggesting the Universe has transitioned from
anti-de Sitter vacua to de Sitter vacua (viz., the cosmological constant
switches sign from negative to positive), at redshift ,
inspired by the graduated dark energy model proposed in Akarsu et al. [Phys.
Rev. D 101, 063528 (2020)]. CDM was previously claimed to
simultaneously relax five cosmological discrepancies, namely, the , ,
and tensions along with the Ly- and anomalies,
which prevail within the standard CDM model as well as its
canonical/simple extensions. In the present work, we extend the previous
analysis by constraining the model using the Pantheon data (with and without
the SH0ES prior) and/or the completed BAO data along with the full Planck
CMB data. We find that CDM exhibits a better fit to the data
compared to CDM, and simultaneously relaxes the six discrepancies of
CDM, viz., the , , , Ly-, , and
discrepancies, all of which are discussed in detail. When the
prior is included in the analyses, CDM performs
significantly better in relaxing the , , and tensions with the
constraint even when the Ly- data (which imposed
the constraint in the previous studies) are excluded. In
contrast, the presence of the prior causes only negligible improvements
for CDM. Thus, the CDM model provides remedy to
various cosmological tensions simultaneously, only that the galaxy BAO data
hinder its success to some extent.Comment: 27 pages, 11 figures, 5 tables; matches the version published in
Physical Review
Omnipotent dark energy: A phenomenological answer to the Hubble tension
This paper introduces the class of omnipotent dark energy (DE) models
characterized by nonmonotonic energy densities that are capable of attaining
negative values with corresponding equation of state parameters featuring
phantom divide line (PDL) crossings and singularities. These nontrivial
features are phenomenologically motivated by findings of previous studies that
reconstruct cosmological functions from observations, and the success of
extensions of CDM, whose actual or effective DE density is omnipotent,
in alleviating the observational discordance within CDM. As an
example, we focus on one embodiment of omnipotent DE, viz., the DE
parametrization introduced in Di Valentino et al. [Dark energy with phantom
crossing and the H0 tension, Entropy 23, 404 (2021)] (DMS20). By updating and
extending the datasets used in the original paper where it was introduced, we
confirm the effectiveness of DMS20 in alleviating the observational
discrepancies. Additionally, we uncover that its negative DE density feature,
importance of which was not previously investigated, plays a crucial role in
alleviating the tensions, along with the PDL crossing feature that the
parametrization presupposes. In particular, we find that there is a positive
correlation between the parameter and the scale () at which DE
density transitions from negative to positive, in agreement with previous
studies that incorporate this transition feature. For our full dataset, the
model yields (68% CL) relaxing the tension with a
preference of crossing to negative DE densities ( at 99% CL), along with
the constraint on the scale of the presupposed
PDL crossing.Comment: 18 pages, 6 figures, 4 tables; matches the version published in
Physical Review
Is the dark energy equation of state parameter singular?
A dark energy with a negative energy density in the past can simultaneously
address various cosmological tensions, and if it is to be positive today to
drive the observed acceleration of the universe, we show that, it should have a
pole in its equation of state parameter. More precisely, in a spatially uniform
universe, a perfect fluid (submitting to the usual continuity equation of local
energy conservation) whose energy density vanishes at an isolated
zero , necessarily has a pole in its equation of state parameter
at , and, diverges to positive infinity in the limit
and it diverges to negative infinity in the limit -- we assume
that is not an accumulation point for poles of . However, the
converse statement that this kind of a pole of corresponds to a
vanishing energy density at that point, is not true as we show by a
counterexample.Comment: 4 pages, 1 figure, no table
Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies
In this paper we will list a few important goals that need to be addressed in
the next decade, also taking into account the current discordances between the
different cosmological probes, such as the disagreement in the value of the
Hubble constant , the -- tension, and other less
statistically significant anomalies. While these discordances can still be in
part the result of systematic errors, their persistence after several years of
accurate analysis strongly hints at cracks in the standard cosmological
scenario and the necessity for new physics or generalisations beyond the
standard model. In this paper, we focus on the tension between
the {\it Planck} CMB estimate of the Hubble constant and the SH0ES
collaboration measurements. After showing the evaluations made from
different teams using different methods and geometric calibrations, we list a
few interesting new physics models that could alleviate this tension and
discuss how the next decade's experiments will be crucial. Moreover, we focus
on the tension of the {\it Planck} CMB data with weak lensing measurements and
redshift surveys, about the value of the matter energy density , and
the amplitude or rate of the growth of structure (). We
list a few interesting models proposed for alleviating this tension, and we
discuss the importance of trying to fit a full array of data with a single
model and not just one parameter at a time. Additionally, we present a wide
range of other less discussed anomalies at a statistical significance level
lower than the -- tensions which may also constitute hints towards
new physics, and we discuss possible generic theoretical approaches that can
collectively explain the non-standard nature of these signals.[Abridged]Comment: Contribution to Snowmass 2021. 224 pages, 27 figures. Accepted for
publication in JHEA