20 research outputs found
CMB Anomalies and the Hubble Tension
The standard CDM model of cosmology is largely successful in
describing many observations, including precise measurements of the Cosmic
Microwave Background (CMB) radiation. However, some intriguing anomalies remain
currently unexplained within this theoretical framework. Such discrepancies can
be broadly categorized into two groups: those involving CMB-independent probes
and those within different CMB experiments. Examples of the former category
include the -tension between the value of the present-day expansion rate
of the Universe inferred by CMB observations and local distance ladder
measurements. The latter category involves anomalies between the values of
cosmological parameters obtained by different CMB experiments, as well as their
consistency with the predictions of CDM. In this chapter, we primarily
focus on this second category and study the agreement among the most recent CMB
measurements to acquire a better understanding of the limitations and
uncertainties underlying both the current data and the cosmological model.
Finally, we discuss the implications for the -tension.Comment: Invited chapter for the edited book "Hubble Constant Tension" (Eds.
E. Di Valentino and D. Brout, Springer Singapore, expected in 2024
Propagating speed of primordial gravitational waves
Primordial gravitational waves, i.e., a background of metric perturbations sourced by the quantum inflationary fluctuations, if measured, could both provide substantial evidence for primordial inflation and shed light on physics at extremely high energy scales. In this work we focus on their propagating speed. Using an effective field theory approach we introduce a time-dependent propagating speed cT(t) showing that also small deviations from the general relativity (GR) prediction cT(t)=c can lead to testable consequences. We derive a set of equations that relate the propagating speed and its time dependence to the inflationary parameters and that generalize the usual slow roll consistency relations. Imposing the new generalized consistency relations and combining small and large scales data, we derive model-independent constraints on inflation with nontrivial primordial tensor speed. In particular, we constrain its scale dependence to be dlogcT/dlogk=0.082-0.11+0.047 at 68% C.L. while we only derive the lower bound cT>0.22c at 95% C.L. We also constrain the tensor-to-scalar ratio at the pivot scale k∗=0.05 Mpc-1 to be r<0.0599 at 95% C.L. in agreement with the result provided by the Planck Collaboration. Thanks to a proper small scale parametrization of the tensor spectrum we derive stringent constraints on the tensor tilt nT=-0.084-0.047+0.10 at 68% C.L. and on its runnings αT=dnT/dlogk=0.0141-0.021+0.0035 and βT=dαT/dlogk=-0.0061-0.0014+0.010 both at 68% C.L. Our results show a remarkable agreement with the standard slow roll predictions and prove that current data can significantly constrain deviations from GR on the inflationary energy scales
Probing the inflationary background of gravitational waves from large to small scales
The detection of Primordial Gravitational Waves (PGWs) is one of the most
important goals of modern cosmology since PGWs can both provide substantial
evidence for primordial inflation and shed light on its physical nature. Small
scale experiments on gravitational waves such as LIGO/VIRGO and, in future,
LISA and Einstein Telescope (ET), being sensitive to the stochastic background
of gravitational waves, can be used together with the CMB data to constrain the
inflationary parameters. In performing these analyses the primordial tensor
spectrum is usually parametrized with a power law that includes only the
amplitude and a scale independent tilt. In this paper, we investigate the
robustness of assuming the tensor tilt as scale independent. We show that due
to the huge difference in the scales probed by CMB and GWs data, even a small
scale dependence can remarkably affect the shape of the primordial spectrum
possibly breaking the power-law assumption. When the non-linear corrections are
considered the final constraints can be significantly changed. We also study
the scale dependence in two different physical models of inflation providing an
example of negligible scale dependence and an example of non-negligible scale
dependence.Comment: 12 Pages, 4 figures. Edited to match Phys. Lett. B published versio
Higher-Curvature Corrections and Tensor Modes
Higher-curvature corrections to the effective gravitational action may leave
signatures in the spectrum of primordial tensor perturbations if the
inflationary energy scale is sufficiently high. In this paper we further
investigate the effects of a coupling of the Inflaton field to higher-curvature
tensors in models with a minimal breaking of conformal symmetry. We show that
an observable violation of the tensor consistency relation from
higher-curvature tensors implies also a relatively large running of the tensor
tilt, enhanced even by some order of magnitude with respect to the standard
slow roll case. This may leave signatures in the tensor two-point function that
we could test to recognize higher-curvature effects, above all if they are
translated into a blue tilted spectrum visible by future Gravitational Wave
experiments. Exploiting current cosmic microwave background and gravitational
wave data we also derive constraints on the inflationary parameters, inferring
that large higher-curvature corrections seem to be disfavored.Comment: 11 pages, 3 figure
Is the Harrison-Zel'dovich spectrum coming back? ACT preference for and its discordance with Planck
The Data Release 4 of the Atacama Cosmology Telescope (ACT) shows an
agreement with an Harrison-Zel'dovich primordial spectrum (), introducing a tension with a significance of CL with the
results from the Planck satellite. The discrepancy on the value of the scalar
spectral index is neither alleviated with the addition of large scale structure
information nor with the low multipole polarization data. We discuss possible
avenues to alleviate the tension relying on either neglecting polarization
measurements from ACT or in extending different sectors of the theory.Comment: 8 pages, 5 figures, 2 tables. Accepted for publication in MNRA
Exploring the tension and the evidence of dark sector interaction from 2D BAO measurements
We explore observational constraints on a cosmological model with an
interaction between dark energy (DE) and dark matter (DM), using a compilation
of 15 measurements of the 2D BAO (i.e., transversal) scale in combination with
Planck-CMB data, to explore the parametric space of a class of interacting DE
models. We find that 2D BAO measurements can generate different observational
constraints compared to the traditional approach of studying the matter
clustering in the 3D BAO measurements. Contrary to the observations for the
CDM and IDE models when analyzed with Planck-CMB + 3D BAO data, we
note that Planck-CMB + 2D BAO data favor high values of the Hubble constant
. From the joint analysis with Planck-CMB + 2D BAO + Gaussian prior on
, we find km/s/Mpc. We conclude that the
tension is solved in the IDE model with strong statistical evidence (more than
3) for the IDE cosmologies.Comment: 7 Pages, 2 Figures, 2 Tables. Matches the version published in PR
Hints of Neutrino Dark Matter scattering in the CMB? Constraints from the Marginalized and Profile Distributions
We study scatter-like interactions between neutrinos and dark matter in light
of different combinations of temperature, polarization and lensing data
released by three independent CMB experiments - the Planck satellite, the
Atacama Cosmology Telescope (ACT), and the South Pole Telescope (SPT) - in
conjunction with Baryon Acoustic Oscillation (BAO) measurements. We apply two
different statistical methodologies. Alongside the usual marginalization
technique, we cross-check all the results through a Profile Likelihood
analysis. As a first step, working under the assumption of massless neutrinos,
we perform a comprehensive (re-)analysis aimed at assessing the validity of
some recent results hinting at a mild preference for non-vanishing interactions
from small-scale CMB data. We find compelling resilience in the results already
documented in the literature, confirming that interactions with a strength
appear to be globally favored by ACT
(both alone and in combination with Planck). This result is corroborated by the
inclusion of additional data, such as the recent ACT-DR6 lensing likelihood, as
well as by the Profile Likelihood analysis. Interestingly, a fully consistent
preference for interactions emerges from SPT, as well, although it is weaker
than the one obtained from ACT. As a second step, we repeat the same analysis
considering neutrinos as massive particles. Despite the larger parameter space,
all the hints pointing towards interactions are confirmed also in this more
realistic case. In addition, we report a very mild preference for interactions
in Planck+BAO alone (not found in the massless case) which aligns with
small-scale data. While this latter result is not fully confirmed by the
Profile Likelihood analysis, the profile distribution does confirm that
interactions are not disfavoured by Planck.Comment: 35 pages, 16 figures, 5 table
The state of the dark energy equation of state circa 2023
We critically examine the state of current constraints on the dark energy
(DE) equation of state (EoS) . Our study is partially motivated by the
observation that, while broadly consistent with the cosmological constant value
, several independent probes appear to point towards a slightly phantom
EoS (). We pay attention to the apparent preference for phantom
DE from Planck Cosmic Microwave Background (CMB) data alone, whose origin we
study in detail and attribute to a wide range of (physical and geometrical)
effects. We deem the combination of Planck CMB, Baryon Acoustic Oscillations,
Type Ia Supernovae, and Cosmic Chronometers data to be particularly
trustworthy, inferring from this final consensus dataset
, in excellent agreement with the cosmological
constant value. Overall, despite a few scattered hints, we find no compelling
evidence forcing us away from the cosmological constant (yet).Comment: 21 pages, 10 figures, 3 table
Revealing the effects of curvature on the cosmological models
In this paper we consider the effects of adding curvature in extended
cosmologies involving a free-to-vary neutrino sector and different
parametrizations of Dark Energy (DE). We make use of the Planck 2018 cosmic
microwave background temperature and polarization data, Baryon Acoustic
Oscillations and Pantheon type Ia Supernovae data. Our main result is that a
non-flat Universe cannot be discarded in light of the current astronomical
data, because we find an indication for a closed Universe in most of the DE
cosmologies explored in this work. On the other hand, forcing the Universe to
be flat can significantly bias the constraints on the equation of state of the
DE component and its dynamical nature.Comment: 40 pages, 17 tables and 22 captioned figures; accepted for
publication in Phys. Rev.