Search

The Data Release 4 of the Atacama Cosmology Telescope (ACT) shows an agreement with an Harrison-Zel'dovich primordial spectrum (ns  = 1.009 ± 0.015), introducing a tension with a significance of 99.3  per cent Confidence Level (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. [ABSTRACT FROM AUTHOR]

Inflationary gravitational waves, behaving as additional radiation in the Early Universe, can increase the effective number of relativistic species (N eff) by a further correction that depends on the integrated energy-density in gravitational waves over all scales. This effect is typically used to constrain (blue-tilted) models of inflation in light of the bounds resulting from the big bang nucleosynthesis. In this paper, we recompute this contribution, discussing some caveats of the state-of-the-art analyses. Through a parametric investigation, we first demonstrate that the calculation is dominated by the ultraviolet frequencies of the integral and therefore by the behaviour of the tensor spectrum on scales corresponding to modes that cross the horizon very close to the end of inflation, when the slow-roll dynamics breaks down and the production of gravitational waves becomes strongly model dependent. Motivated by these results, we realize a theoretical Monte Carlo and, working within the framework of the Effective Field Theory of inflation, we investigate the observable predictions of a very broad class of models. For each model, we solve a system of coupled differential equations whose solution completely specifies the evolution of the spectrum up to the end of inflation. We prove the calculation of |$\Delta N_{\rm eff}^{\rm GW}$| to be remarkably model dependent and therefore conclude that accurate analyses are needed to infer reliable information on the inflationary Universe. [ABSTRACT FROM AUTHOR]

We study the global agreement between the most recent observations of the cosmic microwave background (CMB) temperature and polarization anisotropies angular power spectra released by the Atacama Cosmology Telescope and the Planck satellite in various cosmological models that differ by the inclusion of different combinations of additional parameters. By using the Suspiciousness statistic, we show that the global 'CMB tension' between the two experiments, quantified at the Gaussian equivalent level of |$\sim 2.5\, \sigma$| within the baseline Lambda cold dark matter, is reduced at the level of 1.8σ when the effective number of relativistic particles (N eff) is significantly less than the standard value, while it ranges between |$2.3\, \sigma$| and |$3.5\, \sigma$| in all the other extended models. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Etherington reciprocity theorem, or distance duality relation (DDR), relates the mutual scaling of cosmic distances in any metric theory of gravity where photons are massless and propagate on null geodesics. In this paper, we make use of the DDR to build a consistency check based on its degeneracy with the Hubble constant, H 0. We parametrize the DDR using the form η(z) = 1 + ϵ z , thus only allowing small deviations from its standard value. We use a combination of late-time observational data to provide the first joint constraints on the Hubble parameter and ϵ with percentage accuracy: H 0 = 68.6 ± 2.5 km s−1 Mpc−1 and |$\epsilon = 0.001^{+0.023}_{-0.026}$|⁠. We build our consistency check using these constraints and compare them with the results obtained in extended cosmological models using cosmic microwave background data. We find that extensions to Λ cold dark matter (ΛCDM) involving massive neutrinos and/or additional dark radiation are in perfect agreement with the DDR, while models with non-zero spatial curvature show a preference for DDR violation, i.e. ϵ ≠ 0 at the level of ∼1.5σ. Most importantly, we find a mild 2σ discrepancy between the validity of the DDR and the latest publicly available Cepheid-calibrated Type Ia supernova (SNIa) constraint on H 0. We discuss the potential consequences of this for both the Etherington reciprocity theorem and the H 0 tension. [ABSTRACT FROM AUTHOR]