No abstract

Axions, if realized in nature, can be copiously produced in the early universe via thermal processes, contributing to the mass-energy density of thermal hot relics. In light of the most recent cosmological observations, we analyse two different thermal processes within a realistic mixed hot-dark-matter scenario which includes also massive neutrinos. Considering the axion-gluon thermalization channel we derive our most constraining bounds on the hot relic masses ma < 7.46 eV and ∑mν < 0.114 eV both at 95 per cent CL; while studying the axion-pion scattering, without assuming any specific model for the axion-pion interactions and remaining in the range of validity of the chiral perturbation theory, our most constraining bounds are improved to ma < 0.91 eV and ∑mν < 0.105 eV, both at 95 per cent CL. Interestingly, in both cases, the total neutrino mass lies very close to the inverted neutrino mass ordering prediction. If future terrestrial double beta decay and/or long baseline neutrino experiments find that the nature mass ordering is the inverted one, this could rule out a wide region in the currently allowed thermal axion window. Our results therefore strongly support multi-messenger searches of axions and neutrino properties, together with joint analyses of their expected sensitivities.

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 c T ðtÞ showing that also small deviations from the general relativity (GR) prediction c T ðtÞ ¼ 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 d log c T =d log k ¼ 0.082 þ0.047 −0.11 at 68% C.L. while we only derive the lower bound c T > 0.22c at 95% C.L. We also constrain the tensor-to-scalar ratio at the pivot scale k à ¼ 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 n T ¼ −0.084 þ0.10 −0.047 at 68% C.L. and on its runnings α T ¼ dn T =d log k ¼ 0.0141 þ0.0035 −0.021 and β T ¼ dα T =d log k ¼ −0.0061 þ0.010 −0.0014 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.

A major goal of modern cosmology is the detection of B-modes in the cosmic microwave background polarization originated from primordial gravitational waves. Their detection not only could provide substantial evidence for primordial inflation but also could shed light on its physical nature. Under the assumption of single-field slow-roll inflation, a set of conditions exist for the scalar and tensor parameters. In particular, given a constraint on the scalar spectral index n s , its running α s , its running of running β s , and the tensor-to-scalar ratio r, constraints can be derived on the tensor spectral index n t , its running α t , its running of running β t , and its running of running of running γ t . Using current bounds from the Planck 2015 and BICEP2 datasets and under the slow condition we found the following constraints at 95% C.L.: n t > −0.0157, α t ¼ −0.00018 þ0.00019 −0.00024 , β t ¼ 0.00004 þ0.00022 −0.00013 , and γ t ¼ 0.00017 þ0.00040 −0.00019 . Future measurements of the tensor spectrum could therefore be used to test these bounds and the slow-roll condition.

We study the global agreement between the most recent observations of the Cosmic Microwave Background 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 ∼2.5 σ within the baseline ΛCDM, is reduced at the level of 1.8σ when the effective number of relativistic particles (Neff) is significantly less than the standard value, while it ranges between 2.3 σ and 3.5 σ in all the other extended models.