1,721,169 research outputs found
Planck constraints on the effective neutrino number and the CMB power spectrum lensing amplitude
No full textDark radiation and the CMB bispectrum
No full textNon-Gaussianities in the cosmic microwave background maps arising from correlations between lensing and time variations of the gravitational potential (the so-called integrated Sachs-Wolfe effect) are one of the most important contaminants to the determination of the primordial inflationary bispectrum and may bias its determination. The presence of an extra dark radiation component, as suggested by some recent osmic microwave background measurements from the South Pole Telescope, could bias the expected value of the local bispectrum. In this paper we investigate the impact of dark radiation on the local bispectrum. As a by-product we also quantify the additional information on the dark radiation component that could come from a future precise measurement of the lensing-integrated-Sachs-Wolfe bispectrum
Cornering the Planck A<sub>lens</sub> tension with future CMB data
Full text linkThe precise measurements of cosmic microwave background (CMB) anisotropy angular power spectra made by the Planck satellite show an anomalous value for the lensing amplitude, defined by the parameter Alens, at about 2 standard deviations (2.6 standard deviations when cosmic shear data are included). Moreover, considering Alens brings the values of the cosmological parameters determined by Planck in better agreement with those found by pre-Planck data sets. In this paper, after discussing the current status of the anomaly, we quantify the potential of future CMB measurements in confirming/falsifying the Alens tension. We find that a space-based experiment such as LiteBIRD could falsify the current Alens tension at the level of 5 standard deviations. Similar constraints can be achieved by a stage-III experiment assuming an external prior on the reionization optical depth of τ=0.055±0.010 as already provided by the Planck satellite. A stage-IV experiment could further test the Alens tension at the level of 10 standard deviations. A comparison between temperature and polarization measurements made at different frequencies could further identify possible systematics responsible for Alens>1. We show that, in the case of the CMB-S4 experiment, polarization data alone have the potential of falsifying the current Alens anomaly at more than 5 standard deviations and to strongly bound its frequency dependence. We also evaluate the future constraints on a possible scale dependence for Alens
New cosmological bounds on hot relics: axions and neutrinos
Full text linkAxions, 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 analyze 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 m_a < 7.46 eV and sum m_
u< 0.114 eV both at 95% 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 m_a<0.91 eV and sum m_
u< 0.105 eV, both at 95% 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
Cosmological impact of future constraints on H0 from gravitational-wave standard sirens
No full textGravitational-wave standard sirens present a novel approach for the
determination of the Hubble constant. After the recent spectacular confirmation
of the method thanks to GW170817 and its optical counterpart, additional
standard siren measurements from future gravitational-wave sources are expected
to constrain the Hubble constant to high accuracy. At the same time, improved
constraints are expected from observations of cosmic microwave background (CMB)
polarization and from baryon acoustic oscillations (BAO) surveys. We explore
the role of future standard siren constraints on in light of expected
CMB+BAO data. Considering a -parameters cosmological model, in which
curvature, the dark energy equation of state, and the Hubble constant are
unbounded by CMB observations, we find that a combination of future CMB+BAO
data will constrain the Hubble parameter to . Further extending
the parameter space to a time-varying dark energy equation of state, we find
that future CMB+BAO constraints on are relaxed to . These
accuracies are within reach of future standard siren measurements from the
Hanford-Livingston-Virgo and the Hanford-Livingston-Virgo-Japan-India networks
of interferometers, showing the cosmological relevance of these sources. If
future gravitational-wave standard siren measurements reach on , as
expected, they would significantly improve future CMB+BAO constraints on
curvature and on the dark energy equation of state by up to a factor .
We also show that the inclusion of constraints from gravitational-wave
standard sirens could result in a reduction of the dark energy figure-of-merit
(i.e., the cosmological parameter volume) by up to a factor of
Cosmological constraints on slow roll inflation: An update
No full textIn light of the most recent cosmological observations, we provide new updated constraints on the slow roll inflation in different extended scenarios beyond the ΛCDM cosmological model. Along with the usual six parameters, we simultaneously vary different combinations of additional parameters, including the running of the scalar spectral index αs, its running of running βs, the tensor amplitude r and the spatial curvature ωk. From the Planck 2018 data, we find no evidence for a scalar running or a running of running, while analyzing the Atacama Cosmology Telescope data combined with WMAP 9-years observations data we find a preference for nonzero αs and βs at the level of 2.9σ and 2.7σ, respectively. Anyway, this preference is reduced when the tensor amplitude can vary in the model or βs is fixed to zero. The upper bound on r is only slightly affected by the additional parameters while the differences in the datasets can remarkably change the compatibility among the different inflationary models, sometimes leading to discordant conclusions
Blue gravity waves from Bicep2?
No full textWe present new constraints on the spectral index n(T) of tensor fluctuations from the recent data obtained by the BICEP2 experiment. We found that the BICEP2 data alone slightly prefer a positive, "blue," spectral index with n(T) = 1.36 +/- 0.83 at 68% C. L. However, when a TT prior on the tensor amplitude coming from temperature anisotropy measurements is assumed, we get n(T) = 1.67 +/- 0.53 at 68% C. L., ruling out a scale-invariant n(T) = 0 spectrum at more than three standard deviations. These results are at odds with current bounds on the tensor spectral index coming from pulsar timing, big bang nucleosynthesis, and direct measurements from the LIGO experiment. Considering only the possibility of a "red" n(T) < 0 spectral index, we obtain the lower limit n(T) > -0.76 at 68% C. L. (n(T) > -0.09 when a TT prior is included)
Beyond six parameters: Extending ΛcDM
No full textInternational audienceCosmological constraints are usually derived under the assumption of a six-parameter Λ CDM theoretical framework or simple one-parameter extensions. In this paper we present, for the first time, cosmological constraints in a significantly extended scenario, varying up to 12 cosmological parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the dark energy equation of state, the gravitational wave background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization), we found no significant indication for extensions to the standard Λ CDM scenario, with the notable exception of the angular power spectrum lensing amplitude, Alens , which is larger than the expected value at more than 2 standard deviations, even when combining the Planck data with BAO and supernovae type Ia external data sets. In our extended cosmological framework, we find that a combined Planck+BAO analysis constrains the value of the rms density fluctuation parameter to σ8=0.781-0.063+0.065 at 95 % C.L., helping to relieve the possible tensions with the CFHTlenS cosmic shear survey. We also find a lower value for the reionization optical depth τ =0.058-0.043+0.040 at 95 % C.L. with respect to the one derived under the assumption of Λ CDM . The scalar spectral index nS is now compatible with a Harrison-Zeldovich spectrum to within 2.5 standard deviations. Combining the Planck data set with the Hubble Space Telescope prior on the Hubble constant provides a value for the equation of state w <-1 at more than 2 standard deviations, while the neutrino effective number is fully compatible with the expectations of the standard three neutrino framework
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