1,721,084 research outputs found
Planck constraints on the effective neutrino number and the CMB power spectrum lensing amplitude
No full textν generation: Present and future constraints on neutrino masses from global analysis of cosmology and laboratory experiments
Full text linkWe perform a joint analysis of current data from cosmology and laboratory experiments to constrain theneutrino mass parameters in the framework of Bayesian statistics, also accounting for uncertainties in nuclearmodeling, relevant for neutrinoless doubleβdecay (0ν2β) searches. We find that a combination of currentoscillation, cosmological, and0ν2βdata constrainsmββ<0.045eV (0.014eV<mββ<0.066eV) at95% C.L. for normal (inverted) hierarchy. This result is in practice dominated by the cosmological andoscillation data, so it is not affected by uncertainties related to the interpretation of0ν2βdata, like nuclearmodeling, or the exact particle physics mechanism underlying the process. We then perform forecasts forforthcoming and next-generation experiments, and find that in the case of normal hierarchy, given a total massof 0.1 eV, and assuming a factor-of-two uncertainty in the modeling of the relevant nuclear matrix elements, itwill be possible to measure the total mass itself, the effective Majorana mass and the effective electron masswith an accuracy (at 95% C.L.) of 0.05, 0.015, 0.02 eV, respectively, as well as to be sensitive to one of theMajorana phases. This assumes that neutrinos are Majorana particles and that the mass mechanism gives thedominant contribution to0ν2βdecay. We argue that more precise nuclear modeling will be crucial to improvethese sensitivities
Dark 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
Testing chirality of primordial gravitational waves with Planck and future CMB data: No hope from angular power spectra
No full textWe use the 2015 Planck likelihood in combination with the Bicep2/Keck likelihood (BKP and BK14) to constrain the chirality, chi, of primordial gravitational waves in a scale invariant scenario. In this framework, the parameter chi enters theory always coupled to the tensor -to -scalar ratio, r, e.g. in combination of the form chi . r. Thus, the capability to detect chi critically depends on the value of r. We find that with present data sets chi is de facto unconstrained. We also provide forecasts for chi from future CMB experiments, including COrE+, exploring several fiducial values of r. We find that the current limit on r is tight enough to disfavor a neat detection of chi. For example, in the unlikely case in which r similar to 0.1(0.05), the maximal chirality case, i.e. chi = +/- 1, could be detected with a significance of similar to 2.5(1.5)sigma at best. We conclude that the two-point statistics at the basis of CMB likelihood functions is currently unable to constrain chirality and may only provide weak limits on chi in the most optimistic scenarios. Hence, it is crucial to investigate the use of other observables, e.g. provided by higher order statistics, to constrain these kinds of parity violating theories with the CMB.We use the 2015 Planck likelihood in combination with the Bicep2/Keck likelihood (BKP and BK14) to constrain the chirality, χ, of primordial gravitational waves in a scale-invariant scenario. In this framework, the parameter χ enters theory always coupled to the tensor-to-scalar ratio, r, e.g. in combination of the form χ ċ r. Thus, the capability to detect χ critically depends on the value of r. We find that with present data sets χ is de facto unconstrained. We also provide forecasts for χ from future CMB experiments, including COrE+, exploring several fiducial values of r. We find that the current limit on r is tight enough to disfavor a neat detection of χ. For example, in the unlikely case in which r∼0.1(0.05), the maximal chirality case, i.e. χ = ±1, could be detected with a significance of ∼2.5(1.5)σ at best. We conclude that the two-point statistics at the basis of CMB likelihood functions is currently unable to constrain chirality and may only provide weak limits on χ in the m..
Updated Constraints and Forecasts on Primordial Tensor Modes
No full textWe present new, tight, constraints on the cosmological background of gravitational waves (GWs)using the latest measurements of CMB temperature and polarization anisotropies provided by thePlanck, BICEP2 andKeck Arrayexperiments. These constraints are further improved when the GWcontributionNGWeffto the effective number of relativistic degrees of freedomNeffis also considered.Parametrizing the tensor spectrum as a power law with tensor-to-scalar ratior, tiltntand pivot0.01 Mpc−1, and assuming a minimum value ofr= 0.001, we findr <0.089,nt= 1.7+2.1−2.0(95% CL,noNGWeff) andr <0.082,nt=−0.05+0.58−0.87(95% CL, withNGWeff). When the recently released 95 GHzdata fromKeck Arrayare added to the analysis, the constraints onrare improved tor <0.067(95% CL, noNGWeff),r <0.061 (95% CL, withNGWeff). We discuss the limits coming from directdetection experiments such as LIGO-Virgo, pulsar timing (European Pulsar Timing Array) andCMB spectral distortions (FIRAS). Finally, we show future constraints achievable from a COrE-like mission: if the tensor-to-scalar ratio is of order 10−2and the inflationary consistency relationnt=−r/8 holds, COrE will be able to constrainntwith an error of 0.16 at 95% CL. In the casethat lensingB-modes can be subtracted to 10% of their power, a feasible goal for COrE, these limitswill be improved to 0.11 at (95% C
Improvement of cosmological neutrino mass bounds
No full textThe most recent measurements of the temperature and low-multipole polarization anisotropies of the cosmic microwave background from the Planck satellite, when combined with galaxy clustering data from the Baryon Oscillation Spectroscopic Survey in the form of the full shape of the power spectrum, and with baryon acoustic oscillation measurements, provide a 95% confidence level (C.L.) upper bound on the sum of the three active neutrinos Sigma m(nu) < 0.183 eV, among the tightest neutrino mass bounds in the literature, to date, when the same data sets are taken into account. This very same data combination is able to set, at similar to 70% C.L., an upper limit on Sigma m(nu) of 0.0968 eV, a value that approximately corresponds to the minimal mass expected in the inverted neutrino mass hierarchy scenario. If high-multipole polarization data from Planck is also considered, the 95% C.L. upper bound is tightened to Sigma m(nu) < 0.176 eV. Further improvements are obtained by considering recent measurements of the Hubble parameter. These limits are obtained assuming a specific nondegenerate neutrino mass spectrum; they slightly worsen when considering other degenerate neutrino mass schemes. Low-redshift quantities, such as the Hubble constant or the reionization optical depth, play a very important role when setting the neutrino mass constraints. We also comment on the eventual shifts in the cosmological bounds on Sigma m(nu) when possible variations in the former two quantities are addressed.</p
Constraints on the early and late integrated Sachs-Wolfe effects from the Planck 2015 cosmic microwave background anisotropies in the angular power spectra
Full text linkThe Integrated Sachs-Wolfe (ISW) effect predicts additional anisotropies in the Cosmic MicrowaveBackground due to time variation of the gravitational potential when the expansion of the universeis not matter dominated. The ISW effect is therefore expected in the early universe, due to thepresence of relativistic particles at recombination, and in the late universe, when dark energy startsto dominate the expansion. Deviations from the standard picture can be parameterized byAeISWandAlISW, which rescale the overall amplitude of the early and late ISW effects. Analyzing themost recent CMB temperature spectra from the Planck 2015 release, we detect the presence of theearly ISW at high significance withAeISW= 1.06±0.04 at 68% CL and an upper limit for thelate ISW ofAlISW<1.1 at 95% CL. The inclusion of the recent polarization data from the Planckexperiment erases such 1.5σhint forAeISW6= 1. When considering the recent detections of the lateISW coming from correlations between CMB temperature anisotropies and weak lensing, a value ofAlISW= 0.85±0.21 is predicted at 68% CL, showing a 4σevidence. We discuss the stability of ourresult in the case of an extra relativistic energy component parametrized by the effective neutrinonumberNeffand of a CMB lensing amplitudeA
Breaking Be: A sterile neutrino solution to the cosmological lithium problem
No full textThe possibility that the so-called ''lithium problem'', i.e., the disagreement between the theoretical abundance predicted for primordial 7Li assuming standard nucleosynthesis and the value inferred from astrophysical measurements, can be solved through a non-thermal Big Bang Nucleosynthesis (BBN) mechanism has been investigated by several authors. In particular, it has been shown that the decay of a MeV-mass particle, like, e.g., a sterile neutrino, decaying after BBN not only solves the lithium problem, but also satisfies cosmological and laboratory bounds, making such a scenario worth to be investigated in further detail. In this paper, we constrain the parameters of the model with the combination of current data, including Planck 2015 measurements of temperature and polarization anisotropies of the Cosmic Microwave Background (CMB), FIRAS limits on CMB spectral distortions, astrophysical measurements of primordial abundances and laboratory constraints. We find that a sterile neutrino with mass MS = 4.35-0.17+0.13 MeV (at 95% c.l.), a decay time τS = 1.8-1.3+2.5 · 105 s (at 95% c.l.) and an initial density S/cmb = 1.7-0.6+3.5 · 10-4 (at 95% c.l.) in units of the number density of CMB photons, perfectly accounts for the difference between predicted and observed 7Li primordial abundance. This model also predicts an increase of the effective number of relativistic degrees of freedom at the time of CMB decoupling ΔNeffcmb ≡ Neffcmb -3.046 = 0.34-0.14+0.16 at 95% c.l.. The required abundance of sterile neutrinos is incompatible with the standard thermal history of the Universe, but could be realized in a low reheating temperature scenario. We also provide forecasts for future experiments finding that the combination of measurements from the COrE+ and PIXIE missions will allow to significantly reduce the permitted region for the sterile lifetime and density
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