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Register a new userDetermining the Neutrino Mass Hierarchy with Cosmology
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Francesco De Bernardis
Publication date
2009
fields
Physics
and research's language is
English
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The combination of current large scale structure and cosmic microwave background (CMB) anisotropies data can place strong constraints on the sum of the neutrino masses. Here we show that future cosmic shear experiments, in combination with CMB constraints, can provide the statistical accuracy required to answer questions about differences in the mass of individual neutrino species. Allowing for the possibility that masses are non-degenerate we combine Fisher matrix forecasts for a weak lensing survey like Euclid with those for the forthcoming Planck experiment. Under the assumption that neutrino mass splitting is described by a normal hierarchy we find that the combination Planck and Euclid will possibly reach enough sensitivity to put a constraint on the mass of a single species. Using a Bayesian evidence calculation we find that such future experiments could provide strong evidence for either a normal or an inverted neutrino hierachy. Finally we show that if a particular neutrino hierachy is assumed then this could bias cosmological parameter constraints, for example the dark energy equation of state parameter, by > 1sigma, and the sum of masses by 2.3sigma.
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In this work we update the bounds on $sum m_{ u}$ from latest publicly available cosmological data and likelihoods using Bayesian analysis, while explicitly considering particular neutrino mass hierarchies. In the minimal $Lambdatextrm{CDM}+sum m_{ u}$ model with most recent CMB data from Planck 2018 TT,TE,EE, lowE, and lensing; and BAO data from BOSS DR12, MGS, and 6dFGS, we find that at 95% C.L. the bounds are: $sum m_{ u}<0.12$ eV (degenerate), $sum m_{ u}<0.15$ eV (normal), $sum m_{ u}<0.17$ eV (inverted). The bounds vary across the different mass orderings due to different priors on $sum m_{ u}$. Also, we find that the normal hierarchy is very mildly preferred relative to the inverted, using both minimum $chi^2$ values and Bayesian Evidence ratios. In this paper we also provide bounds on $sum m_{ u}$ considering different hierarchies in various extended cosmological models: $Lambdatextrm{CDM}+sum m_{ u}+r$, $wtextrm{CDM}+sum m_{ u}$, $w_0 w_a textrm{CDM}+sum m_{ u}$, $w_0 w_a textrm{CDM}+sum m_{ u}$ with $w(z)geq -1$, $Lambda textrm{CDM} + sum m_{ u} + Omega_k$, and $Lambda textrm{CDM} + sum m_{ u} + A_{textrm{Lens}}$. We do not find any strong evidence of normal hierarchy over inverted hierarchy in the extended models either.
The relatively large measured value of $theta_{13}$ has opened up the possibility of determining the neutrino mass hierarchy through earth matter effects. Amongst the current accelerator-based experiments only NOvA has a long enough baseline to observe earth matter effects. However, NOvA is plagued with uncertainty on the knowledge of the true value of $delta_{CP}$, and this could drastically reduce its sensitivity to the neutrino mass hierarchy. The earth matter effect on atmospheric neutrinos on the other hand is almost independent of $delta_{CP}$. The 50 kton magnetized Iron CALorimeter at the India-based Neutrino Observatory (ICAL@INO) will be observing atmospheric neutrinos. The charge identification capability of this detector gives it an edge over others for mass hierarchy determination through observation of earth matter effects. We study in detail the neutrino mass hierarchy sensitivity of the data from this experiment simulated using the Nuance based generator developed for ICAL@INO and folded with the detector resolutions and efficiencies obtained by the INO collaboration from a full Geant4-based detector simulation. The data from ICAL@INO is then combined with simulated data from T2K, NOvA, Double Chooz, RENO and Daya Bay experiments and a combined sensitivity study to the mass hierarchy is performed. With 10 years of ICAL@INO data combined with T2K, NOvA and reactor data, one could get about $2.3sigma-5.7sigma$ discovery of the neutrino mass hierarchy, depending on the true value of $sin^2theta_{23}$ [0.4 -- 0.6], $sin^22theta_{13}$ [0.08 -- 0.12] and $delta_{CP}$ [0 -- 2$pi$].
We explore the cosmological signals of theories in which the neutrinos decay into invisible dark radiation after becoming non-relativistic. We show that in this scenario, near-future large scale structure measurements from the Euclid satellite, when combined with cosmic microwave background data from Planck, may allow an independent determination of both the lifetime of the neutrinos and the sum of their masses. These parameters can be independently determined because the Euclid data will cover a range of redshifts, allowing the growth of structure over time to be tracked. If neutrinos are stable on cosmological timescales, these observations can improve the lower limit on the neutrino lifetime by seven orders of magnitude, from $mathcal{O}(10)$ years to $2times 10^8$ years ($95%$ C.L.), without significantly affecting the measurement of neutrino mass. On the other hand, if neutrinos decay after becoming non-relativistic but on timescales less than $mathcal{O}(100)$ million years, these observations may allow, not just the first measurement of the sum of neutrino masses, but also the determination of the neutrino lifetime from cosmology.
We provide a consistent framework to set limits on properties of light sterile neutrinos coupled to all three active neutrinos using a combination of the latest cosmological data and terrestrial measurements from oscillations, $beta$-decay and neutrinoless double-$beta$ decay ($0 ubetabeta$) experiments. We directly constrain the full $3+1$ active-sterile mixing matrix elements $|U_{alpha4}|^2$, with $alpha in ( e,mu ,tau )$, and the mass-squared splitting $Delta m^2_{41} equiv m_4^2-m_1^2$. We find that results for a $3+1$ case differ from previously studied $1+1$ scenarios where the sterile is only coupled to one of the neutrinos, which is largely explained by parameter space volume effects. Limits on the mass splitting and the mixing matrix elements are currently dominated by the cosmological data sets. The exact results are slightly prior dependent, but we reliably find all matrix elements to be constrained below $|U_{alpha4}|^2 lesssim 10^{-3}$. Short-baseline neutrino oscillation hints in favor of eV-scale sterile neutrinos are in serious tension with these bounds, irrespective of prior assumptions. We also translate the bounds from the cosmological analysis into constraints on the parameters probed by laboratory searches, such as $m_beta$ or $m_{beta beta}$, the effective mass parameters probed by $beta$-decay and $0 ubetabeta$ searches, respectively. When allowing for mixing with a light sterile neutrino, cosmology leads to upper bounds of $m_beta < 0.09$ eV and $m_{beta beta} < 0.07$ eV at 95% C.L, more stringent than the limits from current laboratory experiments.
The most sensitive direct method to establish the absolute neutrino mass is observation of the endpoint of the tritium beta-decay spectrum. Cyclotron Radiation Emission Spectroscopy (CRES) is a precision spectrographic technique that can probe much of the unexplored neutrino mass range with $mathcal{O}({rm eV})$ resolution. A lower bound of $m( u_e) gtrsim 9(0.1), {rm meV}$ is set by observations of neutrino oscillations, while the KATRIN Experiment - the current-generation tritium beta-decay experiment that is based on Magnetic Adiabatic Collimation with an Electrostatic (MAC-E) filter - will achieve a sensitivity of $m( u_e) lesssim 0.2,{rm eV}$. The CRES technique aims to avoid the difficulties in scaling up a MAC-E filter-based experiment to achieve a lower mass sensitivity. In this paper we review the current status of the CRES technique and describe Project 8, a phased absolute neutrino mass experiment that has the potential to reach sensitivities down to $m( u_e) lesssim 40,{rm meV}$ using an atomic tritium source.
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