Abstract

We perform a Bayesian analysis of current neutrino oscillation data. When estimating the oscillation parameters we find that the results generally agree with those of the $\chi^2$ method, with some differences involving $s_{23}^2$ and CP-violating effects. We discuss the additional subtleties caused by the circular nature of the CP-violating phase, and how it is possible to obtain correlation coefficients with $s_{23}^2$. When performing model comparison, we find that there is no significant evidence for any mass ordering, any octant of $s_{23}^2$ or a deviation from maximal mixing, nor the presence of CP-violation.

Highlights

  • Several global analyses exist in the literature [7,8,9], which, by fitting the results from the bulk of oscillation experiments, obtain best estimates and allowed ranges for these six oscillation parameters

  • One may question to what degree the current determination of the oscillation parameters is dependent on the assumed statistical approach, and whether Bayesian statistics can shed some light on the presently open issues related to the mass ordering, the octant of θ23, and the presence of CP-violation

  • We have presented the results of a Bayesian global analysis of solar, atmospheric, reactor and accelerator neutrino data in the framework of three-neutrino oscillations and compared them with those from the standard χ2 analysis in NuFIT-2.0 [10]

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Summary

Statistical framework

We will be using Bayesian probability theory, where each proposition is associated with a probability or plausibility, defined to lie between 0 and 1. There are some so-called information criteria which have been used to compare different models (see, e.g., [13, 14]) These do not explicitly depend on any prior, but typically are derived using quite restrictive assumptions. Under the assumption that a model M is true, complete inference of its parameters is given by the posterior distribution, Pr(D|Θ, M ) Pr(Θ|M ) L(Θ)π(Θ) In this case, the evidence is only a normalization factor, since it is independent of the values of the parameters Θ and it is often disregarded in parameter estimation. In this work we use MultiNest [16,17,18], a Bayesian inference tool which, given the prior and the likelihood, calculates the evidence with an uncertainty estimate, and generates posterior samples from distributions that may contain multiple modes and pronounced (curving) degeneracies in high dimensions

Priors on oscillation parameters
Posterior distributions
Determination of s223
Octants of θ23 and maximal mixing
Exploring δCP and CP-violation
Method
CP-violation vs CP-conservation
Correlation between s223 and δCP
Summary
Full Text
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