CMB与中微子振荡实验对比：揭示无菌中微子的新约束

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本文探讨了无菌中微子在宇宙学和粒子物理领域的重要角色，特别是在宇宙微波背景辐射(CMB)和中微子振荡实验之间提供的约束。作者Sarah Bridle、Jack Elvin-Poole、Justin Evans、Susana Fernandez、Pawel Guzowski和Stefan Söldner-Rembold来自曼彻斯特大学，他们合作进行了一项深入研究，将普朗克2015年的CMB观测结果与MINOS、IceCube和SBN等当前及未来中微子振荡实验的数据进行对比。在他们的研究中，一项关键创新是首次将CMB数据转换到中微子振荡实验常用的Δm²（中微子质量差平方）和sin²(2θ)参数空间，以展示对无菌中微子数量（Neff，即额外的光子密度）和其贡献的共同限制。Neff是衡量宇宙中额外热暗物质成分的一个重要参数，其增大会影响宇宙的早期演化和结构形成。此外，作者还在代换宇宙学参数空间中展示了中微子振荡实验对Neff和无菌中微子质量msterile的影响。在假设存在单一无菌中微子种类的标准模型下，研究发现普朗克2015的CMB数据与μon（μ子型中微子）消失的振荡实验在检测无菌中微子信号方面具有相当的敏感度。这表明尽管CMB主要依赖于早期宇宙的信息，而中微子振荡实验则专注于粒子间的能量转移，两者结合可以提供更全面的无菌中微子证据。这项工作对于理解无菌中微子在解释宇宙学难题，如宇宙暗物质和宇宙学常数问题中的可能作用具有重要意义。它也预示着未来通过多源数据融合有望进一步缩小无菌中微子参数空间，从而深化我们对基本粒子物理的理解。同时，这一研究成果对于设计和优化未来实验计划也有指导意义，因为它们揭示了哪些观测区域可能最能揭示无菌中微子的存在或排除其存在可能性。

Physics Letters B 764 (2017) 322–327

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

A combined view of sterile-neutrino constraints from CMB and

neutrino oscillation measurements

Sarah Bridle, Jack Elvin-Poole

∗

, Justin Evans, Susana Fernandez, Pawel Guzowski,

Stefan Söldner-Rembold

The University of Manchester, School of Physics and Astronomy, Manchester, M13 9PL, United Kingdom

a r t i c l e i n f o a b s t r a c t

Article history:

Received

23 November 2016

Accepted

24 November 2016

Available

online 29 November 2016

Editor: S.

Dodelson

Keywords:

Sterile

neutrinos

Cosmology

Oscillation

experiments

We perform a comparative analysis of constraints on sterile neutrinos from the Planck experiment and

from current and future neutrino oscillation experiments (MINOS, IceCube, SBN). For the ﬁrst time,

we express joint constraints on N

eff

and m

sterile

eff

from the CMB in the m

, sin

2θ parameter space

used by oscillation experiments. We also show constraints from oscillation experiments in the N

eff

sterile

eff

cosmology parameter space. In a model with a single sterile neutrino species and using standard

assumptions, we ﬁnd that the Planck 2015 data and the oscillation experiments measuring muon-

neutrino

(ν

) disappearance have similar sensitivity.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

1. Introduction

The search for low-mass sterile neutrinos is motivated by sev-

eral

experimental anomalies that are not consistent with the three-

ﬂavour

paradigm. Sterile neutrinos would change the oscillation

probabilities observed by detecting neutrinos from accelerators,

nuclear reactors, or produced in the atmosphere. On a cosmolog-

ical

scale, they would modify the power spectrum of the Cosmic

Microwave Background (CMB) (Fig. 1).

Both

types of measurement put severe constraints on the exis-

tence

of extra neutrino ﬂavours, but they are evaluated in terms

of different parameter sets. The CMB measurements constrain the

effective number of additional neutrino species, N

eff

(above the

Standard Model (SM) prediction of N

eff

= 3.046), and the effective

sterile neutrino mass m

sterile

eff

. Oscillation experiments parameterize

their constraints in terms of mass-squared differences, m

, be-

tween

the mass eigenstates, and the mixing angles θ

αβ

between

mass and ﬂavour eigenstates. Here, we use the calculation of [1]

and

show the Planck CMB cosmology constraints in the same pa-

rameter

space as used for ν

disappearance measurements.

Several

experimental anomalies related to the appearance and

disappearance of ν

could be explained by light sterile neutri-

nos

with a mass-squared difference relative to the active states

Corresponding author.

E-mail

address: jack.elvin-poole@postgrad.manchester.ac.uk (J. Elvin-Poole).

of m

≈ 1eV

[2–4]. The LSND Collaboration observes an ex-

cess

appearance in a

beam [5], and MiniBooNE measures

an excess of both ν

[6] and

appearance [7,8]. Reactor experi-

ments

observe a deﬁcit of ≈ 6% in the

ﬂux compared to expec-

tations [9].

Furthermore, Gallium experiments observe a smaller

Ga →

Ge+e

−

event rate than expected from

Cr and

sources [10]. The Daya Bay Reactor experiment has searched for

disappearance setting limits on the mixing angle sin

in the

low m

region 0.0002 <m

< 0.2eV

[11]. These results have

been combined with ν

disappearances searches by MINOS [12] to

obtain stringent constraints on the product sin

2θ

sin

[13].

For this analysis, we focus on recent ν

disappearance results,

where no anomalies have been found, and assume that sin

sin

= 0in order to be consistent with the assumptions that

were used for deriving these limits.

Several

studies have combined oscillation and cosmological data

to constrain sterile neutrinos. Several [14–18] use the posterior

probability distribution on m

from short-baseline anomalies as

a prior in the cosmological analysis. Here, we convert the full

CMB cosmology constraints into the oscillation parameterisation

and vise versa, focusing on recent ν

disappearance results. This

conversion has also been studied in [19,20]. Our analysis differs in

several ways: (i) unlike [19] we use the 2D combined constraints

on N

eff

and m

sterile

eff

in the cosmological analysis, rather than con-

verting

1D constraint values in each parameter individually; (ii) we

use the latest CMB data from Planck, updating from the WMAP

http://dx.doi.org/10.1016/j.physletb.2016.11.050

0370-2693/

SCOAP

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