Sterile neutrinos can affect the evolution of the universe, and thus using the cosmological observations can search for sterile neutrinos. In this work, we use the cosmic microwave background (CMB) anisotropy data from the Planck 2018 release, combined with the latest baryon acoustic oscillation (BAO), type Ia supernova (SN), and Hubble constant ($H_0$) data, to constrain the cosmological models with considering sterile neutrinos. In order to test the influences of the properties of dark energy on the {results} of searching for sterile neutrinos, in addition to the $Λ$ cold dark matter ($Λ$CDM) model, we also consider the $w$CDM model and the holographic dark energy (HDE) model. We find that the existence of sterile neutrinos {is not preferred} when the $H_0$ local measurement is not included in the data combination. When the $H_0$ measurement is included in the joint constraints, it is found that $ΔN_{\rm eff}>0$ is {favored} at about 2.7$σ$ level for the $Λ$CDM model and at about 1-1.7$σ$ level for the $w$CDM model. However, $m_{ν,{\rm{sterile}}}^{\rm{eff}}$ still cannot be well constrained and only upper limits can be given. In addition, we find that the HDE model is definitely ruled out by the current data. We also discuss the issue of the Hubble tension, and we conclude that involving sterile neutrinos in the cosmological models cannot truly resolve the Hubble tension.
The strongest bounds on active-sterile neutrino mixing after Planck data
在早期宇宙中，活跃中微子的振荡可以激发出轻的惰性中微子。它们的性质可以通过它们作为额外辐射的贡献来限制，这些额外辐射可以用中微子种类的有效数量N_ eff和今天的宇宙能量密度Ω_ν h ^2来参数化。这两个参数都已通过普朗克卫星实验测量到相当高的精度。我们用这个结果来更新（3+1）无菌中微子情形的参数空间的边界，其中活性-无菌中微子的质量平方分裂在（10^{-5}-10^2）eV ^2范围内。我们认为正常和倒置的质量排序的活跃和不育状态。第一次，我们考虑到两个非零的积极-无菌混合角的可能性。我们发现，边界是更严格的比在实验室实验中得到的。这导致了与轻无菌中微子的短基线暗示的强烈张力。为了消除这种分歧，需要修改标准宇宙学的假设，例如大的原始中微子不对称性。
We reassess the viability of a cosmological model including a fourth additional sterile neutrino species that self-interacts through a new pseudoscalar degree of freedom. We perform a series of extensive analyses fitting various combinations of cosmic microwave background (CMB) data from Planck, the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT), both alone and in combination with Baryon Acoustic Oscillation (BAO) and Supernova Ia (SnIa) observations. We show that the scenario under study, although capable to resolve the Hubble tension without worsening the so-called $S_8…
Considering the gauge model SU(2)_L x U(1) with the extension of the lepton sector by right-handed sterile Majorana neutrinos, we distinguish a "minimal parametric mixing scenario" for a complete matrix of 6 x 6 light (active) and sterile neutrinos, which depends, in addition to experimentally measured physical parameters, only on the masses of sterile neutrinos. For such a scenario, improved cosmological bounds are provided, resulting from the lifetime of sterile neutrinos and the fraction of energy carried by sterile neutrino dark matter.
Both particle physics experiments and cosmological surveys can constrain the properties of sterile neutrinos, but do so with different parameterizations that naturally use different prior information. We present joint constraints on the 3$+$1 sterile neutrino model oscillation parameters, $Δm_{41}^2$ and $\sin^22θ$, with log priors on those parameters using mostly cosmological data from the Planck satellite. Two cases are considered, one where the sterile neutrino mixes with electron neutrinos solely, and another where the sterile neutrino mixes exclusively with muon neutrinos, allowing us to …
We present a quantitative, direct comparison of constraints on sterile neutrinos derived from neutrino oscillation experiments and from Planck data, interpreted assuming standard cosmological evolution. We extend a $1+1$ model, which is used to compare exclusions contours at the 95% CL derived from Planck data to those from $ν_{e}$-disappearance measurements, to a $3+1$ model. This allows us to compare the Planck constraints with those obtained through $ν_μ\rightarrowν_{e}$ appearance searches, which are sensitive to more than one active-sterile mixing angle. We find that the cosmological data…
We investigate how sterile neutrinos with a range of masses influence cosmology in MeV-scale reheating temperature scenarios. By computing the production of sterile neutrinos through the combination of mixing and scattering in the early Universe, we find that light sterile neutrinos, with masses and mixings as inferred from short-baseline neutrino oscillation experiments, are consistent with big-bang nucleosynthesis (BBN) and cosmic microwave background (CMB) radiation for the reheating temperature of ${\cal O}(1)$ MeV if the parent particle responsible for reheating decays into electromagneti…
In this work we revisit the question of whether Cosmology can be made compatible with scenarios with light sterile neutrinos, as invoked to explain the SBL anomalies, in the presence of self-interaction among sterile neutrinos mediated by massive gauge bosons. We examine this proposal by deriving the cosmological predictions of the model in a wide range of the model parameters including the effective interaction strength $G_X$, sterile neutrino mass $m_{\rm st}$ and active-sterile mixings. With those we perform a statistical analysis of the cosmological data from BBN, CMB, and BAO data to infe…
We investigate the cosmological constraints on sterile neutrinos in a universe in which vacuum energy interacts with cold dark matter by using latest observational data. We focus on two specific interaction models, $Q=βHρ_{\rm v}$ and $Q=βHρ_{\rm c}$. To overcome the problem of large-scale instability in the interacting dark energy scenario, we employ the parametrized post-Friedmann (PPF) approach for interacting dark energy to do the calculation of perturbation evolution. The observational data sets used in this work include the Planck 2015 temperature and polarization data, the baryon acoust…
Sterile neutrinos with a mass in the eV range have been invoked as a possible explanation of a variety of short baseline (SBL) neutrino oscillation anomalies. However, if one considers neutrino oscillations between active and sterile neutrinos, such neutrinos would have been fully thermalised in the early universe, and would be therefore in strong conflict with cosmological bounds. In this study we first update cosmological bounds on the mass and energy density of eV-scale sterile neutrinos. We then perform an updated study of a previously proposed model in which the sterile neutrino couples t…
Are Cosmological Data Excluding Sterile Neutrinos or Only the Fully Thermalized Limit?
Universidade Federal do Rio Grande do Sul（南里奥格兰德联邦大学）；Instituto Nacional de Pesquisas Espaciais（国家空间研究所）；University of Sheffield（谢菲尔德大学）；CSIC‐Universitat de València（西班牙高等科学研究理事会-瓦伦西亚大学）；University of Turin（都灵大学）
Minimal dark energy models, described by the same number of free parameters of the standard cosmological model with cold dark matter plus a cosmological constant to parameterize the dark energy component, constitute very appealing scenarios which may solve long-standing, pending tensions. On the one hand, they alleviate significantly the tension between cosmological observations and the presence of one sterile neutrino motivated by the short-baseline anomalies: we obtain a $95\%$ CL cosmological bound on the mass of a fully thermalized fourth sterile neutrino ($N_{\rm eff}=4$) equal to $m_s<0.…
We explore the complementarity between terrestrial neutrino oscillation experiments and astrophysical/cosmological measurements in probing the existence of sterile neutrinos. We find that upcoming accelerator neutrino experiments will not improve on constraints by the time they are operational, but that reactor experiments can already probe parameter space beyond the reach of Planck. We emphasize the tension between cosmological experiments and reactor antineutrino experiments and enumerate several possibilities for resolving this tension.
The detection of a sterile neutrino could constitute the first observation of a particle that could have been produced before Big-Bang Nucleosynthesis (BBN), and could provide information about the yet untested pre-BBN era. The cosmological evolution in this era could be drastically different than typically assumed in what constitutes the standard cosmology, as happens in a variety of motivated particle models. In this work we assess the sensitivity to different pre-BBN cosmologies in which entropy is conserved of 0.01 eV to 1 MeV mass sterile neutrinos produced in the early Universe via reson…
We explore the thermal light sterile neutrino situation from cosmological perspective in the $Λ\textrm{CDM} + r_{0.05} + N_{\textrm{eff}} + m^{\textrm{eff}}_{\textrm{s}}$ model using combinations of latest data sets available. Here, $r_{0.05}$ is the tensor-to-scalar ratio at the pivot scale of $k_*=0.05h$ Mpc$^{-1}$, $N_{\textrm{eff}}$ is the effective number of relativistic species during recombination, and $m^{\textrm{eff}}_{\textrm{s}}$ is the effective mass of the sterile neutrino. Among Cosmic Microwave Background (CMB) datasets, we use Planck 2015 temperature and low-$l$ ($l <$ 30) pola…
Unexplored interactions of neutrinos could be the key to understanding the nature of the dark matter (DM). In particular, active neutrinos with new self-interactions can produce keV-mass sterile neutrinos that account for the whole of the DM through the Dodelson-Widrow mechanism for a large range of active-sterile mixing values. This production typically occurs before Big-Bang Nucleosynthesis (BBN) in a yet uncharted era of the Universe. We assess how the mixing range for keV-mass sterile neutrino DM is affected by the uncertainty in the early Universe pre-BBN cosmology. This is particularly r…
In the presented work we consider the influence of a hypothetical sterile neutrino (with eV-scale mass) on the determination of cosmological parameters. If it is detected, it will be necessary to include it into the $Λ\rm CDM$ model with the fixed values of its mass $m_{\rm s}$ and mixing angle $θ_{s}$, which is the main method used through this paper. Apart from that, the seesaw mechanism requires there to be at least two sterile states, one of them being much heavier than the active ones. The heavier sterile state ($m_{s}\sim1$ keV) would decay and increase the effective number of active neu…
We place constraints on sterile neutrino resonant production (RP) and scalar decay production (SDP) mechanisms assuming that sterile neutrino represents a fraction from the total Cold Dark Matter energy density. For the cosmological analysis, we complement the CMB anisotropies measurements with CMB lensing gravitational potential measurements, that are sensitive to the DM distribution out to high redshifts and with the cosmic shear data, that constraints the gravitational potential at lower redshifts than CMB. We show that our datasets have enough sensitivity to constrain the sterile neutrino …
We discuss how a laboratory detection of a sterile neutrino not only would constitute a fundamental discovery of a new particle, but could also provide an indication of the evolution of the Universe before Big-Bang Nucleosynthesis (BBN), a fundamental discovery in cosmology. These "visible" sterile neutrinos could be detected in experiments such as KATRIN/TRISTAN and HUNTER in the keV mass range and PTOLEMY, KATRIN and reactor neutrino experiments in the eV mass range. Standard assumptions are usually made to compute the relic abundance and momentum distribution of particles produced before th…
We consider relatively heavy neutrinos $ν_H$, mostly contributing to a sterile state $ν_s$, with mass in the range 10 MeV $\lesssim m_s \lesssim m_π \sim 135$ MeV, which are thermally produced in the early universe in collisional processes involving active neutrinos, and freezing out after the QCD phase transition. If these neutrinos decay after the active neutrino decoupling, they generate extra neutrino radiation, but also contribute to entropy production. Thus, they alter the value of the effective number of neutrino species $N_{\rm eff}$ as for instance measured by the cosmic microwave bac…
Unveiling secret interactions among sterile neutrinos with big-bang nucleosynthesis
短基线中微子异常表明存在低质量（m \sim O（1）~eV）的无菌中微子ν_s。在早期宇宙中，这些粒子会通过活跃中微子的振荡而有效地产生，导致无菌态的热布居，这似乎与宇宙学观测不相容。为了缓解这种紧张关系，最近有人推测，由大质量规范玻色子X（M_X << M_W）介导的不育中微子之间的新的“秘密”相互作用，由于产生大的物质势项，可以抑制或抑制不育中微子热化。然而，我们注意到，它们也在无菌中微子部分产生强碰撞项，在遇到物质共振后诱导有效的无菌中微子产生，增加它们对相对论粒子种类N_ eff数量的贡献。此外，在温度T \lesssim几MeV处发生共振的ν_s-ν_s相互作用的参数值，在电子（反）中微子谱中产生显著的畸变，改变了大爆炸核合成（BBN）中轻元素的丰度。使用本确定的$^4$他和氘原始丰度，我们确定的BBN约束的模型参数。我们发现，如果假设重子密度为普朗克实验的最佳拟合值Ω_B h ^2 = 0.02207，则$^2$ H/H密度比排除了大部分的参数空间，而当Ω_B h ^2 =0.02261时（95% C. L. Planck的上界由于实验测定的误差较大，氦的质量分数Y_p没有给出明显的界限。
