We analyze the influence of decaying sterile neutrinos with the masses in the range 1-140 MeV on the primordial Helium-4 abundance, explicitly solving the Boltzmann equations for all particle species, taking into account neutrino flavour oscillations, and paying special attention to systematic uncertainties. We show that the Helium abundance depends only on the sterile neutrino lifetime and not on the way the active-sterile mixing is distributed between flavours, and derive an upper bound on the lifetime. We also demonstrate that the recent results of Izotov & Thuan [arXiv:1001.4440], who find 2sigma higher than predicted by the standard primordial nucleosynthesis value of Helium-4 abundance, are consistent with the presence in the plasma of sterile neutrinos with the lifetime 0.01-2 seconds. The decay of these particles perturbs the spectra of (decoupled) neutrinos and heats photons, changing the ratio of neutrino to photon energy density, that can be interpreted as extra neutrino species at the recombination epoch.
We consider the cosmological effects of sterile neutrinos with the masses of $150- 450$ MeV. The decay of sterile neutrinos changes the thermal history of the Universe and affects the energy density of radiation at the recombination and the big bang nucleosynthesis (BBN) results. We derive severe constraints on the parameters of sterile neutrinos from the primordial abundances of helium-4 and deuterium. We also find that in a particular model the constraints can be considerably relaxed by assuming a large lepton asymmetry in the active neutrinos. In this case, the consistent parameters result …
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。
Multi-momentum and multi-flavour active-sterile neutrino oscillations in the early universe: role of neutrino asymmetries and effects on nucleosynthesis
We study constraints from Big Bang Nucleosynthesis on inert particles in a dark sector which contribute to the Hubble rate and therefore change the predictions of the primordial nuclear abundances. We pay special attention to the case of MeV-scale particles decaying into dark radiation, which are neither fully relativistic nor non-relativistic during all temperatures relevant to Big Bang Nucleosynthesis. As an application we discuss the implications of our general results for models of self-interacting dark matter with light mediators.
During the era of primordial nucleosynthesis the background of non-equilibrium antineutrinos is being formed due to decays of neutrons and nuclei of tritium. The spectra of antineutrinos of this background were calculated taking into account the Coulomb interaction between electron and daughter nucleus in $β^-$-decay. The dependence of these spectra on the value of the baryon-to-photon ratio $η$ at the period of primordial nucleosynthesis is investigated. The observations of these antineutrinos will allow us to look directly at the very early Universe and nonequilibrium processes taken place b…
A Reply to "Comment on 'Big Bang Nucleosynthesis and Active-Sterile Neutrino Mixing: Evidence for Maximal $ν_μ\leftrightarrowν_τ$ Mixing in Super Kamiokande?'"
The success of primordial nucleosynthesis has been limited by the long-standing Lithium problem. We use a self-consistent perturbative analysis of the effects of relevant theoretical parameters on primordial nucleosynthesis, including variations of nature's fundamental constants, to explore the problem and its possible solutions, in the context of the latest observations and theoretical modeling. We quantify the amount of depletion needed to solve the Lithium problem, and show that transport processes of chemical elements in stars are able to account for it. Specifically, the combination of at…
Primordial nucleosynthesis is an observational cornerstone of the Hot Big Bang model and a sensitive probe of physics beyond the standard model. Its success has been limited by the so-called Lithium problem, for which many solutions have been proposed. We report on a self-consistent perturbative analysis of the effects of variations in nature's fundamental constants, which are unavoidable in most extensions of the standard model, on primordial nucleosynthesis, focusing on a broad class of Grand Unified Theory models. A statistical comparison between theoretical predictions and observational me…
Studies of neutrino asymmetries generated by ordinary-sterile neutrino oscillations in the early universe and implications for big bang nucleosynthesis bounds
The success of primordial nucleosynthesis as a cornerstone of the hot Big Bang model has been limited by the long-standing lithium problem. Recent work presented a self-consistent perturbative analysis of the effects of variations in nature's fundamental constants on primordial nucleosynthesis for a broad class of grand unified theory models, showing that such models provide a possible solution to the lithium problem, provided the value of the fine-structure constant $α$ at the nucleosynthesis epoch is larger than the current laboratory one by a few parts per million of relative variation. Her…
Local Universe observations find a value of the Hubble constant $H_0$ that is larger than the value inferred from the Cosmic Microwave Background and other early Universe measurements, assuming known physics and the $Λ$CDM cosmological model. We show that additional radiation in active neutrinos produced just before Big Bang Nucleosynthesis by an unstable sterile neutrino with mass $m_s=$ O(10) MeV can alleviate this discrepancy. The necessary masses and couplings of the sterile neutrino, assuming it mixes primarily with $ν_τ$ and/or $ν_μ$ neutrinos, are within reach of Super-Kamiokande as wel…
Sterile neutrinos can be produced in the early universe via interactions with their active counterparts. For small active-sterile mixing angles, thermal equilibrium with the standard model plasma is not reached and sterile neutrinos are only produced via flavor oscillations. We study in detail this regime, taking into account matter potentials and decoherence effects caused by elastic scatterings with the plasma. We find that resonant oscillations occurring at temperatures $T\lesssim 10\,\mathrm{GeV}$ lead to a significant enhancement of the sterile neutrino production rate. Taking this into a…
Chaotic Amplification of Neutrino Chemical Potentials by Neutrino Oscillations in Big Bang Nucleosynthesis
我们详细研究了在大爆炸核合成时期放大中微子化学势的活动无菌中微子振荡的参数空间。我们计算了放大的幅度，并显示在放大过程中的混沌的证据。我们还讨论了中微子化学势放大在大爆炸核合成中的意义。它表明，与$\sim 1$ eV $\nue$，其化学势的放大，由活跃的无菌中微子振荡可以降低中微子物种在大爆炸核合成的有效数量显着低于3。
