Neutrino refractive effects during their decoupling era in the early universe
R. F. Sawyer
备注：
The equations and fig. 1 are right, but there are big complexities in their solutions that make the general effects questionable for the moment, and make part of the commentary wrong as well
There is an accepted approach to calculation of the neutrino flavor density-matrix in the halo of a supernova, in which neutrino amplitudes, not cross-sections, need to be followed carefully in the region above the region of frequent scatterings. The same reasoning and techniques, applied to the evolution of neutrino flavors and energy distributions in the early universe in the era of neutrino decoupling, leads to radical changes in the prediction of the effects of the neutrino-neutrino interaction.
Predictions for the production of sterile neutrinos, should they exist, will also be changed.
There is an accepted approach to calculation of the neutrino flavor density-matrix in the halo of a supernova, in which neutrino amplitudes, not cross-sections, need to be followed carefully in the region above the region of frequent scatterings. The same reasoning and techniques, applied to the evolution of neutrino flavors and energy distributions in the early universe in the era of neutrino decoupling, leads to radical changes in the predictions of the effects of the neutrino-neutrino interaction. Predictions for the production of sterile neutrinos, should they exist, will also be changed.
An active two-neutrino state's coupling to an intermediate scalar meson, and thence to a two-antineutrino state, is one idea for catalyzing transitions from active to sterile neutrinos, in an implementation of the Dodelson-Widrow proposal for the production of sterile and somewhat massive neutrinos as dark matter candidates. We propose some mechanics that promises to use the very same model with the same mass and coupling parameters, in order to achieve similar results, but orders of magnitude faster; or alternatively, similar results but beginning with vastly reduced coupling constants. The m…
Neutrino physics in the early Universe is key to our understanding of later cosmological stages, such as primordial nucleosynthesis (BBN) or the formation of large-scale structures. The coming decade promises new experimental results to explore and constrain cosmological models even more precisely - which requires robust theoretical predictions. This PhD thesis presents a study of the evolution of neutrinos in the first seconds after the Big Bang, more precisely when the temperature of the Universe is of the order of one mega-electronvolt. This evolution is obtained numerically by solving kine…
We study the early kinetic decoupling effect in a pseudo-Nambu-Goldstone (pNG) dark matter (DM) model. The pNG DM scattering processes with particles in the thermal bath in the early Universe are suppressed by the small momentum transfer. As a result, kinetic equilibrium is not maintained, and the temperature of DM is different from the temperature of the thermal bath at the freeze-out era. This temperature difference affects the thermal relic abundance of DM. We investigate the early kinetic decoupling in the Higgs resonance region, 50 GeV $\lesssim m_χ\lesssim m_h/2$, where $m_χ$ is the mass…
Cosmological evolution of warm dark matter fluctuations II: Solution from small to large scales and keV sterile neutrinos
我们用Volterra积分方程解了暖暗物质（WDM）密度涨落的宇宙学演化。在没有中微子的情况下，各向异性应力消失，Volterra方程减少到一个单一的积分方程。我们数值求解这个方程的DM费米子去耦在平衡和DM不育中微子去耦出平衡。给出了零波数下密度涨落和引力势的精确解析解。我们计算的密度对比度作为一个函数的比例因子a的波数k的范围很广。当a固定时，密度衬度随k的增大而增大，< k_c while it decreases for k >其中k k_c为1.6/Mpc。密度对比度取决于k和a，主要是通过乘积k a表现出自相似行为。我们的数值密度对比小k轻轻接近我们的解析解k = 0。当k < 1/（60 kpc）时，密度衬度一般随时间增长，而当k > 1/（60 kpc）时，密度衬度从RD期开始出现振荡，并随着k的增大而变强。我们计算了热费米子和无菌中微子的密度对比度的传递函数：a）Dodelson-Widrow（DW）模型和b）由标量粒子衰变产生的无菌中微子模型。传递函数随k增大，在k = k_c时达到最大值后减小，反映了密度衬度随时间的变化。Volterra方程中的积分核在时间上是非局部的，它们的衰减决定了自解耦以来过去演化的记忆。当DM在平衡时比在平衡之外时下降得更快。尽管中微子和光子在MD时代可以被忽视，但它们通过RD时代的记忆在MD时代做出了贡献。
The universe has evolved through several phases as its various constituents dominated its energy content. Candidate dark matter particles may have undergone freeze-out during any such phase. While the standard freeze-out scenarios have been explored during the radiation-dominated era, and more recently during scalar field decay, this work extends the study of dark matter freeze-out to a potential early period during which the universe is matter-dominated and its evolution adiabatic. Decoupling during an adiabatic matter dominated era changes the freeze-out dynamics, since the Hubble rate is pa…
A new U(1) gauge symmetry is the simplest extension of the Standard Model and has various theoretical and phenomenological motivations. In this paper, we study the cosmological constraint on the MeV scale dark photon. After the neutrino decoupling era at $T = \mathcal{O}(1)\,$MeV, the decay and annihilation of the dark photon heats up the electron and photon plasma and accordingly decreases the effective number of neutrino $N_{\mathrm{eff}}$ in the recombination era. We derive a conservative lower-limit of the dark photon mass around 8.5 MeV from the current Planck data if the mixing between t…
Relic Neutrinos Probing Small Scale Primordial Non-Gaussianity
Virtual Institute of Astroparticle Physics（虚拟高能天体物理研究所）；KEK Theory Center, Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK)（高能加速器研究机构粒子与核学研究所KEK理论中心）；Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University（名古屋大学小林-益川粒子宇宙起源研究所）；ICREA（加泰罗尼亚高级研究院）；Institute of Space Sciences (ICE-CSIC)（空间科学研究所（ICE-CSIC））；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院（IEEC））；Department of Physics and Astronomy, Vanderbilt University（范德堡大学物理与天文学系）
We study the possibility of keV neutrino dark matter in the minimal $U(1)_{B-L}$ gauge extension of the standard model where three right handed neutrinos are automatically included due to the requirement of anomaly cancellations. Without considering extra additional particles or symmetries, we consider the lightest right handed neutrino to be in the keV mass range which is kinematically long lived. Due to gauge interactions, such a keV neutrino can be thermally produced in the early Universe followed by decoupling while being relativistic. The final relic abundance of such keV neutrino typical…
If primordial black holes (PBHs) had come to dominate the energy density of the early Universe when oscillations in the axion field began, we show that the relic abundance and expected mass range of the QCD axion would be greatly modified. Since the QCD axion is a potential candidate for dark matter (DM), we refer to it as the DM axion. We predominantly explore PBHs in the mass range $(10^6 - 5\times 10^8)\,$g. We investigate the relation between the relic abundance of DM axions and the parameter space of PBHs. We numerically solve the set of Boltzmann equations, that governs the cosmological …
