In this paper we discuss the effect of recombinations to highly excited states (n > 100) in hydrogen during the cosmological recombination epoch. For this purpose, we developed a new ODE solver for the recombination problem, based on an implicit Gear's method. This solver allows us to include up to 350 l-resolved shells or ~61 000 separate levels in the hydrogen model and to solve the recombination problem for one cosmology in ~27 hours. This is a huge improvement in performance over our previous recombination code, for which a 100-shell computation (5050 separate states) already required ~150 hours on a single processor. We show that for 350 shells down to redshift z ~200 the results for the free electron fraction have practically converged. The final modification in the free electron fraction at z ~200 decreases from about \DeltaNe/Ne ~2.8% for 100 shells to \DeltaNe/Ne ~1.6% for 350 shells. However, the associated changes in the CMB power spectra at large multipoles l are rather small, so that for accurate computations in connection with the analysis of Planck data already ~100 shells are expected to be sufficient. Nevertheless, the total value of τcould still be affected at a significant level. We also briefly investigate the effect of collisions on the recombination dynamics. With our current estimates for the collisional rates we find a correction of \DeltaNe/Ne ~ -0.088% at z ~ 700, which is mainly caused by l-changing collisions with protons. Furthermore, we present results on the cosmological recombination spectrum, showing that at low frequencies collisional processes are important. However, the current accuracy of collisional rates is insufficient for precise computations of templates for the recombination spectrum at ν<~1 GHz, and also the effect of collisions on the recombination dynamics suffers from the uncertainty in these rates.
We discuss the evolution of the ratio in number of recombinations due to 2s two photon escape and due to the escape of Lyman-$α$ photons from the resonance during the epoch of cosmological recombination, within the width of the last scattering surface and near its boundaries. We discuss how this ratio evolves in time, and how it defines the profile of the Lyman-$α$ line in the spectrum of CMB. One of the key reasons for explaining its time dependence is the strong overpopulation of the 2p level relative to the 2s level at redshifts $z \la 750$.
Energy-conserving, angular momentum-changing collisions between protons and highly excited Rydberg hydrogen atoms are important for precise understanding of atomic recombination at the photon decoupling era, and the elemental abundance after primordial nucleosynthesis. Early approaches to $\ell$-changing collisions used perturbation theory for only dipole-allowed ($Δ\ell=\pm 1$) transitions. An exact non-perturbative quantum mechanical treatment is possible, but it comes at computational cost for highly excited Rydberg states. In this note we show how to obtain a semi-classical limit that is a…
Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He I spectrum are needed to determine the primordial helium abundance to a precision of $< 1$% in order to constrain Big Bang Nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H I, we showed that differences in $l$-changing collisional rate coefficients predicted by three different theories can translate into 10% changes in predictions for H I spectra. Here we consi…
Dynamo action at recombination epoch of open Friedmann universe spatial sections
Chicone等人[Comm Math Phys（1997）]通过分析频谱运动学磁发电机研究了快速发电机的存在性。在谱的实非退化分支中，运动发电机算子位于具有常负曲率的紧致黎曼二维空间上。在这里，Marklund和Clarkson [MNRAS（2005）]的推广，广义相对论GR-MHD发电机方程，包括平均场发电机。在动力学螺旋度不存在的情况下，绝热常数$γ={1/2}$和空间截面负黎曼曲率的引力坍缩增强了发电机效应$\frac{δB}{B}=2.6\times 10^{-1}$。线性发电机效应分解为曲率的临界时间。在复合时，COBE温度各向异性，意味着磁场增长率为$λ{\approx{10}^{-9}yr^{-1}}$。这就限制了曲率，直到复合磁场通过发电机作用被放大到当前值$B_{0}=10^{-9}G$。目前，负曲率已变为常数，这一结果在宇宙学中是有效的。由于负曲率是非常数的，因此绕过了Hilbert定理，该定理禁止负常曲率曲面嵌入$\textbf{R}^{3}$。
Many quintessence models possess scaling or attractor solutions where the fraction of dark energy follows the dominant component in previous epochs of the expansion, or phase transitions may happen close to matter-radiation equality time. A non-negligible early dark energy (EDE) fraction around matter-radiation equality could contribute to alleviate the $H_0$ tension. We constrain the EDE fraction using two approaches: first, we use a fluid parameterization that mimics the plateaux of the dominant components in the past. An alternative tomographic approach constrains the EDE density in binned …
Density inhomogeneity in the intergalactic medium (IGM) can boost the recombination rate of ionized gas substantially, affecting the growth of HII regions during reionization. Previous attempts to quantify this effect typically failed to resolve down to the Jeans scale in the pre-ionization IGM, which is important in establishing this effect, along with the hydrodynamical back-reaction of reionization on it. Towards that end, we perform a set of fully-coupled, radiation-hydrodynamics simulations from cosmological initial conditions, extending the mass resolution of previous work to the scale o…
Decaying cold dark matter (CDM) has been considered as a mechanism to tackle the tensions in the Hubble expansion rate and the clustering of matter. However, polarization measurements of the cosmic microwave background (CMB) severely constrain the fraction of dark matter decaying before recombination, and lensing of the CMB anisotropies by large-scale structure set strong constraints on dark matter decaying after recombination. Together, these constraints make an explanation of the Hubble tension in terms of decaying dark matter unlikely. In response to this situation, we investigate whether a…
Effects of pair freeze-out on photon distributions in BBN epoch
Ulsan National Institute of Science and Technology (UNIST)（蔚山科学技术院）；Soongsil University（崇实大学）；Incheon National University（仁川国立大学）；Hongik University（弘益大学）；Ewha Womans University（梨花女子大学）；Kyungpook National University（庆北国立大学）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究所）
The origin of cosmic magnetic fields is an unsolved problem and magnetogenesis could have occurred in the early Universe. We study the evolution of such primordial magnetic fields across the cosmological recombination epoch via 3D magnetohydrodynamic numerical simulations. We compute the effective or net heating rate of baryons due to decaying magnetic fields and its dependence on the magnetic field strength and spectral index. In the drag-dominated regime ($z \gtrsim 1500$), prior to recombination, we find no real heating is produced. Our simulations allow us to smoothly trace a new transitio…
Dynamics of Dark Matter in Baryon-Radiation Plasma: Perspectives using Meschersky equation
为了论证冷暗物质在平等和复合时期之间的真正无碰撞性质，我们假设了一个模型，其中强耦合重子辐射等离子体从集中的冷暗物质的小区域中喷出而不失去其平衡。我们使用Meschersky方程来描述冷暗物质在不同质量的强耦合重子辐射等离子体中的动力学。基于这个模型，我们讨论了在金斯理论和膨胀宇宙中冷暗物质中微扰的增长。我们看到了冷暗物质势的扰动对宇宙微波背景各向异性的影响，这些各向异性起源于相等和复合之间的红移，即$1100 < z < z_{eq}$。我们还得到了冷暗物质势扰动下的Sachs-Wolfe效应，即退耦时CMB温度各向异性的表达式。我们得到了类似的解决方案，在静态和膨胀的宇宙，时代的重组。由此，我们推断出暗能量开始占主导地位的时间尺度。
The recent EDGES measurements of the global 21-cm signal from the cosmic dawn suggest that the kinetic temperature of the inter-galactic medium (IGM) might be significantly lower compared to its expected value. The colder IGM directly affects the hydrogen recombination of the universe during the cosmic dawn and dark ages by enhancing the rate of recombinations. Here, we study and quantify, the impact of the colder IGM scenario on the recombination history of the universe in the context of DM-baryonic interaction model which is widely used to explain the depth of the EDGES 21-cm signal. We find…
The cosmological coincidences between the matter and radiation energy densities at recombination as well as between the densities of matter and the cosmological constant at present time are well known. We point out that moreover the third intersection between the energy densities of radiation and the cosmological constant coincides with the reionization epoch. To quantify the statistical relevance of this concurrence, we compute the Bayes factor between the concordance cosmology with free Thomson scattering optical depth and a model for which this parameter is inferred from imposing a match be…
The baryon acoustic oscillations (BAO) have proven to be an invaluable tool in constraining the expansion history of the Universe at late times and are characterized by the comoving sound horizon at the baryon drag epoch $r_\mathrm{s}(z_\mathrm{d})$. The latter quantity can be calculated either numerically using recombination codes or via fitting functions, such as the one by Eisenstein and Hu (EH), made via grids of parameters of the recombination history. Here we quantify the accuracy of these expressions and show that they can strongly bias the derived constraints on the cosmological parame…
We use a set of 3D radiative transfer simulations to study the effect that a large fraction of binary stars in galaxies during the epoch of reionization has on the physical properties of the intergalactic medium (i.e. the gas temperature and the ionization state of hydrogen and helium), on the topology of the ionized bubbles and on the 21 cm power spectra. Consistently to previous literature, we find that the inclusion of binary stars can speed up the reionization process of HI and HeI, while HeII reionization is still dominated by more energetic sources, especially accreting black holes. The …
We compare the results of the semi-classical (SC) and quantum-mechanical (QM) formalisms for angular-momentum changing transitions in Rydberg atom collisions given by Vrinceanu & Flannery, J. Phys. B 34, L1 (2001), and Vrinceanu, Onofrio & Sadeghpour, ApJ 747, 56 (2012), with those of the SC formalism using a modified Monte Carlo realization. We find that this revised SC formalism agrees well with the QM results. This provides further evidence that the rates derived from the QM treatment are appropriate to be used when modelling recombination through Rydberg cascades, an important process in u…
Line Intensity Mapping Prediction from the Cosmic Dawn (CoDa) III Simulation for H$α$ from Galaxies and the Intergalactic Medium during the Epoch of Reionization
Large-scale peculiar motions are commonplace in our universe. Nevertheless, their origin, evolution and implications are still largely unknown. It is generally assumed that bulk motions are a relatively recent addition to the universal kinematics, triggered by the increasing inhomogeneity and anisotropy of the post-recombination epoch. In this work, we focus on the linear evolution of peculiar velocities prior to recombination, namely in the late radiation era and also during a phase of de Sitter inflation. We begin by showing/confirming that bulk motions are triggered and sustained by the non…
