The main goal of this work is to calculate the contributions of bound-bound transitions of helium to the cosmological recombination spectrum. We show that helium in the early Universe causes unique ...features to appear in the total cosmological recombination spectrum. These may provide a unique observational possibility to determine the relative abundance of primordial helium, well before the formation of first stars. We include the effect of the tiny fraction of neutral hydrogen atoms on the dynamics of He II $\rightarrow$ He I recombination at redshifts z ~ 2500. As discussed recently, this process significantly accelerates He II $\rightarrow$ He I recombination, resulting in rather narrow and distinct features in the associated recombination spectrum. In addition this process induces some emission within the hydrogen Lyman-α line, before the actual epoch of hydrogen recombination around z ~ 1100-1500. We also show that some of the fine-structure transitions of neutral helium appear in absorption, again leaving unique traces in the cosmic microwave background blackbody spectrum, which may allow confirmation of our understanding of the early Universe and of detailed atomic physics.
The recombination history of the Universe depends exponentially on the temperature, T sub(0), of the cosmic microwave background. Therefore tiny changes of T sub(0) are expected to lead to ...significant changes in the free electron fraction. Here we show that even the current 1\sigma- uncertainty in the value of T sub(0) results in more than half a percent ambiguity in the ionization history, and more than 0.1\% uncertainty in the TT and EE power spectra at small angular scales. We discuss how the value of T sub(0) affects the highly redshifted cosmological hydrogen recombination spectrum and demonstrate that T sub(0) could, in principle, be measured by looking at the low frequency distortions of the cosmic microwave background spectrum. For this no absolute measurements are necessary, but sensitivities on the level of 30\,nK are required to extract the quasi-periodic frequency-dependent signal with typical Delta nu/\nu\sim 0.1 coming from cosmological recombination. We also briefly mention the possibility of obtaining additional information on the specific entropy of the Universe, and other cosmological parameters.
Here we treat possible perturbative fluctuations in the free electron fraction, X sub(e)(z), by a semi-blind expansion in densely packed modes in redshift. From these we construct parameter ...eigenmodes, which we rank order so that the lowest modes provide the most power to probe X sub(e)(z) with CMB measurements. We use an information-based criterion to truncate the mode hierarchy and show that with even a few modes the method goes a long way from the fiducial recombination model computed with RECFAST, X sub(e,i)(z), toward the precise underlying history given by the new and improved recombination calculations of COSMOREC or HYREC, X sub(e,f)(z), in the hydrogen recombination regime, though not well in the helium regime. We also introduce control parameters that downweight the attention on the visibility peak structure, e.g., focusing the eigenmode probes more strongly on the Xe(z) freezeout tail, as would be appropriate when looking for the X sub(e) signature of annihilating or decaying elementary particles.
For the simplest inflation models, the recent detection of a large primordial B-mode polarization signal by the BICEP2 experiment indicates a slight tension with the upper limit on the ...tensor-to-scalar ratio, r, from the Planck satellite. Here, we discuss spatially varying r as a possible explanation for this discrepancy. This idea seems attractive since it may also explain part of the hemispherical temperature power asymmetry seen by Wilkinson Microwave Anisotropy Probe and Planck at large angular scales. If these two aspects are indeed connected, the model suggests that in the Northern hemisphere r should be much smaller, a hypothesis that could be confirmed with future B-mode experiments, providing a test for the stationarity of primordial tensor contributions across the sky. The BICEP2 measurement furthermore rules out that a simple dipolar modulation of r alone can be responsible for the full hemispherical power asymmetry.
Future high-resolution, high-sensitivity Sunyaev-Zeldovich (SZ) observations of individual clusters will allow us to study the dynamical state of the intracluster medium (ICM). To exploit the full ...potential of this new observational window, it is crucial to understand the origin of different contributions to the total SZ signal. Here, we investigate the signature caused by multiple scatterings at lowest order of the electron temperature. Previous analytic discussions of this problem used the isotropic scattering approximation, which even for the simplest cluster geometries is rather rough. We take a step forward and consistently treat the anisotropy of the ambient radiation field caused by the first scattering. We show that the multiple scattering SZ signal directly probes line-of-sight anisotropies of the ICM, thereby delivering a new set of SZ observables which could be used for 3D cluster-profile reconstruction. The multiple scattering signal should furthermore correlate spatially with the cluster's X-ray and SZ polarization signals, an effect that could allow enhancing the detectability of this contribution.
The CMB angular temperature fluctuations observed by COBE and WMAP enable us to place a lower limit on the spectral distortions of the CMB at any angular scale. These distortions are connected with ...the simple fact that the superposition of blackbodies with different temperatures in general is not a blackbody. We show that in the limit of small temperature fluctuations the superposition of blackbodies leads to a y-type spectral distortion. It is known that the CMB dipole induces a y-type spectral distortion with quadrupole and monopole angular distribution leading to a corresponding whole sky y-parameter of y sub(d) = 2.6 x 10 super(-7). We show here that taking the difference of the CMB signal in the direction of the maximum and minimum of the CMB dipole due to the superposition of two blackbodies leads to a spectral distortion with y sub(opt) = 12 y sub(d) = 3.1 x 10 super(-6). The amplitude of this distortion can be calculated to the same precision as the CMB dipole, i.e. 0.3% today. Therefore it may be used as a source with brightness of several or tens of mu K to cross calibrate and calibrate different frequency channels of CMB surveys with a precision of a few tens or hundreds of nK. We also discuss clusters of galaxies as possible sources for calibration purposes. Furthermore, we show in this work that primordial anisotropies for multipoles 2 less than or equal to l less than or equal to 1000 also lead to spectral distortions but with a much smaller y-parameter, i.e. y similar to 10 super(-11)-10 super(-9).
In this paper, we consider the reprocessing of high-frequency photons emitted by He ii and He i during the epoch of cosmological recombination by He i and H i. We demonstrate that, in comparison to ...computations which neglect all feedback processes, the number of cosmological recombination photons that are related to the presence of helium in the early Universe could be increased by ∼40–70 per cent. Our computations imply that per helium nucleus ∼3–6 additional photons could be produced. Therefore, a total of ∼12–14 helium-related photons per helium atom are emitted during cosmological recombination. This is an important addition to cosmological recombination spectrum which in the future may render it slightly easier to determine the primordial abundance of helium using differential measurements of the cosmic microwave background (CMB) energy spectrum. Also, since these photons are the only witnesses of the feedback process at high redshift, observing them in principle offers a way to check our understanding of the recombination physics. Here, most interestingly, the feedback of He ii photons on He i leads to the appearance of several additional, rather narrow spectral features in the He i recombination spectrum at low frequencies. Consequently, the signatures of helium-related features in the CMB spectral distortion from cosmological recombination at some given frequency can exceed the average level of ∼17 per cent several times. We find that in particular the bands around ν∼ 10, ∼35, ∼80 and ∼200 GHz seem to be affected strongly. In addition, we computed the changes in the cosmological ionization history, finding that only the feedback of primary He i photons on the dynamics of He ii→ He i recombination has an effect, producing a change of ΔNe/Ne∼+0.17 per cent at z∼ 2300. This result seems to be ∼2–3 times smaller than the one obtained in earlier computations for this process, however, the difference will not be very important for the analysis of future CMB data.
class_sz I: Overview Bolliet, B.; Kusiak, A.; McCarthy, F. ...
EPJ Web of conferences,
2024, Letnik:
293
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
class_sz is a versatile, robust and efficient code, in C and Python, optimized to compute theoretical predictions for a wide range of observables relevant to cross-survey science in the Stage IV era. ...The code is public at https://github.com/CLASS-SZ/class_sz along with a series of tutorial notebooks ( https://github.com/CLASS-SZ/notebooks ). It will be presented in full detail in paper II. Here we give a brief overview of key features and usage.
In this letter we compute the emission coming from the direct recombination of free electrons to a given shell ($n\geq 2$) during the epoch of cosmological hydrogen recombination. This contribution ...leads to a total of one photon per recombined hydrogen atom and therefore a ~$30{-}88\%$ increase in the recombination spectrum within the frequency range $1~{\rm GHz}\leq \nu \leq 100~{\rm GHz}$. In particular, the Balmer-continuum emission increases the distortion at $\nu\sim 690$ GHz by roughly $92\%$. With our 100 shell calculations for the hydrogen atom, we find that a total of ~5 photons per hydrogen atom are emitted when including all the bound-bound transitions, the 2s two-photon decay channel, and the optically thin free-bound transitions. Since the direct recombination continuum at high n is very broad, only a few n-series continuua are distinguishable and most of this additional emission below $\nu\la 30$ GHz is completely featureless.
We use our most recent training set for the rico code to estimate the impact of recombination uncertainties on the posterior probability distributions which will be obtained from future cosmic ...microwave background experiments, and in particular the Planck satellite. Using a Monte Carlo Markov Chain (MCMC) analysis to sample the posterior distribution of the cosmological parameters, we find that Planck will have biases of −0.7, −0.3 and −0.4σ for nS, Ωbh2 and log(1010AS), respectively, in the minimal six-parameter Λ cold dark matter model, if the description of the recombination history given by rico is not used. The remaining parameters (e.g. τ or Ωdmh2) are not significantly affected. We also show that the cosmology dependence of the corrections to the recombination history modelled with rico has a negligible impact on the posterior distributions obtained for the case of the Planck satellite. In practice, this implies that the inclusion of additional corrections to existing recombination codes can be achieved using simple cosmology-independent ‘fudge functions’. Finally, we also investigated the impact of some recent improvements in the treatment of hydrogen recombination which are still not included in the current version of our training set for rico, by assuming that the cosmology dependence of those corrections can be neglected. In summary, with our current understanding of the complete recombination process, the expected biases in the cosmological parameters inferred from Planck might be as large as −2.3, −1.7 and −1σ for nS, Ωbh2 and log(1010AS), respectively, if all those corrections are not taken into account. We note that although the list of physical processes that could be of importance for Planck seems to be nearly complete, still some effort has to be put into the validation of the results obtained by the different groups. The new rico training set as well as the fudge functions used for this paper are publicly available on the rico webpage.
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