Small-scale Cosmic Microwave Background Anisotropy Research Articles

LiteBIRD science goals and forecasts: a full-sky measurement of gravitational lensing of the CMB

We explore the capability of measuring lensing signals in LiteBIRD full-sky polarization maps. With a 30 arcmin beam width and an impressively low polarization noise of 2.16 μK-arcmin, LiteBIRD will be able to measure the full-sky polarization of the cosmic microwave background (CMB) very precisely. This unique sensitivity also enables the reconstruction of a nearly full-sky lensing map using only polarization data, even considering its limited capability to capture small-scale CMB anisotropies. In this paper, we investigate the ability to construct a full-sky lensing measurement in the presence of Galactic foregrounds, finding that several possible biases from Galactic foregrounds should be negligible after component separation by harmonic-space internal linear combination. We find that the signal-to-noise ratio of the lensing is approximately 40 using only polarization data measured over 80% of the sky. This achievement is comparable to Planck's recent lensing measurement with both temperature and polarization and represents a four-fold improvement over Planck's polarization-only lensing measurement. The LiteBIRD lensing map will complement the Planck lensing map and provide several opportunities for cross-correlation science, especially in the northern hemisphere.

Redshift-space fluctuations in stochastic gravitational wave background

We study the redshift-space fluctuations induced by a stochastic gravitational wave background (SGWB) via the Sachs-Wolfe effect. The redshift-space fluctuations can be encapsulated in a line-of-sight integral that is useful for studying the imprint of short-wavelength gravitational waves on the cosmic microwave background (CMB) anisotropy. We thus derive constraints on the SGWB from small-scale CMB anisotropy measurements. Our results reproduce the constraint on the short-wavelength SGWB, previously derived from the Planck and BICEP/Keck array CMB data with a CMB Boltzmann numerical code. Furthermore, we improve the constraint and extend it to shorter wavelengths by using the CMB measurements made by the Atacama Cosmology Telescope and the South Pole Telescope. Also, the integral provides us with a precise redshift fluctuation correlation between a pair of pulsars in pulsar timing measurements, which conveniently incorporates the effect of the pulsar term into a small-angle correlation. We further discuss the observation of pulsar pairs in globular clusters to look for this small-angle correlation.

Small-scale CMB anisotropies induced by the primordial magnetic fields

The primordial magnetic fields (PMFs) produced in the early universe are expected to be the origin of the large-scale cosmic magnetic fields. The PMFs are considered to leave a footprint on the cosmic microwave background (CMB) anisotropies due to both the electromagnetic force and gravitational interaction. In this paper, we investigate how the PMFs affect the CMB anisotropies on smaller scales than the mean-free-path of the CMB photons. We solve the baryon Euler equation with Lorentz force due to the PMFs, and we show that the vector-type perturbations from the PMFs induce the CMB anisotropies below the Silk scale as ℓ > 3000. Based on our calculations, we put a constraint on the PMFs from the combined CMB temperature anisotropies obtained by Planck and South Pole Telescope (SPT). We have found that the highly-resolved temperature anisotropies of the SPT 2017 bandpowers at ℓ ≲ 8000 favor the PMF model with a small scale-dependence. As a result, the Planck and SPT's joint-analysis puts a constraint on the PMF strength normalized on the co-moving 1 Mpc scale as B1Mpc < 1.5 nG with Planck and SPT at 95% C.L., while B1Mpc < 3.2 nG only with the Planck data at 95% C.L. We also discuss the effects on the cosmological parameter estimate when including the SPT data and CMB anisotropies induced by the PMFs.

Simulated reconstruction of the remote dipole field using the kinetic Sunyaev Zel’dovich effect

The kinetic Sunyaev Zel'dovich (kSZ) effect, cosmic microwave background (CMB) anisotropies induced by scattering from free electrons in bulk motion, is a primary target of future CMB experiments. Measurements of the kSZ effect have the potential to address fundamental questions about the structure and evolution of our Universe on the largest scales and at the earliest times. This potential is unlocked by combining measurements of small-scale CMB anisotropies with large-scale structure surveys, a technique known as kSZ tomography. Previous work established a quadratic estimator for the remote dipole field, the CMB dipole observed at different locations in the Universe. This previous work did not include gravitational lensing, redshift space distortions, or non-linear evolution of structure. In this paper, we investigate how well the remote dipole field can be reconstructed in the presence of such effects by using mock data from a suite of simulations. To properly model both large and small scales, we develop a novel box-in-box simulation pipeline, where small-scale information is obtained from N-body simulations, and large-scale information obtained by evolving fields using linear theory and adding the resulting corrections to the N-body particle data. This pipeline allows us to create properly correlated maps of the primary CMB including lensing, as well as the kSZ effect and density maps on the past light cone of an observer. Analyzing an ensemble of mocks, we find that the dipole field can be reconstructed with high fidelity over a range of angular scales and redshift bins, although there is evidence of excess power from nonlinear structure. We also analyze correlations with the primary CMB, investigating the ability of kSZ tomography to reconstruct the intrinsic CMB dipole. Our results constitute a proof-of-principle that kSZ tomography is a promising technique for future datasets.

Cosmic microwave background anisotropies from outflows in Lyman break galaxies

Abstract Thomson scattering of the cosmic microwave background (CMB) on moving electrons in the outflows of Lyman break galaxies (LBGs) at redshifts 2–8 contributes to the small-scale CMB anisotropies. The net effect produced by each outflow depends on its level of deviation from spherical symmetry, caused either by an anisotropic energy injection from the nuclear starburst or quasar activity, or by an inhomogeneous intergalactic environment. We find that for plausible outflow parameters consistent with spectroscopic observations of LBGs, the induced CMB anisotropies on arcminute scales reach up to ∼1 μK, comparable to the level produced during the epoch of reionization.

Constraints on the Evolution of the Primordial Magnetic Field from the Small‐Scale Cosmic Microwave Background Angular Anisotropy

Recent observations of the cosmic microwave background (CMB) have extended the measured power spectrum to higher multipoles $l\gtrsim$1000, and there appears to be possible evidence for excess power on small angular scales. The primordial magnetic field (PMF) can strongly affect the CMB power spectrum and the formation of large scale structure. In this paper, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last-scattering surface (PLSS). We then deduce an upper limit on the PMF based on our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_\lambda|\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small-scale CMB anisotropies from the $Wilkinson Microwave Anisotropy Probe$ (WMAP), the Cosmic Background Imager (CBI), and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF.

Extended self-similarity of the small-scale cosmic microwave background anisotropy

The extended self-similarity (ESS) of cosmic microwave background (CMB) radiation has been studied using recent data obtained by the space-craft based Wilkinson Microwave Anisotropy Probe. Using the ESS and the high angular scale resolution (arcminutes) of the data it is shown that the CMB temperature space increments exhibit considerable and systematic declination from Gaussianity for high order moments at the small angular scales. Moreover, the CMB space increment ESS exponents have remarkably close values to the ESS exponents observed in turbulence (in magnetohydrodynamic turbulence).

Constraints on Cosmological Parameters from the Lyα Forest Power Spectrum andCOBEDMR

We combine COBE DMR measurements of cosmic microwave background (CMB) anisotropy with a recent measurement of the mass power spectrum at redshift z = 2.5 from Lyα forest data to derive constraints on cosmological parameters and test the inflationary cold dark matter (CDM) scenario of structure formation. By treating the inflationary spectral index n as a free parameter, we are able to find successful fits to the COBE and Lyα forest constraints in Ωm = 1 models with and without massive neutrinos and in low-Ωm models with and without a cosmological constant. Within each class of model, the combination of COBE and the Lyα forest P(k) constrains a parameter combination of the form ΩmhαnβΩ, with different indices for each case. This new constraint breaks some of the degeneracies in cosmological parameter determinations from other measurements of large-scale structure and CMB anisotropy. The Lyα forest P(k) provides the first measurement of the slope of the linear mass power spectrum on ~Mpc scales, ν = -2.25 ± 0.18, and it confirms a basic prediction of the inflationary CDM scenario: an approximately scale invariant spectrum of primeval fluctuations (n ≈ 1) modulated by a transfer function that bends P(k) toward kn-4 on small scales. Considering additional observational data, we find that COBE-normalized, Ωm = 1 models that match the Lyα forest P(k) do not match the observed masses of rich galaxy clusters, and that low-Ωm models with a cosmological constant provide the best overall fit to the available data, even without the direct evidence for cosmic acceleration from Type Ia supernovae. With our fiducial parameter choices, the flat, low-Ωm models that match COBE and the Lyα forest P(k) also match recent measurements of small-scale CMB anisotropy. Modest improvements in the Lyα forest P(k) measurement could greatly restrict the allowable region of parameter space for CDM models, constrain the contribution of tensor fluctuations to CMB anisotropy, and achieve a more stringent test of the current consensus model of structure formation.

Cosmic Microwave Background Anisotropy Constraints on Open and Flat‐Λ Cold Dark Matter Cosmogonies from UCSB South Pole, ARGO, MAX, White Dish, and SuZIE Data

We use combinations of 10 small-scale cosmic microwave background anisotropy data sets from the UCSB South Pole 1994, ARGO, MAX 4 and 5, White Dish, and SuZIE experiments to constrain cosmogonies. We consider open and spatially flat-? cold dark matter cosmogonies with nonrelativistic mass density parameter ?0 in the range 0.1-1, baryonic mass density parameter ?B in the range 0.005-0.029 h-2, and age of the universe t0 in the range 10-20 Gyr. Marginalizing over all parameters but ?0, the combined data favor a ?01 (1) open (flat-?) model. Excluding the smallest angular scale SuZIE data, an ?00.3 (1) open (flat-?) model is favored. Considering only multifrequency data with error bars consistent with sample variance and noise considerations, i.e., the South Pole 1994 Ka band, the MAX 4 ? Draconis, and the MAX 5 HR5127 data, an ?00.1 (1) open (flat-?) model is favored. For both open and flat-? models and for all three combinations of data sets, after marginalizing over all other parameters, a lower ?Bh2 (~0.005) or younger (t0~10 Gyr) universe is favored. However, the data do not rule out other values of ?0 in the flat-? model and other values of ?Bh2 in both models. At 2 ? confidence, model normalizations deduced from the small-scale data are consistent with those derived from the Differential Microwave Radiometer data. We emphasize that since we consider only a small number of data sets, these results are tentative.

The Damping Tail of Cosmic Microwave Background Anisotropies

By decomposing the damping tail of cosmic microwave background (CMB) anisotropies into a series of transfer functions representing individual physical effects, we provide ingredients that will aid in the reconstruction of the cosmological model from small-scale CMB anisotropy data. We accurately calibrate the model-independent effects of diffusion and reionization damping, which provide potentially the most robust information on the background cosmology. Removing these effects, we uncover model-dependent processes, such as the acoustic peak modulation and gravitational enhancement, that can help distinguish between alternate models of structure formation and provide windows into the evolution of fluctuations at various stages in their growth.

Tentative Appraisal of Compatibility of Small-Scale Cosmic Microwave Background Anisotropy Detections in the Context of [ITAL]COBE[/ITAL]-DMR–normalized Open and Flat-Λ Cold Dark Matter Cosmogonies

Goodness-of-fit statistics are used to quantitatively establish the compatibility of cosmic microwave background (CMB) anisotropy predictions in a wide range of Differential Microwave Radiometer (DMR) normalized, open and spatially flat Λ, cold dark matter cosmogonies with the set of all presently available small-scale CMB anisotropy detection data. Conclusions regarding model viability depend sensitively on the prescription used to account for the 1 σ uncertainty in the assumed value of the DMR normalization, except for low-density, Ω0 ~ 0.3-0.4, open models, which are compatible with the data for all prescriptions used. While old, large baryon density, low-density, flat-Λ models (t0 15-16 Gyr, ΩB 0.0175 h-2, Ω0 ~ 0.2-0.4) might be incompatible, no model is incompatible with the data for all prescriptions. In fact, some open models seem to fit the data better than should be expected, and this might be an indication that some error bars are mildly overconservative.

'Sample variance' in small-scale cosmic microwave background anisotropy experiments

We discuss the effects of finite sky coverage and the uncertainty in extracting information about the power spectrum from experiments on small angular scales. In general the cosmic variance is enhanced by a factor of $4\pi/A$, where $A$ is the solid angle sampled by the experiment. As a rough guide, an experiment with sensitivity peaking at the $\ell$th multipole has to cover $\simgt\ell$ independent patches to have a lower ``sample variance'' than for a whole-sky measurement of the quadrupole. Our approach gives a relatively simple way of attaching an error bar to the theoretical prediction for a particular experiment, and thereby comparing theories with experimental results, without the need for computationally-intensive Maximum Likelihood or Monte Carlo calculations.