The standard theoretical description $Θ(\hat n)$ of the observed CMB temperature anisotropies is gauge-dependent. It is, however, well known that the gauge mode is limited to the monopole and the higher angular multipoles $Θ_l$ ($l\geq1$) are gauge-invariant. Several attempts have been made in the past to properly define the monopole fluctuation, but the resulting values of the monopole power $C_0$ are infinite due to the infrared divergences. The infrared divergences arise from the contribution of the uniform gravitational potential to the monopole fluctuation, in violation of the equivalence principle. Here we present the gauge-invariant theoretical description of the observed CMB temperature anisotropies and compute the monopole power $C_0=1.66\times10^{-9}$ in a $Λ$CDM model. While the gauge-dependence in the standard calculations originates from the ambiguity in defining the hypersurface for the background CMB temperature $\bar T$ today, it is in fact well defined and one of the fundamental cosmological parameters. We argue that once the cosmological parameters are chosen, the monopole fluctuation can be unambiguously inferred from the angle-average of the observed CMB temperature, making it a model-dependent ''observable''. Adopting simple approximations for the anisotropy formation, we derive a gauge-invariant analytical expression for the observed CMB temperature anisotropies to study the CMB monopole fluctuation and the cancellation of the uniform gravitational potential contributions on large scales.
The cosmic microwave background (CMB) monopole temperature evolves with the inverse of the cosmological scale factor, independent of many cosmological assumptions. With sufficient sensitivity, real-time cosmological observations could thus be used to measure the local expansion rate of the Universe using the cooling of the CMB. We forecast how well a CMB spectrometer could determine the Hubble constant via this method. The primary challenge of such a mission lies in the separation of Galactic and extra-Galactic foreground signals from the CMB at extremely high precision. However, overcoming th…
The hot gas in clusters of galaxies creates a distinctive spectral distortion in the cosmic microwave background (CMB) via the Sunyaev-Zel'dovich (SZ) effect. The spectral signature of the SZ can be used to measure the CMB temperature at cluster redshift ($T_{\rm CMB}(z)$) and to constrain the monopole of the y-type spectral distortion of the CMB spectrum. In this work, we start showing the measurements of $T_{\rm CMB}(z)$ for a sample extracted from the Second Catalog of galaxy clusters produced by Planck (PSZ2) and containing 75 clusters selected from CHEX-MATE. Then we show the forecasts fo…
The observer peculiar motion produces boosting effects in the background anisotropies with frequency spectral behaviours related to its spectrum. We study how the frequency spectrum of the background isotropic monopole emission is modified and transferred to the frequency spectra at higher multipoles, l. We perform the analysis in terms of spherical harmonic expansion up to a certain lmax, for various models from radio to far-IR. We derive a system of linear equations to obtain spherical harmonic coefficients and provide explicit solutions up to lmax=6 as linear combinations of the signals at …
We study the effects of pre-recombination physics on the Stochastic Gravitational Wave Background (SGWB) anisotropies induced by the propagation of gravitons through the large-scale density perturbations and their cross-correlation with Cosmic Microwave Background (CMB) temperature and E-mode polarization ones. As examples of Early Universe extensions to the $Λ$CDM model, we consider popular models featuring extra relativistic degrees of freedom, a massless non-minimally coupled scalar field, and an Early Dark Energy component. Assuming the detection of a SGWB, we perform a Fisher analysis to …
The quantity $T_0$, the cosmic microwave background (CMB) monopole, is an often neglected seventh parameter of the standard cosmological model. As well as its variation affecting the physics of the CMB, the measurement of $T_0$ is also used to calibrate the anisotropies, via the orbital dipole. We point out that it is easy to misestimate the effect of $T_0$ because the CMB anisotropies are conventionally provided in temperature units. In fact the anisotropies are most naturally described as dimensionless and we argue for restoring the convention of working with $ΔT/T$ rather than $ΔT$. As a fr…
Our velocity relative to the cosmic microwave background (CMB) generates a dipole from the CMB monopole, which was accurately measured by COBE. The relative velocity also modulates and aberrates the CMB fluctuations, generating a small signature of statistical isotropy violation in the covariance matrix. This signature was first measured by Planck 2013. Galaxy surveys are similarly affected by a Doppler boost. The dipole generated from the number count monopole has been extensively discussed, and measured (at very low accuracy) in the NVSS and TGSS radio continuum surveys. For the first time, …
How Dilatation Invariance Suppresses Loop Corrections to Curvature Perturbations on CMB Scales
Kyoto University（京都大学）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；The University of Tokyo（东京大学）；Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）；The Graduate University for Advanced Studies (SOKENDAI)（综合研究大学院大学）
We discuss the possibility that the observed low-order multipole features of the cosmic microwave background radiation (CMB) all originate in the termination shock (TS) region of the heliosheath that surrounds the solar system. If the intrinsic CMB spectrum is assumed to be a pure monopole (2.73K) then thermodynamic processes occurring within the plasma region of the TS could imprint the observed power spectrum of the low-order multipoles and their alignment (the so-called "axis of evil") onto this background isotropic CMB. Conditions are outlined for the geometric shape of the TS region. A ke…
We evaluate the degradation of the accuracy of the component separation between the cosmic microwave background (CMB) and foreground components caused by neglect of absorption of the monopole component of the CMB by the galactic interstellar matter. The amplitude of the temperature anisotropy caused by the CMB shadow, due to dust components, is about 1 uK. This value is comparable to the required noise level necessary to probe non-Gaussianity studies with upcoming CMB experiments. In addition, the amplitude of the polarization caused by the CMB shadow due to dust is comparable to or larger tha…
The method of weighted addition of multi-frequency maps, more commonly referred to as {\it Internal Linear Combination} (ILC), has been extensively employed in the measurement of cosmic microwave background (CMB) anisotropies and its secondaries along with similar application in 21cm data analysis. Here we argue and demonstrate that ILC methods can also be applied to data from absolutely-calibrated CMB experiments to extract average-sky signals in addition to the conventional CMB anisotropies. The performance of the simple ILC method is, however, limited, but can be significantly improved by a…
Mixing of blackbodies: Increasing our view of inflation to 17 e-folds with spectral distortions from Silk damping
在复合之前和复合过程中，早期宇宙中的丝绸阻尼消除了小尺度上宇宙微波背景（CMB）的各向异性。这种从各向异性中消失的功率出现在晶体管中，如y型、i型和μ型失真。因此，对CMB频谱畸变的观测将使我们能够获得关于原始功率谱的信息，其尺度对应于同向运动波数$8< k < 10^4 Mpc^{-1}$，当与CMB各向异性相结合时，增加了我们对暴胀的总体看法，跨越17个e折叠。这些畸变可以简单地理解为不同温度的黑体的混合和随后的所产生的畸变的康普顿化。
We propose that several of the anomalies that have been observed at large angular scales in the CMB have a common origin in a cosmic bounce that took place before the inflationary era. The bounce introduces a new physical scale in the problem, which breaks the almost scale invariance of inflation. As a result, the state of scalar perturbations at the onset of inflation is no longer the Bunch-Davies vacuum, but it rather contains excitations and non-Gaussianity, which are larger for infrared modes. We argue that the combined effect of these excitations and the correlations between CMB modes and…
The presence of a light vector field coupled to a scalar field during inflation makes a distinct prediction: the observed correlation functions of the cosmic microwave background (CMB) become statistically anisotropic. We study the implications of the current bound on statistical anisotropy derived from the Planck 2013 CMB temperature data for such a model. The previous calculations based on the attractor solution indicate that the magnitude of anisotropy in the power spectrum is proportional to $N^2$, where $N$ is the number of $e$-folds of inflation counted from the end of inflation. In this…
