Signature of local motion in the microwave sky

First Constraints on the Intrinsic CMB Dipole and Our Velocity with Doppler and Aberration

We test the usual hypothesis that the cosmic microwave background (CMB) dipole, its largest anisotropy, is due to our peculiar velocity with respect to the Hubble flow by measuring independently the Doppler and aberration effects on the CMB using Planck 2018 data. We remove the spurious contributions from the conversion of intensity into temperature and arrive at measurements that are independent from the CMB dipole itself for both temperature and polarization maps and both SMICA and NILC component-separation methods. Combining these new measurements with the dipole one, we get the first constraints on the intrinsic CMB dipole. Assuming a standard dipolar lensing contribution, we can put an upper limit on the intrinsic amplitude: 3.7 mK (95% confidence interval). We estimate the peculiar velocity of the Solar System without assuming a negligible intrinsic dipole contribution: v=(300_{-93}^{+111})  km/s with (l,b)=(276±33,51±19)° (SMICA), and v=(296_{-88}^{+111})  km/s with (l,b)=(280±33,50±20)° (NILC) with negligible systematic contributions. These values are consistent with the peculiar velocity hypothesis of the dipole.

Proposal for a Real-Time Detection of our Acceleration through Space

Our proper acceleration with respect to the cosmic microwave background results in a real-time change of the angular position of distant extragalactic sources. The cosmological component of this aberration drift signal, the noninertial motion generated by the large-scale distribution of matter, can, in principle, be detected by future high-precision astrometric experiments. It will provide interesting consistency tests of the standard model of cosmology, set independent constraints on the amplitude of the Hubble constant and the linear growth rate of cosmic structures, and be instrumental in searching for evidence of new physics beyond the standard model. We present the formalism of this novel cosmological test, discuss the physics to which it is sensitive, and show simulated forecasts of the accuracy with which it can be implemented.

Beyond the Boost: Measuring the Intrinsic Dipole of the Cosmic Microwave Background Using the Spectral Distortions of the Monopole and Quadrupole

We present a general framework for the accurate spectral modeling of the low multipoles of the cosmic microwave background (CMB) as observed in a boosted frame. In particular, we demonstrate how spectral measurements of the low multipoles can be used to separate the motion-induced dipole of the CMB from a possible intrinsic dipole component. In a moving frame, the leakage of an intrinsic dipole moment into the CMB monopole and quadrupole induces spectral distortions with distinct frequency functions that, respectively, peak at 337 and 276 GHz. The leakage into the quadrupole moment also induces a geometrical distortion to the spatial morphology of this mode. The combination of these effects can be used to lift the degeneracy between the motion-induced dipole and any intrinsic dipole that the CMB might possess. Assuming the current peculiar velocity measurements, the leakage of an intrinsic dipole with an amplitude of ΔT=30  μK into the monopole and quadrupole moments will be detectable by a PIXIE-like experiment at ∼40  nK (2.5σ) and ∼130  nK (11σ) level at their respective peak frequencies.