Moving dark energy and the CMB dipole

Abstract

We explore the possibility that the rest frames of CMB, matter and dark energy differ one from another, i.e. they do not converge on very large scales. In such a case, the usual interpretation of the CMB dipole as being due to the relative motion of the observer with respect to the CMB rest frame is not appropriate. Instead, we find that the measured dipole is due to the observer motion relative to the cosmic center of mass rest frame. This means, in particular, that even an observer at rest with respect to the CMB radiation could measure a non-vanishing dipole anisotropy, provided dark energy is moving with respect to the CMB. We also consider the consequences of moving dark energy for the determination of cosmic bulk flows.