Abstract

A particle detector undergoing stationary motion has a time-independent response. Well-known examples are inertial motion (no response) and constant proper acceleration (thermal response due to Unruh effect), but there are four other types of stationary motion. One is ``acceleration with drift’’, which is realized by a detector moving with constant velocity in a plane parallel to the horizon of a static black brane. The local temperature on the plane is uniform so, by restricting the angular response to directions within the plane, one has a model for inertial motion in a heatbath.

The standard theory of motion in a radiation heatbath is due to Pauli and Peebles & Wilkinson, and others. It is based on a photon gas model and amounts to an application of the relativistic Doppler shift. This is used to subtract from the CMB measurements a dipole term due to our motion relative to the CMB rest frame.

Using the ``acceleration with drift’’ method, one finds a frequency-dependent dipole that agrees with the standard theory at high frequencies but not at low frequencies. The possible origin of this discrepancy will be discussed.