Evidence for anisotropy of cosmic acceleration

Observations reveal a bulk flow in the local Universe which is faster and extends to much larger scales than are expected around a typical observer in the standard Lambda CDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Light-curve Analysis catalogue of Type Ia supernovae, we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the cosmic microwave background dipole, which falls exponentially with redshift z: q(0) = q(m) + q(d).(n) over cap exp(-z/S). The best fit to data yields q(d) = -8.03 and S = 0.0262 (double right arrow d similar to 100 Mpc), rejecting isotropy (q(d) = 0) with 3.9 sigma statistical significance, while q(m) = 0.157 and consistent with no acceleration (q(m) = 0) at 1.4 sigma. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of dark energy in the Universe.