On the viability of a certain vector-tensor theory of gravitation

Abstract

A certain vector-tensor theory is revisited. Our at tention is focused on cosmology. Against previous sugges tions based on preliminary studies, it is shown that, if the energy density of the vector field is large enough to play the role of the dark energy and its fluctuations are negligi ble, the theory is not simultaneously compatible with current observations on: supernovae, the cosmic microwave back ground (CMB) anisotropy, and the power spectrum of the energy density fluctuations. However, for small enough en ergy densities of the vector field and no scalar fluctuations, the theory becomes compatible with all the above observa tions and, moreover, it leads to an interesting evolution of the so-called vector cosmological modes. This evolution ap pears to be different from that of general relativity, and the difference might be useful to explain the anomalies in the low order CMB multipoles.