Acceleressence: dark energy from a phase transition at the seesaw scale

Simple models are constructed for 'acceleressence' dark energy: the latent heat of a phase transition occurring in a hidden sector governed by the seesaw mass scale v(2)/M-Pl, where v is the electroweak scale and M-Pl the gravitational mass scale. In our models, the seesaw scale is stabilized by supersymmetry, implying that the LHC must discover superpartners with a spectrum that reflects a low scale of fundamental supersymmetry breaking. Newtonian gravity may be modified by effects arising from the exchange of fields in the acceleressence sector whose Compton wavelengths are typically of order the millimetre scale. There are two classes of models. In the first class the universe is currently in a metastable vacuum and will continue to in. ate until tunnelling processes eventually induce a first-order transition. In the simplest such model, the range of the new force is bounded to be larger than 25 mum in the absence of fine-tuning of parameters, and for couplings of order unity it is expected to be approximate to100 mum. In the second class of models thermal effects maintain the present vacuum energy of the universe, but on further cooling, the universe will 'soon' smoothly relax to a matter dominated era. In this case, the range of the new force is also expected to be of order the millimetre scale or larger, although its strength is uncertain. A firm prediction of this class of models is the existence of additional energy density in radiation at the eV era, which can potentially be probed in precision measurements of the cosmic microwave background. An interesting possibility is that the transition towards a matter dominated era has occurred in the very recent past, with the consequence that the universe is currently decelerating.