String freeze-out as dark energy

We model the transplanckian regime by introducing a I-parameter family of smooth non-linear dispersion relations which modify the frequencies at very short distances. The short-distance behaviour is motivated by T-duality. A particular feature of the family of dispersion functions chosen is the production of ultralow frequencies at very high momenta k (for k > M-P). We show that the range of modes with frequencies equal or less than the current Hubble rate H-0 which are still frozen today provides a strong candidate for the dark energy of the Universe.