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- Classical and quantum cosmology of the little rip abrupt eventPublication . Albarran, Imanol; Bouhmadi Lopez, Mariam; Kiefer, Claus; Marto, João; Moniz, PauloWe analyze from a classical and quantum point of view the behavior of the universe close to a little rip, which can be interpreted as a big rip sent towards the infinite future. Like a big rip singularity, a little rip implies the destruction of all bounded structure in the Universe and is thus an event where quantum effects could be important. We present here a new phantom scalar field model for the little rip. The quantum analysis is performed in quantum geometrodynamics, with the Wheeler-DeWitt equation as its central equation. We find that the little rip can be avoided in the sense of the DeWitt criterion, that is, by having a vanishing wave function at the place of the little rip. Therefore our analysis completes the answer to the question: can quantum cosmology smoothen or avoid the divergent behavior genuinely caused by phantom matter? We show that this can indeed happen for the little rip, similar to the avoidance of a big rip and a little sibling of the big rip.
- A varying dark energy effective speed of sound parameter in the phantom UniversePublication . Albarran, Imanol; Bouhmadi Lopez, Mariam; Marto, JoãoWe analyse the phenomenological effects of a varying Dark Energy (DE) effective speed of sound parameter, c2sd, on the cosmological perturbations of three phantom DE models. Each of these models induce a particular abrupt future event known as Big Rip (BR), Little Rip (LR), and Little Sibling of the Big Rip (LSBR). In this class of abrupt events, all the bound structures in the Universe would be ripped apart at a finite cosmic time. We compute the evolution of the perturbations, fσ8 growth rate and forecast the current matter power spectrum. We vary the c2sd parameter in the interval [0, 1] and compute the relative deviation with respect c2sd=1. In addition, we analyse the effect of gravitational potential sign flip that occurs at very large scale factors as compared with the current one.