Speaker: Marco Bruni
Location: Trieste Observatory
In this talk I will illustrate a simple alternative scenario to LCDM where, assuming general relativity, the vacuum can interact with CDM; when the interaction vanishes the vacuum becomes the cosmological constant. When the interaction is switched on, vacuum can be inhomogeneous and thus it affects the evolution of perturbations both through the background, which differs from LCDM, and directly through the perturbations. In this scenario there are no extra degrees of freedom, and the difference from LCDM is all encoded in the specific interaction one considers. Rather than choosing a specific model, we have adopted a purely phenomenological approach: using various datasets, CMB and redshift space distortion (RSD) in particular, we have parametrised the interaction in four redshift bins, asking the data to tell us if there is any interaction. In our preliminary analysis we found a significant indication for interaction at late time; we have then restricted the representation of this interaction vacuum scenario to the case where the interaction is restricted to the two bins at lower redshift, starting at z=0.9. We have found that this scenario greatly alleviates the tension between CMB and RSD that exists in LCDM, so that it performs better than the varying neutrino mass. I will end the talk with an outlook on further work to be done and related questions.