Dark energy can differ from a cosmological constant through either the evolution of its energy density or through coupling to ordinary matter, which results in a fifth force. Upcoming cosmological surveys will be able to constrain both effects at the largest scales, while stars and laboratory experiments already provide small-scale tests of coupled dark energy. My talk will consist of two parts. First, I describe ongoing work to understand the effects of dark energy on the formation of large-scale cosmic structure. Using higher-order perturbation theory as well as N-body simulations, I compare the cosmological constant to early dark energy, which has a rapidly varying equation of state. Though surveys will also probe scale-dependent growth due to fifth forces, we must first understand the effects of massive neutrinos on large-scale structure. Towards that end, I include massive neutrinos along with evolving dark energy in the Time-RG perturbation theory. Part II of my talk discusses my previous work using stars and laboratory experiments to constrain dark energy couplings to Standard Model particles. By considering f(R) gravities as scalar dark energy models, I show that chameleon screening stabilizes neutron stars in the strong-gravity regime and suppresses the scalar monopole radiation expected in variable stars. I demonstrate that the Eot-Wash torsion pendulum experiment excludes fifth forces predicted by a range of chameleon and symmetron models. Finally, I constrain dark energy couplings to photons, which allow for the production of dark energy particles.
Amol Upadhye (Argonne)