Cosmologically viable generalized Einstein-aether theories

We investigate generalized Einstein-aether theories that are compatible with the Planck cosmic microwave background (CMB) temperature anisotropy, polarization, and lensing data. For a given dark energy equation of state, wde, we formulate a designer approach and we investigate their impact on the CMB temperature anisotropy and matter power spectra. We use the equation of state approach to parametrize the perturbations and find that this approach is particularly useful in identifying the most suitable and numerically efficient parameters to explore in a Markov chain Monte Carlo analysis. We find the data constrains models with wde=-1 to be compatible with Λ cold dark matter (ΛCDM). For wde≠-1 models, which avoid the gravitational waves constraint through the entropy perturbation, we constrain wde to be wde=-1.06-0.03+0.08 (CMB) and wde=-1.04-0.02+0.05 (CMB+Lensing) at 68% C.L., and find that these models can be different from ΛCDM and still be compatible with the data. We also find that these models can ameliorate some anomalies in ΛCDM when confronted with data, such as the low- and high-k power in the CMB temperature anisotropy and matter power spectra respectively, but not simultaneously. We also investigate the anomalous lensing amplitude, quantified by Alens, and find that for wde=-1 models, Alens=1.15-0.08+0.07 (CMB) and Alens=1.12±0.05 (CMB+Lensing) at 68% C.L. ∼2σ larger than expected, similar to previous analyses of ΛCDM.