| dc.description.abstract | The beyond-Horndeski gravity has recently been reformulated in the dark energy
paradigm — which has been dubbed, Unified Dark Energy (UDE). The evolution equations
for the given UDE appear to correspond to a non-conservative dark energy scenario, in which
the total energy-momentum tensor is not conserved. We investigate both the background
cosmology and, the large-scale imprint of the UDE by probing the angular power spectrum
of galaxy number counts, on ultra-large scales; taking care to include the full relativistic corrections in the observed overdensity. The background evolution shows that only an effective
mass smaller than the Planck mass is needed in the early universe in order for predictions
in the given theory to match current observational constraints. We found that the effective
mass-evolution-rate parameter, which drives the evolution of the UDE, acts to enhance the
observed power spectrum and, hence, relativistic effects (on ultra-large scales) by enlarging
the UDE sound horizon. Conversely, both the (beyond) Horndeski parameter and the kineticity act to diminish the observed power spectrum, by decreasing the UDE sound horizon. Our
results show that, in a universe with UDE, a multi-tracer analysis will be needed to detect the
relativistic effects in the large-scale structure. In the light of a multi-tracer analysis, the various relativistic effects hold the potential to distinguish different gravity models. Moreover,
while the Doppler effect will remain significant at all epochs and, thus can not be ignored,
the integrated Sachs-Wolfe, the time-delay and the potential (difference) effects, respectively,
will only become significant at epochs near z = 3 and beyond, and may be neglected at late
epochs. In the same vein, the Doppler effect alone can serve as an effective cosmological probe
for the large-scale structure or gravity models, in the angular power spectrum — at all z. | en_US |
