Speaker
Description
The description of gravity, i.e. the theory of general relativity, plays a crucial role in our understanding of the universe. However, confirmations of the validity of this theory on cosmological scales have hitherto eluded us. In this context, the detection of relativistic Doppler via galaxy power spectrum measurements could further confirm the validity of general relativity at scales very far from the strong-gravity-field regime, where instead it has been tested with exquisite accuracy. The Doppler term acts as an imaginary correction in the relation between the galaxy density contrast and that of matter, which mostly affects the large-scales usually plagued by cosmic variance. Cross-correlation power spectra seem to be much more promising than auto-correlation ones, due to the presence of the relativistic effect in a non-vanishing imaginary term that might be relevant even at intermediate scales. Moreover, relativistic Doppler is sample-dependent, so different galaxy populations display different contributions in their power spectra. In the search for the optimal galaxy samples to achieve a detection of the relativistic term, we can split a galaxy population according to luminosity, and even perform a multi-tracer analysis with auto-correlations of the two sub-samples and their cross-power spectrum. We are thus able to devise a technique enjoying multi-tracer benefits out of a single dataset and obtain a detection well above 5σ.
