Cosmic magnification in beyond-Horndeski gravity

Abstract: The cosmic magnification is able to probe the geometry of large scale structure on cosmological scales, thereby providing another window for probing theories of the late-time accelerated expansion of the Universe. It holds the potential to reveal new information on the nature of dark energy and modified gravity. By using the angular power spectrum, with all known relativistic corrections incorporated, we investigated cosmic magnification in beyond-Horndeski gravity. We probed both the total relativistic signal, and the individual relativistic signals. Our results suggest that surveys at low redshifts ($z \,{\lesssim}\, 0.5$) will be able to measure directly the total relativistic signal in the total magnification angular power spectrum without the need for multi-tracer analysis (to beat down cosmic variance). Similarly, for the Doppler signal, our results indicate that it can also be measured directly at the given low redshifts. However, for the integrated-Sachs-Wolfe, the time-delay, and the (gravitational) potential signals, respectively, it will require going to high redshifts ($z \,{\gtrsim}\, 3$) for the signals to surpass cosmic variance. For actual detectability though, proper quantitative methods and error analysis (not considered in this work) will need to be taken into account, i.e. in addition to cosmic variance. We also found that the beyond-Horndeski gravity boosts relativistic effects; consequently, cosmic magnification. Conversely, relativistic effects enhance the potential of the total magnification angular power spectrum to detect the imprint of beyond-Horndeski gravity.