The opportunity of measuring various effects occurring on the largest cosmic scales have recently drawn an increasing attention, thanks also to the strong effort that will lead to next-generation cosmological experiments such as the Euclid satellite, the Large Synoptic Survey Telescope, and the Square Kilometre Array. Such experiments will probe enormous volumes of the Universe, allowing us to have a glimpse at scales near and beyond the cosmological horizon. The study of perturbations on those scales is extremely interesting, because their evolution is fully linear, and we can safely neglect baryonic effects occurring on much smaller scales. Through probes of ultra-large scales we can learn a lot about gravity, inflation and the early Universe. Unfortunately, measurements of such long-wavelength modes are hampered by the poor statistical sampling usually referred to as ‘cosmic variance’. Here, we shall briefly review the so-called ‘multi-tracer’ technique, which will enables us to overcome cosmic variance by comparing the relative clustering of different tracers of the underlying cosmic structure. We shall discuss the most recent results and also illustrate how an incorrect treatment of horizon-scale effects may lead to a seriously biased reconstruction of cosmological parameters.
The multi-tracer technique to detect horizon-scale effects
Camera S.
First
2016-01-01
Abstract
The opportunity of measuring various effects occurring on the largest cosmic scales have recently drawn an increasing attention, thanks also to the strong effort that will lead to next-generation cosmological experiments such as the Euclid satellite, the Large Synoptic Survey Telescope, and the Square Kilometre Array. Such experiments will probe enormous volumes of the Universe, allowing us to have a glimpse at scales near and beyond the cosmological horizon. The study of perturbations on those scales is extremely interesting, because their evolution is fully linear, and we can safely neglect baryonic effects occurring on much smaller scales. Through probes of ultra-large scales we can learn a lot about gravity, inflation and the early Universe. Unfortunately, measurements of such long-wavelength modes are hampered by the poor statistical sampling usually referred to as ‘cosmic variance’. Here, we shall briefly review the so-called ‘multi-tracer’ technique, which will enables us to overcome cosmic variance by comparing the relative clustering of different tracers of the underlying cosmic structure. We shall discuss the most recent results and also illustrate how an incorrect treatment of horizon-scale effects may lead to a seriously biased reconstruction of cosmological parameters.
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