Original Measurement of Energy using a Geometrical Approach – OMEGA

The main difficulty in applying the AP test is to overcome the effect of peculiar velocities. Indeed, peculiar velocities produce a distortion in redshift space, an effect that becomes competitive with the deformation due to the expansion of the Universe (AP effect) and that disrupts the cosmological measure.

The first step of the project was to consolidate the AP test applied to the pairs of galaxies, validating the theoretical assumptions using N-body simulations in real space, expanding the selection pair criteria in redshift space and then applying the test on SDSS/BOSS data for which we have privileged access. This study was conducted on a simulated galaxy catalog which exploits a Millennium Simulation with the WMAP7 cosmology and the galaxy formation model developed during the project by V. Gonzalez-Perez (Perez-Gonzalez et al. 2014). The results, which gave rise to a communication (Gonzalez-Perez et al. 2013), have shown that the selection criteria necessary to overcome the peculiar velocities of galaxies were model dependent, making them difficult to use. So we focus the AP test on cosmic voids that are much more promising. The work of A. Pisani during the project has already demonstrated that it was possible to master the effects of peculiar velocities on the shape of voids (Pisani, Wandelt and Sutter 2015).

We are currently finalizing the analysis of the implementation of the AP test on cosmic voids using the SDSS/BOSS data. This work has required the creation of a cosmic voids catalog from this survey of galaxies. The final publication of the application of AP test on cosmic voids is in progress (Pisani et al. 2016, in preparation), and preliminary results already confirm that the AP test on cosmic voids is not only innovative but also very powerful.

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Scientific production associated with the OMEGA project includes the work directly derived from the study of the AP test on pairs of galaxies and on cosmic voids ( 3 + 1 paper in preparation) but also includes work in the context of wider collaborations within the SDSS/BOSS community (ten papers).

Early in the 20th century, Albert Einstein gave us a new theoretical framework to address the questions of the origin, evolution, and fate of the universe. Technology has now developed to the point where these concepts from general relativity can be substantiated and elaborated by precision measurements. Measuring the history of cosmic expansion is no easy task, but recently, a specific variety of stars, supernovae, has given us a first glimpse at that history and surprised us with an unexpected plot twist: the universe is accelerating. One of the major problems of modern cosmology is to determine whether this phenomenon results from a new cosmic "fluid" (dark energy) or a modified theory of gravity on large scales. Measurements of the history of the expansion of the universe based solely on the Hubble diagram of SNIa cannot unambiguously distinguish between these different theoretical scenarios. We are therefore confronted with the need of improving the quantity and quality of current measurements, by developing and implementing new independent cosmological probes.
Recently two of us [Marinoni & Buzzi, Nature 2010] have developed a new, purely geometric strategy, which allows one to extract information on the dark sector of the universe from the study of the symmetry properties of pairs of distant galaxies. The method, theoretically original and empirically promising, has already been applied to put highly competitive constraints on fundamental cosmological parameters. With this project we request funding to recruit a Post-Doc to help us:
• to further study the proposed test formalism, either analytically and through numerical N-body simulations. The goal is to refine its physical basis and relax some computational approximations that were implemented in the original testing scheme.
• to apply the formalism to enlarge spectroscopic data as from the survey BOSS to which some of us have privileged access. The goal is to improve the constraint on fundamental cosmological parameters that were obtained by implementing the method to local SDSS and DEEP2 data then to study in more detailed the method reliability, and systematical effects.
To maximize the science return of this ambitious and broad program, we have constituted a young, dynamical and motivated inter-laboratory team with inter-disciplinary expertise. We now crucially need to increase the work and competences to continue to maintain international visibility and contribute significantly to the solution to what has been called "the problem of Millennium ".