Seshadri NadathurDennis Sciama Fellow
Institute of Cosmology and Gravitation
University of Portsmouth
Spectroscopic galaxy redshift surveys provide important measurements of the geometry, expansion rate, and growth rate of structure in the Universe. I will present a new method of measuring these quantities using the anisotropic cross-correlation of galaxies with cosmic voids, and the related theory. This method allows simultaneous fits for redshift space distortions and those from the Alcock-Paczynski (AP) effect. Applied to CMASS data from the Baryon Oscillation Spectroscopic Survey (BOSS) at redshift 0.57, this method measures the product D_A(z)H(z) to a much higher precision (by a factor of 3.5) than possible with BAO. The degeneracy directions in parameter space are orthogonal to those from galaxy clustering, and I will show how combining void information with standard galaxy clustering methods reduces measurement errors in each of D_A, H and f\sigma_8 by a factor of ~2. This is equivalent to a massive increase in the effective survey volume, achieved at no extra cost and with no additional observational time! I will discuss the implications for cosmological parameter fits, both within LCDM and for alternative models with dark energy and curvature.
