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Astrophysics Luncheon Seminar

Using BOSS Galaxy Clustering and other Cosmological Data to Understand Neutrinos
Presented by Roland De Putter
Jet Propulsion Laboratory, California Institute of Technology

Monday, February 11, 2013
12:00 noon in 169-336

While the observation of neutrino oscillations has provided a measurement of the mass differences of neutrinos, thus proving that at least two species are massive, the absolute mass scale (often quantified by the sum of neutrino masses) is still unknown. Interestingly, the best way to probe this quantity is not through conventional particle physics experiments, but through cosmology, using the universe itself as a laboratory. Most notably, massive relic neutrinos suppress the growth of cosmological structure on scales smaller than the neutrino free streaming distance, leaving a distinct signature in the matter power spectrum. This effect (and others) can be looked for in galaxy clustering data to measure the neutrino mass, or, in the absence of a signal, to derive an upper bound. In this talk, I will discuss new neutrino mass bounds obtained from clustering in the Baryon Oscillation Spectroscopic Survey CMASS sample of luminous galaxies (redshift z~0.57), in combination with other cosmological data sets. Making use of photometric redshifts, we are able to use the entire volume of ~3 (h^{-1} Gpc)^3, leading to some of the strongest upper bounds on neutrino mass to date. While the standard model contains three neutrino species, there are recent hints from both cosmological and particle physics experiments for the existence of one or two additional (sterile) species. In the second part of this talk, I will discuss current constraints from cosmic microwave background, large scale structure, and background expansion data on the number of additional species and their masses, paying particular attention to the observational degeneracies between the number of neutrino species and neutrino mass, and how these can be broken. We show that current data indeed allow for additional relativistic species, but that their masses are in tension with the values preferred by recent neutrino oscillation data.

SVCP Astrophysics

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