Research @ KICP
November 19, 2009
Last Scattering Surface of Primordial Neutrinos
by Scott Dodelson
Figure one illustrates the distance to the LSS for neutrinos of various masses and for the CMB photons.
This result is at first glance counterintuitive since the photons in the CMB were emitted at t = 380,000 years, much later than the neutrinos, and thus have had less time to travel since decoupling. However, neutrinos are massive (at least one species of neutrino must have a mass of 0.05 eV or larger), and thus propagate at subluminal velocities. The effects calculated by Dodelson and Vesterinin are dramatic - for neutrinos with a mass of 1 eV the surface of last scattering is only several hundred Mpc away, hundreds of times closer than the CMB surface of last scattering.
Current detectors are not able to observe the CNB, but if (far) future experiments can detect these neutrinos they offer a unique window into the evolution of structure. Anisotropies in the CNB could be directly compared with data from galaxy surveys, providing snapshots of the overdensities in a given location at two very different times.
Publication: Dodelson and Vesterinen, Cosmic Neutrino Last Scattering Surface, Phys. Rev. Lett. 103, 171301(2009)
KICP Members: Scott Dodelson