Limits on neutrino-neutrino scattering in the early Universe
Abstract
In the standard model neutrinos are assumed to have streamed across the Universe since they last scattered when the standard-model plasma temperature was ∼MeV . The shear stress of free-streaming neutrinos imprints itself gravitationally on the cosmic microwave background (CMB) and makes the CMB a sensitive probe of neutrino scattering. Yet, the presence of nonstandard physics in the neutrino sector may alter this standard chronology and delay neutrino free streaming until a much later epoch. We use observations of the CMB to constrain the strength of neutrino self interactions Geff and put limits on new physics in the neutrino sector from the early Universe. Within the context of conventional Λ CDM parameters cosmological data are compatible with Geff≲1 /(56 MeV )2 and neutrino free streaming might be delayed until their temperature has cooled to as low as ∼25 eV . Intriguingly, we also find an alternative cosmology compatible with cosmological data in which neutrinos scatter off each other until z ∼1 04 with a preferred interaction strength in a narrow region around Geff≃1 /(10 MeV )2≃8.6 ×1 08GF , where GF is the Fermi constant. This distinct self-interacting neutrino cosmology is characterized by somewhat lower values of both the scalar spectral index and the amplitude of primordial fluctuations. While we phrase our discussion here in terms of a specific scenario, our constraints on the neutrino visibility function are very general.
- Publication:
-
Physical Review D
- Pub Date:
- December 2014
- DOI:
- 10.1103/PhysRevD.90.123533
- arXiv:
- arXiv:1306.1536
- Bibcode:
- 2014PhRvD..90l3533C
- Keywords:
-
- 98.80.Cq;
- 14.60.St;
- 98.70.Vc;
- Particle-theory and field-theory models of the early Universe;
- Non-standard-model neutrinos right-handed neutrinos etc.;
- Background radiations;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- High Energy Physics - Phenomenology
- E-Print:
- 9 Pages, 4 figures, 1 table. v2: Version accepted for publication, enhanced discussion on neutrino interaction beyond the SM, enhanced figures, references added