Silk Damping at a Redshift of a Billion: New Limit on Small-Scale Adiabatic Perturbations
Abstract
We study the dissipation of small-scale adiabatic perturbations at early times when the Universe is hotter than T ≃0.5 keV. When the wavelength falls below the damping scale kD-1, the acoustic modes diffuse and thermalize, causing entropy production. Before neutrino decoupling, kD is primarily set by the neutrino shear viscosity, and we study the effect of acoustic damping on the relic neutrino number, primordial nucleosynthesis, dark-matter freeze-out, and baryogenesis. This sets a new limit on the amplitude of primordial fluctuations of ΔR2<0.007 at 104 Mpc-1≲k ≲105 Mpc-1 and a model-dependent limit of ΔR2≲0.3 at k ≲1020-25 Mpc-1.
- Publication:
-
Physical Review Letters
- Pub Date:
- August 2014
- DOI:
- 10.1103/PhysRevLett.113.061301
- arXiv:
- arXiv:1403.3697
- Bibcode:
- 2014PhRvL.113f1301J
- Keywords:
-
- 98.80.Cq;
- 26.35.+c;
- 95.35.+d;
- 98.70.Vc;
- Particle-theory and field-theory models of the early Universe;
- Big Bang nucleosynthesis;
- Dark matter;
- Background radiations;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- High Energy Physics - Phenomenology
- E-Print:
- 4 pages, 3 figures