Damping of tensor modes in cosmology
By S. Weinberg. 2003
219 citations recorded by the source corpus.
An analytic formula is given for the traceless transverse part of the anisotropic stress tensor due to free streaming neutrinos, and used to derive an integro-differential equation for the propagation of cosmological gravitational waves. The solution shows that anisotropic stress reduces the squared amplitude by 35.6% for wavelengths that enter the horizon during the radiation-dominated phase, independent of any cosmological parameters. This decreases the tensor temperature and polarization correlation functions for these wavelengths by the same amount. The effect is less for wavelengths that enter the horizon at later times. At the longest wavelengths the decrease in the tensor correlation functions due to neutrino free streaming ranges from 10.7% for ${\ensuremath{\Omega}}_{M}{h}^{2}=0.1$ to 9.0% for ${\ensuremath{\Omega}}_{M}{h}^{2}=0.15.$ An appendix gives a general proof that tensor as well as scalar modes satisfy a conservation law for perturbations outside the horizon, even when the anisotropic stress tensor is not negligible.
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/ea63d51182aa76b8d8af9ab0e2c4f727fd48887f
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Citations in the corpus
- Gravitational-wave cosmology across 29 decades in frequency (2015, background): “Note that, in evaluating the observed GW spectrum, we neglect the effects of neutrino free streaming [38] and phase transitions occurring in the early Universe [35].”
- The Quest for B Modes from Inflationary Gravitational Waves (2015, background): “The anisotropic stress of this fluid (to which the neutrino background contributes after neutrinos decouple) modifies slightly the time evolution, a calculable ∼ 10% correction to Equation 21 (Weinberg 2004; Pritchard & Kamionkowski 2005; Dicus & Repko 2005).”
- New physics from the polarized light of the cosmic microwave background (2022, background): “After inflation, the primordial GW evolved according to equation (34) with T t ij provided mostly by free-streaming neutrinos 195 .”
- Primordial gravitational waves, precisely: the role of thermodynamics in the Standard Model (2018, background): “Weinberg’s paper was the first one to point out that this effect might indeed be relevant to observations. interactions of elementary particles.”