AI Article Synopsis
- The study focuses on how small-scale adiabatic perturbations dissipate when the Universe is hotter than approximately 0.5 keV, examining the effects of acoustic damping on various cosmic processes.
- When wavelength falls below a critical damping scale, acoustic modes diffuse and thermalize, resulting in increased entropy and impacting phenomena like relic neutrino numbers and primordial nucleosynthesis.
- The research establishes a new limit on the amplitude of primordial fluctuations, showing Δ(R)(2) < 0.007 for certain scales and a model-dependent limit of Δ(R)(2) < 0.3 for much larger scales.
Article 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 k(D)(-1), the acoustic modes diffuse and thermalize, causing entropy production. Before neutrino decoupling, k(D) 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 Δ(R)(2)<0.007 at 10(4) Mpc(-1)≲k≲10(5) Mpc(-1) and a model-dependent limit of Δ(R)(2)≲0.3 at k≲10(20-25) Mpc(-1).
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| http://dx.doi.org/10.1103/PhysRevLett.113.061301 | DOI Listing |
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