2015/04/30 by Jacopo Ghiglieri, J. Ghiglieri, M. Laine · 1 citation
Physics and Astronomy · #Astrophysics #Classical mechanics #Computational physics #Cosmology and Gravitation Theories #Gravitation #Gravitational wave #Nuclear physics #Optics #Particle physics theoretical and experimental studies #Physics #Plasma #Pulsars and Gravitational Waves Research #Quantum mechanics #Range (aeronautics) #Viscosity #Wavelength #astro-ph.CO #hep-ph
paper · pdf · doi:10.1088/1475-7516/2015/07/022
published as JCAP 1507 (2015) 022 · 19 pages. v2: clarifications and references added, published version
openalex publication_date 2015/07/16 · arxiv created 2015/07/17 · arxiv updated 2015/08/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Because of physical processes ranging from microscopic particle collisions to macroscopic hydrodynamic fluctuations, any plasma in thermal equilibrium emits gravitational waves. For the largest wavelengths the emission rate is proportional to the shear viscosity of the plasma. In the Standard Model at 0 T > 16 GeV, the shear viscosity is dominated by the most weakly interacting particles, right-handed leptons, and is relatively large. We estimate the order of magnitude of the corresponding spectrum of gravitational waves. Even though at small frequencies (corresponding to the sub-Hz range relevant for planned observatories such as eLISA) this background is tiny compared with that from non-equilibrium sources, the total energy carried by the high-frequency part of the spectrum is non-negligible if the production continues for a long time. We suggest that this may constrain (weakly) the highest temperature of the radiation epoch. Observing the high-frequency part directly sets a very ambitious goal for future generations of GHz-range detectors.