« Turbulence of weak gravitational waves in the early Universe » |
Sébastien Galtier |
We are currently experiencing a revolution in astronomy with the multiplication of direct observations of gravitational waves (GWs). What about the theoretical study of GWs? We have studied analytically [1] the non-linear behaviour of a random set of weak GWs. Such a situation can be expected in extreme cases such as the black hole environment or the very primordial Universe around 10-36s. In this seminar I will present the weak GW turbulence theory and give the analytical solutions which correspond to a double cascade of the space-time metric. The direct cascade is limited by the Planck scale below which the general relativity equations become invalid. Interestingly the inverse cascade is explosive with in principle the possibility to excite fluctuations from the forcing wave-number kF to k=0 in a finite time. However, this mechanism ends up at the scale where the GW turbulence becomes strong. I will show numerical simulations to illustrate the cascade mechanism and get additional information. I will eventually discuss the possible link between the inverse cascade and a mechanism of expansion of the Universe.
[1] S. Galtier & S.N. Nazarenko, Turbulence of weak gravitational waves in the early Universe, Physical Review Letters 119, 221101 (2017). |
vendredi 8 juin 2018 - 11:00 Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris |
Page web du séminaire / Seminar's webpage |