Regular Article - Theoretical Physics
Linear analysis of the gravitational beam–plasma instability
Departament de Física Teòrica and IFIC, Centro Mixto Universitat de València-CSIC, Universitat de València, 46100, Burjassot, València, Spain
2 Physics Department, “Sapienza” University of Rome, P.le Aldo Moro 5, 00185, Rome, Italy
3 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044, Frascati, Rome, Italy
Accepted: 21 May 2023
Published online: 9 June 2023
We investigate the well-known phenomenon of the beam–plasma instability in the gravitational sector when a fast population of particles interacts with the massive scalar mode of a Horndeski theory of gravity, resulting in linear growth of the latter amplitude. Following the approach used in the standard electromagnetic case, we start from the dielectric representation of the gravitational plasma, as introduced in a previous analysis of the Landau damping for the scalar Horndeski mode. We then set up the modified Vlasov–Einstein equation, using a Dirac delta function to describe the fast beam distribution. We thus provide an analytical expression for the dispersion relation, and we demonstrate the existence of a nonzero growth rate for the linear evolution of the Horndeski scalar mode. A numerical investigation is then performed with a trapezoidal beam distribution function, which confirms the analytical results and allows us to demonstrate how the growth rate decreases as the beam spread increases.
© The Author(s) 2023
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