General-relativistic radiation reaction cooling in pulsar magnetospheres

The origin of coherent radio emission in pulsars is a long-standing open problem in astrophysics. A promising candidate is radiation reaction cooling, which has recently been shown to trigger the development of anisotropic ring-shaped distributions in momentum space. Radiation reaction continuously sustains population inversion across timescales comparable to the dynamical evolution of the system in the relativistic pair plasmas present in the magnetospheres of pulsars, thereby powering the emission of linearly polarized coherent radiation via the electron cyclotron maser (ECM) instability.

In this Thesis, we further investigate this mechanism by studying how the phase-space dynamics of radiatively cooled plasmas are modified by curved spacetime effects. For this purpose, we derived the radiative Einstein–Vlasov–Maxwell system, along with the curved spacetime extension of the Landau-Lifshitz model of radiation reaction, in the 3+1 formalism of general relativity. In addition, we developed a general-relativistic particle pusher to integrate particle trajectories in stationary electromagnetic fields and background spacetime metrics, by extending an existing parallelized code.

Our simulations show that ring distributions are generated in Schwarzschild and slowly rotating Kerr spacetimes, with enhanced properties. Increasing the stellar compactness amplifies the momentum-space gradient that regulates the growth rate of the ECM instability, while frame-dragging induces a stellar electric field and acts as an external source of perpendicular momentum, extending the duration of the ring structure. This work constitutes the first systematic investigation of radiation reaction cooling in curved spacetime, and establishes the foundation for future investigations of this mechanism in realistic astrophysical conditions.