  In my doctoral thesis, I have focussed my attention on radiation processes in
high-energy astrophysics connected with the accretion flow physics around
compact objects. Generally, a radiation field beside to exert an outward
radiation pressure, there is also the presence of a radiation drag force, which
both can drastically change or even halt the motion of the surrounding matter.
The radiation drag force, known as Poynting-Robertson effect, acts as a
dissipative force against the matter's orbital motion, removing very
efficiently angular momentum and energy from it. The thesis is organised in
three parts: (1) for ray-tracing purposes, I have developed a mathematical
method for deriving a set of high-accurate approximate polynomial formulae to
easily integrate photon geodesics in a Schwarzschild spacetime; (2) I gave two
fundamental contributions in the field of the general relativistic treatment of
the Poynting-Robertson effect (Lagrangian formulations and extension of the
model in three dimensions); (3) I reduced the data of three accreting
millisecond X-ray pulsars: IGR J00291+5934, IGR J18245-2452, and SAX
J1748.9-2021. This thesis offers innovative ideas in the field of radiation
processes involving the Poynting-Robertson effect in high-energy astrophysics,
opening thus up future interesting perspectives both in theoretical and
observational physics.
