Dissipative systems in General Relativity, with an application to the Poynting..

Il giorno 11 Dicembre 2019 alle ore 11:00, in aula 2N44
il Prof. Emmanuele Battista (Silesian University in Opava, Czech Republic)
terrà un seminario dal titolo:
"Dissipative systems in General Relativity, with an application to the Poynting-Robertson effect"
In this talk the following problem is investigated: given the equations of motion of a dissipative system, determine the Lagrangian function and the potential of the dissipative forces which reproduce the dynamics when inserted in the the Euler-Lagrange equations. Such problem is known as inverse problem of the calculus of variations. 
Dissipative forces cannot be derived in terms of a conservative or a generalized potential, due to their dependence on the velocity field. Therefore, a viable solution consists in considering the derivative with respect to the velocity field of a potential function known in the literature as Rayleigh potential. Determining the Rayleigh potential in general relativity settings represents a demanding task due to the non-linearities of the background geometry. Recently, I introduced a new method which allows to derive the analytical form of the Rayleigh potential in general relativity and to infer important dynamical information on the system under investigation. During the seminar I will describe the formal aspects of the method, highlighting the advantages and its limiting aspects. As an astrophysical application, I consider the general relativistic Poynting-Robertson effect. This phenomenon fulfills an important role in high-energy astrophysics and occurs each time the radiation field from an emitting source around a compact object (such as neutron star or black hole) invests a relatively small-sized test particle. The process of absorption and re-emission of radiation generates a recoil force opposite to the test particle orbital
motion, removing thus very efficiently energy and angular momentum from the test particle, and forcing it to spiral inward or outward depending on the radiation field intensity. Poynting-Robertson effect configures thus as a relativistic dissipative mechanism. I present the underlying model, the analytical form of its Rayleigh potential, and discuss its theoretical and observational implications.
Eventually, I comment on future projects and other possible applications of the proposed method. 
Data: 11/12/2019