Perspectives on Gravity-Induced Radiative Processes in Astrophysics

Abstract

Single-vertex Feynman diagrams represent the dominant contribution to physical processes, but are frequently forbidden kinematically. This is changed when the particles involved propagate in a gravitational background and acquire an effective mass. Procedures are introduced that allow the calculation of lowest order diagrams, their corresponding transition probabilities, emission powers and spectra to all orders in the metric deviation, for particles of any spin propagating in gravitational fields described by any metric. Physical properties of the "space-time medium" are also discussed. It is shown in particular that a small dissipation term in the particle wave equations can trigger a strong back-reaction that introduces resonances in the radiative process and affects the resulting gravitational background.

Classical and quantum aspects of particle propagation in external gravitational fields

“…We have already used some of the properties of ( 18) and ( 19) elsewhere [5,10]. P µ of (18) describes the geometrical optics of particles correctly and gives the correct deflection predicted by general relativity.…”

“…Over the years solutions of covariant wave equations have been found [1][2][3][4][5] that are exact to first order in the metric deviation γ µν = g µν − η µν , where η µν is the Minkowski metric, and do not depend on the choice of any field equations for γ µν . They are a useful tool in the study of the interaction of gravity with quantum systems and have been applied to interferometry and gyroscopy [2], the optics of particles [4], the observation of gravitational effects [2], the spin-flip of particles under the action of inertial and gravitational fields [3], spin currents [6], neutrino physics [7,8] and radiative processes in astrophysics [9][10][11][12].…”

“…is the angular momentum about the base point x α . Maxwell-type equations Fµλ,σ + Fλσ,µ + Fσµ,λ = 0 (10) and…”

Structured objects in quantum gravity. The external field approximation

“…Here we consider the possibility that similar phenomena occur in quantum gravity, still far from the essential quantum regime that is supposed to take over at Planck's length. The suggestion comes from studies of covariant wave equations [1-5] that can be solved exactly to first order in the metric deviation γ µν = g µν − η µν , where η µν is the Minkowski metric and whose solutions are a useful tool in the study of the interaction of gravity with quantum systems [6][7][8][9][10][11][12].In the EFA context, gravity is represented exclusively by a two-point vector K λ (z, x) [13,14] that is known only if γ µν and its derivatives are known. In what follows the coordinates z µ refer to a frame that is moved by parallel displacement along a particle path and x µ to a particle local inertial frame.…”

Maximal acceleration and radiative processes

“…There are processes, however, in which massive particles emitting a photon are not kinematically forbidden. This is certainly the case when gravitation alters the dispersion relations of at least one of the particles involved [75,76]. This is also the case with MA [77].…”