On uniform decay of the Maxwell fields on black hole space-times

This is the second in a series of papers in which we take a systematic study of gauge field theories such as the Maxwell equations and the Yang-Mills equations, on curved space-times. In this paper, we study the Maxwell equations in the domain of outer-communication of the Schwarzschild black hole. We show that if we assume that the middle components of the non-stationary solutions of the Maxwell equations verify a Morawetz type estimate supported around the trapped surface, then we can prove uniform decay properties for components of the Maxwell fields in the entire exterior of the Schwarzschild black hole, including the event horizon, by making only use of Sobolev inequalities combined with energy estimates using the Maxwell equations directly. This proof is entirely gauge independent, and does not pass through the scalar wave equation on the Schwarzschild black hole, and does not need to separate the middle components for the Maxwell fields. However, proving a Morawetz estimate directly using the Maxwell equations, without refering to the scalar wave equation, seems to be out of reach of the mathematical community as of today; which I was not able to solve yet in this work. If one is able to prove the Morawetz estimate directly using the Maxwell equations, this combined with the present work would give full conceptual proof of decay of the Maxwell fields on the Schwarzschild black hole, and would then be in particular useful for the non-abelian case of the Yang-Mills equations where the separation of the middle components cannot occur. The whole manuscript is written in an expository way where we detail all the calculations.