The intended setting is non-quantum general relativity.
My question: What is the relation between the energy-momentum tensor Tμν and the baryon four-current Jμ in the case of antimatter, or in the case where the baryon density J0 is zero but there's a non-zero baryon flux Ji? I'd be thankful to anyone who could share references about this.
To make the question clear:
In the simplified case of matter without internal forces ("dust"), the twice-contravariant energy-momentum for matter can be connected to the baryon four-current in several ways, eg:
Tμν=ρuμuνwithuμ=cJμ/√∣JαgαβJβ∣
where ρ is the (rest) mass density (mass divided by volume), or as
Tμν=cmJμJν/√∣JαgαβJβ∣
where m is the (rest) mass per baryon (or molar mass density, if we measure J in moles).
It seems to me that both expressions could be used in the case of antimatter: irrespective of whether J0⋛, we would still have T^{00} \ge 0 as confirmed by the Alpha-g experiments. But I'd be happy if anyone could share some references that discuss this kind of situations.
(Note: zero baryon density but a non-zero baryon current can occurr, for instance, if at an event there is a flux of baryons in one direction and a flux of antibaryons in the opposite direction – similarly to what can happen with electric current:zero charge density but non-zero current)