"After they are produced axions rapidly decay into 2 electron pairs, an electron and a positron."
Seems like axions have enough mass to form the 2 particles and some energy is usually given off during decay. Unless the decomposition is endothermic but the decay apperars to go from high enery to lower energy particles. Thats why a super collider is needed to make them.
Where is your BS meter at right now concerning this article?
If you think your BS meter is going off from me please tell me.
The mass of the axion is between 10-3 and 10-6 eV. That's very small. All the energy is contained essentially in the momentum of the particle.
E = p*c.
Thermodynamics isn't important here. The energy of the particle before the decay equals the E after the decay. The momentum of the tiny mass is turned into a particle pair. It's the reletivistic mass which is is important here. The speed is very close to the speed of light so the mass is 106 to 109 times higher.