To those not interested in readin the whole paper the crux of the problem is in the abstract and to put it succinctly is as follows:

The paper hypothesises that gravity is an attractive force between two (or more) particles of normal matter and similarly between particles of anti-matter, but the force between a particle of matter and one of antimatter is repulsive. The author then goes on to use this factor to explain the accleration of the universe and dark energy, but that is not part of my question.

As far as I am aware anti-matter still has positive mass and therefore is gravitationally attractive to both matter and anti-matter. Is this correct? IMHO it must be as if there were a repulsive force between matter and anti-matter then one of the fundamental reactions i.e. mutual annihilation of particle and anti-particle could not take place as they would repulse each other. Alternatively is the electrostatic attraction of positive and negative charges overcoming this much weaker gravitational repulsion?

I would appreciate it if someone could enlighten me as to the known facts.

All experiments to date have shown that matter and antimatter behave identically in a gravitational field (or at least, very close to identically, to within much less than a part per thousand). Certainly, the existing body of experiments is enough to very confidently say that gravitation effects on matter and antimatter have the same sign. Keep in mind that papers on the Arxiv are not yet peer-reviewed, so there’s considerable room for a crackpot to sneak in. I suspect that this is one such.

Incidentally, even if matter and antimatter did gravitationally repell each other (which, as I said, is not the case), this gravitational repulsion would not be a significant barrier to annihilation. Electromagnetic forces are much stronger than gravitational ones for all of the elementary particles.

If antimatter was repelled by ordinary matter, then it could be used to distinguish gravity from acceleration- a big no-no under General Relativity. If I’m not mistaken, only objects with either negative mass/energy or with imaginary mass/energy would be repelled by a gravitational field.

It is possible however that matter and antimatter are not completely symmetrical. So a piece of antimatter and a piece of matter might not have exactly the same gravitational attraction to each other as either two pieces of matter or two pieces of antimatter. One reason physicists would love to be able to store neutral anti-hydrogen for extended periods is to test it’s reaction to the Earth’s gravity to a lot finer precision than one in a thousand.

Chronos thanks for your reply that clears thing up, sorry if I was a bit unclear on the EM force being much greater than gravity, I was tired and did not proof read before posting.

Which one is it? Is there a difference between these two things, or are they both the same? I’m curious about the math. Can theory predict the behavior of particles with -/imag. energy?

Imaginary mass (mass equals the square root of a negative number) is what you get when you plug a velocity faster than light into Relativity equations, i.e. tachyons.

Matter and antimatter both have the same sort of mass. Though I love the arXiv, it’s still not a peer-reviewed journal and so idiocy slips through a lot.