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A new study suggests that many theorized heavy particles, if they exist at all, do not have the properties needed to explain the predominance of matter over antimatter in the universe.
If confirmed, the findings would force significant revisions to several prominent theories posed as alternatives to the Standard Model of particle physics, which was developed in the early 1970s. Researchers from Yale, Harvard, and Northwestern University conducted the study, which was published Oct. 17 in the journal Nature.
The discovery is a window into the mind-bending nature of particles, energy, and forces at infinitesimal scales, specifically in the quantum realm, where even a perfect vacuum is not truly empty. Whether that emptiness is located between stars or between molecules, numerous experiments have shown that any vacuum is filled with every type of subatomic particle — and their antimatter counterparts — constantly popping in and out of existence.
Source: https://news.yale.edu/2018/10/17/new-study-sets-size-limit-undiscovered-subatomic-particles
(Score: 2, Informative) by Anonymous Coward on Sunday October 28 2018, @02:39PM
anti-matter has positive inertial mass (we know because it's been created in the lab).
even anti-hydrogen has been created.
there's no reason to assume there's a factor of -1 in the equivalence principle for anti-matter, although it must be specified that we did not, in fact ever measure gravitational forces between a clump of anti-matter an anything else (equivalence prinicple says inertial mass is equal to gravitational mass).
however, since it has positive rest energy, current predictions are that it will be affected by gravity just like regular matter.
additional comment: photons are routinely viewed as their own anti-particle, and they are known to be affected by gravity as expected under general relativity.