In general, a body of some mass in spacetime fabric bend spacetime fabric around it. What will happen if there is a body with negative mass? Does it will make a crest like shape in spacetime fabric?
The gravity will be repulsive, so there will be no orbits possible around it. Also the gravitational time dilation will make the clocks go faster instead of slower the nearer the get to the body. Effectiveley, a negative mass in positive space acts like a positive mass in negative space, see David Madore's article and Roy Black's video on the subject.