Hawking radiation is explained by particle-antiparticle creation. A particle with positive energy escapes away from the black hole while the particle with negative energy falls down.
Why isn't that vice versa? A particle with positive mass should fall down due to gravity force, while the negative mass is to be repeled by the gravity force?
Edit: I think was wrong about the gravity repeling the negative mass. Even though the force is directed away from the black hole, a=F/m so the particle still falls down the black hole! Now I see no point why any particles should be escaping more than the other?