Physics scientists Costas J. Efthimiou and Sohang Gandhi have discovered a mathematical theory that proves that vampires, zombies, ghosts and such things can't possibly exists in this current universe.
Their theory is based on the reduction to the absurd. In short, they prooved that, according to mathematical calculations, the way the vampire population would increase as time passed by, would dramatically reduce the human population to almost zero in a matter of months...
They also try to proove why is it a nonsense believing that ghosts can go through walls.
Javier Pazos has given another opinion to refute this paper in his blog: Ghosts, Vampires and Zombies. A good one that presents the humourous side of this matter.
As for me I think these scientists are missing the simple fact that justify the mere existence of "paranormal effects": THEY ARE MEANT TO CONTRADICT PHYSICS!!! Or else... they wouldn't be "paranormal" and "behind human understanding".
And since even physics change over time to reveal strange and bizarre theories such as quantum mechanics that contradict the common sense, why should we trust that there are such things as "the-ones-that-cannot-exist"?