# Massive gravity

1. Jul 28, 2013

hi
i read this text(Theoretical Aspects of Massive Gravity BY Kurt Hinterbichler ) about massive gravity and now, have some questions

"i f we wish
to describe long range macroscopic forces, only bosonic fi elds will do, since fermionic fi elds
cannot build up classical coherent states."
what's classical coherent state and why fermonic particle can not do it?

massive gravity is a theory that modified Einstein-Hilbert action by adding a mass term to it, but since GR is essentially unique theory of a massless spin 2 degree of freedom, it should be remembered that modifying gravity means changing its degrees of freedom.
when you vary massive gravity action, obtain equations
$(\nabla^{i}\nabla_{i}-m^2)h_{\mu\nu}=0$, $\partial^{\mu}h_{\mu\nu}=0$, h=0
the number of degree of freedom of these equations are 5 for 4 dimensional space, but if we have massless spin 2 particle, it has 5 degree of freedom.
my question is, how massive gravity change degree of freedom of Einstein - Hilbert action?