Hi dear all Please explain to a stupid dummy a very simple thing. Take an a photon in 1+3 dimensions. How DOF it has? We all know that 2. How we calculate it? a) 1) We have a spin 1 particle that should have 2s+1=3 spin state. So DOF=3. 2) We have 4 Aμ guys. One is out because of gauge invariance. So we have 3 left. Does EOM gives us smth? 3) Electromagnetic tensor has 4×4 components. Its anti-symmetric so 4*3/2=6 components left. Bianci identities F(αβ;γ)=0 gives us C43=4!/3!1!= 4 conditions (is it true? Or it is 6eq? Its the same as a symmetry conditions???), so we left with 2 DOF. 4) Electric and magnetic fields have three components each so we have 6. (4 Maxwell equations? ->2 ) What about photon in 1+D dim? Where and how zero photon mass get into play? b) For graviton in 1+3. 1) hαβ has 16 components. The matrix is symmetric so 4*5/2=10 components left. Bianci gives us h[αβ;γ]=0 - 4 equations. The gauge conditions (i.e. coordinate transformations with non zero Jacobian) gives me 4 tranformation (1 for each coordinate). Left with 2 - Fine 2. In the 1+4 the same calculation give 5*6/2=15 (symetric matrix) 15-5=10 (because of gauge) Bianci gives us how? How DOF in the 5dim case???? Help!!!