Hi, From perusing books on QFT, I've gathered that the photon is written as a 4-vector in field theory and transforms under the standard Lorentz group operators, while an electron for instance is a 2-component spinor and transforms under a special representation of the Lorentz group as part of a bispinor with its positron partner. But I remember as an undergrad working out the spin-1 representation of SU(2), which gives basically a set of 3x3 "Pauli matrices". Could the photon be represented as a three-component object that transforms under some other representation of the Lorentz group? Is the reason we write the photon as a 4-vector fundamental or does this just make it easy to work with the 4-component bispinor? Thanks! I guess a more general follow-up question might be: is there any fundamental connection between su(2) and spin-1/2? Or is it just convenient to use su(2) for spin-1/2 particles and so(3) for spin-1?