Recent content by Pradyuman

I am currently studying qft and in that I considered the spinor lagrangian, i made it local gauge invariant I had to replace derivative with covariant derivative, and added #F_{\mu\nu}# term but how do I say that this gauge field correspond to the EM field

Suppose I finished making my lagrangian invariant and i found ohh I have to add this term to my lagrangian, to make it invariant, now how come I can say oh that's the term associated with EM fields,

When we make our lagrangian invariant by U(1) symmetry we employ the fact that nature doesn't care how I describe it, but, how come that I can associate the real physical particles with the coordinates I use to describe? Even though gauge symmetry is not a physical Symmetry,

A wavepacket is composed of many waves and I imagine the light travel as a quanta which is equivalent to wavepacket, and since it spreads over all wavelengths, the net result must be spread of crust and trough of the wavepacket which in essence is like increasing wavelength

Any wave mass term decays, similarly if I want to explain redshift by considering massive photon, how much should be the mass? Is it less than today's upper limit. Solution of wave equation ##□ϕ=0## gives a wave that doesn't disperse over time. But wave solution of the form ##(□+m^2)ϕ=0## has...

In the book "Group theory and it's Applications to the Quantum Mechanics of atomic spectra " by Eugene P. Wigner in chapter 4 The elements of quantum mechanics it is written What does the wave-packet and the refractive index implies here.How to interpret this?