EL

Science Advisor

- 541

- 0

## Main Question or Discussion Point

Since my discussion with Juan R in the thread "photon's mass is zero?" under Special and General relativity went off topic I will try to continue it here:

Then this problem can be solved by noticing that if we in the Lagrangian substitute m with the bare mass m0 instead, the amplitudes turn out to be finite when we express them in terms of the physical mass. (Of course we also have to do a charge renormalization, but let's just stick to the mass for simplicity.)

Hence the correct Lagrangian density should include the bare mass (as well as the bare charge), and not the physical (since that leads to infinities). However, all results will of course be expressed in terms of the physical mass (i.e. the one we find in tables).

Please could any mentor or advisor verify or crank down on what I am saying, so we can get an end to this...

As I wrote before (#88) books often start with assuming that m in the Lagrangian is the ordinary mass (i.e. the one you can find in tables) just to later find out that this leads to infinities when calculating higher order processes.Juan R said:One always begins with real physical mass m. After one may apply renormalization for eliminate infinites, but real electron mass is m, what is the mass that appears in tables of universal constants.

...

On any case i see no signifcant error in my initial claim one begins with mass m before renormalization. You said "NO, one begins with bare mass", but in at least three standard books one begins with the same m i used in my definition.

Then this problem can be solved by noticing that if we in the Lagrangian substitute m with the bare mass m0 instead, the amplitudes turn out to be finite when we express them in terms of the physical mass. (Of course we also have to do a charge renormalization, but let's just stick to the mass for simplicity.)

Hence the correct Lagrangian density should include the bare mass (as well as the bare charge), and not the physical (since that leads to infinities). However, all results will of course be expressed in terms of the physical mass (i.e. the one we find in tables).

Please could any mentor or advisor verify or crank down on what I am saying, so we can get an end to this...