Energy of massless particles before electroweak symmetry breaking

[Ranku]

Would it be correct to represent the energy of massless particles before electroweak symmetry breaking as $E = cp$, just as we do with photons post-symmetry breaking?

 

[Gaussian97]

Well, I'm not quite sure, and I'm not an expert, but I would say no. Because this equation is a kinematic equation, therefore it should not care about the dynamic process that gives mass to the particles. In the same way that even after SSB, if a particle acquires a mass $m_0$ is still not correct to write $E=\sqrt{p^2+m_0^2}$, but rather you need the renormalized mass.

 

[PeterDonis]

Would it be correct to represent the energy of massless particles before electroweak symmetry breaking as $E = cp$, just as we do with photons post-symmetry breaking?

Massless means $E = cp$, so yes.

this equation is a kinematic equation, therefore it should not care about the dynamic process that gives mass to the particles

It's a kinematic equation describing massless particles. If a particle gains mass by a dynamic process, it's not massless any more and no longer satisfies a kinematic equation for massless particles. But if that dynamic process hasn't happened yet, and the particle is still massless, it obeys the massless kinematic equation.

even after SSB, if a particle acquires a mass $m_0$ is still not correct to write $E=\sqrt{p^2+m_0^2}$, but rather you need the renormalized mass

Yes, you would write $E = \sqrt{p^2 + m_r^2}$, where $m_r$ is the renormalized mass. But this has nothing to do with what kinematic equation you would write before symmetry breaking, when the particle is still massless.