- We said that the EM and weak interactions are unified as Electroweak Unification. However, for usual Grand Unification, it requires that the gauge group G is
**simple Lie group** -- which means the G has no nontrivial normal subgroup other than itself.

However, neither $U(1) \times SU(2)$ nor $U(2)$ are **simple Lie groups**. So why do we call Electroweak Unification? They are still two different forces with two different couplings in Weinberg model?

- There are many energy scales related to Electroweak scale: https://en.wikipedia.org/wiki/Electroweak_scale

**What are these 3 scales so close to each other around 200 GeV?** Are they related in some way or they are totally independent in the parameters of models? e.g. in Electroweak Unification, GUT or other models? For example, the Higgs potential has two parameters, the quadratic and quartic terms, so they seem not need to be so close in 200 GeV scales?

This post imported from StackExchange Physics at 2020-11-30 18:54 (UTC), posted by SE-user annie marie heart