# How will things change after irrelevant operators are confirmed?

1. Jun 30, 2013

### Physics Monkey

I want to consider a thought experiment:

Suppose, at some point in the near future, the effects of irrelevant operators in the standard model are firmly confirmed by experiment. In other words, we see some effect, perhaps the muon g-2, which simply cannot be accounted for without including some higher dimension operator.

How will the discussion of BSM physics change? Does naturalness become an even greater issue?

2. Jun 30, 2013

### Finbar

Good question. I suppose the scale at which you expect this to happen is quite large though(?). The energy scale at which the fine structure constant approaches one. It is interesting that the reason we consider only relevant operators has changed since the 70's. Originally is was supposed that only renormalizable term were included in order for the theory to make sense. However now we know that, when viewed as an effective theory, all terms can be renormalized and therefore the reason we observe only renormalisable terms is that they are the only ones which are relevant at low energies.

I think if we observed some higher order operators we would then have to find a way of predicting (or postdicting) the value of the coupling. This could either come from some new physics (e.g. string theory) or an asymptotic safety scenario for the standard model.

3. Jun 30, 2013

### Physics Monkey

It's not clear to me that the scale of new physics needs to be so large. I guess I don't have much of a sense of the data and constraints. Is a new particle, say a new fermion, with mass above 1 TeV ruled out? Or 10 TeV?

Suppose I think the "desert" scenario and susy are just crazy and that its probably complicated physics all the way from 1 TeV to the Planck scale. Is it crazy to imagine that we just happen to be sitting at a point in the energy landscape where irrelevant operators are fairly small?

4. Jun 30, 2013

### atyy

Did one of the ways to model Neutrino mass involve irrelevant operators?