How will things change after irrelevant operators are confirmed?

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Discussion Overview

The discussion revolves around the implications of confirming the effects of irrelevant operators in the standard model, particularly in the context of beyond the standard model (BSM) physics. Participants explore how such confirmation might influence theoretical frameworks, naturalness issues, and the understanding of energy scales related to new physics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant proposes a thought experiment regarding the confirmation of irrelevant operators and questions how this would change discussions in BSM physics, particularly concerning naturalness.
  • Another participant suggests that the energy scale for observing these effects might be large, referencing the fine structure constant and the evolution of the understanding of relevant versus irrelevant operators since the 1970s.
  • There is a consideration that if higher-order operators are observed, it would necessitate predicting or postdicting coupling values, potentially through new physics or an asymptotic safety scenario.
  • One participant expresses uncertainty about the scale of new physics, questioning whether particles above certain mass thresholds, like 1 TeV or 10 TeV, are ruled out and whether the "desert" scenario is valid.
  • A later reply raises the possibility that irrelevant operators might have been involved in modeling neutrino mass, suggesting a connection to the broader topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of irrelevant operators or the scale of new physics, indicating multiple competing views and ongoing uncertainty in the discussion.

Contextual Notes

Participants express varying assumptions about energy scales, the nature of new physics, and the relevance of certain theoretical models, which remain unresolved.

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

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