Conventional wisdom in the particle theory for about 30 years has been that the Standard Model has a huge “hierarchy” or “naturalness” problem, the solution to which is supposed to appear at the LHC via SUSY or some other new BSM physics. With no SUSY or other BSM physics appearing at the LHC, this conventional wisdom is now moving towards claims that fundamental physics has been shown by the LHC to be “unnatural”, with parameters that are environmental, artifacts of our position in the multiverse generated by the anthropic landscape of string theory. For an example of this, see Seiberg’s Now What? talk at Aspen (Arkani-Hamed also spoke, with presumably a similar point of view, although the talk is not available).
It seems to me that a much more logical conclusion to draw would be that the LHC has just shown that the hierarchy/naturalness argument was mistaken. I’ve never understood why people found it convincing, and have often argued about this here on the blog. From the “hierarchy” angle, the problem is why the ratio of the electroweak-breaking scale to the GUT or Planck scale is such a small number, but we don’t actually have any evidence for GUT physics or for quantum gravitational physics, so no good reason to be sure that such high scales are relevant to anything or the cause of a hierarchy problem. From the “naturalness” side, while the theory is renormalizable, one can worry about the sensitivity to high energies of its cutoff dependence, but it’s unclear to me why one should be that concerned about this. More worrisome is that the Higgs sector introduces most of the undetermined parameters of the SM, a much more serious defect of the standard theory.
Today at a workshop on The First Three Years of the LHC, Joe Lykken gave a talk on Higgs without Supersymmetry, in which he argues that there is no naturalness problem or need for supersymmetry, and makes a specific suggestion about how to think about the high energy behavior of the Higgs. He starts off with:
is there a Higgs naturalness problem?
•For decades the HEP community has asserted that naturalness is the central issue
•Simply put, we have assumed that either EWSB is natural, in which case we need to explain why, or that it is fine-tuned, in which case we also need to explain why
•I will argue that this is a false dichotomy,and that LHC results are hinting at a third path
then explains the standard dogma about quadratic sensitivity to the cutoff. He argues that the solution to this problem lies in properly understanding the scaling behavior of the Higgs, following ideas that go back at least to W. Bardeen in 1995 (see here). The fact that the renormalization group flow of the quartic term in the Higgs potential takes it to zero at high energies is interpreted as a suggestion that the right UV boundary condition is that the Higgs potential vanish. From there Lykken goes on to discuss more specific ideas, which may lead to observable new physics at LHC scales.
These aren’t really new ideas, but I think Lykken is drawing the right lesson from the LHC results: the naturalness argument for SUSY has now been shown to have been misguided, and it’s time not to give up and adopt the pseudo-science of anthropics, but instead to question the dogmas that have dominated the subject for decades.
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