Thursday, 7 July 2016

SUSY 2016 Liveblog: Day Four Session Three

The first post-lunch parallel sesion, discussion of non-SUSY models.  I don't come to SUSY to talk about SUSY :)

2:00 pm: The Hierarchy Problem in Non-Supersymmetric Extended Models, David Miller

Light Higgs is most easily accommodated with SUSY, but what if we don't find it?

Light Higgs also intriguing because of what it tells us about the SM vacuum stability.  The quartic coupling runs to zero or below at the Planck scale.  The quartic beta function also vanishing at this scale; not a fixed point and special for 125 GeV.  Indeed, this was "predicted" in 2010 within a couple of GeV.  The idea was asymptotic safety, with quantum gravity proposed as a way to tame the higher-order corrections.  Unfortunately, their calculation was not fully gauge invariant, raising some problems.

Another interesting prediction from 1995 is the Multiple Moint Principle: that there is another vacuum at the Planck scale and degenerate with the EW vacuum.  It was a prediction of the Higgs mass and a postdiction of the top mass (just after discovery).  The original computation was at one-loop; improving to 3 loops is not such a good prediction, going for a Higgs mass around 128 GeV.  (Still within three sigma of observation.)  Note that there is an (obvious) dependence on the UV boundary condition, e.g. Planck/reduced Planck mass.

Can idea be implemented in a non-SUSY GUT?  New fields will modify the running.  Toy model: new complex scalar.  Enforce stability at all scales.  Kind of works, but extra quartic: should really obey similar boundary conditions, which makes things worse.  Also consider 2HDM with similar conclusions.

Various planned efforts, e.g. postdiction of Higgs mass.

Bugger - I'm out of power and there aren't any convenient power outlets.

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