Monday, October 8, 2018

More Higgs Boson Based Limitations On BSM Physics

The way that this is described in the abstract is ass backward, but the bottom line is that the Higgs boson mass poses serious problems to a model that has a particle with a large Yukawa coupling to the Higgs boson that is heavier than the top quark.
We revisited the scenario of electroweak baryogenesis in the presence of large Yukawa couplings, in which it was found previously that a strongly first order electroweak phase transition can occur with the Higgs mass at its observed value of 125 GeV. 
Given the sensitivity of the running of the Higgs quartic coupling on the Yukawa coupling constants, we find that the addition of order one Yukawa couplings beyond the top quark drastically lowers the scale at which the Higgs potential becomes unstable. Specifically, even with only one additional order one Yukawa coupling, the scalar potential becomes unstable already at the TeV scale, assuming the Standard Model values for the Higgs sector parameters at the electroweak scale. 
Furthermore, by assuming the Standard Model values for the Higgs sector parameters at the TeV scale, the quartic coupling constant is driven to be larger than its Standard Model value at the electroweak scale. This in turn predicts a much lighter Higgs mass than the measured value of 125 GeV. In this scenario, the strength of the electroweak phase transition is also significantly weakened.
Arianna Braconi, Mu-Chun Chen, Geoffrey Gaswint, "Revisiting Electroweak Phase Transition with Varying Yukawa Coupling Constants" (October 5, 2018).

The conclusion of the paper connects the dots, noting that:
All together, these limitations render this simplest setup with large varying Yukawa couplings not a viable mechanism for baryogenesis.
This shouldn't be surprising. 


neo said...

" particle with a large Yukawa coupling to the Higgs boson that is heavier than the top quark"

wouldn't most, if not all, SUSY extensions be strongly disfavored then?

unless the SUSY partners get their mass from some other mechanism

andrew said...

Yes indeed.

neo said...

is the implication of this paper, if correct, new particles must have mass below the EW scale?

how then do string theorists and SUSY theorists get around this?

perhaps mitchell can reply

andrew said...

This doesn't work either.

neo said...

i think 2 ways to get around this is

reject the scenario of electroweak baryogenesis, perhaps baryogenesis is on some other scale, like GUT

or the higher masses of SUSY partners comes from something other than the Higgs, or no yukawa intereactions between squarks and -ino's and the higgs

or there's some problem with the paper or some loop hole

Mitchell said...

This paper says essentially nothing about supersymmetry, it is about the effect of new fermions with a yukawa coupling to the standard model Higgs, on the running of that Higgs. When supersymmetry is broken, supersymmetric particles get their masses from a variety of interactions that have little or nothing to do with the Higgs; for an illustration see the bottom of page 102 in hep-ph/9709356.

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