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SUMMARY:Extracting and constraining scalar-only couplings in generic BSM t
 heories - Mark Goodsell
DTSTART:20180504T150000Z
DTEND:20180504T160000Z
UID:TALK105643@talks.cam.ac.uk
CONTACT:Francesco Coradeschi
DESCRIPTION:In theories defined by high-energy boundary conditions (such a
 s supersymmetry)\, the Higgs mass is a prediction. On the other hand\, in 
 the Standard Model\, it is an input\, that we need to use to calculate the
  Higgs quartic coupling\, to predict the cubic coupling and also to test f
 or vacuum stability. However\, since the Higgs is a scalar\, its mass is v
 ery sensitive to those of other particles such as the top quark -- or any 
 new physics (hence we have a hierarchy problem) but this also means that w
 e need to calculate as many loop corrections as we can in order to obtain 
 accurate results. Once we reach two loops\, however\, we find a technical 
 "Catastrophe" associated with the would-be Goldstone Bosons of the W and Z
  bosons: in Landau gauge their masses vanish\, and this leads to infra-red
  divergences in the amplitudes. I will show how this problem can be avoide
 d for general renormalisable field theories\, with applications in the Sta
 ndard Model and several popular extensions (such as the NMSSM)\, and descr
 ibe how the results have been implemented in the public code SARAH. I will
  then discuss how this can impact the extraction of the quartic couplings 
 and the predictions for vacuum stability and cutoff scale.\n\nFurthermore\
 , when we consider that the scale of new physics might be high\, we need a
  method of making predictions for the Higgs mass (or predictions for the p
 roperties of the high-energy theory's stability) using the Standard Model 
 as an effective field theory. These calculations are beset by a similar bu
 t worse infra-red problem\, in that the infra-red divergences appear alrea
 dy at one-loop order. I will briefly describe some work in progress to sho
 w the relation between the two problems and how to solve the latter\, so f
 ar at one-loop order.\n\nFinally\, the Standard Model quartic coupling was
  famously bounded from above by Lee\, Quigg and Thacker using unitarity of
  scattering amplitudes\, giving an upper limit on the Higgs boson mass. Si
 nce then\, similar arguments have been used to bound the quartic couplings
  of BSM theories\, but bounds on *trilinear* scalar couplings are generall
 y only derived from requiring no charge/colour-breaking alternative vacua.
  I will describe the automation of unitarity calculations that can bound t
 rilinear and quartic scalar couplings for generic theories\, and give some
  first results for popular models.
LOCATION:MR19 (Potter Room\, Pavilion B)\, CMS
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