Is SMEFT Enough? ** Note Unusual Time: 13:00 **

The four scalar degrees of freedom of the Standard Model, the
Higgs and the longitudinal components of the Ws and Z, are amenable to
different effective field theory descriptions. "SMEFT" wraps them up in
a single Higgs doublet, whereas "HEFT" treats the Higgs and the
Goldstones separately. We seek to understand the suitability of "SMEFT"
and "HEFT" for describing the effects of possible heavy new physics in,
e.g., LHC measurements.
First, we identify (field redefinition invariant) features of the scalar
field space manifold that can only be described by HEFT, and thereby
identify two classes of UV completions for which a HEFT description of
their low energy physics is required: i) those which contain extra
sources of electroweak symmetry breaking, ii) those which contain
particles getting most of their mass from electroweak symmetry breaking.
We show how some "HEFTy" theories are still viable given current
experimental constraints. We also show how these geometric features map
on to pieces of amplitudes that grow with energy, and therefore how
"HEFTy" theories are guaranteed to violate unitarity at the TeV scale.