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Abstract

We discuss the role of the top-quark Yukawa coupling $y_t$ concerning the
hierarchy problem and construct an alternative scheme to the conventional
solutions with top partners. In traditional models, like SUSY or composite
Higgs, top partners cancel the top loop contribution to the Higgs quadratic
term. The lack of evidence for such colored partners however drives these
models into more and more fine-tuned regions. Here, an alternative means to
mitigate the top loop, allowing for natural electroweak symmetry breaking, is
presented. Emphasizing that we have not measured the top-Higgs interactions at
high scales yet, we envisage scenarios where this interaction is only
approaching its sizable strength in the infra-red, but gets strongly suppressed
at high scales. We first discuss possible effects via a modification of the
running of the top Yukawa coupling. Then, we turn to models where the top
Yukawa is generated at one-loop level. Originated from a dimension-six
operator, it drops when crossing the mass threshold of new degrees of freedom.
In either case, the top partners are replaced by some new top-philic particles
with strong interaction. Thus, a very different phenomenology, such as large
top mass running and signals in four top final states, is introduced, which
will be discussed in detail. With the assistance of this mechanism, the
solution to the hierarchy problem can be pushed to a (well-defined) higher
scale, and a final test of naturalness might be deferred to a 100 TeV Collider,
like the FCC.