Consistency of Scalar and Vector Effective Field Theories
In the absence of a theory of everything, modern physicists need to rely on other predictive tools and turned to Effective Field Theories (EFTs) in a number of fields, including but not limited to statistical mechanics, condensed matter, particle physics, cosmology and gravity. The coefficients of a...
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Zusammenfassung: | In the absence of a theory of everything, modern physicists need to rely on
other predictive tools and turned to Effective Field Theories (EFTs) in a
number of fields, including but not limited to statistical mechanics, condensed
matter, particle physics, cosmology and gravity. The coefficients of an EFT can
be constrained with high precision by experiments, which can involve
high-energy particle colliders for instance but are generally left free from
the theoretical point of view. The focus of this thesis is to use various
consistency criteria to get theoretical constraints on the low-energy
coefficients of EFTs. In particular, we construct a new model of massive spin-1
field by requiring that the theory is free of any ghostly degree of freedom. We
then study its cosmological perturbations and ask that all propagating modes
are stable and subluminal, reducing the space of viable cosmological solutions.
Finally, we implement a method to get 'causality bounds', which are obtained by
requiring infrared causality. This is imposed by forbidding any resolvable time
advance in the EFT. We derive such 'causality bounds' for shift-symmetric and
Galileon scalar EFTs, before turning to gauge-symmetric vector fields. We prove
that our causality bounds can be competitive with positivity bounds and can
even be used in scenarios that are out of reach of the positivity approach. The
result of this thesis, by exploring several consistency criteria, is to provide
compact causality bounds for low-energy EFT coefficients, in addition to
constraints coming from the absence of ghosts, stability and cosmological
viability. |
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DOI: | 10.48550/arxiv.2308.05172 |