Symmetries and unitarity of theories with spontaneously broken boosts

Tanguy Grall (DAMTP, University of Cambridge)

04-Dec-2020, 18:00-19:00 (3 years ago)

Abstract: Systems with spontaneously broken Lorentz boosts are found everywhere in nature, from condensed matter to the early universe. In this talk I will discuss Effective Field Theories (EFTs) of a single, shift-symmetric, phonon that parametrises the breaking of time translations and Lorentz boosts. Such theories include for instance scalar modes in the EFT of inflation, superfluid or galileid phonons (the broken phase of Galileon scalar EFTs).

In the first part, I will present an algebraic classification of such theories, based on their non-linearly realised symmetries, in direct analogy with previous classifications of so-called Exceptional (Lorentz invariant) EFTs. In doing so I will present, for instance, a new galileid theory, “the extended galileid”, as well as other better known superfluid and galileid theories.

In the second part, I will discuss perturbative unitarity of such theories, making use of the unbroken symmetries of 2-to-2 scattering amplitudes. A common feature of non-Lorentz invariant EFTs is that they have a cut-off not only in energy but also in momentum. I will show how this arises in our EFTs and derive partial-wave bounds that can be used to probe their strong coupling regime. As a practical application, I will discuss the implications of these results on the EFT of inflation in the sub-horizon region.

cosmology and nongalactic astrophysicsother condensed matterquantum gasesstrongly correlated electronssuperconductivitygeneral relativity and quantum cosmologyHEP - theory

Audience: researchers in the topic


Carnegie Mellon theoretical physics

Organizer: Riccardo Penco*
*contact for this listing

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