BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Tanguy Grall (DAMTP\, University of Cambridge) DTSTART:20201204T180000Z DTEND:20201204T190000Z DTSTAMP:20260423T022810Z UID:CMU-TP/19 DESCRIPTION:Title: Symmetries and unitarity of theories with spontaneously broken boosts\ nby Tanguy Grall (DAMTP\, University of Cambridge) as part of Carnegie Mel lon theoretical physics\n\n\nAbstract\nSystems with spontaneously broken L orentz boosts are found everywhere in nature\, from condensed matter to th e early universe. In this talk I will discuss Effective Field Theories (EF Ts) of a single\, shift-symmetric\, phonon that parametrises the breaking of time translations and Lorentz boosts. Such theories include for instanc e scalar modes in the EFT of inflation\, superfluid or galileid phonons (t he broken phase of Galileon scalar EFTs).\n\nIn the first part\, I will pr esent an algebraic classification of such theories\, based on their non-li nearly realised symmetries\, in direct analogy with previous classificatio ns of so-called Exceptional (Lorentz invariant) EFTs. In doing so I will p resent\, for instance\, a new galileid theory\, “the extended galileid ”\, as well as other better known superfluid and galileid theories.\n\nI n 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 o ur EFTs and derive partial-wave bounds that can be used to probe their str ong coupling regime. As a practical application\, I will discuss the impli cations of these results on the EFT of inflation in the sub-horizon region .\n LOCATION:https://researchseminars.org/talk/CMU-TP/19/ END:VEVENT END:VCALENDAR