BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Prashanth Raman (Indian Institute of Science) DTSTART:20220927T193000Z DTEND:20220927T203000Z DTSTAMP:20260423T024550Z UID:HET/45 DESCRIPTION:Title: Pos itivity Constraints on EFT’s and Geometric Function Theory\nby Prash anth Raman (Indian Institute of Science) as part of Purdue HET\n\nLecture held in Room 242\, Department of Physics and Astronomy.\n\nAbstract\nIn th is talk\, we shall look at the implications of crossing symmetry\, localit y\, and unitarity in the UV on low-energy EFT’s. We will begin by lookin g at 2-2scattering amplitudes with identical external particles and introd uce a crossing symmetric dispersive representation (CSDR) of the amplitude that makes full (s\,t\,u)-crossing symmetry manifest\, unlike the usual f ixed-t dispersion relations. Though the CSDR makes crossing symmetry manif est\, locality is lost and has to be restored by demanding that certain sp urious singularities cancel in the low energy expansion of the amplitude l eading to locality constraints. \n\nFor massive external particles\, the C SDR and unitarity make a certain analytic property of the amplitude called typically-realness manifest and enables us to use techniques from the geo metric function theory of typically-real functions to show that the low en ergy Wilson coefficients have to be o(1) numbers and that the space of the se Wilson coefficients is finite. \nFor massless external particles with massive exchanges we look at the celestial amplitude (CA) corresponding to our original 2-2 scattering amplitude and show that the locality constrai nts imply an infinite linear system of equations that the partial wave mom ents of any local theory need to satisfy. By additionally imposing linear unitarity (positivity of partial wave moments)\, we show that these natura lly lead to the phenomenon of low-spin dominance (LSD). Finally\, we show that the crossing symmetric partial waves with spurious singularities rem oved\, dubbed as Feynman blocks are typically-real and using this we obtai n two-sided bounds on low-energy Wilson coefficients for this case.\nThis is based on work with Sudip Ghosh and Aninda Sinha.\n\nHost: Martin Krucze nski\n LOCATION:https://researchseminars.org/talk/HET/45/ END:VEVENT END:VCALENDAR