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SUMMARY:Gravity Beyond a Single Metric Ghost-free interactions of spin-2 f
 ields
DTSTART:20260515T110000Z
DTEND:20260515T140000Z
DTSTAMP:20260430T083100Z
UID:indico-event-9694@indico.fysik.su.se
DESCRIPTION:Speakers: Joakim Flinckman (Stockholm University)\n\nAbstractT
 he mathematical formulations of the fundamental interactions in nature are
  all expressed in terms of fields classified bytheir mass and spin. The st
 ructure of two of the most successful theories in physics\, General Relati
 vity and the StandardModel of particle physics\, can both be derived more 
 or less uniquely from fields with fixed mass and spin\, guided bytheoretic
 al consistency conditions. The Standard Model contains well-understood int
 eractions of particles with spins lessthan two\, while theories involving 
 spins higher than two are generally problematic. Theories of spin-2 fields
  are much lessexplored\, and in particular\, any consistent multiplet stru
 cture\, crucial for the Standard Model\, is practically unknown.Even witho
 ut considering multiplet structures\, classical theories with interacting 
 spin-2 fields generically propagateadditional pathological fields\, so-cal
 led Boulware–Deser ghosts\, rendering such theories physically unaccepta
 ble. Untilrecently\, only a non-derivative interaction between two spin-2 
 fields\, called bimetric theory\, had been proven consistent.While the bim
 etric interaction can to some extent be trivially extended to more than tw
 o fields\, genuine ghost-free multifieldinteractions have remained elusive
 .In this thesis\, we derive necessary conditions on ghost-free non-derivat
 ive interactions between multiple spin-2 fields.With a suitable parametris
 ation of the fields\, the ghost mode can be isolated\, allowing one to der
 ive necessary conditionsfor it to be non-propagating. These conditions ess
 entially determine the form of the interaction potential uniquely\, up toa
  set of free constant parameters. The admissible class contains all previo
 usly known ghost-free theories\, but is not itselfghost-free in general. I
 mposing an additional necessary condition for ghost-freedom on these param
 eters further restrictsthe interaction to the Hassan–Schmidt–May theor
 y and trivial extensions thereof. Thus\, much as for the lower-spin theori
 esin the Standard Model\, the requirement of theoretical consistency\, her
 e the absence of ghosts\, essentially singles out theadmissible theory. We
  then show that this theory possesses the full set of constraints needed t
 o eliminate all ghost modes\,establishing it as the most general known gho
 st-free multi-gravity interaction. Finally\, we derive the mass spectrum\,
  findingone massless and multiple massive spin-2 fields with a non-tachyon
 ic spectrum.\n\nhttps://indico.fysik.su.se/event/9694/
LOCATION:FB42 (AlbaNova Main Building)
URL:https://indico.fysik.su.se/event/9694/
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