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SUMMARY:Perturbative unitarity and Goldstone effective field theory in mod
 ified Genesis
DTSTART;VALUE=DATE-TIME:20261029T152500Z
DTEND;VALUE=DATE-TIME:20261029T154000Z
DTSTAMP;VALUE=DATE-TIME:20261101T205607Z
UID:indico-contribution-6262@cern.ch
DESCRIPTION:Speakers: Zlata Evarovskaya (Moscow State U.)\nWe develop a ma
 nifestly conformal-frame-independent approach to assessing perturbative un
 itarity and apply it to modified Genesis in a $G_2+G_3$ Horndeski model. T
 he construction uses an effective metric determined by the tensor quadrati
 c action\, its associated conformal time\, and canonically normalized scal
 ar perturbations. We determine the quadratic coefficients and scalar sound
  speed\, analyze linear stability\, and express the scalar cubic action in
  frame-invariant variables\, retaining interactions generated by time-depe
 ndent canonical normalization. Power counting identifies potentially restr
 ictive interactions and estimates their characteristic scales relative to 
 the background evolution scale in the asymptotic past. \n\nWe then compute
  the tree-level scalar-exchange contribution to $2 \\rightarrow 2$ scatter
 ing in a local high-energy approximation. Explicit cancellations among the
  nominally leading interactions demonstrate the limitations of estimates b
 ased on individual operators. The retained leading exchange amplitude cont
 ains only the $\\ell=0$ and $\\ell=2$ partial waves\, and we evaluate thes
 e projections to estimate the perturbative validity range and its dependen
 ce on the scalar sound speed. \n\nAs a complementary description of the sc
 alar sector\, we derive the cubic Goldstone action for the relevant unitar
 y-gauge effective-field-theory operators on a fixed FLRW background\, reta
 ining the time dependence of their coefficients and the interactions gener
 ated by restoring time diffeomorphisms.\n\nhttps://indico.particle.mephi.r
 u/event/626/contributions/6262/
LOCATION: Conference Hall 5
URL:https://indico.particle.mephi.ru/event/626/contributions/6262/
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