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VERSION:2.0
PRODID:icalendar-ruby
CALSCALE:GREGORIAN
X-WR-TIMEZONE;VALUE=TEXT:Europe/Zurich
BEGIN:VEVENT
DTSTAMP:20261102T235908Z
UID:a23529be-2713-4702-a8f8-a0c311106fda
DTSTART:20261103T140000
DTEND:20261103T153000
DESCRIPTION:I will discuss the Effective Field Theory of Dark Energy\, wher
 e the ghost condensate (GC) exhibits a sixth-order dispersion relation of 
 the form $\\omega^2 \\sim k^6$. I will analyze scalar and tensor perturbat
 ions in FLRW and de Sitter backgrounds\, demonstrating that higher-derivat
 ive operators in the unitary-gauge action induce nontrivial\, scale-depend
 ent modifications of gravity. In particular\, the speed of gravitational w
 aves becomes frequency-dependent\, with deviations from luminal propagatio
 n arising at momenta $k \\sim M_{\\rm Pl}/\\sqrt{\\sigma_1}$\, where $\\si
 gma_1$ is the coefficient of the operator $\\gamma^{\\mu\nu}\nabla_\\mu K_
 {\\alpha\\beta}\nabla_\nu K^{\\alpha\\beta}$. Requiring the absence of gho
 sts at high momenta\, together with consistency with LIGO observations\, p
 laces bounds on $\\sigma_1$\, while gradient stability in the scalar and v
 ector sectors constrains $\\sigma_1$ and the couplings associated with the
  remaining combinations of $(\nabla_\\alpha K_{\\beta\\sigma})^2$ operator
 s. In an FLRW background\, we compute the effective gravitational constant
 \, $G_{\\rm eff}$\, and the gravitational slip parameter\, $\\gamma$\, in 
 the sub-horizon regime\, $k/a \\gg H$\, and demonstrate their explicit sca
 le dependence. Unlike the quartic ghost condensate\, the sextic theory mod
 ifies the Newtonian potential through both spatial and temporal variations
  of the matter density. At late times\, when the gravitational potential b
 ecomes static\, these modifications exhibit oscillations with characterist
 ic spatial and temporal scales of order $M_{\\rm Pl}/M^2$ and $M^4/M_{\\rm
  Pl}^3$\, respectively\, where $M$ denotes the ghost condensate scale. Fin
 ally\, we derive the scalar--tensor theory equivalent to the unitary-gauge
  action that gives rise to a GC with a sextic dispersion relation. The app
 earance of third derivatives of the scalar field in the covariant action i
 ndicates that this theory belongs to a previously unexplored class of scal
 ar--tensor theories.
LOCATION:ETH Zürich\, Hönggerberg HIT F 12
ORGANIZER:Amjad Ashoorioon
SUMMARY:Extended Effective Field Theory of Dark Energy: Ghost Condensate Da
 rk Energy with Sextic Dispersion Relation
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