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CATEGORIES:DAMTP Friday GR Seminar
SUMMARY:Scalar-tensor theories of gravity beyond Horndesky
- Prof. Juan Garcia-Bellido (IFT-UAM/CSIC)
DTSTART;TZID=Europe/London:20141031T130000
DTEND;TZID=Europe/London:20141031T140000
UID:TALK55974AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/55974
DESCRIPTION:In this talk I will briefly review structure of sc
alar-tensor theories of gravity based on derivativ
e couplings between the scalar and the matter degr
ees of freedom. Such interactions are classified b
y their tensor structure into conformal (scalar)\,
disformal (vector) and extended disformal (tracel
ess tensor)\, as well as by the derivative order o
f the scalar field. Relations limited to first der
ivatives of the field ensure second order equation
s of motion in the Einstein frame and hence the ab
sence of Ostrogradski ghost degrees of freedom. Th
e existence of a mapping to the Jordan frame is no
t trivial in the general case\, and can be address
ed using the Jacobian of the frame transformation
through its eigenvalues and eigentensors. Although
sane in the Einstein frame\, generic disformally
coupled theories are described by higher order equ
ations of motion in the Jordan frame. This apparen
t contradiction is solved by the use of a hidden c
onstraint: the contraction of the metric equations
with a Jacobian eigentensor provides a constraint
relation for the higher field derivatives\, which
allows one to express the dynamical equations in
a second order form. This signals a loophole in Ho
rndeski's theorem and allows one to enlarge the se
t of scalar-tensor theories which are Ostrogradski
-stable.
LOCATION:Pavilion B Potter Room (B1.19)
CONTACT:Benson Way
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