15,869 research outputs found
On the stability of field-theoretical regularizations of negative tension branes
Any attempt to regularize a negative tension brane through a bulk scalar
requires that this field is a ghost. One can try to improve in this aspect in a
number of ways. For instance, it has been suggested to employ a field whose
kinetic term is not sign definite, in the hope that the background may be
overall stable. We show that this is not the case; the physical perturbations
(gravity included) of the system do not extend across the zeros of the kinetic
term; hence, all the modes are entirely localized either where the kinetic term
is positive, or where it is negative; this second type of modes are ghosts. We
show that this conclusion does not depend on the specific choice for the
kinetic and potential functions for the bulk scalar.Comment: 7 pages, 3 figure
Three-form inflation and non-Gaussianity
We calculate the perturbed action, at second and third order, for a massive
three-form field minimally coupled to gravity, and use it to explore the
observational predictions of three-form inflation. One intriguing result is
that the value of the spectral index is nearly independent of the three-form
potential, being fixed solely by the number of e-folds of inflation, with
n_s=0.97 for the canonical number of 60. Considering the bispectrum, we employ
standard techniques to give explicit results for two models, one of which
produces a large non-Gaussianity. Finally, we confirm our results by employing
a duality relating the three-form theory to a non-canonical scalar field theory
and explicitly re-computing results in this dual picture.Comment: 23 pages, 6 figures. Typos corrected and addition of one appendix.
Accepted in JCA
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