4 research outputs found
Slow-roll inflation in (R+R*4) gravity
We reconsider the toy-model of topological inflation, based on the
R*4-modified gravity. By using its equivalence to the certain scalar-tensor
gravity model in four space-time dimensions, we compute the inflaton scalar
potential and investigate a possibility of inflation. We confirm the existence
of the slow-roll inflation with an exit. However, the model suffers from the
eta-problem that gives rise to the unacceptable value of the spectral index n_s
of scalar perturbations.Comment: 12 pages, 3 figures, LaTeX, misprints corrected and references
update
Palatini versus metric formulation in higher curvature gravity
We compare the metric and the Palatini formalism to obtain the Einstein
equations in the presence of higher-order curvature corrections that consist of
contractions of the Riemann tensor, but not of its derivatives. We find that
there is a class of theories for which the two formalisms are equivalent. This
class contains the Palatini version of Lovelock theory, but also more
Lagrangians that are not Lovelock, but respect certain symmetries. For the
general case, we find that imposing the Levi-Civita connection as an Ansatz,
the Palatini formalism is contained within the metric formalism, in the sense
that any solution of the former also appears as a solution of the latter, but
not necessarily the other way around. Finally we give the conditions the
solutions of the metric equations should satisfy in order to solve the Palatini
equations.Comment: 13 pages, latex. V2: reference added, major changes in section 3,
conclusions partially correcte
Scalar potential in F(R) supergravity
We derive a scalar potential in the recently proposed N=1 supersymmetric
generalization of f(R) gravity in four space-time dimensions. Any such
higher-derivative supergravity is classically equivalent to the standard N=1
supergravity coupled to a chiral (matter) superfield, via a Legendre-Weyl
transform in superspace. The Kaehler potential, the superpotential and the
scalar potential of that theory are all governed by a single holomorphic
function. We also find the conditions for the vanishing cosmological constant
and spontaneous supersymmetry breaking, without fine-tuning, which define a
no-scale F(R) supergravity. The F(R) supergravities are suitable for physical
applications in the inflationary cosmology based on supergravity and
superstrings.Comment: 10 pages, LateX, no figures; section 4 extende