3,280 research outputs found
Conformal Transformations and Weak Field Limit of Scalar-Tensor Gravity
The weak field limit of scalar tensor theories of gravity is discussed in
view of conformal transformations. Specifically, we consider how physical
quantities, like gravitational potentials derived in the Newtonian
approximation for the same scalar-tensor theory, behave in the Jordan and in
the Einstein frame. The approach allows to discriminate features that are
invariant under conformal transformations and gives contributions in the debate
of selecting the true physical frame. As a particular example, the case of
gravity is considered.Comment: 11 pages, preliminary versio
Galaxy rotation curves in -gravity
We investigate the possibility to explain theoretically the galaxy rotation
curves by a gravitational potential in total absence of dark matter. To this
aim an analytic fourth-order theory of gravity, nonminimally coupled with a
massive scalar field is considered. Specifically, the interaction term is given
by an analytic function where is the Ricci scalar and is
the scalar field. The gravitational potential is generated by a point-like
source and compared with the so called Sanders's potential that can be exactly
reproduced in this case. This result means that the problem of dark matter in
spiral galaxies could be fully addressed by revising general relativity at
galactic scales and requiring further gravitational degrees of freedom instead
of new material components that have not been found out up to now.Comment: 17 pages, 6 figures. To appear in Phys. Rev.
Fourth order gravity and experimental constraints on Eddington parameters
PPN-limit of higher order theories of gravity represents a still
controversial matter of debate and no definitive answer has been provided, up
to now, about this issue. By exploiting the analogy between scalar-tensor and
fourth-order theories of gravity, one can generalize the PPN-limit formulation.
By using the definition of the PPN-parameters and in term of
the derivatives, we show that a family of third-order polynomial
theories, in the Ricci scalar , turns out to be compatible with the
PPN-limit and the deviation from General Relativity theoretically predicted
agree with experimental data.Comment: 7 pages, 3 figure
The Quadratic Coefficient of the Electron Cloud Mapping
The Electron Cloud is an undesirable physical phenomenon which might produce
single and multi-bunch instability, tune shift, increase of pressure ultimately
limiting the performance of particle accelerators. We report our results on the
analytical study of the electron dynamics.Comment: 5 pages, 7 figures, presented at ECLOUD12: Joint
INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects, La Biodola, Isola
d Elba, Italy, 5-9 June 201
Hydrostatic equilibrium and stellar structure in f(R)-gravity
We investigate the hydrostatic equilibrium of stellar structure by taking
into account the modi- fied La\'e-Emden equation coming out from f(R)-gravity.
Such an equation is obtained in metric approach by considering the Newtonian
limit of f(R)-gravity, which gives rise to a modified Poisson equation, and
then introducing a relation between pressure and density with polytropic index
n. The modified equation results an integro-differential equation, which, in
the limit f(R) \rightarrow R, becomes the standard La\'e-Emden equation. We
find the radial profiles of gravitational potential by solving for some values
of n. The comparison of solutions with those coming from General Relativity
shows that they are compatible and physically relevant.Comment: 9 pages, 1 figur
Maps for Electron Clouds: Application to LHC Conditioning
In this communication we present a generalization of the map formalism,
introduced in [1] and [2], to the analysis of electron flux at the chamber wall
with particular reference to the exploration of LHC conditioning scenarios.Comment: 3 pages, 4 figure
- …