7 research outputs found
Microlensing by natural wormholes: theory and simulations
We provide an in depth study of the theoretical peculiarities that arise in
effective negative mass lensing, both for the case of a point mass lens and
source, and for extended source situations. We describe novel observational
signatures arising in the case of a source lensed by a negative mass. We show
that a negative mass lens produces total or partial eclipse of the source in
the umbra region and also show that the usual Shapiro time delay is replaced
with an equivalent time gain. We describe these features both theoretically, as
well as through numerical simulations. We provide negative mass microlensing
simulations for various intensity profiles and discuss the differences between
them. The light curves for microlensing events are presented and contrasted
with those due to lensing produced by normal matter. Presence or absence of
these features in the observed microlensing events can shed light on the
existence of natural wormholes in the Universe.Comment: 16 pages, 24 postscript figures (3 coloured), revtex style, submitted
to Phys. Rev.
Energy Conditions in Modified Gravity with Non-minimal Coupling to Matter
In this paper we study a model of modified gravity with non-minimal coupling
between a general function of the Gauss-Bonnet invariant, , and matter
Lagrangian from the point of view of the energy conditions. Such model has been
introduced in Ref. [21] for description of early inflation and late-time cosmic
acceleration. We present the suitable energy conditions for the above mentioned
model and then, we use the estimated values of the Hubble, deceleration and
jerk parameters to apply the obtained energy conditions to the specific class
of modified Gauss-Bonnet models.Comment: 12 pages, no figur, Accepted for publication in Astrophysics and
Space Scienc
f(R,L_m) gravity
We generalize the type gravity models by assuming that the
gravitational Lagrangian is given by an arbitrary function of the Ricci scalar
and of the matter Lagrangian . We obtain the gravitational field
equations in the metric formalism, as well as the equations of motion for test
particles, which follow from the covariant divergence of the energy-momentum
tensor. The equations of motion for test particles can also be derived from a
variational principle in the particular case in which the Lagrangian density of
the matter is an arbitrary function of the energy-density of the matter only.
Generally, the motion is non-geodesic, and takes place in the presence of an
extra force orthogonal to the four-velocity. The Newtonian limit of the
equation of motion is also considered, and a procedure for obtaining the
energy-momentum tensor of the matter is presented. The gravitational field
equations and the equations of motion for a particular model in which the
action of the gravitational field has an exponential dependence on the standard
general relativistic Hilbert--Einstein Lagrange density are also derived.Comment: 6 pages, no figures; minor modifications, references added; accepted
for publication in EPJ