4 research outputs found
Cosmological evolution, future singularities, Little Rip and Pseudo-Rip in viable f(R) theories and their scalar-tensor counterpart
Modified f(R) gravity is one of the most promising candidates for dark
energy, and even for the unification of the whole cosmological evolution,
including the inflationary phase. Within this class of theories, the so-called
viable modified gravities represent realistic theories that are capable of
reproducing late-time acceleration, and satisfy strong constraints at local
scales, where General Relativity is recovered. The present manuscript deals
with the analysis of the cosmological evolution for some of these models, which
indicates that the evolution may enter into a phantom phase, but the behavior
may be asymptotically stable. Furthermore, the scalar-tensor equivalence of
f(R) gravity is considered, which provides useful information about the
possibility of the occurrence of a future singularity. The so-called Little Rip
and Pseudo-Rip are also studied in the framework of this class of modified
gravities.Comment: 20 pages. Extended version, new figures and additional analysis.
Version to be published in Class. Quant. Gra
Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star
We present the discovery and mass measurement of the cold, low-mass planet
MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This
planet has a mass of m_p = 10.4 +- 1.7 Earth masses and orbits a star of mass
M_* = 0.56 +- 0.09 Solar masses at a semi-major axis of a = 3.2 (+1.9 -0.5) AU
and an orbital period of P = 7.6 (+7.7 -1.5} yrs. The planet and host star mass
measurements are enabled by the measurement of the microlensing parallax
effect, which is seen primarily in the light curve distortion due to the
orbital motion of the Earth. But, the analysis also demonstrates the capability
to measure microlensing parallax with the Deep Impact (or EPOXI) spacecraft in
a Heliocentric orbit. The planet mass and orbital distance are similar to
predictions for the critical core mass needed to accrete a substantial gaseous
envelope, and thus may indicate that this planet is a "failed" gas giant. This
and future microlensing detections will test planet formation theory
predictions regarding the prevalence and masses of such planets.Comment: 38 pages with 7 figure