Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We report the discovery and confirmation of a transiting circumbinary planet (PH1b) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625. The 6.18 +/- 0.17 Earth radii planet orbits outside the 20-day orbit of an eclipsing binary consisting of an F dwarf (1.734 +/- 0.044 Solar radii, 1.528 +/- 0.087 Solar masses) and M dwarf (0.378+/- 0.023 Solar radii, 0.408 +/- 0.024 Solar masses). For the planet, we find an upper mass limit of 169 Earth masses (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is well within the planetary regime. Outside the planet's orbit, at ~1000 AU,a previously unknown visual binary has been identified that is likely bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet.

Abstract:

We study the dynamics of homogeneous, isotropic universes which are governed by the Eddington-inspired alternative theory of gravity which has a single extra parameter, $\kappa$. Previous results showing singularity-avoiding behaviour for $\kappa > 0$ are found to be upheld in the case of domination by a perfect fluid with equation of state parameter $w > 0$. The range $-1/3 < w < 0$ is found to lead to universes which experience unbounded expansion rate whilst still at a finite density. In the case $\kappa < 0$ the addition of spatial curvature is shown to lead to the possibility of oscillation between two finite densities. Domination by a scalar field with an exponential potential is found to also lead to singularity-avoiding behaviour when $\kappa > 0$. Certain values of the parameters governing the potential lead to behaviour in which the expansion rate of the universe changes sign several times before transitioning to regular GR-like behaviour.