2 research outputs found
Perturbations of dark energy models
>Magister Scientiae - MScThe growth of structure in the Universe proceeds via the collapse of dark matter
and baryons. This process is retarded by dark energy which drives an accelerated
expansion of the late Universe. In this thesis we use cosmological perturbation theory
to investigate structure formation for a particular class of dark energy models,
i.e. interacting dark energy models. In these models there is a non-gravitational interaction between dark energy and dark matter, which alters the standard evolution
(with non-interacting dark energy) of the Universe. We consider a simple form of
the interaction where the energy exchange in the background is proportional to the
dark energy density. We analyse the background dynamics to uncover the e ect of
the interaction. Then we develop the perturbation equations that govern the evolution
of density perturbations, peculiar velocities and the gravitational potential. We
carefully account for the complex nature of the perturbed interaction, in particular
for the momentum transfer in the dark sector. This leads to two di erent types of
model, where the momentum exchange vanishes either in the dark matter rest-frame
or the dark energy rest-frame. The evolution equations for the perturbations are
solved numerically, to show how structure formation is altered by the interaction
The Magellan-TESS Survey I: Survey Description and Mid-Survey Results
One of the most significant revelations from Kepler is that roughly one-third
of Sun-like stars host planets which orbit their stars within 100 days and are
between the size of Earth and Neptune. How do these super-Earth and sub-Neptune
planets form, what are they made of, and do they represent a continuous
population or naturally divide into separate groups? Measuring their masses and
thus bulk densities can help address these questions of their origin and
composition. To that end, we began the Magellan-TESS Survey (MTS), which uses
Magellan II/PFS to obtain radial velocity (RV) masses of 30 transiting
exoplanets discovered by TESS and develops an analysis framework that connects
observed planet distributions to underlying populations. In the past, RV
measurements of small planets have been challenging to obtain due to the
faintness and low RV semi-amplitudes of most Kepler systems, and challenging to
interpret due to the potential biases in the existing ensemble of small planet
masses from non-algorithmic decisions for target selection and observation
plans. The MTS attempts to minimize these biases by focusing on bright TESS
targets and employing a quantitative selection function and multi-year
observing strategy. In this paper, we (1) describe the motivation and survey
strategy behind the MTS, (2) present our first catalog of planet mass and
density constraints for 25 TESS Objects of Interest (TOIs; 20 in our population
analysis sample, five that are members of the same systems), and (3) employ a
hierarchical Bayesian model to produce preliminary constraints on the
mass-radius (M-R) relation. We find qualitative agreement with prior
mass-radius relations but some quantitative differences (abridged). The the
results of this work can inform more detailed studies of individual systems and
offer a framework that can be applied to future RV surveys with the goal of
population inferences.Comment: 101 pages (39 of main text and references, the rest an appendix of
figures and tables). Submitted to AAS Journal