121 research outputs found
Determining Eccentricities of Transiting Planets: A Divide in the Mass-Period Plane
The two dominant features in the distribution of orbital parameters for
close-in exoplanets are the prevalence of circular orbits for very short
periods, and the observation that planets on closer orbits tend to be heavier.
The first feature is interpreted as a signature of tidal evolution, while the
origin of the second, a "mass-period relation" for hot Jupiters, is not
understood. In this paper we re-consider the ensemble properties of transiting
exoplanets with well-measured parameters, focussing on orbital eccentricity and
the mass-period relation. We recalculate the constraints on eccentricity in a
homogeneous way, using new radial-velocity data, with particular attention to
statistical biases. We find that planets on circular orbits gather in a
well-defined region of the mass-period plane, close to the minimum period for
any given mass. Exceptions to this pattern reported in the Literature can be
attributed to statistical biases. The ensemble data is compatible with
classical tide theory with orbital circularisation caused by tides raised on
the planet, and suggest that tidal circularisation and the stopping mechanisms
for close-in planets are closely related to each other. The position
mass-period relation is compatible with a relation between a planet's Hill
radius and its present orbit.Comment: 8 pages, to be published in MNRA
Microgravity experiments on the collisional behavior of Saturnian ring particles
In this paper we present results of two novel experimental methods to
investigate the collisional behavior of individual macroscopic icy bodies. The
experiments reported here were conducted in the microgravity environments of
parabolic flights and the Bremen drop tower facility. Using a cryogenic
parabolic-flight setup, we were able to capture 41 near-central collisions of
1.5-cm-sized ice spheres at relative velocities between 6 and . The analysis of the image sequences provides a uniform distribution
of coefficients of restitution with a mean value of and values ranging from to 0.84. Additionally, we
designed a prototype drop tower experiment for collisions within an ensemble of
up to one hundred cm-sized projectiles and performed the first experiments with
solid glass beads. We were able to statistically analyze the development of the
kinetic energy of the entire system, which can be well explained by assuming a
granular `fluid' following Haff's law with a constant coefficient of
restitution of . We could also show that the setup is
suitable for studying collisions at velocities of
appropriate for collisions between particles in Saturn's dense main rings.Comment: Accepted for publication in the Icarus Special Issue "Cassini at
Saturn
Post-quantum Zero Knowledge in Constant Rounds
We construct a constant-round zero-knowledge classical argument for NP secure
against quantum attacks. We assume the existence of Quantum Fully-Homomorphic
Encryption and other standard primitives, known based on the Learning with
Errors Assumption for quantum algorithms. As a corollary, we also obtain a
constant-round zero-knowledge quantum argument for QMA.
At the heart of our protocol is a new no-cloning non-black-box simulation
technique
On the accumulation of planetesimals near disc gaps created by protoplanets
We have performed three-dimensional two-fluid (gas-dust) hydrodynamical
models of circumstellar discs with embedded protoplanets (3 - 333 M\oplu) and
small solid bodies (radii 10cm to 10m). We find that high mass planets (\gtrsim
Saturn mass) open sufficiently deep gaps in the gas disc such that the density
maximum at the outer edge of the gap can very efficiently trap metre-sized
solid bodies. This allows the accumulation of solids at the outer edge of the
gap as solids from large radii spiral inwards to the trapping region. This
process of accumulation occurs fastest for those bodies that spiral inwards
most rapidly, typically metre-sized boulders, whilst smaller and larger objects
will not migrate sufficiently rapidly in the discs lifetime to benefit from the
process. Around a Jupiter mass planet we find that bound clumps of solid
material, as large as several Earth masses, may form, potentially collapsing
under self-gravity to form planets or planetesimals. These results are in
agreement with Lyra et al. (2009), supporting their finding that the formation
of a second generation of planetesimals or of terrestrial mass planets may be
triggered by the presence of a high mass planet.Comment: 14 pages, 10 figures. Accepted for publication in MNRA
A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus
The Trojan population consists of two swarms of asteroids following the same
orbit as Jupiter and located at the L4 and L5 Lagrange points of the
Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid
617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit
of this double system was hitherto unknown. Here we report that the components,
separated by 680 km, move around the system centre of mass, describing roughly
a circular orbit. Using the orbital parameters, combined with thermal
measurements to estimate the size of the components, we derive a very low
density of 0.8 g/cc. The components of Patroclus are therefore very porous or
composed mostly of water ice, suggesting that they could have been formed in
the outer part of the solar system.Comment: 10 pages, 3 figures, 1 tabl
Inefficient star formation: The combined effects of magnetic fields and radiative feedback
We investigate the effects of magnetic fields and radiative protostellar
feedback on the star formation process using self-gravitating radiation
magnetohydrodynamical calculations. We present results from a series of
calculations of the collapse of 50 solar mass molecular clouds with various
magnetic field strengths and with and without radiative transfer.
We find that both magnetic fields and radiation have a dramatic impact on
star formation, though the two effects are in many ways complementary. Magnetic
fields primarily provide support on large scales to low density gas, whereas
radiation is found to strongly suppress small-scale fragmentation by increasing
the temperature in the high-density material near the protostars. With strong
magnetic fields and radiative feedback the net result is an inefficient star
formation process with a star formation rate of ~< 10% per free-fall time that
approaches the observed rate, although we have only been able to follow the
calculations for ~1/3 of a free-fall time beyond the onset of star formation.Comment: 14 pages, 6 figures, accepted for publication in MNRAS. Movies for
all the runs and version with high-res figures available from
http://users.monash.edu.au/~dprice/pubs/mclusterRT/ v2: minor changes to
match published versio
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
Mean Motion Resonances in Extrasolar Planetary Systems with Turbulence, Interactions, and Damping
This paper continues previous work on the effects of turbulence on mean
motion resonances in extrasolar planetary systems. Turbulence is expected to
arise in the disks that form planets, and these fluctuations act to compromise
resonant configurations. This paper extends previous work by considering how
interactions between the planets and possible damping effects imposed by the
disk affect the outcomes. These physical processes are studied using three
approaches: numerical integrations of the 3-body problem with additional
forcing due to turbulence, model equations that reduce the problem to
stochastically driven oscillators, and Fokker-Planck equations that describe
the time evolution of an ensemble of systems. With this combined approach, we
elucidate the physics of how turbulence can remove extrasolar planetary systems
from mean motion resonance. As expected, systems with sufficiently large
damping (dissipation) can maintain resonance, in spite of turbulent forcing. In
the absence of strong damping, ensembles of these systems exhibit two regimes
of behavior, where the fraction of the bound states decreases as a power-law or
as an exponential. Both types of behavior can be understood through the model
developed herein. For systems with weak interactions between planets, the model
reduces to a stochastic pendulum, and the fraction of bound states decreases as
a power-law. For highly interactive systems, the dynamics are more complicated
and the fraction of bound states decreases exponentially. We show how planetary
interactions lead to drift terms in the Fokker-Planck equation and account for
this exponential behavior. In addition to clarifying the physical processes
involved, this paper strengthens the finding that turbulence implies that mean
motions resonances should be rare.Comment: accepted to ApJ, 42 pages, 7 figure
Ferret: Fast Extension for coRRElated oT with small communication
Correlated oblivious transfer (COT) is a crucial building block for secure multi-party computation (MPC) and can be generated efficiently via OT extension. Recent works based on the pseudorandom correlation generator (PCG) paradigm presented a new way to generate random COT correlations using only communication sublinear to the output length. However, due to their high computational complexity, these protocols are only faster than the classical IKNP-style OT extension under restricted network bandwidth.
In this paper, we propose new COT protocols in the PCG paradigm that achieve unprecedented performance. With 50 Mbps network bandwidth, our maliciously secure protocol can produce one COT correlation in 22 nanoseconds. More specifically, our results are summarized as follows:
- We propose a semi-honest COT protocol with sublinear communication and linear computation. This protocol assumes primal-LPN and is built upon a recent VOLE protocol with semi-honest security by Schoppmann et al. (CCS 2019). We are able to apply various optimizations to reduce its communication cost by roughly 15x, not counting a one-time setup cost that diminishes as we generate more COTs.
- We strengthen our COT protocol to malicious security with no loss of efficiency. Among all optimizations, our new protocol features a new checking technique that ensures correctness and consistency essentially for free. In particular, our maliciously secure protocol is only 1-3 nanoseconds slower for each COT.
- We implemented our protocols, and the code will be publicly available at EMP-toolkit. We observe at least 9x improvement in running time compared to the state-of-the-art protocol by Boyle et al. (CCS 2019) in both semi-honest and malicious settings under any network faster than 50 Mbps.
With this new record of efficiency for generating COT correlations, we anticipate new protocol designs and optimizations will flourish on top of our protocol
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