New Classes of Partial Geometries and Their Associated LDPC Codes

The use of partial geometries to construct parity-check matrices for LDPC codes has resulted in the design of successful codes with a probability of error close to the Shannon capacity at bit error rates down to $10^{-15}$. Such considerations have motivated this further investigation. A new and simple construction of a type of partial geometries with quasi-cyclic structure is given and their properties are investigated. The trapping sets of the partial geometry codes were considered previously using the geometric aspects of the underlying structure to derive information on the size of allowable trapping sets. This topic is further considered here. Finally, there is a natural relationship between partial geometries and strongly regular graphs. The eigenvalues of the adjacency matrices of such graphs are well known and it is of interest to determine if any of the Tanner graphs derived from the partial geometries are good expanders for certain parameter sets, since it can be argued that codes with good geometric and expansion properties might perform well under message-passing decoding.Comment: 34 pages with single column, 6 figure

WASP-12b as a prolate, inflated and disrupting planet from tidal dissipation

The class of exotic Jupiter-mass planets that orbit very close to their parent stars were not explicitly expected before their discovery. The recently found transiting planet WASP-12b has a mass Mp = 1.4(+/-0.1) Jupiter masses (MJ), a mean orbital distance of only 3.1 stellar radii (meaning it is subject to intense tidal forces), and a period of 1.1 days. Its radius 1.79(+/- 0.09) RJ is unexpectedly large and its orbital eccentricity 0.049(+/-0:015) is even more surprising as such close orbits are in general quickly circularized. Here we report an analysis of its properties, which reveals that the planet is losing mass to its host star at a rate ~ 10^-7 MJ yr^-1. The planets surface is distorted by the stars gravity and the light curve produced by its prolate shape will differ by about ten per cent from that of a spherical planet. We conclude that dissipation of the stars tidal perturbation in the planets convective envelope provides the energy source for its large volume. We predict up to 10mJy CO band-head (2.292 micron) emission from a tenuous disk around the host star, made up of tidally stripped planetary gas. It may also contain a detectable resonant super-Earth, as a hypothetical perturber that continually stirs up WASP-12b's eccentricity.Comment: Accepted to Nature, 14 pages, 1 figur

Embryo impacts and gas giant mergers II: Diversity of Hot Jupiters' internal structure

We consider the origin of compact, short-period, Jupiter-mass planets. We propose that their diverse structure is caused by giant impacts of embryos and super-Earths or mergers with other gas giants during the formation and evolution of these hot Jupiters. Through a series of numerical simulations, we show that typical head-on collisions generally lead to total coalescence of impinging gas giants. Although extremely energetic collisions can disintegrate the envelope of gas giants, these events seldom occur. During oblique and moderately energetic collisions, the merger products retain higher fraction of the colliders' cores than their envelopes. They can also deposit considerable amount of spin angular momentum to the gas giants and desynchronize their spins from their orbital mean motion. We find that the oblateness of gas giants can be used to infer the impact history. Subsequent dissipation of stellar tide inside the planets' envelope can lead to runaway inflation and potentially a substantial loss of gas through Roche-lobe overflow. The impact of super-Earths on parabolic orbits can also enlarge gas giant planets' envelope and elevates their tidal dissipation rate over $\sim$ 100 Myr time scale. Since giant impacts occur stochastically with a range of impactor sizes and energies, their diverse outcomes may account for the dispersion in the mass-radius relationship of hot Jupiters.Comment: 19 pages, 7 figures, 7 tables. Accepted for publication in MNRA

Electron Flavored Dark Matter

In this paper we investigate the phenomenology of the electron flavored Dirac dark matter with two types of portal interactions. We analyze constraints from the electron magnetic moment anomaly, LHC searches of singly charged scalar, dark matter relic abundance as well as direct and indirect detections. Our study shows that the available parameter space is quite constrained, but there are parameter space that is compatible with the current data. We further show that the DAMPE cosmic ray electron excess, which indicates cosmic ray excess at around 1.5 TeV, can be interpreted as the annihilation of dark matter into electron positron pairs in this model.Comment: 6 pages, 5 figure