1909.02615
Game of cones: a nulling strategy for modelling lensing convergence in cones with large deviation theory
Barthelemy, et al
The distribution of the cosmic convergence field is modelled from first principles using a large deviation principle. The geometry of the past light cone is accounted for by constructing the total weak-lensing signal from contributions of the matter density in thin disk slices. The prediction of this model is successfully tested against numerical simulation with ray tracing, and found to be accurate within at least 5 per cent in the tails at redshift 1 and opening angle of 10 arcmin and even more so with increasing source redshift and opening angle. An accurate analytical approximation to the theory is also provided for practical implementation. The lensing kernel that mixes physical scales along the line-of-sight tends to reduce the domain of validity of this theoretical approach compared to the three dimensional case of cosmic densities in spherical cells. This effect is shown to be avoidable if a nulling procedure is implemented in order to localise the lensing line-of-sight integrations in a tomographic analysis. Accuracy in the tails is thus achieved within a percent for source redshifts between 0.5 and 1.5 and an opening angle of 10 arcmin. Applications to future weak-lensing surveys like Euclid and the specific issue of shape noise are discussed.
Game of cones: a nulling strategy for modelling lensing convergence in cones with large deviation theory
Barthelemy, et al
The distribution of the cosmic convergence field is modelled from first principles using a large deviation principle. The geometry of the past light cone is accounted for by constructing the total weak-lensing signal from contributions of the matter density in thin disk slices. The prediction of this model is successfully tested against numerical simulation with ray tracing, and found to be accurate within at least 5 per cent in the tails at redshift 1 and opening angle of 10 arcmin and even more so with increasing source redshift and opening angle. An accurate analytical approximation to the theory is also provided for practical implementation. The lensing kernel that mixes physical scales along the line-of-sight tends to reduce the domain of validity of this theoretical approach compared to the three dimensional case of cosmic densities in spherical cells. This effect is shown to be avoidable if a nulling procedure is implemented in order to localise the lensing line-of-sight integrations in a tomographic analysis. Accuracy in the tails is thus achieved within a percent for source redshifts between 0.5 and 1.5 and an opening angle of 10 arcmin. Applications to future weak-lensing surveys like Euclid and the specific issue of shape noise are discussed.
1909.02908
Study on the 3D anisotropic propagation of Galactic cosmic rays
Liu, et al
Conventional cosmic-ray propagation models usually assume an isotropic diffusion coefficient to account for the random deflection of cosmic rays by the turbulent interstellar magnetic field. Such a picture is very successful in explaining a lot of observational phenomena related to the propagation of galactic cosmic rays, such as broken power-law energy spectra, secondary-to-primary ratios, etc. However, the isotropic diffusion presupposition is facing severe challenges from observations. In particular, recent observations on the large-scale anisotropy of TeV cosmic rays show that the dipole direction differs from the prediction of the conventional model. One possible reason is that the large-scale regular magnetic field, which leads to an anisotropic diffusion of cosmic rays, has not been included in the model provided by the public numerical packages. In this work, we propose a pseudo source method to solve the 3-dimensional anisotropic transport equation. Based on a realistic configuration of Galactic magnetic field, both proton energy spectrum and B/C ratio are reproduced with proper transport parameters.
1909.02928
Oceanographic constrations on exoplanet life
Olson, et al
Liquid water oceans are at the center of our search for life on exoplanets because water is a strict requirement for life as we know it. However, oceans are dynamic habitats--and some oceans may be better hosts for life than others. In Earth's ocean, circulation transports essential nutrients such as P and controls the distribution and productivity of life. Of particular importance is upwelling due to wind-driven divergence in surface layers, which returns essential nutrients that tend to accumulate at depth via the biological pump back to the sunlit regions where life is concentrated. Atmospheric buildup of biogenic gases like CH$_4$ that are produced in the subsurface ocean also depends on upwelling. Ocean circulation is likely to impose constraints on the activity and atmospheric expression of life in exo-oceans as well, but we lack an understanding of how ocean dynamics may differ on other planets. We address this issue by using ROCKE-3D, a fully coupled ocean-atmosphere GCM, to investigate ocean dynamics on a diversity of habitable planets. Our results suggest that planets that rotate slower and have higher surface pressure than Earth may be attractive targets for remote life detection because upwelling is enhanced on these planets. Seasonal deepening of the mixed layer on high obliquity planets may also enhance nutrient return from depth into the surface mixed layer. Efficient nutrient recycling favors greater biological activity, more biosignature production, and more detectable life. We also find that an absence of continents may be problematic for sustaining a globally active, remotely detectable ocean biosphere due to limited nutrient fluxes from coastal upwelling and continental weathering. Our results demonstrate the importance of considering oceanographic phenomena for exoplanet life detection and motivate further contributions to the emerging field of exo-oceanography.
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