5,417 research outputs found
Local points on Shimura coverings of Shimura curves at bad reduction primes
Let XD be the Shimura curve associated with an indefinite rational quaternion algebra of reduced discriminant D>1. For each prime l|D, there is a natural cyclic Galois covering of Shimura curves XD,l → XD constructed by adding certain level structure at l. The main goal of this note is to study the existence of local points at primes p≠l of bad reduction on the intermediate curves of these coverings and their Atkin–Lehner quotients.Peer ReviewedPostprint (author's final draft
Constraints on the shape of the Milky Way dark matter halo from the Sagittarius stream
We propose a new model for the dark matter halo of the Milky Way that fits
the properties of the stellar stream associated with the Sagittarius dwarf
galaxy. Our dark halo is oblate with q_z = 0.9 for r < 10 kpc, and can be made
to follow the Law & Majewski model at larger radii. However, we find that the
dynamical perturbations induced by the Large Magellanic Cloud on the orbit of
Sgr cannot be neglected when modeling its streams. When taken into account,
this leads us to constrain the Galaxy's outer halo shape to have minor-to-major
axis ratio (c/a)_\Phi = 0.8 and intermediate-to-major axis ratio (b/a)_\Phi =
0.9, in good agreement with cosmological expectations.Comment: 5 pages, 5 figures. Accepted for publication in ApJ Letters. Minor
changes to match published versio
Pullbacks of Saito-Kurokawa lifts and a central value formula for degree 6 L-series
We prove an explicit central value formula for a family of complex L-series of degree 6 for GL2 × GL3 which arise as factors of certain Garret–Rankin triple product L-series associated with modular forms. Our result generalizes a previous formula of Ichino involving Saito–Kurokawa lifts, and as an application we prove Deligne’s conjecture stating the algebraicity of the central values of the considered L-series up to the relevant periods.Peer ReviewedPostprint (author's final draft
Matching the dark matter profiles of dSph galaxies with those of simulated satellites: a two parameter comparison
We compare the dark matter halos' structural parameters derived for four
Milky Way dwarf spheroidal galaxies to those of subhalos found in cosmological
-body simulations. We confirm that estimates of the mass at a single fixed
radius are fully consistent with the observations. However, when a second
structural parameter such as the logarithmic slope of the dark halo density
profile measured close to the half-light radius is included in the comparison,
we find little to no overlap between the satellites and the subhalos. Typically
the right mass subhalos have steeper profiles at these radii than measurements
of the dSph suggest. Using energy arguments we explore if it is possible to
solve this discrepancy by invoking baryonic effects. Assuming that feedback
from supernovae can lead to a reshaping of the halos, we compute the required
efficiency and find entirely plausible values for a significant fraction of the
subhalos and even as low as 0.1%. This implies that care must be taken not to
exaggerate the effect of supernovae feedback as this could make the halos too
shallow. These results could be used to calibrate and possibly constrain
feedback recipes in hydrodynamical simulations.Comment: 6 pages, 3 figures, submitted to ApJ
The effect of radial migration on galactic disks
We study the radial migration of stars driven by recurring multi-arm spiral
features in an exponential disk embedded in a dark matter halo. The spiral
perturbations redistribute angular momentum within the disk and lead to
substantial radial displacements of individual stars, in a manner that largely
preserves the circularity of their orbits and that results, after 5 Gyr (~40
full rotations at the disk scalelength), in little radial heating and no
appreciable changes to the vertical or radial structure of the disk. Our
results clarify a number of issues related to the spatial distribution and
kinematics of migrators. In particular, we find that migrators are a heavily
biased subset of stars with preferentially low vertical velocity dispersions.
This "provenance bias" for migrators is not surprising in hindsight, for stars
with small vertical excursions spend more time near the disk plane and thus
respond more readily to non-axisymmetric perturbations. We also find that the
vertical velocity dispersion of outward migrators always decreases, whereas the
opposite holds for inward migrators. To first order, newly arrived migrators
simply replace stars that have migrated off to other radii, thus inheriting the
vertical bias of the latter. Extreme migrators might therefore be recognized,
if present, by the unexpectedly small amplitude of their vertical excursions.
Our results show that migration, understood as changes in angular momentum that
preserve circularity, can affect strongly the thin disk, but cast doubts on
models that envision the Galactic thick disk as a relic of radial migration.Comment: 10 pages, 12 figures. ApJ in pres
Seismic probabilistic safety assessment and risk control of nuclear power plants in Northwest Europe
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