10 research outputs found
Strongly magnetized accretion in ultracompact binary systems
AM CVn systems are binary star systems with orbital periods less than 70 minutes in which a white dwarf accretes matter from a companion star, which must be either a stripped helium burning star, or a white dwarf of lower mass than the accretor. Here, we present the discoveries of two of these systems in which there is mass transfer from the lighter white dwarf or helium star onto a strongly magnetized heavier white dwarf. These represent the first clear example of magnetized accretion in ultracompact binaries. These systems, along with similar systems that are slightly more widely separated, and that have not started to transfer mass yet, are expected to be the primary source of gravitational waves to be detected by space-based gravitational wave observatories. The presence of strong magnetic fields can substantially affect both the evolution of the binaries, and also the particular wave forms of the gravitational waves themselves, and understanding these magnetic effects is vital for understanding what to expect from the Laser Interferometer Space Antenna
Strongly magnetized accretion in two ultracompact binary systems
We present the discoveries of two of AM CVn systems, Gaia14aae and
SDSS~J080449.49+161624.8, which show X-ray pulsations at their orbital periods,
indicative of magnetically collimated accretion. Both also show indications of
higher rates of mass transfer relative to the expectations from binary
evolution driven purely by gravitational radiation, based on existing optical
data for Gaia14aae, which show a hotter white dwarf temperature than expected
from standard evolutionary models, and X-ray data for SDSS~J080449.49+161624.8
which show a luminosity 10-100 times higher than those for other AM~CVn at
similar orbital periods. The higher mass transfer rates could be driven by
magnetic braking from the disk wind interacting with the magnetosphere of the
tidally locked accretor. We discuss implications of this additional angular
momentum transport mechanism for evolution and gravitational wave detectability
of AM CVn objects.Comment: 5 pages, 3 figures, accepted to MNRAS Letter
Non-Abelian Dark Sectors and Their Collider Signatures
Motivated by the recent proliferation of observed astrophysical anomalies,
Arkani-Hamed et al. have proposed a model in which dark matter is charged under
a non-abelian "dark" gauge symmetry that is broken at ~ 1 GeV. In this paper,
we present a survey of concrete models realizing such a scenario, followed by a
largely model-independent study of collider phenomenology relevant to the
Tevatron and the LHC. We address some model building issues that are easily
surmounted to accommodate the astrophysics. While SUSY is not necessary, we
argue that it is theoretically well-motivated because the GeV scale is
automatically generated. Specifically, we propose a novel mechanism by which
mixed D-terms in the dark sector induce either SUSY breaking or a super-Higgs
mechanism precisely at a GeV. Furthermore, we elaborate on the original
proposal of Arkani-Hamed et al. in which the dark matter acts as a messenger of
gauge mediation to the dark sector. In our collider analysis we present
cross-sections for dominant production channels and lifetime estimates for
primary decay modes. We find that dark gauge bosons can be produced at the
Tevatron and the LHC, either through a process analogous to prompt photon
production or through a rare Z decay channel. Dark gauge bosons will decay back
to the SM via "lepton jets" which typically contain >2 and as many as 8
leptons, significantly improving their discovery potential. Since SUSY decays
from the MSSM will eventually cascade down to these lepton jets, the discovery
potential for direct electroweak-ino production may also be improved.
Exploiting the unique kinematics, we find that it is possible to reconstruct
the mass of the MSSM LSP. We also present decay channels with displaced
vertices and multiple leptons with partially correlated impact parameters.Comment: 44 pages, 25 figures, version published in JHE
Images of Earth and Space: The Role of Visualization in NASA Science
This compilation video contains visualizations of Earth and Space Sciences resulting from supercomputer models. The excerpted visualizations include: Ocean Planet, El Nino, Ozone 1991, Clouds, Changes in Glacier Bay, Alaska, Biosphere, Lunar Topography from the Clementine Mission, Musculoskeletal Modeling Dynamic Simulations, Simulations of the Breakup and Dynamical Evolution of Comet Shoemaker-Levy 9, Convective Penetration in Stellar Interiors, Topological Features of a Compressible Plasma Vortex Sheet: A Model for the Outer Heliospheric Solar Wind, R-Aquarii Jet, The Evolution of Distorted Black Holes, Rayleigh-Taylor Instability in a Supernova, Galaxy Harassment, N-Body Simulation of the Cold Dark Matter Cosmology. Educational levels: Undergraduate lower division, Undergraduate upper division, Graduate or professional
Simplified Models for Dark Matter Searches at the LHC
This document a outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both -channel and -channel scenarios. For -channel, spin-0 and spin-1 mediations are discussed, and also realizations where the Higgs particle provides a portal between the dark and visible sectors. The guiding principles underpinning the proposed simplified models are spelled out, and some suggestions for implementation are presented