13,571 research outputs found
Trapping of ultracold polar molecules with a Thin Wire Electrostatic Trap
We describe the realization of a dc electric-field trap for ultracold polar
molecules, the thin-wire electrostatic trap (TWIST). The thin wires that form
the electrodes of the TWIST allow us to superimpose the trap onto a
magneto-optical trap (MOT). In our experiment, ultracold polar NaCs molecules
in their electronic ground state are created in the MOT via photoassociation,
achieving a continuous accumulation in the TWIST of molecules in low-field
seeking states. Initial measurements show that the TWIST trap lifetime is
limited only by the background pressure in the chamber.Comment: 4 pages, 3 figure
Study of high voltage solar array configurations with integrated power control electronics
Solar array electrical configurations for voltage regulatio
Consistent Scenarios for Cosmic-Ray Excesses from Sommerfeld-Enhanced Dark Matter Annihilation
Anomalies in direct and indirect detection have motivated models of dark
matter consisting of a multiplet of nearly-degenerate states, coupled by a new
GeV-scale interaction. We perform a careful analysis of the thermal freezeout
of dark matter annihilation in such a scenario. We compute the range of "boost
factors" arising from Sommerfeld enhancement in the local halo for models which
produce the correct relic density, and show the effect of including constraints
on the saturated enhancement from the cosmic microwave background (CMB). We
find that boost factors from Sommerfeld enhancement of up to ~800 are possible
in the local halo. When the CMB bounds on the saturated enhancement are
applied, the maximal boost factor is reduced to ~400 for 1-2 TeV dark matter
and sub-GeV force carriers, but remains large enough to explain the observed
Fermi and PAMELA electronic signals. We describe regions in the DM mass-boost
factor plane where the cosmic ray data is well fit for a range of final states,
and show that Sommerfeld enhancement alone is enough to provide the large
annihilation cross sections required to fit the data, although for light
mediator masses (less than ~200 MeV) there is tension with the CMB constraints
in the absence of astrophysical boost factors from substructure. Additionally,
we consider the circumstances under which WIMPonium formation is relevant and
find for heavy WIMPs (greater than ~2 TeV) and soft-spectrum annihilation
channels it can be an important consideration; we find regions with dark matter
mass greater than 2.8 TeV that are consistent with the CMB bounds and have
~600-700 present-day boost factors.Comment: Related web application at
http://astrometry.fas.harvard.edu/mvogelsb/sommerfeld . v2: added brief
clarification regarding propagation parameters, plots now show effect of
relaxing CMB bounds. 35 pages in JCAP format, 4 figures. Accepted for
publication in JCA
Neutrino Oscillations as a Probe of Dark Energy
We consider a class of theories in which neutrino masses depend significantly
on environment, as a result of interactions with the dark sector. Such theories
of mass varying neutrinos (MaVaNs) were recently introduced to explain the
origin of the cosmological dark energy density and why its magnitude is
apparently coincidental with that of neutrino mass splittings. In this Letter
we argue that in such theories neutrinos can exhibit different masses in matter
and in vacuum, dramatically affecting neutrino oscillations. Both long and
short baseline experiments are essential to test for these interactions. As an
example of modifications to the standard picture, we consider simple models
which may simultaneously account for the LSND anomaly, KamLAND, K2K and studies
of solar and atmospheric neutrinos, while providing motivation to continue to
search for neutrino oscillations in short baseline experiments such as BooNE.Comment: 5 pages, 1 figure, refs added, additional data considered, minor
change in conclusions about LSN
Kinematic Evolution of Simulated Star-Forming Galaxies
Recent observations have shown that star-forming galaxies like our own Milky
Way evolve kinematically into ordered thin disks over the last ~8 billion years
since z=1.2, undergoing a process of "disk settling." For the first time, we
study the kinematic evolution of a suite of four state of the art "zoom in"
hydrodynamic simulations of galaxy formation and evolution in a fully
cosmological context and compare with these observations. Until now, robust
measurements of the internal kinematics of simulated galaxies were lacking as
the simulations suffered from low resolution, overproduction of stars, and
overly massive bulges. The current generation of simulations has made great
progress in overcoming these difficulties and is ready for a kinematic
analysis. We show that simulated galaxies follow the same kinematic trends as
real galaxies: they progressively decrease in disordered motions (sigma_g) and
increase in ordered rotation (Vrot) with time. The slopes of the relations
between both sigma_g and Vrot with redshift are consistent between the
simulations and the observations. In addition, the morphologies of the
simulated galaxies become less disturbed with time, also consistent with
observations, and they both have similarly large scatter. This match between
the simulated and observed trends is a significant success for the current
generation of simulations, and a first step in determining the physical
processes behind disk settling.Comment: ApJ accepted; 6 pages; A pdf with full resolution figures can be
found at https://db.tt/8y4Vzaff (2.8M
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