6,916 research outputs found
Using Red Clump Stars to Decompose the Galactic Magnetic Field with Distance
A new method for measuring the large-scale structure of the Galactic magnetic
field is presented. The Galactic magnetic field has been probed through the
Galactic disk with near-infrared starlight polarimetry, however the distance to
each background star is unknown. Using red clump stars as near-infrared
standard candles, this work presents the first attempt to decompose the line of
sight structure of the sky-projected Galactic magnetic field. Two example
lines-of-sight are decomposed: toward a field with many red clump stars and
toward a field with few red clump stars. A continuous estimate of magnetic
field orientation over several kiloparsecs of distance is possible in the field
with many red clump stars, while only discrete estimates are possible in the
sparse example. toward the Outer Galaxy, there is a continuous field
orientation with distance that shows evidence of perturbation by the Galactic
warp. toward the Inner Galaxy, evidence for a large-scale change in the
magnetic field geometry is consistent with models of magnetic field reversals,
independently derived from Faraday rotation studies. A photo-polarimetric
method for identifying candidate intrinsically polarized stars is also
presented. The future application of this method to large regions of the sky
will begin the process of mapping the Galactic magnetic field in a way never
before possible.Comment: 11 pages, 8 figures, 2 tables, accepted for publication in The
Astronomical Journa
Theory for Baryon Number and Dark Matter at the LHC
We investigate the possibility to test the simplest theory for spontaneous
baryon number violation at the Large Hadron Collider. In this context the
baryon number is a local gauge symmetry spontaneously broken at the low scale
through the Brout-Englert-Higgs mechanism. This theory predicts the existence
of a leptophobic neutral gauge boson and a fermionic dark matter candidate with
baryon number. We study the gauge boson and Higgs decays, and explore the
connection between collider signatures and constraints coming from dark matter
experiments. We point out an upper bound on the symmetry breaking scale using
the relic density constraints which tells us that this model can be tested or
ruled out at current or future collider experiments.Comment: 30 pages, 9 figures, typos corrected, new appendix, version to appear
in PR
Baryonic Dark Matter
We investigate a simple extension of the Standard Model where the baryon
number is a local gauge symmetry and the cold dark matter in the Universe can
be described by a fermionic field with baryon number. We refer to this scenario
as "Baryonic Dark Matter''. The stability of the dark matter candidate is a
natural consequence of the spontaneous breaking of baryon number at the low
scale and there is no need to impose an extra discrete symmetry. The
constraints from the relic density and the predictions for direct detection are
discussed in detail. We briefly discuss the testability of this model using the
correlation between the Large Hadron Collider data and possible results from
dark matter experiments.Comment: to appear in Physics Letters
On thermal fluctuations and the generating functional in relativistic hydrodynamics
We discuss a real-time generating functional for correlation functions in
dissipative relativistic hydrodynamics which takes into account thermal
fluctuations of the hydrodynamic variables. Starting from the known form of
these correlation functions in the linearized regime, we integrate to find a
generating functional which we can interpret within the CTP formalism, provided
the space-time and internal global symmetries are realized in a specific manner
in the (r,a) sectors. We then verify that this symmetry realization, when
implemented in an effective action for hydrodynamic fields in the (r,a) basis,
leads to a consistent derivative expansion for the constitutive relations at
the nonlinear level, modulo constraints associated with the existence of an
equilibrium state.Comment: 23 page
A Lack of Resolved Near-Infrared Polarization Across the Face of M51
The galaxy M51 was observed using the Mimir instrument on the Perkins
telescope to constrain the resolved H-band (1.6 m) polarization across the
galaxy. These observations place an upper limit of on the -band
polarization across the face of M51, at 0.6 arcsecond pixel sampling. Even with
smoothing to coarser angular resolutions, to reduce polarization uncertainty,
the -band polarization remains undetected. The polarization upper limit at
-band, when combined with previous resolved optical polarimetry, rules out a
Serkowski-like polarization dependence on wavelength. Other polarization
mechanisms cannot account for the observed polarization ratio () across the face of M51.Comment: 4 pages, 2 figures, Accepted for publication in ApJ
H II Region Driven Galactic Bubbles And Their Relationship To The Galactic Magnetic Field
The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations-no preferential alignment with respect to the Galactic disk was found. A subsample of H II region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal H II regions, based on hydrogen radio recombination linewidths, the subthermal H II regions showed a marginal deviation from random orientations, but the suprathermal H II regions showed significant alignment with the Galactic plane. The mean orientation of the Galactic disk magnetic field was characterized using new near-infrared starlight polarimetry and the suprathermal H II regions were found to preferentially align with the disk magnetic field. If suprathermal linewidths are associated with younger H II regions, then the evolution of young H II regions is significantly affected by the Galactic magnetic field. As H II regions age, they cease to be strongly linked to the Galactic magnetic field, as surrounding density variations come to dominate their morphological evolution. From the new observations, the ratios of magnetic-to-ram pressures in the expanding ionization fronts were estimated for younger H II regions.NSF AST 06-07500, 09-07790NASAW. M. Keck FoundationAstronom
An Elimination Method for Solving Bivariate Polynomial Systems: Eliminating the Usual Drawbacks
We present an exact and complete algorithm to isolate the real solutions of a
zero-dimensional bivariate polynomial system. The proposed algorithm
constitutes an elimination method which improves upon existing approaches in a
number of points. First, the amount of purely symbolic operations is
significantly reduced, that is, only resultant computation and square-free
factorization is still needed. Second, our algorithm neither assumes generic
position of the input system nor demands for any change of the coordinate
system. The latter is due to a novel inclusion predicate to certify that a
certain region is isolating for a solution. Our implementation exploits
graphics hardware to expedite the resultant computation. Furthermore, we
integrate a number of filtering techniques to improve the overall performance.
Efficiency of the proposed method is proven by a comparison of our
implementation with two state-of-the-art implementations, that is, LPG and
Maple's isolate. For a series of challenging benchmark instances, experiments
show that our implementation outperforms both contestants.Comment: 16 pages with appendix, 1 figure, submitted to ALENEX 201
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