14,661 research outputs found
Non-Equilibrium Electrons and the Sunyaev-Zel'dovich Effect of Galaxy Clusters
We present high-resolution cosmological hydrodynamic simulations of three
galaxy clusters employing a two-temperature model for the intracluster medium.
We show that electron temperatures in cluster outskirts are significantly lower
than the mean gas temperature, because Coulomb collisions are insufficient to
keep electrons and ions in thermal equilibrium. This deviation is larger in
more massive and less relaxed systems, ranging from 5% in relaxed clusters to
30% for clusters undergoing major mergers. The presence of non-equilibrium
electrons leads to significant suppression of the SZE signal at large
cluster-centric radius. The suppression of the electron pressure also leads to
an underestimate of the hydrostatic mass. Merger-driven, internal shocks may
also generate significant populations of non-equilibrium electrons in the
cluster core, leading to a 5% bias on the integrated SZ mass proxy during
cluster mergers.Comment: 5 pages, 4 figures, Accepted for publication in ApJ
A possible nuclear effect on the NuTeV sin^2 theta_W anomaly
We investigate a possible explanation for the NuTeV anomaly in terms of a
nuclear correction difference between u_v and d_v distributions. Analyzing deep
elastic scattering and Drell-Yan data for nuclear targets, we try to determine
the correction difference and its effect on the anomaly. We find that the
difference cannot be precisely determined at this stage due to the lack of data
which are sensitive to the difference. Therefore, it is difficult to draw a
solid conclusion about its effect although the anomaly could be explained, at
least partially, by this kind of nuclear correction.Comment: 3 pages, 1 figure, to be published in the proceedings of the XVIIth
Particles and Nuclei International Conference (PANIC), Santa Fe, New Mexico,
USA, October 24-28, 200
Long-range nematic order and anomalous fluctuations in suspensions of swimming filamentous bacteria
We study the collective dynamics of elongated swimmers in a very thin fluid
layer by devising long, filamentous, non-tumbling bacteria. The strong
confinement induces weak nematic alignment upon collision, which, for large
enough density of cells, gives rise to global nematic order. This homogeneous
but fluctuating phase, observed on the largest experimentally-accessible scale
of millimeters, exhibits the properties predicted by standard models for
flocking such as the Vicsek-style model of polar particles with nematic
alignment: true long-range nematic order and non-trivial giant number
fluctuations.Comment: 6 pages, 4 figures. Supplemental Material: 6 pages, 3 figure
Bilinear Equations and B\"acklund Transformation for Generalized Ultradiscrete Soliton Solution
Ultradiscrete soliton equations and B\"acklund transformation for a
generalized soliton solution are presented. The equations include the
ultradiscrete KdV equation or the ultradiscrete Toda equation in a special
case. We also express the solution by the ultradiscrete permanent, which is
defined by ultradiscretizing the signature-free determinant, that is, the
permanent. Moreover, we discuss a relation between B\"acklund transformations
for discrete and ultradiscrete KdV equations.Comment: 11 page
Vertex operator for the non-autonomous ultradiscrete KP equation
We propose an ultradiscrete analogue of the vertex operator in the case of
the ultradiscrete KP equation--several other ultradiscrete equations--which
maps N-soliton solutions to N+1-soliton ones.Comment: 9 page
ALMA polarization observations of the particle accelerators in the hot spot of the radio galaxy 3C 445
We present Atacama Large Millimeter Array (ALMA) polarization observations at
97.5 GHz of the southern hot spot of the radio galaxy 3C 445. The hot spot
structure is dominated by two bright components enshrouded by diffuse emission.
Both components show fractional polarization between 30 and 40 per cent,
suggesting the presence of shocks. The polarized emission of the western
component has a displacement of about 0.5 kpc outward with respect to the total
intensity emission, and may trace the surface of a front shock. Strong
polarization is observed in a thin strip marking the ridge of the hot spot
structure visible from radio to optical. No significant polarization is
detected in the diffuse emission between the main components, suggesting a
highly disordered magnetic field likely produced by turbulence and
instabilities in the downstream region that may be at the origin of the
extended optical emission observed in this hot spot. The polarization
properties support a scenario in which a combination of both multiple and
intermittent shock fronts due to jet dithering, and spatially distributed
stochastic second-order Fermi acceleration processes are present in the hot
spot complex.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Lette
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