1,830 research outputs found
Combined EISCAT radar and optical multispectral and tomographic observations of black aurora
Black auroras are recognized as spatially well-defined regions within a uniform diffuse auroral background where the optical emission is significantly reduced. Black auroras typically appear post-magnetic midnight and during the substorm recovery phase, but not exclusively so. We report on the first combined multimonochromatic optical imaging, bistatic white-light TV recordings and incoherent scatter radar observations of black aurora by EISCAT of the phenomenon. From the relatively larger reduction in luminosity at 4278 Ã… than at 8446 Ã… we show that nonsheared black auroras are most probably not caused by downward directed electrical fields at low altitude. From the observations, we determine this by relating the height and intensity of the black aurora to precipitating particle energy within the surrounding background diffuse aurora. The observations are more consistent with an energy selective loss cone. Hence the mechanism causing black aurora is most probably active in the magnetosphere rather than close to Earth
Electromagnetic waves and bursty electron acceleration: implications from Freja
International audienceDispersive Alfvén wave activity is identified in four dayside auroral oval events measured by the Freja satellite. The events are characterized by ion injection, bursty electron precipitation below about 1 keV, transverse ion heating and broadband extremely low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few kHz). Large-scale density depletions/cavities, as determined by the Langmuir probe measurements, and strong electrostatic emissions are often observed simultaneously. A correlation study has been carried out between the E and B field fluctuations below 64 Hz and 10 Hz, respectively, (the DC instruments upper threshold) and the characteristics of the precipitating electrons. This study revealed that the energisation of electrons is indeed related to the broadband ELF emissions and that the electrostatic component plays a predominant role during very active magnetospheric conditions. Furthermore, the effect of the ELF electromagnetic emissions on the larger scale field-aligned current systems has been investigated, and it is found that such an effect cannot be detected. Instead, the Alfvénic activity creates a local region of field-aligned currents. It is suggested that dispersive Alfvén waves set up these local field-aligned current regions and, in turn, trigger more electrostatic emissions during certain conditions. In these regions, ions are transversely heated, and large-scale density depletions/cavities may be created during especially active periods
Branes from a non-Abelian (2,0) tensor multiplet with 3-algebra
In this paper, we study the equations of motion for non-Abelian N=(2,0)
tensor multiplets in six dimensions, which were recently proposed by Lambert
and Papageorgakis. Some equations are regarded as constraint equations. We
employ a loop extension of the Lorentzian three-algebra (3-algebra) and examine
the equations of motion around various solutions of the constraint equations.
The resultant equations take forms that allow Lagrangian descriptions. We find
various (5+d)-dimensional Lagrangians and investigate the relation between them
from the viewpoint of M-theory duality.Comment: 44+1 pages, reference added, typos corrected, and several discussions
added; v3, reference added, many typos corrected, the language improved; v4,
some typos and references corrected, final version to appear in J. Phys.
Supersymmetry Breaking in Chern-Simons-matter Theories
Some of supersymmetric Chern-Simons theories are known to exhibit
supersymmetry breaking when the Chern-Simons level is less than a certain
number. The mechanism of the supersymmetry breaking is, however, not clear from
the field theory viewpoint. In this paper, we discuss vacuum states of pure Chern-Simons theory and Chern-Simons-matter theories of
quiver type using related theories in which Chern-Simons terms are replaced
with (anti-)fundamental chiral multiplets. In the latter theories,
supersymmetry breaking can be shown to occur by examining that the vacuum
energy is non-zero.Comment: 17 pages, 3 figures, v2) references adde
Constructing Self-Dual Strings
We present an ADHMN-like construction which generates self-dual string
solutions to the effective M5-brane worldvolume theory from solutions to the
Basu-Harvey equation. Our construction finds a natural interpretation in terms
of gerbes, which we develop in some detail. We also comment on a possible
extension to stacks of multiple M5-branes.Comment: 1+19 pages, presentation improved, minor corrections, published
versio
Realization of an Excited, Strongly-Correlated Quantum Gas Phase
Ultracold atomic physics offers myriad possibilities to study strongly
correlated many-body systems in lower dimensions. Typically, only ground state
phases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we
realize and control in one dimensional geometry a highly excited quantum phase
that is stabilized in the presence of attractive interactions by maintaining
and strengthening quantum correlations across a confinement-induced resonance.
We diagnose the crossover from repulsive to attractive interactions in terms of
the stiffness and the energy of the system. Our results open up the
experimental study of metastable excited many-body phases with strong
correlations and their dynamical properties
KK6 from M2 in BLG
We study the possibility that the Kaluza-Klein monopole (KK6) world-volume
action may be obtained from the multiple membranes (M2) action which is
described by BLG theory. We first point out that the infinite dimensional Lie
3-algebra based on the Nambu-Poisson structure could not only provide three
dimensional manifolds to allow M5 from M2, which was studied by previous
authors, but also provide five dimensional manifolds to allow KK6 from M2. We
next present a possible way that the U(1) field on KK6 world-volume action
could be produced form the gauge potential in BLG theory.Comment: Latex, 15 pages. V3: Add theorem 2 to complete proof. V4: Detail
physical interpretations and calculations in section
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