1,093 research outputs found
Large-scale current systems and ground magnetic disturbance during deep substorm injections
We present a detailed analysis of the large-scale current systems and their effects on the
ground magnetic field disturbance for an idealized substorm event simulated with the
equilibrium version of the Rice Convection Model. The objective of this study is to evaluate
how well the bubble-injection picture can account for some classic features of the
substorm expansion phase. The entropy depletion inside the bubble is intentionally
designed to be so severe that it can penetrate deep into geosynchronous orbit. The
results are summarized as follows: (1) Both the region-1-sense and region-2-sense
field-aligned currents (FACs) intensify substantially. The former resembles the
substorm current wedge and flows along the eastern and western edges of the bubble.
The latter is connected to the enhanced partial ring current in the magnetosphere
associated with a dipolarization front earthward of the bubble. In the ionosphere, these
two pairs of FACs are mostly interconnected via Pedersen currents. (2) The horizontal
ionospheric currents show a significant westward electrojet peaked at the equatorward
edge of the footprint of the bubble. The estimated ground magnetic disturbance is
consistent with the typical features at various locations relative to the center of the westward
electrojet. (3) A prominent Harang-reversal-like boundary is seen in both ground DH
disturbance and plasma flow pattern, appearing in the westward portion of the equatorward
edge of the bubble footprint, with a latitudinal extent of 5 and a longitudinal extent of the
half width of the bubble. (4) The dramatic dipolarization inside the bubble causes the
ionospheric map of the inner plasma sheet to exhibit a bulge-like structure, which may be
related to auroral poleward expansion. (5) The remarkable appearance of the westward
electrojet, Harang-reversal-like boundary and poleward expansion starts when the
bubble reaches the magnetic transition region from tail-like to dipole-like
configuration. We also estimate the horizontal and vertical currents using magnetograms at
tens of ground stations for a deep injection substorm event occurred on April 9, 2008,
resulting in a picture that is qualitatively consistent with the simulation. Based on the
simulations and the observations, an overall picture of the ionospheric dynamics and its
magnetospheric drivers during deep bubble injections is obtained
Fermion zero-modes of a new constrained instanton in Yang-Mills-Higgs theory
Self-consistent Ansaetze are presented for the left- and right-handed
isodoublet fermion zero-modes of the constrained instanton Istar in the vacuum
sector of euclidean SU(2) Yang-Mills-Higgs theory. These left- and right-handed
fermion wave functions do not coincide and, most likely, have maxima at
different positions. This may be important for the fermion zero-mode
contribution to the euclidean 4-point Green's function in chiral
Yang-Mills-Higgs theory and the high-energy behaviour of fermion-fermion
scattering processes.Comment: Version to be published, changes in last two sections. 20 pages LaTeX
Final version
Z-string global gauge anomaly and Lorentz non-invariance
Certain (3+1)-dimensional chiral non-Abelian gauge theories have been shown
to exhibit a new type of global gauge anomaly, which in the Hamiltonian
formulation is due to the fermion zero-modes of a Z-string-like configuration
of the gauge potential and the corresponding spectral flow. Here, we clarify
the relation between this Z-string global gauge anomaly and other anomalies in
both 3+1 and 2+1 dimensions. We then point out a possible trade-off between the
(3+1)-dimensional Z-string global gauge anomaly and the violation of CPT and
Lorentz invariance.Comment: 11 pages, LaTe
Instability of generalised AdS black holes and thermal field theory
We study black holes in AdS-like spacetimes, with the horizon given by an
arbitrary positive curvature Einstein metric. A criterion for classical
instability of such black holes is found in the large and small black hole
limits. Examples of large unstable black holes have a B\"ohm metric as the
horizon. These, classically unstable, large black holes are locally
thermodynamically stable. The gravitational instability has a dual description,
for example by using the version of the AdS/CFT
correspondence. The instability corresponds to a critical temperature of the
dual thermal field theory defined on a curved background.Comment: 1+16 pages. 1 figure. LaTeX. Minor clarification
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