4,266 research outputs found
Extended Charged Events and Chern-Simons Couplings
Recently, the concept of dynamical extended charged events has been
introduced, and it has been argued that they should play as central a role as
that played by particles or ordinary branes. In this article we show that in
the presence of a Chern-Simons coupling, a magnetically charged extended event
emits an extended object, which geometrically is just like a Dirac string, but
it is observable, obeys equations of motion, and may be electrically charged.
We write a complete action principle which accounts for this effect. The action
involves two Chern-Simons terms, one integrated over spacetime and the other
integrated over the worldvolume of the submanifold that is the union of the
Dirac world-sheet and the history of the emitted physical object. By demanding
that the total charge emitted by a composite extended magnetic event be
quantized according to Dirac's rule, we find a quantization condition for the
Chern-Simons coupling. For a 1-form electric potential in D=2n+1 spacetime
dimensions, the composite event is formed by n elementary extended magnetic
events separated in time such that the product of their transverse spaces,
together with the time axis, is the entire spacetime. We show that the emitted
electric charge is given by the integral of the (n-1)-th exterior power of the
electromagnetic field strength over the last elementary event, or,
equivalently, over an appropriate closed surface. The extension to more general
p-form potentials and higher dimensions is also discussed. For the case D=11,
p=3, our result for the quantization of the Chern-Simons coupling was obtained
previously in the context of M-theory, a remarkable agreement that makes the
existence of events even more compelling
Stable p-branes in Chern-Simons AdS supergravities
We construct static codimension-two branes in any odd dimension D, with
negative cosmological constant, and show that they are exact solutions of
Chern-Simons (super)gravity theory for (super)AdS coupled to external sources.
The stability of these solutions is analyzed by counting the number of
preserved supersymmetries. It is shown that static massive (D-3)-branes are
unstable unless some suitable gauge fields are added and the brane is extremal.
In particular, in three dimensions, a 0-brane is recognized as the negative
mass counterpart of the BTZ black hole. For these 0-branes, we write explicitly
electromagnetically charged BPS states with various number of preserved
supersymmetries within the OSp(p|2) x OSp(q|2) supergroups. In five dimensions,
we prove that stable 2-branes with electromagnetic charge always exist for the
generic supergroup SU(2,2|N), where N is different than 4. For the special case
N=4, in which the CS supergravity requires the addition of a nontrivial gauge
field configuration in order to preserve maximal number of degrees of freedom,
we show for two different static 2-branes that they are BPS states (one of
which is the ground state), and from the corresponding algebra of charges we
show that the energy is bounded from below. In higher dimensions, our results
admit a straightforward generalization, although there are presumably more
solutions corresponding to different intersections of the elementary objects.Comment: 43 pages, revtex4.cls; v2: slight amendments and references added to
match published versio
Far-ultraviolet Emission-line Morphologies of the Supernova Remnant G65.3+5.7
We present the first far-ultraviolet (FUV) emission-line morphologies of the
whole region of the supernova remnant (SNR) G65.3+5.7 using the FIMS/SPEAR
data. The morphologies of the C IV {\lambda}{\lambda}1548, 1551, He II
{\lambda}1640, and O III] {\lambda}{\lambda}1661, 1666 lines appear to be
closely related to the optical and/or soft X-ray images obtained in previous
studies. Dramatic differences between the C IV morphology and the optical [O
III] {\lambda}5007 image provide clues to a large resonant-scattering region
and a foreground dust cloud. The FUV morphologies also reveal the overall
distribution of various shocks in different evolutionary phases and an
evolutionary asymmetry between the east and the southwest sides in terms of
Galactic coordinates, possibly due to a Galactic density gradient in the global
scale. The relative X-ray luminosity of G65.3+5.7 to C IV luminosity is
considerably lower than those of the Cygnus Loop and the Vela SNRs. This
implies that G65.3+5.7 has almost evolved into the radiative stage in the
global sense and supports the previous proposal that G65.3+5.7 has lost its
bright X-ray shell and become a member of mixed-morphology SNRs as it has
evolved beyond the adiabatic stage.Comment: 6 pages, 3 figures, accepted for publication in The Ap
Modulation of calmodulin lobes by different targets: an allosteric model with hemiconcerted conformational transitions
Calmodulin, the ubiquitous calcium-activated second messenger in eukaryotes,
is an extremely versatile molecule involved in many biological processes:
muscular contraction, synaptic plasticity, circadian rhythm, and cell cycle,
among others. The protein is structurally organised into two globular lobes,
joined by a flexible linker. Calcium modulates calmodulin activity by favoring
a conformational transition of each lobe from a closed conformation to an open
conformation. Most targets have a strong preference for one conformation over
the other, and depending on the free calcium concentration in a cell,
particular sets of targets will preferentially interact with calmodulin. In
turn, targets can increase or decrease the calcium affinity of the calmodulin
molecules to which they bind. Interestingly, experiments with the tryptic
fragments showed that most targets have a much lower affinity for the N-lobe
than for the C-lobe. Hence, the latter predominates in the formation of most
calmodulin-target complexes. We showed that a relatively simple allosteric
mechanism, based the classic MWC model, can capture the observed modulation of
both the isolated C-lobe, and intact calmodulin, by individual targets.
Moreover, our model can be naturally extended to study how the calcium affinity
of a single pool of calmodulin is modulated by a mixture of competing targets
in vivo
Self-dual solitons in N=2 supersymmetric semilocal Chern-Simons theory
We embed the semilocal Chern-Simons-Higgs theory into an N=2 supersymmetric
system. We construct the corresponding conserved supercharges and derive the
Bogomol'nyi equations of the model from supersymmetry considerations. We show
that these equations hold provided certain conditions on the coupling constants
as well as on the Higgs potential of the system, which are a consequence of the
huge symmetry of the theory, are satisfied. They admit string-like solutions
which break one half of the supersymmetries --BPS Chern-Simons semilocal cosmic
strings-- whose magnetic flux is concentrated at the center of the vortex. We
study such solutions and show that their stability is provided by supersymmetry
through the existence of a lower bound for the energy, even though the manifold
of the Higgs vacuum does not contain non-contractible loops.Comment: 12 pages, LaTeX, no figures, to appear in Modern Physics Letters
Effective Superpotentials for SO/Sp with Flavor from Matrix Models
We study matrix models related to gauge theories with flavors. We
give the effective superpotentials for gauge theories with arbitrary tree level
superpotential up to first instanton level. For quartic tree level
superpotential we obtained exact one-cut solution. We also derive
Seiberg-Witten curve for these gauge theories from matrix model argument.Comment: 17pp,2 figures, v2;refs added and to appear in MPL
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