2,299 research outputs found
p-brane superalgebras via integrability
It has long been appreciated that superalgebras with bosonic and fermionic
generators additional to those in the super-Poincare algebra underlie p-brane
and D-brane actions in superstring theory. These algebras have been revealed
via "bottom up" approaches, involving consideration of Noether charges, and by
"top down" approaches, involving the construction of manifestly supersymmetry
invariant Wess-Zumino actions. In this paper, we give an alternative derivation
of these algebras based on integrability of supersymmetry transformations
assigned to fields in order to solve a cohomology problem related to the
construction of Wess-Zumino terms for p-brane and D-brane actions.Comment: 22 pages, typo corrected, reference adde
Deriving all p-brane superalgebras via integrability
In previous work we demonstrated that the enlarged super-Poincare algebras
which underlie p-brane and D-brane actions in superstring theory can be
directly determined based on the integrability of supersymmetry transformations
assigned to fields appearing in Wess-Zumino terms. In that work we derived
p-brane superalgebras for p = 2 and 3. Here we extend our previous results and
give a compact expression for superalgebras for all valid p.Comment: 26 pages, table added, typos corrected, a few remarks added for
clarificatio
Coherent transport structures in magnetized plasmas II: Numerical results
In a pair of linked articles (called Article I and II respectively) we apply
the concept of Lagrangian Coherent Structures borrowed from the study of
Dynamical Systems to magnetic field configurations in order to separate regions
where field lines have different kind of behavior. In the present article,
article II, by means of a numerical procedure we investigate the Lagrangian
Coherent Structures in the case of a two-dimensional magnetic configuration
with two island chains that are generated by magnetic reconnection and evolve
nonlinearly in time. The comparison with previous results, obtained by assuming
a fixed magnetic field configuration, allows us to explore the dependence of
transport barriers on the particle velocity
Coherent transport structures in magnetized plasmas, I : Theory
In a pair of linked articles (called Article I and II respectively) we apply
the concept of Lagrangian Coherent Structures (LCSs) borrowed from the study of
Dynamical Systems to magnetic field configurations in order to separate regions
where field lines have different kind of behaviour. In the present article,
article I, after recalling the definition and the properties of the LCSs, we
show how this conceptual framework can be applied to the study of particle
transport in a magnetized plasma. Futhermore we introduce a simplified model
that allows us to consider explicitly the case where the magnetic configuration
evolves in time on timescales comparable to the particle transit time through
the configuration. In contrast with previous works on this topic, this analysis
requires that a system that is aperiodic in time be investigated. In this case
the Poincar\'e map technique cannot be applied and LCSs remain the only viable
tool
Lagrangian Coherent Structures as a new frame to investigate the particle transport in highly chaotic magnetic systems
Mediterranean ants can increase nymph mortality in the stink bug Nezara viridula without interfering with its egg parasitoid Trissolcus basalis
Ants (Hymenoptera: Formicidae) play a relevant ecological role across terrestrial ecosystems. Recent studies suggest that the presence of ants in crops could lead to a decrease in the populations of insect pests, but how these actions can vary along the different trophic levels is not well known. The southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), is a cosmopolitan agricultural pest which is regularly found on horticultural agroecosystems closely associated with its main egg parasitoid, Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae). We conducted laboratory experiments to test whether two Mediterranean ant species, the generalist predators Crematogaster scutellaris (Olivier) and Tapinoma magnum Mayr, attack N. viridula eggs or nymphs, and whether they interfere with the parasitization activity of T. basalis. The experiment showed that both ant species significantly increased the mortality of N. viridula nymphs, whereas they do not attack their eggs and do not interfere with the egg parasitoids. Our results suggest that ants and egg parasitoids may have an integrable role in biocontrol strategies against this pest
String cosmological model in the presence of a magnetic flux
A Bianchi type I string cosmological model in the presence of a magnetic flux
is investigated. A few plausible assumptions regarding the parametrization of
the cosmic string and magneto-fluid are introduced and some exact analytical
solutions are presented.Comment: 9 pages, 4 Figure
Plasma waves driven by gravitational waves in an expanding universe
In a Friedmann-Robertson-Walker (FRW) cosmological model with zero spatial
curvature, we consider the interaction of the gravitational waves with the
plasma in the presence of a weak magnetic field. Using the relativistic
hydromagnetic equations it is verified that large amplitude magnetosonic waves
are excited, assuming that both, the gravitational field and the weak magnetic
field do not break the homogeneity and isotropy of the considered FRW
spacetime.Comment: 14 page
Radiative Neutrino Decay in Media
In this letter we introduce a new method to determine the radiative neutrino
decay rate in the presence of a medium. Our approach is based on the
generalisation of the optical theorem at finite temperature and density.
Differently from previous works on this subject, our method allows to account
for dispersive and dissipative electromagnetic properties of the medium. Some
inconsistencies that are present in the literature are pointed-out and
corrected here. We shortly discuss the relevance of our results for neutrino
evolution in the early universe.Comment: 11 pages, 3 encapsulated figure
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