3,671 research outputs found
Dual descriptions of massive spin-3 particles in via Noether gauge embedment
We present here a relationship among massive self-dual models for spin-3
particles in via the Noether Gauge Embedment procedure.
Starting with a first order model (in derivatives) we have obtained
a sequence of four self-dual models where . We
demonstrate that the procedure generate the correct action for the
auxiliary fields automatically. We obtain the whole action for the order
self-dual model including all the needed auxiliary fields to get rid of the
ghosts of the theory.Comment: 16 pages, 1 tabl
Master actions for massive spin-3 particles in D=2+1
We present here a relationship among massive self-dual models for spin-3
particles in via the master action procedure. Starting with a first
order model (in derivatives) we have constructed a master action
which interpolates among a sequence of four self-dual models where
. By analyzing the particle content of mixing terms, we give
additional arguments that explain why it is apparently impossible to jump from
the fourth order model to a higher order model. We have also analyzed
similarities and differences between the fourth order -term in the spin-2
case and the analogous fourth order term in the spin-3 context.Comment: 16 page
Turning it inside out: The organization of human septin heterooligomers.
Septin family proteins are quite similar to each other both within and between eukaryotic species. Typically, multiple discrete septins co-assemble into linear heterooligomers (usually hexameric or octameric rods) with a variety of cellular functions. We know little about how incorporation of different septins confers different properties to such complexes. This issue is especially acute in human cells where 13 separate septin gene products (often produced in multiple forms arising from alternative start codons and differential splicing) are expressed in a tissue-specific manner. Based on sequence alignments and phylogenetic criteria, human septins fall into four distinct groups predictive of their interactions, that is, members of the same group appear to occupy the same position within oligomeric septin protomers, which are "palindromic" (have twofold rotational symmetry about a central homodimeric pair). Many such protomers are capable of end-to-end polymerization, generating filaments. Over a decade ago, a study using X-ray crystallography and single-particle electron microscopy deduced the arrangement within recombinant heterohexamers comprising representatives of three human septin groups-SEPT2, SEPT6, and SEPT7. This model greatly influenced subsequent studies of human and other septin complexes, including how incorporating a septin from a fourth group forms heterooctamers, as first observed in budding yeast. Two recent studies, including one in this issue of Cytoskeleton, provide clear evidence that, in fact, the organization of subunits within human septin heterohexamers and heterooctamers is inverted relative to the original model. These findings are discussed here in a broader context, including possible causes for the initial confusion
Bump-on-tail instability of twisted excitations in rotating cold atomic clouds
We develop a kinetic theory for twisted density waves (phonons), carrying a
finite amount of orbital angular momentum, in large magneto optical traps,
where the collective processes due to the exchange of scattered photons are
considered. Explicit expressions for the dispersion relation and for the
kinetic (Landau) damping are derived and contributions from the orbital angular
momentum are discussed. We show that for rotating clouds, exhibiting
ring-shaped structures, phonons carrying orbital angular momentum can cross the
instability threshold and grow out of noise, while the usual plane wave
solutions are kinetically damped.Comment: 5 pages, 5 figure
Two-stream instability in quasi-one-dimensional Bose-Einstein condensates
We apply a kinetic model to predict the existence of an instability mechanism in elongated Bose-Einstein condensates. Our kinetic description, based on the Wigner formalism, is employed to highlight the existence of unstable Bogoliubov waves that may be excited in the counterpropagation configuration. We identify a dimensionless parameter, the Mach number at T=0, that tunes different regimes of stability. We also estimate the magnitude of the main parameters at which two-stream instability is expected to be observed under typical experimental conditions
Generalized soldering of helicity states in
The direct sum of a couple of Maxwell-Chern-Simons (MCS) gauge theories of
opposite helicities does not lead to a Proca theory in ,
although both theories share the same spectrum. However, it is known that by
adding an interference term between both helicities we can join the
complementary pieces together and obtain the physically expected result. A
generalized soldering procedure can be defined to generate the missing
interference term. Here we show that the same procedure can be applied to join
together helicity states in a full off-shell manner. In particular, by
using second-order (in derivatives) self-dual models of helicities
(spin two analogues of MCS models) the Fierz-Pauli theory is obtained after
soldering. Remarkably, if we replace the second-order models by third-order
self-dual models (linearized topologically massive gravity) of opposite
helicities we end up after soldering exactly with the new massive gravity
theory of Bergshoeff, Hohm and Townsend in its linearized approximation.Comment: 12 pages, to appear in Phys. Rev.
Massive "spin-2" theories in arbitrary dimensions
Here we show that in arbitrary dimensions there are two families of
second order Lagrangians describing massive "spin-2" particles via a
nonsymmetric rank-2 tensor. They differ from the usual Fierz-Pauli theory in
general. At zero mass one of the families is Weyl invariant. Such massless
theory has no particle content in and gives rise, via master action, to a
dual higher order (in derivatives) description of massive spin-2 particles in
where both the second and the fourth order terms are Weyl invariant,
contrary to the linearized New Massive Gravity. However, only the fourth order
term is invariant under arbitrary antisymmetric shifts. Consequently, the
antisymmetric part of the tensor propagates at large momentum as
instead of . So, the same kind of obstacle for the
renormalizability of the New Massive Gravity reappears in this nonsymmetric
higher order description of massive spin-2 particles.Comment: 11 pages, 0 figure
- …