3,987 research outputs found
Frame-like Lagrangians and presymplectic AKSZ-type sigma models
We study supergeometric structures underlying frame-like Lagrangians. We show
that for the theory in n spacetime dimensions both the frame-like Lagrangian
and its gauge symmetries are encoded in the target supermanifold equipped with
the odd vector field, the closed 2-form of ghost degree n-1, and the scalar
potential of ghost degree n. These structures satisfy a set of compatibility
conditions ensuring the gauge invariance of the theory. The Lagrangian and the
gauge symmetries have the same structures as those of AKSZ sigma model so that
frame-like formulation can be seen as its presymplectic generalization. In
contrast to the conventional AKSZ model the generalization allows to describe
systems with local degrees of freedom in terms of finite-dimensional target
space. We argue that the proposed frame-like approach is directly related de
Donder-Weyl polymomentum Hamiltonian formalism. Along with the standard
field-theoretical examples like Einstein-Yang-Mills theory we consider free
higher spin fields, multi-frame gravity, and parameterized systems. In
particular, we propose the frame-like action for free totally symmetric
massless fields that involves all higher spin connections on an equal footing.Comment: 28 pages; v2: references added; v3: 34 pages, exposition improved,
typos removed, comments and refs added, new section 3.6.3 added with an
action for spin-s massless fields involving all HS connections on an equal
footin
Uniformizing higher-spin equations
Vasiliev's higher-spin theories in various dimensions are uniformly
represented as a simple system of equations. These equations and their gauge
invariances are based on two superalgebras and have a transparent algebraic
meaning. For a given higher-spin theory these algebras can be inferred from the
vacuum higher-spin symmetries. The proposed system of equations admits a
concise AKSZ formulation. We also discuss novel higher-spin systems including
partially-massless and massive fields in AdS, as well as conformal and massless
off-shell fields.Comment: 29 pages, references added, final versio
Unified formulation for helicity and continuous spin fermionic fields
We propose a unified BRST formulation of general massless fermionic fields of
arbitrary mixed-symmetry type in -dimensional Minkowski space. Depending on
the value of the real parameter the system describes either helicity fields or
continuous spin fields. Starting with the unified formulation we derive a
number of equivalent descriptions including the triplet formulation,
Fang-Fronsdal-Labastida formulation, light-cone formulation and discuss the
unfolded formulation.Comment: v2: exposition of the triplet formulation is improved and the triplet
Lagrangian for fermionic helicity fields is made precise, references and
acknowledgements added; v4: corrected typos, reference and comments adde
Theory of the Shubnikov-de Haas effect in quasi-two-dimensional metals
The Shubnikov - de Haas effect in quasi-two-dimensional normal metals is
studied. The interlayer conductivity is calculated using the Kubo formula. The
electron scattering on short-range is considered in the self-consistent Born
approximation. The result obtained differs from that derived from the Boltzmann
transport equation. This difference is shown to be a general feature of
conductivity in magnetic field. A detailed description of the two new
qualitative effects -- the field-dependent phase shift of beats and of the slow
oscillations of conductivity is provided. The results obtained are applicable
to strongly anisotropic organic metals and to other quasi-two-dimensional
compounds.Comment: 10 page
Reply to "Comment on 'Origin of combination frequencies in quantum magnetic oscillations of two-dimensional multiband metals' " by A.S. Alexandrov and A.M. Bratkovsky [cond-mat/0207173]
In their comment on the paper (Phys. Rev. B 65, 153403 (2002);
cond-mat/0110154), Alexandrov and Bratkovsky (cond-mat/0207173) argue that they
correctly took into account the chemical potential oscillations in their
analytical theory of combination frequencies in multiband low-dimensional
metals by expanding the free energy in powers of the chemical potential
oscillations. In this reply, we show that this claim contradicts their original
paper (Phys. Rev. B 63, 033105 (2001)). We demonstrate that the condition given
for the expansion is mathematically incorrect. The correct condition allows to
understand the limits of validity of the analytical theory.Comment: 4 page
Supersymmetry Flows, Semi-Symmetric Space Sine-Gordon Models And The Pohlmeyer Reduction
We study the extended supersymmetric integrable hierarchy underlying the
Pohlmeyer reduction of superstring sigma models on semi-symmetric superspaces
F/G. This integrable hierarchy is constructed by coupling two copies of the
homogeneous integrable hierarchy associated to the loop Lie superalgebra
extension f of the Lie superalgebra f of F and this is done by means of the
algebraic dressing technique and a Riemann-Hilbert factorization problem. By
using the Drinfeld-Sokolov procedure we construct explicitly, a set of 2D spin
\pm1/2 conserved supercharges generating supersymmetry flows in the phase space
of the reduced model. We introduce the bi-Hamiltonian structure of the extended
homogeneous hierarchy and show that the two brackets are of the
Kostant-Kirillov type on the co-adjoint orbits defined by the light-cone Lax
operators L_\pm. By using the second symplectic structure, we show that these
supersymmetries are Hamiltonian flows, we compute part of the supercharge
algebra and find the supersymmetric field variations they induce. We also show
that this second Poisson structure coincides with the canonical
Lorentz-Invariant symplectic structure of the WZNW model involved in the
Lagrangian formulation of the extended integrable hierarchy, namely, the
semi-symmetric space sine-Gordon model (SSSSG), which is the Pohlmeyer reduced
action functional for the transverse degrees of freedom of superstring sigma
models on the cosets F/G. We work out in some detail the Pohlmeyer reduction of
the AdS_2xS^2 and the AdS_3xS^3 superstrings and show that the new conserved
supercharges can be related to the supercharges extracted from 2D superspace.
In particular, for the AdS_2xS^2 example, they are formally the same.Comment: V2: Two references added, V3: Modifications in section 2.6, V4:
Published versio
Slow oscillations of magnetoresistance in quasi-two-dimensional metals
Slow oscillations of the interlayer magnetoresistance observed in the layered
organic metal -(BEDT-TTF)IBr are shown to originate from the
slight warping of its Fermi surface rather than from independent small
cyclotron orbits. Unlike the usual Shubnikov-de Haas effect, these oscillations
are not affected by the temperature smearing of the Fermi distribution and can
therefore become dominant at high enough temperatures. We suggest that the slow
oscillations are a general feature of clean quasi-two-dimensional metals and
discuss possible applications of the phenomenon.Comment: 11 pages, 3 figure
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