593 research outputs found
An action principle for Vasiliev's four-dimensional higher-spin gravity
We provide Vasiliev's fully nonlinear equations of motion for bosonic gauge
fields in four spacetime dimensions with an action principle. We first extend
Vasiliev's original system with differential forms in degrees higher than one.
We then derive the resulting duality-extended equations of motion from a
variational principle based on a generalized Hamiltonian sigma-model action.
The generalized Hamiltonian contains two types of interaction freedoms: One set
of functions that appears in the Q-structure of the generalized curvatures of
the odd forms in the duality-extended system; and another set depending on the
Lagrange multipliers, encoding a generalized Poisson structure, i.e. a set of
polyvector fields of ranks two or higher in target space. We find that at least
one of the two sets of interaction-freedom functions must be linear in order to
ensure gauge invariance. We discuss consistent truncations to the minimal Type
A and B models (with only even spins), spectral flows on-shell and provide
boundary conditions on fields and gauge parameters that are compatible with the
variational principle and that make the duality-extended system equivalent, on
shell, to Vasiliev's original system.Comment: 37 pages. References added, corrected typo
Supersymmetric Higher Spin Theories
We revisit the higher spin extensions of the anti de Sitter algebra in four
dimensions that incorporate internal symmetries and admit representations that
contain fermions, classified long ago by Konstein and Vasiliev. We construct
the , Euclidean and Kleinian version of these algebras, as well as the
corresponding fully nonlinear Vasiliev type higher spin theories, in which the
reality conditions we impose on the master fields play a crucial role. The
supersymmetric higher spin theory in , on which we elaborate
further, is included in this class of models. A subset of Konstein-Vasiliev
algebras are the higher spin extensions of the superalgebras
for mod 4 and can be realized using
fermionic oscillators. We tensor the higher superalgebras of the latter kind
with appropriate internal symmetry groups and show that the mod 4
higher spin algebras are isomorphic to those with mod 4. We
describe the fully nonlinear higher spin theories based on these algebras as
well, and we elaborate further on the supersymmetric theory,
providing two equivalent descriptions one of which exhibits manifestly its
relation to the supersymmetric higher spin theory.Comment: 30 pages. Contribution to J. Phys. A special volume on "Higher Spin
Theories and AdS/CFT" edited by M. R. Gaberdiel and M. Vasilie
Miocene initiation and acceleration of extension in the South Lunggar rift, western Tibet: Evolution of an active detachment system from structural mapping and (U-Th)/He thermochronology
This is the publisher's version, also available electronically from http://onlinelibrary.wiley.com/doi/10.1002/tect.20053/abstractOngoing extension in Tibet may have begun in the middle to late Miocene, but there are few robust estimates of the rates, timing, or magnitude of Neogene deformation within the Tibetan plateau. We present a comprehensive study of the seismically active South Lunggar rift in southwestern Tibet incorporating mapping, U-Pb geochronology and zircon (U-Th)/He thermochronology. The South Lunggar rift is the southern continuation of the North Lunggar rift and comprises a ~50 km N-S central horst bound by two major normal faults, the west-dipping South Lunggar detachment and the east-dipping Palung Co fault. The SLD dips at the rangefront ~20°W and exhumes a well-developed mylonite zone in its footwall displaying fabrics indicative of normal-sense shear. The range is composed of felsic orthogneiss, mafic amphibolite, and leucogranite intrusions dated at ~16 and 63 Ma. Zircon (U-Th)/He cooling ages are Oligocene through late Pliocene, with the youngest ages observed in the footwall of the SLD. We tested ~25,000 unique thermokinematic forward models in Pecube against the structural and (U-Th)/He data to fully bracket the allowable ranges in fault initiations, accelerations, and slip rates. We find that normal faulting in the SLR began in the middle Miocene with horizontal extension rates of ~1 mm a−1, and in the north accelerated at 8 Ma to 2.5–3.0 mm a−1 as faulting commenced on the SLD. Cumulative horizontal extension across the SLR ranges from <10 km in the south to 19–21 km in the north
Invariant Differential Operators and Characters of the AdS_4 Algebra
The aim of this paper is to apply systematically to AdS_4 some modern tools
in the representation theory of Lie algebras which are easily generalised to
the supersymmetric and quantum group settings and necessary for applications to
string theory and integrable models. Here we introduce the necessary
representations of the AdS_4 algebra and group. We give explicitly all singular
(null) vectors of the reducible AdS_4 Verma modules. These are used to obtain
the AdS_4 invariant differential operators. Using this we display a new
structure - a diagram involving four partially equivalent reducible
representations one of which contains all finite-dimensional irreps of the
AdS_4 algebra. We study in more detail the cases involving UIRs, in particular,
the Di and the Rac singletons, and the massless UIRs. In the massless case we
discover the structure of sets of 2s_0-1 conserved currents for each spin s_0
UIR, s_0=1,3/2,... All massless cases are contained in a one-parameter
subfamily of the quartet diagrams mentioned above, the parameter being the spin
s_0. Further we give the classification of the so(5,C) irreps presented in a
diagramatic way which makes easy the derivation of all character formulae. The
paper concludes with a speculation on the possible applications of the
character formulae to integrable models.Comment: 30 pages, 4 figures, TEX-harvmac with input files: amssym.def,
amssym.tex, epsf.tex; version 2 1 reference added; v3: minor corrections;
v.4: minor corrections, v.5: minor corrections to conform with version in J.
Phys. A: Math. Gen; v.6.: small correction and addition in subsections 4.1 &
4.
Propagating modes of non-Abelian tensor gauge field of second rank
In the recently proposed extension of the YM theory, non-Abelian tensor gauge
field of the second rank is represented by a general tensor whose symmetric
part describes the propagation of charged gauge boson of helicity two and its
antisymmetric part - the helicity zero charged gauge boson. On the
non-interacting level these polarizations are similar to the polarizations of
the graviton and of the Abelian antisymmetric B field, but the interaction of
these gauge bosons carrying non-commutative internal charges cannot be directly
identified with the interaction of gravitons or B field. Our intention here is
to illustrate this result from different perspectives which would include
Bianchi identity for the corresponding field strength tensor and the analysis
of the second-order partial differential equation which describes in this
theory the propagation of non-Abelian tensor gauge field of the second rank.Comment: 22 pages, Latex fil
A minimal BV action for Vasiliev's four-dimensional higher spin gravity
The action principle for Vasiliev's four-dimensional higher-spin gravity
proposed recently by two of the authors, is converted into a minimal BV master
action using the AKSZ procedure, which amounts to replacing the classical
differential forms by vectorial superfields of fixed total degree given by the
sum of form degree and ghost number. The nilpotency of the BRST operator is
achieved by imposing boundary conditions and choosing appropriate gauge
transitions between charts leading to a globally-defined formulation based on a
principal bundle.Comment: 39 pages, 1 figure. Additional comments in the conclusion
Iron Age and Anglo-Saxon genomes from East England reveal British migration history
British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. By analysing shared rare variants with hundreds of modern samples from Britain and Europe, we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. We gain further insight with a new method, rarecoal, which infers population history and identifies fine-scale genetic ancestry from rare variants. Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain
Ab initio simulations of the kinetic properties of the hydrogen monomer on graphene
The understanding of the kinetic properties of hydrogen (isotopes) adatoms on
graphene is important in many fields. The kinetic properties of
hydrogen-isotope (H, D and T) monomers were simulated using a composite method
consisting of density functional theory, density functional perturbation theory
and harmonic transition state theory. The kinetic changes of the magnetic
property and the aromatic bond of the hydrogenated graphene during the
desorption and diffusion of the hydrogen monomer was discussed. The vibrational
zero-point energy corrections in the activation energies were found to be
significant, ranging from 0.072 to 0.205 eV. The results obtained from
quantum-mechanically modified harmonic transition state theory were compared
with the ones obtained from classical-limit harmonic transition state theory
over a wide temperature range. The phonon spectra of hydrogenated graphene were
used to closely explain the (reversed) isotope effects in the prefactor,
activation energy and jump frequency of the hydrogen monomer. The kinetic
properties of the hydrogen-isotope monomers were simulated under conditions of
annealing for 10 minutes and of heating at a constant rate (1.0 K/s). The
isotope effect was observed; that is, a hydrogen monomer of lower mass is
desorbed and diffuses more easily (with lower activation energies). The results
presented herein are very similar to other reported experimental observations.
This study of the kinetic properties of the hydrogen monomer and many other
involved implicit mechanisms provides a better understanding of the interaction
between hydrogen and graphene.Comment: Accepted by J. Phys. Chem.
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