2,789 research outputs found
Extension of the Poincar\'e group with half-integer spin generators: hypergravity and beyond
An extension of the Poincar\'e group with half-integer spin generators is
explicitly constructed. We start discussing the case of three spacetime
dimensions, and as an application, it is shown that hypergravity can be
formulated so as to incorporate this structure as its local gauge symmetry.
Since the algebra admits a nontrivial Casimir operator, the theory can be
described in terms of gauge fields associated to the extension of the
Poincar\'e group with a Chern-Simons action. The algebra is also shown to admit
an infinite-dimensional non-linear extension, that in the case of fermionic
spin- generators, corresponds to a subset of a contraction of two copies
of WB. Finally, we show how the Poincar\'e group can be extended with
half-integer spin generators for dimensions.Comment: 12 pages, no figures. Matches published versio
Asymptotic structure of supergravity in 3D: extended super-BMS and nonlinear energy bounds
The asymptotically flat structure of supergravity in
three spacetime dimensions is explored. The asymptotic symmetries are spanned
by an extension of the super-BMS algebra, with two independent
currents of electric and magnetic type. These currents are associated to
fields being even and odd under parity, respectively. Remarkably, although the
fields do not generate a backreaction on the metric, they provide
nontrivial Sugawara-like contributions to the BMS generators, and hence to
the energy and the angular momentum. The entropy of flat cosmological
spacetimes with fields then acquires a nontrivial dependence on the
charges. If the spin structure is odd, the ground state
corresponds to Minkowski spacetime, and although the anticommutator of the
canonical supercharges is linear in the energy and in the electric-like
charge, the energy becomes bounded from below by the energy of the
ground state shifted by the square of the electric-like charge. If
the spin structure is even, the same bound for the energy generically holds,
unless the absolute value of the electric-like charge is less than minus the
mass of Minkowski spacetime in vacuum, so that the energy has to be
nonnegative. The explicit form of the Killing spinors is found for a wide class
of configurations that fulfills our boundary conditions, and they exist
precisely when the corresponding bounds are saturated. It is also shown that
the spectra with periodic or antiperiodic boundary conditions for the fermionic
fields are related by spectral flow, in a similar way as it occurs for the
super-Virasoro algebra. Indeed, our super-BMS algebra can
be recovered from the flat limit of the superconformal algebra with
, truncating the fermionic generators of the right copy.Comment: 32 pages, no figures. Talk given at the ESI Programme and Workshop
"Quantum Physics and Gravity" hosted by ESI, Vienna, June 2017. V3: minor
changes and typos corrected. Matches published versio
Closed-shell interaction in silver and gold chlorides
Hartree-Fock and coupled-cluster calculations have been performed for cubic
AgCl and for AuCl having a cubic or the observed structure with space group
I4_1/amd. Cohesive energies and lattice constants are in excellent agreement
with experiment for AgCl; for AuCl we find good agreement, and the experimental
structure is correctly predicted to be lower in energy than the cubic one.
Electron-correlation effects on lattice constants are very large, of up to 0.8
\AA for cubic AuCl. We especially discuss the strength of the closed-shell
interactions, and for the first time a quantitative analysis of the so-called
"aurophilic" Au(I)-Au(I) interaction is presented in solids.Comment: accepted by J. Chem. Phy
Asymptotic gauge symmetries and gauge-invariant Poincar\'e generators in higher spacetime dimensions
The asymptotic symmetries of electromagnetism in all higher spacetime
dimensions are extended, by incorporating consistently angle-dependent
gauge transformations with a linear growth in the radial coordinate at
spatial infinity. Finiteness of the symplectic structure and preservation of
the asymptotic conditions require to impose a set of strict parity conditions,
under the antipodal map of the -sphere, on the leading order fields at
infinity. Canonical generators of the asymptotic symmetries are obtained
through standard Hamiltonian methods. Remarkably, the theory endowed with this
set of asymptotic conditions turns out to be invariant under a six-fold set of
angle-dependent transformations, whose generators form a centrally
extended abelian algebra. The new charges generated by the
gauge parameter are found to be conjugate to those associated to the now
improper subleading transformations, while the standard gauge transformations are canonically conjugate to the subleading
transformations. This algebraic structure,
characterized by the presence of central charges, allows us to perform a
nonlinear redefinition of the Poincar\'e generators, that results in the
decoupling of all of the charges from the Poincar\'e algebra. Thus, the
mechanism previously used in to find gauge-invariant Poincar\'e
generators is shown to be a robust property of electromagnetism in all
spacetime dimensions .Comment: 25 pages, no figures. References added. Matches with published
versio
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