117 research outputs found
Spinning particles and higher spin fields on (A)dS backgrounds
Spinning particle models can be used to describe higher spin fields in first
quantization. In this paper we discuss how spinning particles with gauged O(N)
supersymmetries on the worldline can be consistently coupled to conformally
flat spacetimes, both at the classical and at the quantum level. In particular,
we consider canonical quantization on flat and on (A)dS backgrounds, and
discuss in detail how the constraints due to the worldline gauge symmetries
produce geometrical equations for higher spin fields, i.e. equations written in
terms of generalized curvatures. On flat space the algebra of constraints is
linear, and one can integrate part of the constraints by introducing gauge
potentials. This way the equivalence of the geometrical formulation with the
standard formulation in terms of gauge potentials is made manifest. On (A)dS
backgrounds the algebra of constraints becomes quadratic, nevertheless one can
use it to extend much of the previous analysis to this case. In particular, we
derive general formulas for expressing the curvatures in terms of gauge
potentials and discuss explicitly the cases of spin 2, 3 and 4.Comment: 35 pages, added reference
Patterns of co-occurrence of rare and threatened species in winter arable plant communities of Italy
Detecting patterns of species co-occurrence is among the main tasks of plant community ecology. Arable plant communities are important elements of agroecosystems, because they support plant and animal biodiversity and provide ecosystem services. These plant communities are shaped by both agricultural and environmental drivers. The pressure of intensive agriculture worldwide has caused the decline of many characteristic arable species and communities. Italy is the European country where arable plant biodiversity is the best preserved. In this study, we assessed the patterns of co-occurrence of rare and threatened arable plants in 106 plots of winter arable vegetation located from Piedmont to Calabria, in the mainland part of the country. For this purpose, we based our
investigation on the analysis of a recently acquired dataset and on the European list of rare and threatened arable plants. We highlight how dierent species of conservation interest tend to occur in the same community. On the other hand, generalist and more competitive taxa show similar patterns of co-occurrence. We suggest that single species of conservation value could be suitable indicators of
a well-preserved community. On the other hand, to be eective, conservation strategies should target the whole community, rather than single species
Quantum Klein Space and Superspace
We give an algebraic quantization, in the sense of quantum groups, of the
complex Minkowski space, and we examine the real forms corresponding to the
signatures , , , constructing the corresponding quantum
metrics and providing an explicit presentation of the quantized coordinate
algebras. In particular, we focus on the Kleinian signature . The
quantizations of the complex and real spaces come together with a coaction of
the quantizations of the respective symmetry groups. We also extend such
quantizations to the supersetting
Poincare-Einstein Holography for Forms via Conformal Geometry in the Bulk
We study higher form Proca equations on Einstein manifolds with boundary data
along conformal infinity. We solve these Laplace-type boundary problems
formally, and to all orders, by constructing an operator which projects
arbitrary forms to solutions. We also develop a product formula for solving
these asymptotic problems in general. The central tools of our approach are (i)
the conformal geometry of differential forms and the associated exterior
tractor calculus, and (ii) a generalised notion of scale which encodes the
connection between the underlying geometry and its boundary. The latter also
controls the breaking of conformal invariance in a very strict way by coupling
conformally invariant equations to the scale tractor associated with the
generalised scale. From this, we obtain a map from existing solutions to new
ones that exchanges Dirichlet and Neumann boundary conditions. Together, the
scale tractor and exterior structure extend the solution generating algebra of
[31] to a conformally invariant, Poincare--Einstein calculus on (tractor)
differential forms. This calculus leads to explicit holographic formulae for
all the higher order conformal operators on weighted differential forms,
differential complexes, and Q-operators of [9]. This complements the results of
Aubry and Guillarmou [3] where associated conformal harmonic spaces parametrise
smooth solutions.Comment: 85 pages, LaTeX, typos corrected, references added, to appear in
Memoirs of the AM
Massive and massless higher spinning particles in odd dimensions
We study actions for massive bosonic particles of higher spins by
dimensionally reducing an action for massless particles. For the latter we take
a model with a SO(N) extended local supersymmetry on the worldline, that is
known to describe massless (conformal) particles of higher spins in flat
spacetimes of even dimensions. Dimensional reduction produces an action for
massive spinning particles in odd dimensions. The field equations that emerge
in a quantization a la Dirac are shown to be equivalent to the Fierz-Pauli
ones. The massless limit generates a multiplet of massless states with higher
spins, whose first quantized field equations have a geometric form with fields
belonging to various types of Young tableaux. These geometric equations can be
partially integrated to show their equivalence with the standard
Fronsdal-Labastida equations. We covariantize our model to check whether an
extension to curved spacetimes can be achieved. Restricting to (A)dS spaces, we
find that the worldline gauge algebra becomes nonlinear, but remains first
class. This guarantees consistency on such backgrounds. A light cone analysis
confirms the presence of the expected propagating degrees of freedom. A
covariant analysis is worked out explicitly for the massive case, which is seen
to give rise to the Fierz-Pauli equations extended to (A)dS spaces. It is worth
noting that in D=3 the massless limit of our model when N goes to infinity has
the same field content of the Vasiliev's theory that accommodates each spin
exactly once.Comment: 31 page
Development of a new GIS-based method to detect high natural value farmlands. A case study in central Italy
An original method for the identification of High Natural Value farmlands is presented. Gathering information about land use (CORINE Land Cover), geomorphology (elevation and Terrain Ruggedness Index) and remote sensing data in a GIS environment we were able to develop a new detection process; its application to a wide sector of central Italy, in areas characterized by high biodiversity and relevant agronomic and cultural value, is presented. Thus, a new tool for diminishing sampling efforts and economic and time wastes in territorial studies is provided
Particles with non abelian charges
Efficient methods for describing non abelian charges in worldline approaches
to QFT are useful to simplify calculations and address structural properties,
as for example color/kinematics relations. Here we analyze in detail a method
for treating arbitrary non abelian charges. We use Grassmann variables to take
into account color degrees of freedom, which however are known to produce
reducible representations of the color group. Then we couple them to a U(1)
gauge field defined on the worldline, together with a Chern-Simons term, to
achieve projection on an irreducible representation. Upon gauge fixing there
remains a modulus, an angle parametrizing the U(1) Wilson loop, whose
dependence is taken into account exactly in the propagator of the Grassmann
variables. We test the method in simple examples, the scalar and spin 1/2
contribution to the gluon self energy, and suggest that it might simplify the
analysis of more involved amplitudes.Comment: 14 page
Higher spin fields from a worldline perspective
Higher spin fields in four dimensions, and more generally conformal fields in
arbitrary dimensions, can be described by spinning particle models with a
gauged SO(N) extended supergravity on the worldline. We consider here the
one-loop quantization of these models by studying the corresponding partition
function on the one-dimensional torus. After gauge fixing the supergravity
multiplet, the partition function reduces to an integral over the corresponding
moduli space which is computed using orthogonal polynomial techniques. We
obtain a compact formula which gives the number of physical degrees of freedom
for all N in all dimensions. As an aside we compute the physical degrees of
freedom of the SO(4) = SU(2)xSU(2) model with only a SU(2) factor gauged, which
has attracted some interest in the literature
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