1,258 research outputs found
Estimation of the methane emission factor for the Italian Mediterranean buffalo
In order to contribute to the improvement of the national greenhouse gas emission inventory, this work aimed at estimating a country-specific enteric methane (CH4) emission factor for the Italian Mediterranean buffalo. For this purpose, national agriculture statistics, and information on animal production and farming conditions were analysed, and the emission factor was estimated using the Tier 2 model of the Intergovernmental Panel on Climate Change. Country-specific CH4 emission factors for buffalo cows (630 kg body weight, BW) and other buffalo (313 kg BW) categories were estimated for the period 1990–2004. In 2004, the estimated enteric CH4 emission factor for the buffalo cows was 73 kg/head per year, whereas that for other buffalo categories it was 56 kg/head per year. Research in order to determine specific CH4 conversion rates at the predominant production system is suggested
Finite density and temperature in hybrid bag models
We introduce the chemical potential in a system of two-flavored massless
fermions in a chiral bag by imposing boundary conditions in the Euclidean time
direction. We express the fermionic mean number in terms of a functional trace
involving the Green function of the boundary value problem, which is studied
analytically. Numerical evaluations for the fermionic number are presented.Comment: 19 pages, 4 figure
Maxwell-like Lagrangians for higher spins
We show how implementing invariance under divergence-free gauge
transformations leads to a remarkably simple Lagrangian description of massless
bosons of any spin. Our construction covers both flat and (A)dS backgrounds and
extends to tensors of arbitrary mixed-symmetry type. Irreducible and traceless
fields produce single-particle actions, while whenever trace constraints can be
dispensed with the resulting Lagrangians display the same reducible,
multi-particle spectra as those emerging from the tensionless limit of free
open-string field theory. For all explored options the corresponding kinetic
operators take essentially the same form as in the spin-one, Maxwell case.Comment: 77 pages, revised version. Erroneous interpretation and proof of the
gauge-fixing procedure for mixed-symmetry fields corrected. As a consequence,
the mixed-symmetry, one-particle Lagrangians are to be complemented with
conditions on the divergences of the fields; all other conclusions unchanged.
Additional minor changes including references added. To appear in JHE
On the relation between local and geometric Lagrangians for higher spins
Equations of motion for free higher-spin gauge fields of any symmetry can be
formulated in terms of linearised curvatures. On the other hand, gauge
invariance alone does not fix the form of the corresponding actions which, in
addition, either contain higher derivatives or involve inverse powers of the
d'Alembertian operator, thus introducing possible subtleties in degrees of
freedom count. We suggest a path to avoid ambiguities, starting from local,
unconstrained Lagrangians previously proposed, and integrating out the
auxiliary fields from the functional integral, thus generating a unique
non-local theory expressed in terms of curvatures.Comment: 14 pages. Contribution to the proceedings of the 1st Mediterranean
Conference on Classical and Quantum Gravity, Kolymbary (Crete, Greece)
September 14-18 200
Confined two-dimensional fermions at finite density
We introduce the chemical potential in a system of two-dimensional massless
fermions, confined to a finite region, by imposing twisted boundary conditions
in the Euclidean time direction. We explore in this simple model the
application of functional techniques which could be used in more complicated
situations.Comment: 15 pages, LaTe
Effective action in a higher-spin background
We consider a free massless scalar field coupled to an infinite tower of
background higher-spin gauge fields via minimal coupling to the traceless
conserved currents. The set of Abelian gauge transformations is deformed to the
non-Abelian group of unitary operators acting on the scalar field. The gauge
invariant effective action is computed perturbatively in the external fields.
The structure of the various (divergent or finite) terms is determined. In
particular, the quadratic part of the logarithmically divergent (or of the
finite) term is expressed in terms of curvatures and related to conformal
higher-spin gravity. The generalized higher-spin Weyl anomalies are also
determined. The relation with the theory of interacting higher-spin gauge
fields on anti de Sitter spacetime via the holographic correspondence is
discussed.Comment: 40 pages, Some errors and typos corrected, Version published in JHE
Half-integer Higher Spin Fields in (A)dS from Spinning Particle Models
We make use of O(2r+1) spinning particle models to construct linearized
higher-spin curvatures in (A)dS spaces for fields of arbitrary half-integer
spin propagating in a space of arbitrary (even) dimension: the field
potentials, whose curvatures are computed with the present models, are
spinor-tensors of mixed symmetry corresponding to Young tableaux with D/2 - 1
rows and r columns, thus reducing to totally symmetric spinor-tensors in four
dimensions. The paper generalizes similar results obtained in the context of
integer spins in (A)dS.Comment: 1+18 pages; minor changes in the notation, references updated.
Published versio
On the cubic interactions of massive and partially-massless higher spins in (A)dS
Cubic interactions of massive and partially-massless totally-symmetric
higher-spin fields in any constant-curvature background of dimension greater
than three are investigated. Making use of the ambient-space formalism, the
consistency condition for the traceless and transverse parts of the
parity-invariant interactions is recast into a system of partial differential
equations. The latter can be explicitly solved for given s_1-s_2-s_3 couplings
and the 2-2-2 and 3-3-2 examples are provided in detail for general choices of
the masses. On the other hand, the general solutions for the interactions
involving massive and massless fields are expressed in a compact form as
generating functions of all the consistent couplings. The St\"uckelberg
formulation of the cubic interactions as well as their massless limits are also
analyzed.Comment: 42 pages, 2 tables, LaTex. Comments on two-derivative couplings
involving partially-massless spin-2 fields added, typos corrected, references
added. v2: final version to appear in JHEP. v3: formulae (3.4) and (3.9)
correcte
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