565 research outputs found
An Exotic Theory of Massless Spin-Two Fields in Three Dimensions
It is a general belief that the only possible way to consistently deform the
Pauli-Fierz action, changing also the gauge algebra, is general relativity.
Here we show that a different type of deformation exists in three dimensions if
one allows for PT non-invariant terms. The new gauge algebra is different from
that of diffeomorphisms. Furthermore, this deformation can be generalized to
the case of a collection of massless spin-two fields. In this case it describes
a consistent interaction among them.Comment: 21+1 pages. Minor corrections and reference adde
A note on the uniqueness of D=4 N=1 Supergravity
We investigate in 4 spacetime dimensions, all the consistent deformations of
the lagrangian , which is the sum of the
Pauli-Fierz lagrangian for a free massless spin 2 field and the
Rarita-Schwinger lagrangian for a free massless spin 3/2
field. Using BRST cohomogical techniques, we show, under the assumptions of
locality, Poincar\'e invariance, conservation of the number of gauge symmetries
and the number of derivatives on each fields, that N=1 D=4 supergravity is the
only consistent interaction between a massless spin 2 and a massless spin 3/2
field. We do not assume general covariance. This follows automatically, as does
supersymmetry invariance. Various cohomologies related to conservations laws
are also given.Comment: 22+1 pages, LaTeX. References adde
Extension of the Poincar\'e Group and Non-Abelian Tensor Gauge Fields
In the recently proposed generalization of the Yang-Mills theory the group of
gauge transformation gets essentially enlarged. This enlargement involves an
elegant mixture of the internal and space-time symmetries. The resulting group
is an extension of the Poincar\'e group with infinitely many generators which
carry internal and space-time indices. This is similar to the super-symmetric
extension of the Poincar\'e group, where instead of an anti-commuting spinor
variable one should introduce a new vector variable. The construction of
irreducible representations of the extended Poincar\'e algebra identifies a
vector variable with the derivative of the Pauli-Lubanski vector over its
length. As a result of this identification the generators of the gauge group
have nonzero components only in the plane transversal to the momentum and are
projecting out non-Abelian tensor gauge fields into the transversal plane,
keeping only their positively definite space-like components.Comment: 21 page
Slowly decaying classical fields, unitarity, and gauge invariance
In classical external gauge fields that fall off less fast than the inverse
of the evolution parameter (time) of the system the implementability of a
unitary perturbative scattering operator (-matrix) is not guaranteed,
although the field goes to zero. The importance of this point is exposed for
the counter-example of low-dimensionally expanding systems. The issues of gauge
invariance and of the interpretation of the evolution at intermediate times are
also intricately linked to that point.Comment: 8 pages, no figure
Production of non-Abelian tensor gauge bosons. Tree amplitudes in generalized Yang-Mills theory and BCFW recursion relation
The BCFW recursion relation allows to calculate tree-level scattering
amplitudes in generalized Yang-Mills theory and, in particular, four-particle
amplitudes for the production rate of non-Abelian tensor gauge bosons of
arbitrary high spin in the fusion of two gluons. The consistency of the
calculations in different kinematical channels is fulfilled when all
dimensionless cubic coupling constants between vector bosons (gluons) and high
spin non-Abelian tensor gauge bosons are equal to the Yang-Mills coupling
constant. There are no high derivative cubic vertices in the generalized
Yang-Mills theory. The amplitudes vanish as complex deformation parameter tends
to infinity, so that there is no contribution from the contour at infinity. We
derive a generalization of the Parke-Taylor formula in the case of production
of two tensor gauge bosons of spin-s and N gluons (jets). The expression is
holomorhic in the spinor variables of the scattered particles, exactly as the
MHV gluon amplitude is, and reduces to the gluonic MHV amplitude when s=1. In
generalized Yang-Mills theory the tree level n-particle scattering amplitudes
with all positive helicities vanish, but tree amplitudes with one negative
helicity particle are already nonzero.Comment: 19 pages, LaTex fil
On the Velo-Zwanziger phenomenon
The Rarita-Schwinger equation in a curved background and an external
electromagnetic field is discussed. We analyse the equation in the 2-component
spinor formalism and derive Buchdahl conditions for them. The result is that
the equation can consistently be imposed only on Einstein manifolds with
vanishing electromagnetic field
Graviton Mass or Cosmological Constant?
To describe a massive graviton in 4D Minkowski space-time one introduces a
quadratic term in the Lagrangian. This term, however, can lead to a
readjustment or instability of the background instead of describing a massive
graviton on flat space. We show that for all local Lorentz-invariant mass terms
Minkowski space is unstable. We start with the Pauli-Fierz (PF) term that is
the only local mass term with no ghosts in the linearized approximation. We
show that nonlinear completions of the PF Lagrangian give rise to instability
of Minkowski space. We continue with the mass terms that are not of a PF type.
Although these models are known to have ghosts in the linearized
approximations, nonlinear interactions can lead to background change due to
which the ghosts are eliminated. In the latter case, however, the graviton
perturbations on the new background are not massive. We argue that a consistent
theory of a massive graviton on flat space can be formulated in theories with
extra dimensions. They require an infinite number of fields or non-local
description from a 4D point of view.Comment: 16 pages; references and comments adde
Interacting Dark Matter and Dark Energy
We discuss models for the cosmological dark sector in which the energy
density of a scalar field approximates Einstein's cosmological constant and the
scalar field value determines the dark matter particle mass by a Yukawa
coupling. A model with one dark matter family can be adjusted so the
observational constraints on the cosmological parameters are close to but
different from what is predicted by the Lambda CDM model. This may be a useful
aid to judging how tightly the cosmological parameters are constrained by the
new generation of cosmological tests that depend on the theory of structure
formation. In a model with two families of dark matter particles the scalar
field may be locked to near zero mass for one family. This can suppress the
long-range scalar force in the dark sector and eliminate evolution of the
effective cosmological constant and the mass of the nonrelativistic dark matter
particles, making the model close to Lambda CDM, until the particle number
density becomes low enough to allow the scalar field to evolve. This is a
useful example of the possibility for complexity in the dark sector.Comment: 15 pages, 6 figures; added a reference and a minor correctio
Parent form for higher spin fields on anti-de Sitter space
We construct a first order parent field theory for free higher spin gauge
fields on constant curvature spaces. As in the previously considered flat case,
both Fronsdal's and Vasiliev's unfolded formulations can be reached by two
different straightforward reductions. The parent theory itself is formulated
using a higher dimensional embedding space and turns out to be geometrically
extremely transparent and free of the intricacies of both of its reductions.Comment: 39 pages, LaTeX; misprints corrected, references adde
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