19,329 research outputs found
Massive "spin-2" theories in arbitrary dimensions
Here we show that in arbitrary dimensions there are two families of
second order Lagrangians describing massive "spin-2" particles via a
nonsymmetric rank-2 tensor. They differ from the usual Fierz-Pauli theory in
general. At zero mass one of the families is Weyl invariant. Such massless
theory has no particle content in and gives rise, via master action, to a
dual higher order (in derivatives) description of massive spin-2 particles in
where both the second and the fourth order terms are Weyl invariant,
contrary to the linearized New Massive Gravity. However, only the fourth order
term is invariant under arbitrary antisymmetric shifts. Consequently, the
antisymmetric part of the tensor propagates at large momentum as
instead of . So, the same kind of obstacle for the
renormalizability of the New Massive Gravity reappears in this nonsymmetric
higher order description of massive spin-2 particles.Comment: 11 pages, 0 figure
Massive spin-2 particles via embedment of the Fierz-Pauli equations of motion
Here we obtain alternative descriptions of massive spin-2 particles by an
embedding procedure of the Fierz-Pauli equations of motion. All models are free
of ghosts at quadratic level although most of them are of higher order in
derivatives. The models that we obtain can be nonlinearly completed in terms of
a dynamic and a fixed metric. They include some massive gravities
recently considered in the literature. In some cases there is an infrared (no
derivative) modification of the Fierz-Pauli mass term altogether with higher
order terms in derivatives. The analytic structure of the propagator of the
corresponding free theories is not affected by the extra terms in the action as
compared to the usual second order Fierz-Pauli theory.Comment: 13 page
Coherent State Path Integrals in the Weyl Representation
We construct a representation of the coherent state path integral using the
Weyl symbol of the Hamiltonian operator. This representation is very different
from the usual path integral forms suggested by Klauder and Skagerstan in
\cite{Klau85}, which involve the normal or the antinormal ordering of the
Hamiltonian. These different representations, although equivalent quantum
mechanically, lead to different semiclassical limits. We show that the
semiclassical limit of the coherent state propagator in Weyl representation is
involves classical trajectories that are independent on the coherent states
width. This propagator is also free from the phase corrections found in
\cite{Bar01} for the two Klauder forms and provides an explicit connection
between the Wigner and the Husimi representations of the evolution operator.Comment: 23 page
Fluctuating local moments, itinerant electrons and the magnetocaloric effect: the compositional hypersensitivity of FeRh
We describe an ab-initio Disordered Local Moment Theory for materials with
quenched static compositional disorder traversing first order magnetic phase
transitions. It accounts quantitatively for metamagnetic changes and the
magnetocaloric effect. For perfect stoichiometric B2-ordered FeRh, we calculate
the transition temperature of the ferromagnetic-antiferromagnetic transition to
be 495K and a maximum isothermal entropy change in 2 Tesla of J~K~kg. A large (40\%) component of is
electronic. The transition results from a fine balance of competing electronic
effects which is disturbed by small compositional changes - e.g. swapping just
2\% Fe of `defects' onto the Rh sublattice makes drop by 290K. This
hypersensitivity explains the narrow compositional range of the transition and
impurity doping effects.Comment: 11 pages, 4 figure
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