25,145 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
Ising Spin Glass in a Transverse Magnetic Field
We study the three-dimensional quantum Ising spin glass in a transverse
magnetic field following the evolution of the bond probability distribution
under Renormalisation Group transformations. The phase diagram (critical
temperature {\em vs} transverse field ) we obtain shows a finite
slope near , in contrast with the infinite slope for the pure case. Our
results compare very well with the experimental data recently obtained for the
dipolar Ising spin glass LiHoYF, in a transverse field.
This indicates that this system is more apropriately described by a model with
short range interactions than by an equivalent Sherrington-Kirkpatrick model in
a transverse field.Comment: 7 pages, RevTeX3, Nota Cientifica PUC-Rio 23/9
Coupling vortex dynamics with collective excitations in Bose-Einstein Condensates
Here we analyze the collective excitations as well as the expansion of a
trapped Bose-Einstein condensate with a vortex line at its center. To this end,
we propose a variational method where the variational parameters have to be
carefully chosen in order to produce reliable results. Our variational
calculations agree with numerical simulations of the Gross-Pitaevskii equation.
The system considered here turns out to exhibit four collective modes of which
only three can be observed at a time depending of the trap anisotropy. We also
demonstrate that these collective modes can be excited using well established
experimental methods such as modulation of the s-wave scattering length
Some numerical verification examples for plane stress elasto-viscoplasticity
This paper presents analytical, semi-analytical and numerical reference examples which can be employed for code verification of elasto-viscoplastic models under plane stress conditions. Mainly because of the overstress function the algorithms traditionally employed in elasto-plastic implementations must be rewritten to correctly impose the plane stress state along with the viscoplastic flow. The viscoplastic formulation presented here considers the strain-rate hardening effects by means of a hardening law that are assumed to have terms depending on the strain rate, which removed can represent a Voce type hardening. The proposed verification tests were employed for the numerical verification of an in-house implementation of the so-called stress-projected procedure inside the finite element method context. Although the focus of this paper is on the stressprojected algorithms the examples presented here can be employed for the verification of other algorithms intended to impose the plane stress state in viscoplasticit
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