38,221 research outputs found
Quantum spin circulator in Y junctions of Heisenberg chains
We show that a quantum spin circulator, a nonreciprocal device that routes
spin currents without any charge transport, can be achieved in Y junctions of
identical spin- Heisenberg chains coupled by a chiral three-spin
interaction. Using bosonization, boundary conformal field theory, and
density-matrix renormalization group simulations, we find that a chiral fixed
point with maximally asymmetric spin conductance arises at a critical point
separating a regime of disconnected chains from a spin-only version of the
three-channel Kondo effect. We argue that networks of spin-chain Y junctions
provide a controllable approach to construct long-sought chiral spin liquid
phases.Comment: 9 pages, 3 figure
A model for structural defects in nanomagnets
A model for describing structural pointlike defects in nanoscaled
ferromagnetic materials is presented. Its details are explicitly developed
whenever interacting with a vortex-like state comprised in a thin nanodisk.
Among others, our model yields results for the vortex equilibrium position
under the influence of several defects along with an external magnetic field in
good qualitative agreement with experiments. We also discuss how such defects
may affect the vortex motion, like its gyrotropic oscillation and dynamical
polarization reversal.Comment: 8 pages, resubmitted to Journal of Applied Physic
Particle creation in a f(R) theory with cosmological constraints
In this paper we study the creation of super-massive real scalar particles in
the framework of a modified gravity theory, with parameters
constrained by observational data. The analysis is restrict to a homogeneous
and isotropic flat and radiation dominated universe. We compare the results to
the standard Einstein gravity with cosmological constant ( model),
and we show that the total number density of created particles in the
model is very close to the standard case. Another interesting result is that
the spectrum of created particles is independent at early times.Comment: To appear in the General Relativity and Gravitation. arXiv admin
note: text overlap with arXiv:1108.334
Gribov ambiguities at the Landau -- maximal Abelian interpolating gauge
In a previous work, we presented a new method to account for the Gribov
ambiguities in non-Abelian gauge theories. The method consists on the
introduction of an extra constraint which directly eliminates the infinitesimal
Gribov copies without the usual geometric approach. Such strategy allows to
treat gauges with non-hermitian Faddeev-Popov operator. In this work, we apply
this method to a gauge which interpolates among the Landau and maximal Abelian
gauges. The result is a local and power counting renormalizable action, free of
infinitesimal Gribov copies. Moreover, the interpolating tree-level gluon
propagator is derived.Comment: Several changes: figures removed, typos corrected and discussions
included. 24 pages, to appear in EPJ
On the elimination of infinitesimal Gribov ambiguities in non-Abelian gauge theories
An alternative method to account for the Gribov ambiguities in gauge theories
is presented. It is shown that, to eliminate Gribov ambiguities, at
infinitesimal level, it is required to break the BRST symmetry in a soft
manner. This can be done by introducing a suitable extra constraint that
eliminates the infinitesimal Gribov copies. It is shown that the present
approach is consistent with the well established known cases in the literature,
i.e., the Landau and maximal Abelian gauges. The method is valid for gauges
depending exclusively on the gauge field and is restricted to classical level.
However, occasionally, we deal with quantum aspects of the technique, which are
used to improve the results.Comment: 29 pp. No figures. Discussions added. Final version to appear in EPJ
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