5,793 research outputs found
An all-order proof of the equivalence between Gribov's no-pole and Zwanziger's horizon conditions
The quantization of non-Abelian gauge theories is known to be plagued by
Gribov copies. Typical examples are the copies related to zero modes of the
Faddeev-Popov operator, which give rise to singularities in the ghost
propagator. In this work we present an exact and compact expression for the
ghost propagator as a function of external gauge fields, in SU(N) Yang-Mills
theory in the Landau gauge. It is shown, to all orders, that the condition for
the ghost propagator not to have a pole, the so-called Gribov's no-pole
condition, can be implemented by demanding a nonvanishing expectation value for
a functional of the gauge fields that turns out to be Zwanziger's horizon
function. The action allowing to implement this condition is the
Gribov-Zwanziger action. This establishes in a precise way the equivalence
between Gribov's no-pole condition and Zwanziger's horizon condition.Comment: 11 pages, typos corrected, version accepted for publication in Phys.
Lett.
Dynamic RKKY interaction in graphene
The growing interest in carbon-based spintronics has stimulated a number of
recent theoretical studies on the RKKY interaction in graphene, based on which
the energetically favourable alignment between magnetic moments embedded in
this material can be calculated. The general consensus is that the strength of
the RKKY interaction in graphene decays as 1/D3 or faster, where D is the
separation between magnetic moments. Such an unusually fast decay for a
2-dimensional system suggests that the RKKY interaction may be too short ranged
to be experimentally observed in graphene. Here we show in a mathematically
transparent form that a far more long ranged interaction arises when the
magnetic moments are taken out of their equilibrium positions and set in
motion. We not only show that this dynamic version of the RKKY interaction in
graphene decays far more slowly but also propose how it can be observed with
currently available experimental methods.Comment: 7 pages, 2 figures, submitte
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