11,472 research outputs found
Results from a Non-Perturbative Renormalization of Lattice Operators
We propose a general renormalization method, which avoids completely the use
of lattice perturbation theory. We present the results from its numerical
applications to two-fermion operators on a lattice, at
.Comment: 3 pages postscript file. Contribution to Lattice '9
Tetragonal to orthorhombic phase transition in SmFeAsO: a synchrotron powder diffraction investigation
The crystal structure of SmFeAsO has been investigated by means of Rietveld
refinement of high resolution synchrotron powder diffraction data collected at
300 K and 100 K. The compound crystallizes in the tetragonal P4/nmm space group
at 300 K and in the orthorhombic Cmma space group at 100 K; attempts to refine
the low temperature data in the monoclinic P112/n space group diverged. On the
basis of both resistive and magnetic analyses the tetragonal to orthorhombic
phase transition can be located at T about 140 K.Comment: Submitted to: Superconductor Science and Technology PACS: 61.05.cp,
61.66.Fn, 74.10.+v, 74.62.Dh, 74.70.D
Mixing length scales of low temperature spin plaquettes models
Plaquette models are short range ferromagnetic spin models that play a key
role in the dynamic facilitation approach to the liquid glass transition. In
this paper we perform a rigorous study of the thermodynamic properties of two
dimensional plaquette models, the square and triangular plaquette models. We
prove that for any positive temperature both models have a unique infinite
volume Gibbs measure with exponentially decaying correlations. We analyse the
scaling of three a priori different static correlation lengths in the small
temperature regime, the mixing, cavity and multispin correlation lengths.
Finally, using the symmetries of the model we determine an exact self
similarity property for the infinite volume Gibbs measure.Comment: 33 pages, 9 figure
E-ELT constraints on runaway dilaton scenarios
We use a combination of simulated cosmological probes and astrophysical tests
of the stability of the fine-structure constant , as expected from the
forthcoming European Extremely Large Telescope (E-ELT), to constrain the class
of string-inspired runaway dilaton models of Damour, Piazza and Veneziano. We
consider three different scenarios for the dark sector couplings in the model
and discuss the observational differences between them. We improve previously
existing analyses investigating in detail the degeneracies between the
parameters ruling the coupling of the dilaton field to the other components of
the universe, and studying how the constraints on these parameters change for
different fiducial cosmologies. We find that if the couplings are small (e.g.,
) these degeneracies strongly affect the constraining
power of future data, while if they are sufficiently large (e.g.,
, as in agreement with current
constraints) the degeneracies can be partially broken. We show that E-ELT will
be able to probe some of this additional parameter space.Comment: 16 pages, 8 figures. Updated version matching the one accepted by
JCA
Non-Perturbative Renormalisation of the Lattice Four-Fermion Operator
We compute the renormalised four-fermion operator using a
non-perturbative method recently introduced for determining the renormalisation
constants of generic lattice composite operators. Because of the presence of
the Wilson term, mixes with operators of different
chiralities. A projection method to determine the mixing coefficients is
implemented. The numerical results for the renormalisation constants have been
obtained from a simulation performed using the SW-Clover quark action, on a
lattice, at . We show that the use of the constants
determined non-perturbatively improves the chiral behaviour of the lattice kaon
matrix element \_{\latt}.Comment: LaTeX, 16 pages, 2 postscript figure
Constraining spatial variations of the fine-structure constant in symmetron models
We introduce a methodology to test models with spatial variations of the
fine-structure constant , based on the calculation of the angular power
spectrum of these measurements. This methodology enables comparisons of
observations and theoretical models through their predictions on the statistics
of the variation. Here we apply it to the case of symmetron models. We
find no indications of deviations from the standard behavior, with current data
providing an upper limit to the strength of the symmetron coupling to gravity
() when this is the only free parameter, and not able to
constrain the model when also the symmetry breaking scale factor is
free to vary.Comment: Phys. Lett. B (in press
Direct Production of Tripartite Pump-Signal-Idler Entanglement in the Above-Threshold Optical Parametric Oscillator
We calculate the quantum correlations existing among the three output fields
(pump, signal, and idler) of a triply resonant non-degenerate Optical
Parametric Oscillator operating above threshold. By applying the standard
criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)], we
show that strong tripartite continuous-variable entanglement is present in this
well-known and simple system. Furthermore, since the entanglement is generated
directly from a nonlinear process, the three entangled fields can have very
different frequencies, opening the way for multicolored quantum information
networks.Comment: 4 pages, 3 figure
Non-Perturbative Renormalisation of Composite Operators
It is shown that the renormalisation constants of two quark operators can be
accurately determined (to a precision of a few per-cent using 18 gluon
configurations) using Chiral Ward identities. A method for computing
renormalisation constants of generic composite operators without the use of
lattice perturbation theory is proposed.Comment: 3 pages, uuencoded compressed postscript file, to appear in the
Proceedings of the International Symposium on Lattice Field Theory, Dallas,
Texas, 12-17 October 1993, Southampton Preprint 93/94-0
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