11,824 research outputs found
Critical Correlations for Short-Range Valence-Bond Wave Functions on the Square Lattice
We investigate the arguably simplest -invariant wave functions capable
of accounting for spin-liquid behavior, expressed in terms of nearest-neighbor
valence-bond states on the square lattice and characterized by different
topological invariants. While such wave-functions are known to exhibit
short-range spin correlations, we perform Monte Carlo simulations and show that
four-point correlations decay algebraically with an exponent . This is
reminiscent of the {\it classical} dimer problem, albeit with a slower decay.
Furthermore, these correlators are found to be spatially modulated according to
a wave-vector related to the topological invariants. We conclude that a
recently proposed spin Hamiltonian that stabilizes the here considered
wave-function(s) as its (degenerate) ground-state(s) should exhibit gapped spin
and gapless non-magnetic excitations.Comment: 4 pages, 5 figures. Updated versio
Coexistence of long-range and algebraic correlations for short-range valence-bond wave functions in three dimensions
We investigate nearest-neighbor valence-bond wave functions on bipartite
three-dimensional lattices. By performing large-scale Monte Carlo simulations,
we find that long-range magnetic order coexists with dipolar four-spin
correlations on the cubic lattice, this latter feature being reminiscent of the
Coulomb phase for classical dimers on the same lattice. Similar properties are
found for the lower-coordination diamond lattice. While this suggests that the
coexistence of magnetic order and dipolar four-spin correlations is generic for
bipartite three-dimensional lattices, we show that simple generalizations of
these wave functions can encode different ordering behaviors.Comment: 4+ pages, 5 figures. Updated version, to appear in Phys. Rev. Let
Nature of the X(5568) : a critical Laplace sum rule analysis at N2LO
We scrutinize recent QCD spectral sum rules (QSSR) results to lowest order
(LO) predicting the masses of the BK molecule and (su)\bar(bd) four-quark
states. We improve these results by adding NLO and N2LO corrections to the PT
contributions giving a more precise meaning on the b-quark mass definition used
in the analysis. We extract our optimal predictions using Laplace sum rule
(LSR) within the standard stability criteria versus the changes of the external
free parameters (\tau-sum rule variable, t_c continuum threshold and
subtraction constant \mu). The smallness of the higher order PT corrections
justifies (a posteriori) the LO order results + the uses of the ambiguous heavy
quark mass to that order. However, our predicted spectra in the range (5173\sim
5226) MeV, summarized in Table 7, for exotic hadrons built with four different
flavours (buds), do not support some previous interpretations of the D0
candidate[1], X(5568), as a pure molecule or a four-quark state. If
experimentally confirmed, it could result from their mixing with an angle: sin
2\theta\approx 0.15. One can also scan the region (2327~ 2444) MeV (where the
D*_{s0}(2317) might be a good candidate) and the one (5173~ 5226) MeV for
detecting these (cuds) and (buds) unmixed exotic hadrons (if any) via,
eventually, their radiative or \pi+hadrons decays.Comment: Version matching with the publised version : some references added
and updated, comments added, misprint corrected (51 pages, 66 figures, 7
tables
Empowering Rural Citizen Journalism Via Web 2.0 Technologies
Once acquainted with the modern information and communication tools made available with the advent of the Internet, five Brazilian rural communities participating in a pilot project to develop a self-sustaining telecenter model, engaged in citizen journalism using inexpensive digital video cameras. Community members used Web 2.0 collaborative tools to post short videos on the telecenter portal. The 95 video blogs published between September 2006 and May 2008 recorded various aspects of community life,including religious celebrations,oral history arts and crafts traditions,folklore,and envirnmental concerns. This study evaluates the impact of video blogging in these communities
The effect of temperature on generic stable periodic structures in the parameter space of dissipative relativistic standard map
In this work, we have characterized changes in the dynamics of a
two-dimensional relativistic standard map in the presence of dissipation and
specially when it is submitted to thermal effects modeled by a Gaussian noise
reservoir. By the addition of thermal noise in the dissipative relativistic
standard map (DRSM) it is possible to suppress typical stable periodic
structures (SPSs) embedded in the chaotic domains of parameter space for large
enough temperature strengths. Smaller SPSs are first affected by thermal
effects, starting from their borders, as a function of temperature. To estimate
the necessary temperature strength capable to destroy those SPSs we use the
largest Lyapunov exponent to obtain the critical temperature () diagrams.
For critical temperatures the chaotic behavior takes place with the suppression
of periodic motion, although, the temperature strengths considered in this work
are not so large to convert the deterministic features of the underlying system
into a stochastic ones.Comment: 8 pages and 7 figures, accepted to publication in EPJ
ENCORE: An Extended Contractor Renormalization algorithm
Contractor renormalization (CORE) is a real-space renormalization-group
method to derive effective Hamiltionians for microscopic models. The original
CORE method is based on a real-space decomposition of the lattice into small
blocks and the effective degrees of freedom on the lattice are tensor products
of those on the small blocks. We present an extension of the CORE method that
overcomes this restriction. Our generalization allows the application of CORE
to derive arbitrary effective models whose Hilbert space is not just a tensor
product of local degrees of freedom. The method is especially well suited to
search for microscopic models to emulate low-energy exotic models and can guide
the design of quantum devices.Comment: 5 pages, 4 figure
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