207 research outputs found
Correction induced by irrelevant operators in the correlators of the 2d Ising model in a magnetic field
We investigate the presence of irrelevant operators in the 2d Ising model
perturbed by a magnetic field, by studying the corrections induced by these
operators in the spin-spin correlator of the model. To this end we perform a
set of high precision simulations for the correlator both along the axes and
along the diagonal of the lattice. By comparing the numerical results with the
predictions of a perturbative expansion around the critical point we find
unambiguous evidences of the presence of such irrelevant operators. It turns
out that among the irrelevant operators the one which gives the largest
correction is the spin 4 operator T^2 + \bar T^2 which accounts for the
breaking of the rotational invariance due to the lattice. This result agrees
with what was already known for the correlator evaluated exactly at the
critical point and also with recent results obtained in the case of the thermal
perturbation of the model.Comment: 28 pages, no figure
Irrelevant operators in the two-dimensional Ising model
By using conformal-field theory, we classify the possible irrelevant
operators for the Ising model on the square and triangular lattices. We analyze
the existing results for the free energy and its derivatives and for the
correlation length, showing that they are in agreement with the conformal-field
theory predictions. Moreover, these results imply that the nonlinear scaling
field of the energy-momentum tensor vanishes at the critical point. Several
other peculiar cancellations are explained in terms of a number of general
conjectures. We show that all existing results on the square and triangular
lattice are consistent with the assumption that only nonzero spin operators are
present.Comment: 32 pages. Added comments and reference
Global Standards in Action: Insights from Anti-Money Laundering Regulation
As organizations have come under the increasing influence of global rules of all sorts, organization scholars have started studying the dynamics of global regulation. The purpose of this article is to identify and evaluate the contribution to this interdisciplinary field by the âStockholm Centre for Organisational Researchâ. The latterâs key proposition is that while global regulation often consists of voluntary best practice rules it can nevertheless become highly influential under certain conditions. We assess how innovative this approach is using as a benchmark the state of the art in another field of relevance to the study of global regulation, i.e. âInternational Relationsâ. Our discussion is primarily theoretical but we draw on the case of global anti-money laundering regulation to illustrate our arguments and for inspirations of how to further elaborate the approach
Finite-size scaling corrections in two-dimensional Ising and Potts ferromagnets
Finite-size corrections to scaling of critical correlation lengths and free
energies of Ising and three-state Potts ferromagnets are analysed by numerical
methods, on strips of width sites of square, triangular and honeycomb
lattices. Strong evidence is given that the amplitudes of the ``analytical''
correction terms, , are identically zero for triangular-- and honeycomb
Ising systems. For Potts spins, our results are broadly consistent with this
lattice-dependent pattern of cancellations, though for correlation lengths
non-vanishing (albeit rather small) amplitudes cannot be entirely ruled out.Comment: 11 pages, LaTeX with Institute of Physics macros, 2 EPS figures; to
appear in Journal of Physics
Global public policy, transnational policy communities, and their networks
Public policy has been a prisoner of the word "state." Yet, the state is reconfigured by globalization. Through "global publicâprivate partnerships" and "transnational executive networks," new forms of authority are emerging through global and regional policy processes that coexist alongside nation-state policy processes. Accordingly, this article asks what is "global public policy"? The first part of the article identifies new public spaces where global policies occur. These spaces are multiple in character and variety and will be collectively referred to as the "global agora." The second section adapts the conventional policy cycle heuristic by conceptually stretching it to the global and regional levels to reveal the higher degree of pluralization of actors and multiple-authority structures than is the case at national levels. The third section asks: who is involved in the delivery of global public policy? The focus is on transnational policy communities. The global agora is a public space of policymaking and administration, although it is one where authority is more diffuse, decision making is dispersed and sovereignty muddled. Trapped by methodological nationalism and an intellectual agoraphobia of globalization, public policy scholars have yet to examine fully global policy processes and new managerial modes of transnational public administration
Recycling bins, garbage cans or think tanks? Three myths regarding policy analysis institutes
The phrase 'think tank' has become ubiquitous â overworked and underspecified â in the political lexicon. It is entrenched in scholarly discussions of public policy as well as in the 'policy wonk' of journalists, lobbyists and spin-doctors. This does not mean that there is an agreed definition of think tank or consensual understanding of their roles and functions. Nevertheless, the majority of organizations with this label undertake policy research of some kind. The idea of think tanks as a research communication 'bridge' presupposes that there are discernible boundaries between (social) science and policy. This paper will investigate some of these boundaries. The frontiers are not only organizational and legal; they also exist in how the 'public interest' is conceived by these bodies and their financiers. Moreover, the social interactions and exchanges involved in 'bridging', themselves muddy the conception of 'boundary', allowing for analysis to go beyond the dualism imposed in seeing science on one side of the bridge, and the state on the other, to address the complex relations between experts and public policy
Quenched bond dilution in two-dimensional Potts models
We report a numerical study of the bond-diluted 2-dimensional Potts model
using transfer matrix calculations. For different numbers of states per spin,
we show that the critical exponents at the random fixed point are the same as
in self-dual random-bond cases. In addition, we determine the multifractal
spectrum associated with the scaling dimensions of the moments of the spin-spin
correlation function in the cylinder geometry. We show that the behaviour is
fully compatible with the one observed in the random bond case, confirming the
general picture according to which a unique fixed point describes the critical
properties of different classes of disorder: dilution, self-dual binary
random-bond, self-dual continuous random bond.Comment: LaTeX file with IOP macros, 29 pages, 14 eps figure
Renormalization group analysis of the spin-gap phase in the one-dimensional t-J model
We study the spin-gap phase in the one-dimensional t-J model, assuming that
it is caused by the backward scattering process. Based on the renormalization
group analysis and symmetry, we can determine the transition point between the
Tomonaga-Luttinger liquid and the spin-gap phases, by the level crossing of the
singlet and the triplet excitations. In contrast to the previous works, the
obtained spin-gap region is unexpectedly large.
We also check that the universality class of the transition belongs to the
SU(2) Wess-Zumino-Witten model.Comment: 4 pages(RevTeX), 5 figures(EPS), TITCMT-97-10, to appear in Phys.
Rev. Let
Genetic diversity in nutritional parameters in response to drought of Coffea canephora cultivated in Rondonia state, Brazil.
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