31,494 research outputs found
Maximal entropy random networks with given degree distribution
Using a maximum entropy principle to assign a statistical weight to any
graph, we introduce a model of random graphs with arbitrary degree distribution
in the framework of standard statistical mechanics. We compute the free energy
and the distribution of connected components. We determine the size of the
percolation cluster above the percolation threshold. The conditional degree
distribution on the percolation cluster is also given. We briefly present the
analogous discussion for oriented graphs, giving for example the percolation
criterion.Comment: 22 pages, LateX, no figur
A Classification of random Dirac fermions
We present a detailed classification of random Dirac hamiltonians in two
spatial dimensions based on the implementation of discrete symmetries. Our
classification is slightly finer than that of random matrices, and contains
thirteen classes. We also extend this classification to non-hermitian
hamiltonians with and without Dirac structure.Comment: 15 pages, version2: typos in the table of classes are correcte
Dipolar SLEs
We present basic properties of Dipolar SLEs, a new version of stochastic
Loewner evolutions (SLE) in which the critical interfaces end randomly on an
interval of the boundary of a planar domain. We present a general argument
explaining why correlation functions of models of statistical mechanics are
expected to be martingales and we give a relation between dipolar SLEs and
CFTs. We compute SLE excursion and/or visiting probabilities, including the
probability for a point to be on the left/right of the SLE trace or that to be
inside the SLE hull. These functions, which turn out to be harmonic, have a
simple CFT interpretation. We also present numerical simulations of the
ferromagnetic Ising interface that confirm both the probabilistic approach and
the CFT mapping.Comment: 22 pages, 4 figure
Yang-Baxter equation in spin chains with long range interactions
We consider the spin chains with long range interactions and the
spin generalization of the Calogero-Sutherland models. We show that their
properties derive from a transfer matrix obeying the Yang-Baxter equation. We
obtain the expression of the conserved quantities and we diagonalize them.Comment: Saclay-t93/00
A Lattice Study of the Gluon Propagator in Momentum Space
We consider pure glue QCD at beta=5.7, beta=6.0 and beta=6.3. We evaluate the
gluon propagator both in time at zero 3-momentum and in momentum space. From
the former quantity we obtain evidence for a dynamically generated effective
mass, which at beta=6.0 and beta=6.3 increases with the time separation of the
sources, in agreement with earlier results. The momentum space propagator G(k)
provides further evidence for mass generation. In particular, at beta=6.0, for
k less than 1 GeV, the propagator G(k) can be fit to a continuum formula
proposed by Gribov and others, which contains a mass scale b, presumably
related to the hadronization mass scale. For higher momenta Gribov's model no
longer provides a good fit, as G(k) tends rather to follow an inverse power
law. The results at beta=6.3 are consistent with those at beta=6.0, but only
the high momentum region is accessible on this lattice. We find b in the range
of three to four hundred MeV and the exponent of the inverse power law about
2.7. On the other hand, at beta=5.7 (where we can only study momenta up to 1
GeV) G(k) is best fit to a simple massive boson propagator with mass m. We
argue that such a discrepancy may be related to a lack of scaling for low
momenta at beta=5.7. {}From our results, the study of correlation functions in
momentum space looks promising, especially because the data points in Fourier
space turn out to be much less correlated than in real space.Comment: 19 pages + 12 uuencoded PostScript picture
B Mixing
The neutral mesons, and , can oscillate between their particle
and antiparticle states owing to flavor-changing weak interactions. In recent
years, techniques to detect these oscillations as a function of the meson's
decay time have been developed. In this article the physics of flavor
oscillations is reviewed and theoretical predictions are summarized. The many
observations that demonstrate the time-dependence of B^0-\B0bar oscillations
are presented along with a combined measurement of its frequency, .
The attempts to measure the oscillation frequency, both directly and
indirectly, are then summarized. Finally, values for the CKM elements
and are extracted
Tripartite entanglement in parametric down-conversion with spatially-structured pump
Most investigations of multipartite entanglement have been concerned with
temporal modes of the electromagnetic field, and have neglected its spatial
structure. We present a simple model which allows to generate tripartite
entanglement between spatial modes by parametric down-conversion with two
symmetrically-tilted plane waves serving as a pump. The characteristics of this
entanglement are investigated. We also discuss the generalization of our scheme
to 2N+1-partite entanglement using 2N symmetrically-tilted plane pump waves.
Another interesting feature is the possibility of entanglement localization in
just two spatial modes.Comment: 6 pages, 2 figure
Chiral logs with staggered fermions
We compute chiral logarithms in the presence of "taste" symmetry breaking of
staggered fermions. The lagrangian of Lee and Sharpe is generalized and then
used to calculate the logs in and masses. We correct an error in Ref.
[1] [C. Bernard, hep-lat/0111051]; the issue turns out to have implications for
the comparison with simulations, even at tree level. MILC data with three light
dynamical flavors can be well fit by our formulas. However, two new chiral
parameters, which describe order hairpin diagrams for taste-nonsinglet
mesons, enter in the fits. To obtain precise results for the physical
coefficients at order , these new parameters will need to be bounded, at
least roughly.Comment: talk presented by C. Bernard at Lattice2002(spectrum); 3 pages, 2
figure
Cross-Border Valuation: The International Cost of Equity Capital
How does a firm in one country evaluate an investment in a firm in another country, or how does it evaluate a foreign project that the firm itself is undertaking? The firm must estimate future free cash flows just as in a domestic project, but choosing an appropriate discount rate is a particular challenge. This study examines the determinants of the discount rate for an international acquisition or project by examining the sources of risk in an international setting. These risks include stock-market price risk measured with various versions of the capital asset pricing model, as well as exchange rate risk and political risk. To measure stock market risk, both segmented and integrated models of the world equity markets are considered. The emphasis of the study is on some of the practical aspects of estimation, particular for markets where no comparable investments exist on which to base estimates of risk premiums. To show how each of these risks might be measured, the study reports estimates for a representative French firm, Thals. The estimates range widely depending on whether or not the equity market is globally integrated.
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