1,344 research outputs found
Metastable States in Spin Glasses and Disordered Ferromagnets
We study analytically M-spin-flip stable states in disordered short-ranged
Ising models (spin glasses and ferromagnets) in all dimensions and for all M.
Our approach is primarily dynamical and is based on the convergence of a
zero-temperature dynamical process with flips of lattice animals up to size M
and starting from a deep quench, to a metastable limit. The results (rigorous
and nonrigorous, in infinite and finite volumes) concern many aspects of
metastable states: their numbers, basins of attraction, energy densities,
overlaps, remanent magnetizations and relations to thermodynamic states. For
example, we show that their overlap distribution is a delta-function at zero.
We also define a dynamics for M=infinity, which provides a potential tool for
investigating ground state structure.Comment: 34 pages (LaTeX); to appear in Physical Review
Introducing Small-World Network Effect to Critical Dynamics
We analytically investigate the kinetic Gaussian model and the
one-dimensional kinetic Ising model on two typical small-world networks (SWN),
the adding-type and the rewiring-type. The general approaches and some basic
equations are systematically formulated. The rigorous investigation of the
Glauber-type kinetic Gaussian model shows the mean-field-like global influence
on the dynamic evolution of the individual spins. Accordingly a simplified
method is presented and tested, and believed to be a good choice for the
mean-field transition widely (in fact, without exception so far) observed on
SWN. It yields the evolving equation of the Kawasaki-type Gaussian model. In
the one-dimensional Ising model, the p-dependence of the critical point is
analytically obtained and the inexistence of such a threshold p_c, for a finite
temperature transition, is confirmed. The static critical exponents, gamma and
beta are in accordance with the results of the recent Monte Carlo simulations,
and also with the mean-field critical behavior of the system. We also prove
that the SWN effect does not change the dynamic critical exponent, z=2, for
this model. The observed influence of the long-range randomness on the critical
point indicates two obviously different hidden mechanisms.Comment: 30 pages, 1 ps figures, REVTEX, accepted for publication in Phys.
Rev.
Shortest paths on systems with power-law distributed long-range connections
We discuss shortest-path lengths on periodic rings of size L
supplemented with an average of pL randomly located long-range links whose
lengths are distributed according to P_l \sim l^{-\xpn}. Using rescaling
arguments and numerical simulation on systems of up to sites, we show
that a characteristic length exists such that for
. For small p we find
that the shortest-path length satisfies the scaling relation
\ell(r,\xpn,p)/\xi = f(\xpn,r/\xi). Three regions with different asymptotic
behaviors are found, respectively: a) \xpn>2 where , b)
1<\xpn<2 where 0<\theta_s(\xpn)<1/2 and, c) \xpn<1 where
behaves logarithmically, i.e. . The characteristic length is
of the form with \nu=1/(2-\xpn) in region b), but depends
on L as well in region c). A directed model of shortest-paths is solved and
compared with numerical results.Comment: 10 pages, 10 figures, revtex4. Submitted to PR
Branching Fractions for D0 -> K+K- and D0 -> pi+pi-, and a Search for CP Violation in D0 Decays
Using the large hadroproduced charm sample collected in experiment E791 at
Fermilab, we have measured ratios of branching fractions for the two-body
singly-Cabibbo-suppressed charged decays of the D0:
(D0 -> KK)/(D0 -> Kpi) = 0.109 +- 0.003 +- 0.003,
(D0 -> pipi)/(D0 -> Kpi) = 0.040 +- 0.002 +- 0.003, and
(D0 -> KK)/(D0 -> pipi) = 2.75 +- 0.15 +- 0.16. We have looked for
differences in the decay rates of D0 and D0bar to the CP eigenstates K+K- and
pi+pi-, and have measured the CP asymmetry parameters
A_CP(K+K-) = -0.010 +- 0.049 +- 0.012 and
A_CP(pi+pi-) = -0.049 +- 0.078 +- 0.030, both consistent with zero.Comment: 10 Postscript pages, including 2 figures. Submitted to Phys. Lett.
Asymmetries between the production of D+ and D- mesons from 500 GeV/c pi- nucleon interactions as a function of xF and pt**2
We present asymmetries between the production of D+ and D- mesons in Fermilab
experiment E791 as a function of xF and pt**2. The data used here consist of
74,000 fully-reconstructed charmed mesons produced by a 500 GeV/c pi- beam on C
and Pt foils. The measurements are compared to results of models which predict
differences between the production of heavy-quark mesons that have a light
quark in common with the beam (leading particles) and those that do not
(non-leading particles). While the default models do not agree with our data,
we can reach agreement with one of them, PYTHIA, by making a limited number of
changes to parameters used
Search for CP Violation in Charged D Meson Decays
We report results of a search for CP violation in the singly
Cabibbo-suppressed decays D+ -> K- K+ pi+, phi pi+, K*(892)0 K+, and pi- pi+
pi+ based on data from the charm hadroproduction experiment E791 at Fermilab.
We search for a difference in the D+ and D- decay rates for each of the final
states. No evidence for a difference is seen. The decay rate asymmetry
parameters A(CP), defined as the difference in the D+ and D- decay rates
divided by the sum of the decay rates, are measured to be: A(CP)(K K pi) =
-0.014 +/- 0.029, A(CP)(phi pi) = -0.028 +/- 0.036, A(CP)(K*(892) K) = -0.010
+/- 0.050, and A(CP)(pi pi pi) = -0.017 +/- 0.042.Comment: 13 pages, 5 figures, 1 table; Elsevier LaTe
Differential cross sections, charge production asymmetry, and spin-density matrix elements for D*(2010) produced in 500 GeV/c pi^- nucleon interactions
We report differential cross sections for the production of D*(2010) produced
in 500 GeV/c pi^- nucleon interactions from experiment E791 at Fermilab, as
functions of Feynman-x (x_F) and transverse momentum squared (p_T^2). We also
report the D* +/- charge asymmetry and spin-density matrix elements as
functions of these variables. Investigation of the spin-density matrix elements
shows no evidence of polarization. The average values of the spin alignment are
\eta= 0.01 +- 0.02 and -0.01 +- 0.02 for leading and non-leading particles,
respectively.Comment: LaTeX2e (elsart.cls). 13 pages, 6 figures (eps files). Submitted to
Physics Letters
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