7,066 research outputs found
Quantum Topology Change in (2 + 1)d
The topology of orientable (2 + 1)d spacetimes can be captured by certain
lumps of non-trivial topology called topological geons. They are the
topological analogues of conventional solitons. We give a description of
topological geons where the degrees of freedom related to topology are
separated from the complete theory that contains metric (dynamical) degrees of
freedom. The formalism also allows us to investigate processes of quantum
topology change. They correspond to creation and annihilation of quantum geons.
Selection rules for such processes are derived.Comment: LaTeX file, 33 pages, 10 postscript figures, some typos corrected,
references updated, and other minor change
Some aspects of the synchronization in coupled maps
Through numerical simulations we analyze the synchronization time and the
Lyapunov dimension of a coupled map lattice consisting of a chain of chaotic
logistic maps exhibiting power law interactions. From the observed behaviors we
find a lower bound for the size of the lattice, independent of the range
and strength of the interaction, which imposes a practical lower bound in
numerical simulations for the system to be considered in the thermodynamic
limit. We also observe the existence of a strong correlation between the
averaged synchronization time and the Lyapunov dimension. This is an
interesting result because it allows an analytical estimation of the
synchronization time, which otherwise requires numerical simulations.Comment: 4 pages, 6 figure
Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5)
We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.Comment: 5 pages, 4 figures include
Variational Mote Carlo Study of Flat Band Ferromagnetism -- Application to CeRh_3 B_2
A new mechanism for ferromagnetism in CeRh_3B_2 is proposed on the basis of
variational Monte Carlo results. In a one-dimensional Anderson lattice where
each 4f electron hybridizes with a ligand orbital between neighboring Ce sites,
ferromagnetism is stabilized due to a nearly flat band which is a mixture of
conduction and 4f electron states. Because of the strong spin-orbit interaction
in 4f electron states, and of considerable amount of hybridization in the
nearly flat band, the magnetic moments from 4f and conduction electrons tend to
cancel each other. The resultant ferromagnetic moment becomes smaller as
compared with the local 4f moment, and the Fermi surface in the ferromagnetic
ground state is hardly affected by the presence of 4f electrons. These
theoretical results are consistent with experimental observations in CeRh_3B_2
by neutron scattering and dHvA effects.Comment: to be published in J.Phys.Soc.Jp
Magnetic field-induced phase transitions in a weakly coupled s = 1/2 quantum spin dimer system BaCrO
By using bulk magnetization, electron spin resonance (ESR), heat capacity,
and neutron scattering techniques, we characterize the thermodynamic and
quantum phase diagrams of BaCrO. Our ESR measurements indicate that
the low field paramagnetic ground state is a mixed state of the singlet and the
S = 0 triplet for . This suggests the presence of an intra-dimer
Dzyaloshinsky-Moriya (DM) interaction with a DM vector perpendicular to the
c-axis
Statistics of finite-time Lyapunov exponents in the Ulam map
The statistical properties of finite-time Lyapunov exponents at the Ulam
point of the logistic map are investigated. The exact analytical expression for
the autocorrelation function of one-step Lyapunov exponents is obtained,
allowing the calculation of the variance of exponents computed over time
intervals of length . The variance anomalously decays as . The
probability density of finite-time exponents noticeably deviates from the
Gaussian shape, decaying with exponential tails and presenting spikes
that narrow and accumulate close to the mean value with increasing . The
asymptotic expression for this probability distribution function is derived. It
provides an adequate smooth approximation to describe numerical histograms
built for not too small , where the finiteness of bin size trimmes the sharp
peaks.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Regge Analysis of Diffractive and Leading Baryon Structure Functions from DIS
In this paper we present a combined analysis of the H1 data on leading baryon
and diffractive structure functions from DIS, which are handled as two
components of the same semi-inclusive process. The available structure function
data are analyzed in a series of fits in which three main exchanges are taking
into account: pomeron, reggeon and pion. For each of these contributions, Regge
factorization of the correspondent structure function is assumed. By this
procedure, we extract information about the interface between the diffractive,
pomeron-dominated, region and the leading proton spectrum, which is mostly
ruled by secondary exchanges. One of the main results is that the relative
reggeon contribution to the semi-inclusive structure function is much smaller
than the one obtained from a analysis of the diffractive structure function
alone.Comment: ps file, 22 pages, 5 figures. Totally revised version with major
changes, to appear in Physical Review
Behavior of the diffractive cross section in hadron-nucleus collisions
A phenomenological analysis of diffractive dissociation of nuclei in
proton-nucleus and meson-nucleus collisions is presented. The theoretical
approach employed here is able to take into account at once data of the HELIOS
and EHS/NA22 collaborations that exhibit quite different atomic mass
dependences. Possible extensions of this approach to hard diffraction in
nuclear processes are also discussed.Comment: 5 pages, 2 figure
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