1,218 research outputs found
Phase Structure of a Compact U(1) Gauge Theory from the Viewpoint of a Sine-Gordon Model
We discuss the phase structure of the four-dimensional compact U(1) gauge
theory at finite temperature using a deformation of the topological model. Its
phase structure can be determined by the behavior of the Coulomb gas (CG)
system on the cylinder. We utilize the relation between the CG system and the
sine-Gordon (SG) model, and investigate the phase structure of the gauge theory
in terms of the SG model. Especially, the critical-line equation of the gauge
theory in the strong-coupling and high-temperature region is obtained by
calculating the one-loop effective potential of the SG model.Comment: 9 pages, 6 figures, REVTeX4, typos corrected, reference added; to
appear in Phys.Rev.
Controlling Decoherence of Transported Quantum Spin Information in Semiconductor Spintronics
We investigate quantum coherence of electron spin transported through a
semiconductor spintronic device, where spins are envisaged to be controlled by
electrical means via spin-orbit interactions. To quantify the degree of spin
coherence, which can be diminished by an intrinsic mechanism where spin and
orbital degrees of freedom become entangled in the course of transport
involving spin-orbit interaction and scattering, we study the decay of the
off-diagonal elements of the spin density matrix extracted directly from the
Landauer transmission matrix of quantum transport. This technique is applied to
understand how to preserve quantum interference effects of fragile
superpositions of spin states in ballistic and non-ballistic multichannel
semiconductor spintronic devices.Comment: 7 pages, 3 color EPS figures, prepared for Proceedings of
International Symposium on Mesoscopic Superconductivity and Spintronics 2004
(Atsugi, Japan, March 1-4, 2004
Non-Trivial Ultraviolet Fixed Point in Quantum Gravity
The non-trivial ultraviolet fixed point in quantum gravity is calculated by
means of the exact renormalization group equation in d-dimensions . It is shown that the ultraviolet non-Gaussian fixed point which is
expected from the perturbatively -expanded calculations in
gravity theory remains in d=4. Hence it is possible that quantum
gravity is an asymptotically safe theory and renormalizable in 2<d.Comment: 17 pages with 5 eps figures, to be published in Prog. Theor. Phy
Spatial Characteristics of Joint Application Networks in Japanese Patents
Technological innovation has extensively been studied to make firms
sustainable and more competitive. Within this context, the most important
recent issue has been the dynamics of collaborative innovation among firms. We
therefore investigated a patent network, especially focusing on its spatial
characteristics. The results can be summarized as follows. (1) The degree
distribution in a patent network follows a power law. A firm can then be
connected to many firms via hubs connected to the firm. (2) The neighbors'
average degree has a null correlation, but the clustering coefficient has a
negative correlation. The latter means that there is a hierarchical structure
and bridging different modules may shorten the paths between the nodes in them.
(3) The distance of links not only indicates the regional accumulations of
firms, but the importance of time it takes to travel, which plays a key role in
creating links. (4) The ratio of internal links in cities indicates that we
have to consider the existing links firms have to facilitate the creation of
new links
Response of Firm Agent Network to Exogenous Shock
This paper describes an agent-based model of interacting firms, in which
interacting firm agents rationally invest capital and labor in order to
maximize payoff. Both transactions and production are taken into account in
this model. First, the performance of individual firms on a real transaction
network was simulated. The simulation quantitatively reproduced the cumulative
probability distribution of revenue, material cost, capital, and labor. Then,
the response of the firms to a given exogenous shock, defined as a sudden
change of gross domestic product, is discussed. The longer tail in cumulative
probability and skewed distribution of growth rate are observed for a high
growth scenario.Comment: 8 pages, 9 figures, APFA
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