14,835 research outputs found
AB effect and Aharonov-Susskind charge non-superselection
We consider a particle in a coherent superposition of states with different
electric charge moving in the vicinity of a magnetic flux. Formally, it should
acquire a (gauge-dependent) AB relative phase between the charge states, even
for an incomplete loop. If measureable, such a geometric, rather than
topological, AB-phase would seem to break gauge invariance. Wick, Wightman and
Wigner argued that since (global) charge-dependent phase transformations are
physically unobservable, charge state superpositions are unphysical (`charge
superselection rule'). This would resolve the apparent paradox in a trivial
way. However, Aharonov and Susskind disputed this superselection rule: they
distinguished between such global charge-dependent transformations, and
transformations of the relative inter-charge phases of two particles, and
showed that the latter \emph{could} in principle be observable! Finally, the
paradox again disappears once we considers the `calibration' of the phase
measured by the Aharonov-Susskind phase detectors, as well as the phase of the
particle at its initial point. It turns out that such a detector can only
distinguish between the relative phases of two paths if their (oriented)
difference forms a loop around the flux
Correlated Equilibria of Classical Strategic Games with Quantum Signals
Correlated equilibria are sometimes more efficient than the Nash equilibria
of a game without signals. We investigate whether the availability of quantum
signals in the context of a classical strategic game may allow the players to
achieve even better efficiency than in any correlated equilibrium with
classical signals, and find the answer to be positive.Comment: 8 pages, LaTe
Zeno effect and ergodicity in finite-time quantum measurements
We demonstrate that an attempt to measure a non-local in time quantity, such
as the time average \la A\ra_T of a dynamical variable , by separating
Feynman paths into ever narrower exclusive classes traps the system in
eigensubspaces of the corresponding operator \a. Conversely, in a long
measurement of \la A\ra_T to a finite accuracy, the system explores its
Hilbert space and is driven to a universal steady state in which von Neumann
ensemble average of \a coincides with \la A\ra_T. Both effects are
conveniently analysed in terms of singularities and critical points of the
corresponding amplitude distribution and the Zeno-like behaviour is shown to be
a consequence of conservation of probability
Long-Term Contracts and Asset Specificity Revisited –An Empirical Analysis of Producer-Importer Relations in the Natural Gas Industry
In this paper, we analyze structural changes in long-term contracts in the international trade of natural gas. Using a unique data set of 262 long-term contracts between natural gas producers and importers, we estimate the impact of different institutional, structural and technical variables on the duration of contracts. We find that contract duration decreases as the market structure of the industry develops to more competitive regimes. Our main finding is that contracts that are linked to an asset specific investment are on average four years longer than those who are not
Long-Term Contracts and Asset Specificity Revisited: An Empirical Analysis of Producer-Importer Relations in the Natural Gas Industry
In this paper, we analyze structural changes in long-term contracts in the international trade of natural gas. Using a unique data set of 262 long-term contracts between natural gas producers and importers, we estimate the impact of different institutional, structural and technical variables on the duration of contracts. We find that contract duration decreases as the market structure of the industry develops to more competitive regimes. Our main finding is that contracts that are linked to an asset specific investment are on average four years longer than those who are not.asset specificity, econometric analysis, long-term contracts, natural gas
Computations of eigenvalue avoidance in planar domains
The phenomenon of eigenvalue avoidance is of growing interest in applications ranging from quantum mechanics to the theory of the Riemann zeta function. Until now the computation of eigenvalues of the Laplace operator in planar domains has been a difficult problem, making it hard to compute eigenvalue avoidance. Based on a new method this paper presents the computation of eigenvalue avoidance for such problems to almost machine precision
No-cloning theorem in thermofield dynamics
We discuss the relation between the no-cloning theorem from quantum
information and the doubling procedure used in the formalism of thermofield
dynamics (TFD). We also discuss how to apply the no-cloning theorem in the
context of thermofield states defined in TFD. Consequences associated to mixed
states, von Neumann entropy and thermofield vacuum are also addressed.Comment: 16 pages, 3 figure
Magnetic dipole excitations in nuclei: elementary modes of nucleonic motion
The nucleus is one of the most multi-faceted many-body systems in the
universe. It exhibits a multitude of responses depending on the way one
'probes' it. With increasing technical advancements of beams at the various
accelerators and of detection systems the nucleus has, over and over again,
surprised us by expressing always new ways of 'organized' structures and layers
of complexity. Nuclear magnetism is one of those fascinating faces of the
atomic nucleus we discuss in the present review. We shall not just limit
ourselves to presenting the by now very large data set that has been obtained
in the last two decades using various probes, electromagnetic and hadronic
alike and that presents ample evidence for a low-lying orbital scissors mode
around 3 MeV, albeit fragmented over an energy interval of the order of 1.5
MeV, and higher-lying spin-flip strength in the energy region 5 - 9 MeV in
deformed nuclei, nor to the presently discovered evidence for low-lying
proton-neutron isovector quadrupole excitations in spherical nuclei. To the
contrary, we put the experimental evidence in the perspectives of understanding
the atomic nucleus and its various structures of well-organized modes of motion
and thus enlarge our discussion to more general fermion and bosonic many-body
systems.Comment: 59 pages, 59 figures, accepted for publication in Rev. Mod. Phys
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