1,418 research outputs found
POTENTIAL IMPLICATIONS OF FREER TRADE FOR THE UNITED STATES AND CANADIAN DAIRY SECTORS: A SPATIAL ANALYSIS
International Relations/Trade,
Non-equilibrium steady states in the Klein-Gordon theory
We construct non-equilibrium steady states in the Klein-Gordon theory in
arbitrary space dimension following a local quench. We consider the
approach where two independently thermalized semi-infinite systems, with
temperatures and , are connected along a
-dimensional hypersurface. A current-carrying steady state, described by
thermally distributed modes with temperatures and for
left and right-moving modes, respectively, emerges at late times. The
non-equilibrium density matrix is the exponential of a non-local conserved
charge. We obtain exact results for the average energy current and the complete
distribution of energy current fluctuations. The latter shows that the
long-time energy transfer can be described by a continuum of independent
Poisson processes, for which we provide the exact weights. We further describe
the full time evolution of local observables following the quench. Averages of
generic local observables, including the stress-energy tensor, approach the
steady state with a power-law in time, where the exponent depends on the
initial conditions at the connection hypersurface. We describe boundary
conditions and special operators for which the steady state is reached
instantaneously on the connection hypersurface. A semiclassical analysis of
freely propagating modes yields the average energy current at large distances
and late times. We conclude by comparing and contrasting our findings with
results for interacting theories and provide an estimate for the timescale
governing the crossover to hydrodynamics. As a modification of our Klein-Gordon
analysis we also include exact results for free Dirac fermions.Comment: 42 pages, 7 figure
Entanglement Content of Quantum Particle Excitations II. Disconnected Regions and Logarithmic Negativity
In this paper we study the increment of the entanglement entropy and of the (replica) logarithmic negativity in a zero-density excited state of a free massive bosonic theory, compared to the ground state. This extends the work of two previous publications by the same authors. We consider the case of two disconnected regions and find that the change in the entanglement entropy depends only on the combined size of the regions and is independent of their connectivity. We subsequently generalize this result to any number of disconnected regions. For the replica negativity we find that its increment is a polynomial with integer coefficients depending only on the sizes of the two regions. The logarithmic negativity turns out to have a more complicated functional structure than its replica version, typically involving roots of polynomials on the sizes of the regions. We obtain our results by two methods already employed in previous work: from a qubit picture and by computing four-point functions of branch point twist fields in finite volume. We test our results against numerical simulations on a harmonic chain and find excellent agreement
Investment behavior of Canadian Egg Producers: Analyzing the Impacts of Risk Aversion and Variability of Prices and Costs of Production
Animal welfare is a major concern for consumers. This concern has not gone unnoticed by sector stakeholders, especially egg producers. One of the fundamental changes likely to affect egg producers regards modes of production, specifically changes in housing systems, ranging from conventional cages to free range. From farmers’ perspective, changing their mode of production generates a technological and economic/marketing risk. This study documents the level of risk in the Canadian egg sector (conventional and specialty eggs) using data from 2009 to 2011. Our results indicate multiple uncertainty sources (technological, cost of production, price of eggs) that vary according to the types of eggs. We use a quadratic programming approach applied to expected mean-variance models to analyze the impact of risk on decision to invest when the resources must be allocated to different types of production that have different risk levels. Overall our results show how, given risk aversion parameters, producers minimize their risk levels by devoting their resources to the least risky type of eggs. An important result of our study is that supply management, by reducing the perceived risk level, has favored the development of specialty eggs, for the benefit of consumers
A Near-Infrared Survey of the Inner Galactic Plane for Wolf-Rayet Stars I. Methods and First Results: 41 New WR Stars
The discovery of new Wolf-Rayet (WR) stars in our Galaxy via large-scale
narrowband optical surveys has been severely limited by dust extinction. Recent
improvements in infrared technology have made narrowband-broadband imaging
surveys viable again. We report a new J, K and narrow-band imaging survey of
300 square degrees of the plane of the Galaxy, spanning 150 degrees in Galactic
longitude and reaching 1 degree above and below the Galactic plane. The survey
has a useful limiting magnitude of K = 15 over most of the observed Galactic
plane, and K = 14 within a few degrees of the Galactic center. Thousands of
emission line candidates have been detected. In spectrographic follow-ups of
173 WR star candidates we have discovered 41 new WR stars, 15 of type WN and 26
of type WC. Star subtype assignments have been confirmed with K band spectra,
and distances approximated using the method of spectroscopic parallax. A few of
the new WR stars are amongst the most distant known in our Galaxy. The
distribution of these new WR stars is seen to follow that of previously known
WR stars along the spiral arms of the Galaxy. Tentative radial velocities were
also measured for most of the new WR stars.Comment: 55 pages, 23 figures, 7 tables, accepted to Astronomical Journa
Non-Equilibrium Dynamics and Weakly Broken Integrability
Motivated by dynamical experiments on cold atomic gases, we develop a quantum
kinetic approach to weakly perturbed integrable models out of equilibrium.
Using the exact matrix elements of the underlying integrable model we establish
an analytical approach to real-time dynamics. The method addresses a broad
range of timescales, from the intermediate regime of pre-thermalization to
late-time thermalization. Predictions are given for the time-evolution of
physical quantities, including effective temperatures and thermalization rates.
The approach provides conceptual links between perturbed quantum many-body
dynamics and classical Kolmogorov-Arnold-Moser (KAM) theory. In particular, we
identify a family of perturbations which do not cause thermalization in the
weakly perturbed regime.Comment: v4: Improved discussion of perturbed Lieb-Liniger model and
interactions. 5+10 pages, 3+7 figures. v3: New discussion of perturbed
Lieb-Liniger model, mentioned in text and new section in SM. 5+10 pages, 3+7
figures. v2: references added and discussion of nearly-integrable
perturbations improved. 5+9 pages, 3+5 figure
Finite Temperature Dynamical Correlations in Massive Integrable Quantum Field Theories
We consider the finite-temperature frequency and momentum dependent two-point
functions of local operators in integrable quantum field theories. We focus on
the case where the zero temperature correlation function is dominated by a
delta-function line arising from the coherent propagation of single particle
modes. Our specific examples are the two-point function of spin fields in the
disordered phase of the quantum Ising and the O(3) nonlinear sigma models. We
employ a Lehmann representation in terms of the known exact zero-temperature
form factors to carry out a low-temperature expansion of two-point functions.
We present two different but equivalent methods of regularizing the divergences
present in the Lehmann expansion: one directly regulates the integral
expressions of the squares of matrix elements in the infinite volume whereas
the other operates through subtracting divergences in a large, finite volume.
Our central results are that the temperature broadening of the line shape
exhibits a pronounced asymmetry and a shift of the maximum upwards in energy
("temperature dependent gap"). The field theory results presented here describe
the scaling limits of the dynamical structure factor in the quantum Ising and
integer spin Heisenberg chains. We discuss the relevance of our results for the
analysis of inelastic neutron scattering experiments on gapped spin chain
systems such as CsNiCl3 and YBaNiO5.Comment: 54 pages, 10 figure
- …