445 research outputs found
A stochastic golden rule and quantum Langevin equation for the low density limit
A rigorous derivation of quantum Langevin equation from microscopic dynamics
in the low density limit is given. We consider a quantum model of a microscopic
system (test particle) coupled with a reservoir (gas of light Bose particles)
via interaction of scattering type. We formulate a mathematical procedure (the
so-called stochastic golden rule) which allows us to determine the quantum
Langevin equation in the limit of large time and small density of particles of
the reservoir. The quantum Langevin equation describes not only dynamics of the
system but also the reservoir. We show that the generator of the corresponding
master equation has the Lindblad form of most general generators of completely
positive semigroups
Dynamics of Dissipative Two-Level Systems in the Stochastic Approximation
The dynamics of the spin-boson Hamiltonian is considered in the stochastic
approximation. The Hamiltonian describes a two-level system coupled to an
environment and is widely used in physics, chemistry and the theory of quantum
measurement. We demonstrate that the method of the stochastic approximation
which is a general method of consideration of dynamics of an arbitrary system
interacting with environment is powerful enough to reproduce qualitatively
striking results by Leggett at al. found earlier for this model. The result
include an exact expression of the dynamics in terms of the spectral density
and show an appearance of two most interesting regimes for the system, i.e.
pure oscillating and pure damping ones. Correlators describing environment are
also computed.Comment: 13 pages, plainte
Nuclear physics with a medium-energy Electron-Ion Collider
A polarized ep/eA collider (Electron-Ion Collider, or EIC) with variable
center-of-mass energy sqrt(s) ~ 20-70 GeV and a luminosity ~ 10^{34} cm^{-2}
s^{-1} would be uniquely suited to address several outstanding questions of
Quantum Chromodynamics (QCD) and the microscopic structure of hadrons and
nuclei: (i) the three-dimensional structure of the nucleon in QCD (sea quark
and gluon spatial distributions, orbital motion, polarization, correlations);
(ii) the fundamental color fields in nuclei (nuclear parton densities,
shadowing, coherence effects, color transparency); (iii) the conversion of
color charge to hadrons (fragmentation, parton propagation through matter,
in-medium jets). We briefly review the conceptual aspects of these questions
and the measurements that would address them, emphasizing the qualitatively new
information that could be obtained with the collider. Such a medium-energy EIC
could be realized at Jefferson Lab after the 12 GeV Upgrade (MEIC), or at
Brookhaven National Lab as the low-energy stage of eRHIC.Comment: 9 pages, 5 figures. Mini-review compiled in preparation for the MEIC
Conceptual Design Report, Jefferson Lab (2011
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