4,789 research outputs found
Spontaneous symmetry breaking by double lithium adsorption in polyacenes
We show that adsorption of one lithium atom to a polyacenes, i.e. chains of
linearly fused benzene rings, will cause this chain to be slightly deformed. If
we adsorb a second identical atom on the opposite side of the same ring, this
deformation is dramatically enhanced despite of the fact, that a symmetric
configuration seems possible. We argue, that this may be due to an instability
of the Jahn-Teller type possibly indeed to a Peierls instability.Comment: 8 pages, 9 figure
Symmetry breaking: A tool to unveil the topology of chaotic scattering with three degrees of freedom
We shall use symmetry breaking as a tool to attack the problem of identifying
the topology of chaotic scatteruing with more then two degrees of freedom.
specifically we discuss the structure of the homoclinic/heteroclinic tangle and
the connection between the chaotic invariant set, the scattering functions and
the singularities in the cross section for a class of scattering systems with
one open and two closed degrees of freedom.Comment: 13 pages and 8 figure
Decoherence of spin echoes
We define a quantity, the so-called purity fidelity, which measures the rate
of dynamical irreversibility due to decoherence, observed e.g in echo
experiments, in the presence of an arbitrary small perturbation of the total
(system + environment) Hamiltonian. We derive a linear response formula for the
purity fidelity in terms of integrated time correlation functions of the
perturbation. Our relation predicts, similarly to the case of fidelity decay,
faster decay of purity fidelity the slower decay of time correlations is. In
particular, we find exponential decay in quantum mixing regime and faster,
initially quadratic and later typically gaussian decay in the regime of
non-ergodic, e.g. integrable quantum dynamics. We illustrate our approach by an
analytical calculation and numerical experiments in the Ising spin 1/2 chain
kicked with tilted homogeneous magnetic field where part of the chain is
interpreted as a system under observation and part as an environment.Comment: 22 pages, 10 figure
Correlations between spectra with different symmetry: any chance to be observed?
A standard assumption in quantum chaology is the absence of correlation
between spectra pertaining to different symmetries. Doubts were raised about
this statement for several reasons, in particular, because in semiclassics
spectra of different symmetry are expressed in terms of the same set of
periodic orbits. We reexamine this question and find absence of correlation in
the universal regime. In the case of continuous symmetry the problem is reduced
to parametric correlation, and we expect correlations to be present up to a
certain time which is essentially classical but larger than the ballistic time
Using wellbeing for public policy: Theory, measurement, and recommendations
Indicators of social progress are the primary drivers of public policy.  If existing economic measures of prosperity are complemented with wellbeing metrics that better capture changes in individuals’ quality of life, decision makers will be better informed to assess and design policy.  The science of wellbeing has yielded extensive knowledge and measurement instruments during more than three decades.  We review the existing wellbeing literature and answer three questions: (1) What is wellbeing? (2) How do we measure wellbeing? And, importantly, distinguishing this review from previous ones, (3) How do we use wellbeing metrics to assess and design policy? We suggest that the science of wellbeing is empirically mature enough to complement economic assessments of national progress.  We build on existing work to provide recommendations on metrics and new, specific policies for societal wellbeing
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