99 research outputs found
Scattering rates and lifetime of exact and boson excitons
Although excitons are not exact bosons, they are commonly treated as such
provided that their composite nature is included in effective scatterings
dressed by exchange. We here \emph{prove} that, \emph{whatever these
scatterings are}, they cannot give both the scattering rates and
the exciton lifetime , correctly: A striking factor 1/2 exists between
and the sum of 's, which originates from the
composite nature of excitons, irretrievably lost when they are bosonized. This
result, which appears as very disturbing at first, casts major doubts on
bosonization for problems dealing with \emph{interacting} excitons
Rank differences for overpartitions
In 1954, Atkin and Swinnerton-Dyer proved Dyson's conjectures on the rank of
a partition by establishing formulas for the generating functions for rank
differences in arithmetic progressions. In this paper, we prove formulas for
the generating functions for rank differences for overpartitions. These are in
terms of modular functions and generalized Lambert series.Comment: 17 pages, final version, accepted for publication in the Quarterly
Journal of Mathematic
Theory of spin precession monitored by laser pulse
We first predict the splitting of a spin degenerate impurity level when this
impurity is irradiated by a circularly polarized laser beam tuned in the
transparency region of a semiconductor. This splitting, which comes from
different exchange processes between the impurity electron and the virtual
pairs coupled to the pump beam, induces a spin precession around the laser beam
axis, which lasts as long as the pump pulse. It can thus be used for ultrafast
spin manipulation. This effect, which has similarities with the exciton optical
Stark effect we studied long ago, is here derived using the concepts we
developed very recently to treat many-body interactions between composite
excitons and which make the physics of this type of effects quite transparent.
They, in particular, allow to easily extend this work to other experimental
situations in which a spin rotates under laser irradiation.Comment: 12 pages + 1 figur
Time and Games
Abstract. We add the notion of time to denotational models of the λcalculus. The denotation is no longer constant through reduction, but rather decreases with respect to an appropriate order. Categorically, w
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