Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The trion: two electrons plus one hole versus one electron plus one
  exciton   We first show that, for problems dealing with trions, it is totally hopeless
to use the standard many-body description in terms of electrons and holes and
its associated Feynman diagrams. We then show how, by using the description of
a trion as an electron interacting with an exciton, we can obtain the trion
absorption through far simpler diagrams, written with electrons and
\emph{excitons}. These diagrams are quite novel because, for excitons being not
exact bosons, we cannot use standard procedures designed to deal with
interacting true fermions or true bosons. A new many-body formalism is
necessary to establish the validity of these electron-exciton diagrams and to
derive their specific rules. It relies on the ``commutation technique'' we
recently developed to treat interacting close-to-bosons. This technique
generates a scattering associated to direct Coulomb processes between electrons
and excitons and a dimensionless ``scattering'' associated to electron exchange
inside the electron-exciton pairs -- this ``scattering'' being the original
part of our many-body theory. It turns out that, although exchange is crucial
to differentiate singlet from triplet trions, this ``scattering'' enters the
absorption explicitly when the photocreated electron and the initial electron
have the same spin -- \emph{i}. \emph{e}., when triplet trions are the only
ones created -- \emph{but not} when the two spins are different, although
triplet trions are also created in this case. The physical reason for this
rather surprising result will be given.

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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: cs
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The categories of this paper are: eess
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The categories of this paper are: math
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: dg-ga
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph