Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Demystifying the constancy of the Ermakov-Lewis invariant for a time
  dependent oscillator   It is well known that the time dependent harmonic oscillator possesses a
conserved quantity, usually called Ermakov-Lewis invariant. I provide a simple
physical interpretation of this invariant as well as a whole family of related
invariants. This interpretation does not seem to have been noticed in the
literature before. The procedure also allows one to tackle some key conceptual
issues which arise in the study of quantum fields in external, time dependent,
backgrounds like in the case of particle production in an expanding universe
and Schwinger effect.

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The categories of this paper are: mtrl-th
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The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: astro-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol