Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: No large population of unbound or wide-orbit Jupiter-mass planets   Gravitational microlensing is the only method capable of exploring the entire
population of free-floating planets down to Mars-mass objects, because the
microlensing signal does not depend on the brightness of the lensing object. A
characteristic timescale of microlensing events depends on the mass of the
lens: the less massive the lens, the shorter the microlensing event. A previous
analysis of 474 microlensing events found an excess of very short events (1-2
days) - more than known stellar populations would suggest - indicating the
existence of a large population of unbound or wide-orbit Jupiter-mass planets
(reported to be almost twice as common as main-sequence stars). These results,
however, do not match predictions of planet formation theories and are in
conflict with surveys of young clusters. Here we report the analysis of a six
times larger sample of microlensing events discovered during the years
2010-2015. Although our survey has very high sensitivity (detection efficiency)
to short-timescale (1--2 days) microlensing events, we found no excess of
events with timescales in this range, with a 95% upper limit on the frequency
of Jupiter-mass free-floating or wide-orbit planets of 0.25 planet per
main-sequence star. We detected a few possible ultrashort-timescale events
(with timescales of less than 0.5 day), which may indicate the existence of
Earth- and super-Earth-mass free-floating planets, as predicted by
planet-formation theories. [abridged]

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The categories of this paper are: supr-con
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: q-bio
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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: nucl-ex
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The categories of this paper are: quant-ph
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The categories of this paper are: q-fin