5,494 research outputs found
Integrals, Partitions, and Cellular Automata
We prove that where
is the decreasing function that satisfies , for . When
is an integer and we deduce several combinatorial results. These
include an asymptotic formula for the number of integer partitions not having
consecutive parts, and a formula for the metastability thresholds of a
class of threshold growth cellular automaton models related to bootstrap
percolation.Comment: Revised version. 28 pages, 2 figure
Searching For Dark Matter Subhalos In the Fermi-LAT Second Source Catalog
The dark matter halo of the Milky Way is expected to contain an abundance of
smaller subhalos. These subhalos can be dense and produce potentially
observable fluxes of gamma rays. In this paper, we search for dark matter
subhalo candidates among the sources in the Fermi-LAT Second Source Catalog
which are not currently identified or associated with counterparts at other
wavelengths. Of the nine high-significance, high-latitude (|b|>60 degrees),
non-variable, unidentified sources contained in this catalog, only one or two
are compatible with the spectrum of a dark matter particle heavier than
approximately 50-100 GeV. The majority of these nine sources, however, feature
a spectrum that is compatible with that predicted from a lighter (~5-40 GeV)
dark matter particle. This population is consistent with the number of
observable subhalos predicted for a dark matter candidate in this mass range
and with an annihilation cross section of a simple thermal relic (sigma
v~3x10^{-26} cm^3/s). Observations in the direction of these sources at other
wavelengths will be necessary to either reveal their astrophysical nature (as
blazars or other active galactic nuclei, for example), or to further support
the possibility that they are dark matter subhalos by failing to detect any
non-gamma ray counterpart.Comment: 8 pages, 4 figure
To Review or Not to Review? Limited Strategic Thinking at the Movie Box Office
Film distributors occasionally withhold movies from critics before their release. Cold openings
provide a natural field setting to test models of limited strategic thinking. In a set of 856 widely
released movies, cold opening produces a significant 15% increase in domestic box office revenue
(though not in foreign markets and DVD sales), consistent with the hypothesis that some moviegoers
do not infer low quality from cold opening. Structural parameter estimates indicate 1–2 steps of
strategic thinking by moviegoers (comparable to experimental estimates). However, movie studios
appear to think moviegoers are sophisticated since only 7% of movies are opened cold
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