6,017 research outputs found
Set Representations of Linegraphs
Let be a graph with vertex set and edge set . A family
of nonempty sets is a set representation of
if there exists a one-to-one correspondence between the vertices in and the sets in such that if and only if S_i\cap S_j\neq \es. A set representation
is a distinct (respectively, antichain, uniform and simple) set representation
if any two sets and in have the property (respectively, , and ). Let . Two set
representations and are isomorphic if
can be obtained from by a bijection from
to . Let denote a class of set
representations of a graph . The type of is the number of equivalence
classes under the isomorphism relation. In this paper, we investigate types of
set representations for linegraphs. We determine the types for the following
categories of set representations: simple-distinct, simple-antichain,
simple-uniform and simple-distinct-uniform
Constraints on Axion-like Particles from Observations of Mrk 421 using the Method
Axion-like particles (ALPs) could mix with photons in the presence of
astrophysical magnetic fields, and result in oscillations in the high energy
-ray spectra observed by experiments. In this work, we investigate the
ALP-photon oscillation effect through the blazar Mrk 421 spectra of 15 periods
observed by Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) and
Fermi Large Area Telescope (Fermi-LAT). Compared with previous studies, we
generate the mock data under the ALP hypothesis and apply the
method to set constraints on the ALP parameters. This method is widely employed
in high energy experiments and could avoid the possibility of excluding some
parameter regions due to the fluctuation. We find that the ALP-photon coupling
is constrained to be smaller than
GeV for ALP mass ranging from eV to eV at a 95\%
confidence level. The constraints obtained with the method based on the TS
distribution under the null hypothesis, which is adopted in many previous
astrophysical ALP studies, are also shown. Our results demonstrate that the
joint constraints of all the periods from both methods are consistent. However,
the latter method fails to provide constraints for some observation periods,
whereas the method remains effective in such cases.Comment: 10 pages, 26 figure
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