27,552 research outputs found
Bicyclic graphs with exactly two main signless Laplacian eigenvalues
A signless Laplacian eigenvalue of a graph is called a main signless
Laplacian eigenvalue if it has an eigenvector the sum of whose entries is not
equal to zero. In this paper, all connected bicyclic graphs with exactly two
main eigenvalues are determined
Geometric dark energy traversable wormholes constrained by astrophysical observations
In this letter, we introduce the astrophysical observations into the wormhole
research, which is not meant to general parameters constraints for the dark
energy models, in order to understand more about in which stage of the universe
evolutions wormholes may exist through the investigation of the evolution
behavior of the cosmic equation of state parameter. As a concrete instance, we
investigate the Ricci dark energy (RDE) traversable wormholes constrained by
astrophysical data-sets. Particularly, we can discover from Fig. \ref{fig5} of
the present work, when the effective equation of state parameter ,
namely, the Null Energy conditions (NEC) is violated clearly, the wormholes
will appear (open). Subsequently, six specific solutions of static and
spherically symmetric traversable wormhole supported by the RDE are obtained.
Except for the case of constant redshift function, in which the solution is not
only asymptotically flat but also traversable, the remaining five solutions are
all not asymptotically flat, therefore, the exotic matter from the RDE fluids
is spatially distributed in the vicinity of the throat. Furthermore, we analyze
the physical characteristics and properties of the RDE traversable wormholes.
It is worth noting that, through the astrophysical observations, we get
constraints on the parameters of RDE model, explore the type of exotic RDE
fluids in different stages of the universe changing, limit the number of
available models for wormhole research, reduce the number of the wormholes
corresponding to different parameters for RDE model and provide a more apparent
picture for wormhole investigations from the new perspective of observational
cosmology backgroundComment: 17ps, 7fig
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