13,641 research outputs found
Some general aspects of thin-shell wormholes with cylindrical symmetry
In this article we study a general class of non-rotating thin-shell wormholes
with cylindrical symmetry. We consider two physically sound definitions of the
flare-out condition and we show that the less restrictive one allows for the
construction of wormholes with positive energy density at the throat. We also
analyze the mechanical stability of these objects under perturbations
preserving the symmetry, proving that previous results are particular cases of
a general property. We present examples of wormholes corresponding to
Einstein-Maxwell spacetimes.Comment: 9 pages, 2 figures; v4: corrected versio
Charged shells in a (2+1)-dimensional spacetime
We study circular shells in a (2+1)-dimensional background within the
framework of Einstein-Born-Infeld theory. For shells around black holes we
analyze the mechanical stability under perturbations preserving the symmetry.
Shells around vacuum are also discussed. We find a large range in the values of
the parameters compatible with stable configurations.Comment: 10 pages, 6 figures; v2: improved version, new references adde
Asymptotically anti-de Sitter cylindrical thin-shell wormholes
In this article we investigate cylindrical thin-shell wormholes which are
asymptotically anti-de Sitter. We analyze their stability under perturbations
preserving the symmetry by using two different methods. We compare the results
with those corresponding to the wormholes constructed from the Levi-Civita
spacetime. We find that the configurations always require the presence of
exotic matter at the throat, and, in the case of the linearized stability
analysis, they can be stable for suitable values of the parametersComment: 11 pages, 3 figures; v2: improved versio
Cosmological simulations of screened modified gravity out of the static approximation: effects on matter distribution
In the context of scalar tensor theories for gravity, there is a universally
adopted hypothesis when running N-body simulations that time derivatives in the
equation of motion for the scalar field are negligible. In this work we propose
to test this assumption for one specific scalar-tensor model with a gravity
screening mechanism: the symmetron. To this end, we implemented the necessary
modifications to include the non-static terms in the N-body code Ramses. We
present test cases and results from cosmological simulations. Our main finding
when comparing static vs. non-static simulations is that the global power
spectrum is only slightly modified when taking into account the inclusion of
non-static terms. On the contrary, we find that the calculation of the local
power spectrum gives different measurements. Such results imply one must be
careful when assuming the quasi-static approximation when investigating the
environmental effects of modified gravity and screening mechanisms in structure
formation of halos and voids distributions.Comment: 12 pages, 8 figures, matches version accepted for publication in PR
Shape of Clusters as a Probe of Screening Mechanisms in Modified Gravity
Scalar fields are crucial components in high energy physics and extensions of
General Relativity. The fact they are not observed in the solar system may be
due to a mechanism which screens their presence in high dense regions. We show
how observations of the ellipticity of galaxy clusters can discriminate between
models with and without scalar fields and even between different screening
mechanisms. Using nowadays X-ray observations we put novel constraints on the
different models.Comment: 4 pages, 3 figures, matches version accepted for publication in PR
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