2,211 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
General formalism for the stability of thin-shell wormholes in 2+1 dimensions
In this article we theoretically construct circular thin-shell wormholes in a
2+1 dimensional spacetime. The construction is symmetric with respect to the
throat. We present a general formalism for the study of the mechanical
stability under perturbations preserving the circular symmetry of the
configurations, adopting a linearized equation of state for the exotic matter
at the throat. We apply the formalism to several examples.Comment: 14 pages, 7 figures; v2: improved version, new references adde
Renormalized Stress Tensor for trans-Planckian Cosmology
Finite expressions for the mean value of the stress tensor corresponding to a
scalar field with a generalized dispersion relation in a
Friedman--Robertson--Walker universe are obtained using adiabatic
renormalization. Formally divergent integrals are evaluated by means of
dimensional regularization. The renormalization procedure is shown to be
equivalent to a redefinition of the cosmological constant and the Newton
constant in the semiclassical Einstein equations.Comment: 14 pages. Minor changes; version published in Physical Review
Neutrino telescopes
In recent years the astro-particle community is involved in the realization of experimental apparatuses for the detection of high-energy neutrinos originated in cosmic sources or produced in the interaction of Cosmic Rays with
the Cosmic Microwave Background. For neutrino energies in the TeV-PeV range, the optical Cherenkov technique is considered optimal. Water (or Ice)-Cherenkov technique is based on the detection of the charged leptons generated in the neutrino charged current weak interactions with the medium surrounding the detector. Those detectors measure the visible Cherenkov photons originated by charged particles propagating at velocities greater than the speed of light through a transparent medium and consist of array of photomultipliers. The charged-particle track can be reconstructed measuring the time of arrival of the Cherenkov photons on the photomultipliers. An overview of the current status of those experiments will be given
5G Wireless Network Slicing for eMBB, URLLC, and mMTC: A Communication-Theoretic View
The grand objective of 5G wireless technology is to support three generic
services with vastly heterogeneous requirements: enhanced mobile broadband
(eMBB), massive machine-type communications (mMTC), and ultra-reliable
low-latency communications (URLLC). Service heterogeneity can be accommodated
by network slicing, through which each service is allocated resources to
provide performance guarantees and isolation from the other services. Slicing
of the Radio Access Network (RAN) is typically done by means of orthogonal
resource allocation among the services. This work studies the potential
advantages of allowing for non-orthogonal sharing of RAN resources in uplink
communications from a set of eMBB, mMTC and URLLC devices to a common base
station. The approach is referred to as Heterogeneous Non-Orthogonal Multiple
Access (H-NOMA), in contrast to the conventional NOMA techniques that involve
users with homogeneous requirements and hence can be investigated through a
standard multiple access channel. The study devises a communication-theoretic
model that accounts for the heterogeneous requirements and characteristics of
the three services. The concept of reliability diversity is introduced as a
design principle that leverages the different reliability requirements across
the services in order to ensure performance guarantees with non-orthogonal RAN
slicing. This study reveals that H-NOMA can lead, in some regimes, to
significant gains in terms of performance trade-offs among the three generic
services as compared to orthogonal slicing.Comment: Submitted to IEE
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