308 research outputs found
Tachyon Effects on the 2-Dim Black Hole Geometry
We study solutions of the tree level string effective action in the presence
of the tachyon mode.We find that the 2-dim. static black hole is stable against
tachyonic perturbations.For a particular ansatz for the tachyon field we find
an exact solution of the equations of motion which exhibits a naked
singularity.In the case of static fields we find numerically that the full
system has a black hole solution,with the tachyon regular at the horizon.Comment: NTUA 45/94, Pages 11, Latex, 3 Figures on reques
Inflation in supergravity with non-minimal superpotentials
We investigate the cosmological inflation in a class of supergravity models
that are generalizations of non-supersymmetric models. Although such
models have been extensively studied recently, especially after the launch of
the PLANCK and BICEP2 data, the class of models that can be constructed has not
been exhausted. In this note, working in a supergravity model that is a
generalization of Cecotti's model, we show that the appearance of new
superpotential terms, which are quadratic in the superfield that
couples to the Ricci supermultiplet, alters substantially the form of the
scalar potential. The arising potential has the form of the Starobinsky
potential times a factor that is exponential in the inflaton field and
dominates for large inflaton values. We show that the well-known Starobinsky
inflation scenario is maintained only for unnaturally small fine-tuned values
of the coupling describing the superpotential terms. A welcome
feature is the possible increase of the tensor to scalar ratio , within the
limits set by the new Planck and BICEP2 data.Comment: 13 pages, 9 figures, text and references added, version submitted to
Phys. Lett.
Cosmological Evolution in a Type-0 String Theory
We study the cosmological evolution of a type-0 string theory by employing
non-criticality, which may be induced by fluctuations of the D3 brane worlds.
We check the consistency of the approach to O(alpha ') in the corresponding
sigma-model. The ten-dimensional theory is reduced to an effective
four-dimensional model, with only time dependent fields. We show that the
four-dimensional universe has an inflationary phase and graceful exit from it,
while the other extra dimensions are stabilized to a constant value, with the
fifth dimension much larger than the others. We pay particular attention to
demonstrating the role of tachyonic matter in inducing these features. The
Universe asymptotes, for large times, to a non-accelerating linearly-expanding
Universe with a time-dependent dilaton and a relaxing to zero vacuum energy a
la quintessence.Comment: 33 pages LATEX, seven eps figures incorporate
Network-based telemetry to facilitate the programmable management plane for optical transport infrastructure
Large network operator environments are composed of thousands of nodes and devices capable of performing multiple roles. This network infrastructure is multi-layered, multi-vendor and underpinned by a high capacity and complex optical transport network. Managing this network requires millions of lines of configuration files and hundreds of Operational Support Systems. Typically, the management data structure uses a hierarchical namespace containing tens of thousands of object identifiers (OID). Each OID identifies a variable that can be read, modified or set via management protocol. The British Telecom network collects many millions of OIDs every 10 minutes, and executes many thousands of configuration changes per month via many tools, and multiple generations of protocols, data models and software components. Blending Software Defined Network (SDN) model-driven management and Network Functions Virtualisation (NFV), for on-demand (scale-in and scale-out) virtual network functions (Big Data nodes, network heuristics and analytics), provides an exciting opportunity for significant operational savings: reduced outage impact, simplification of management stack, fault correlation and network healing, and network usage trending for efficient resource allocation and scaling. This paper and talk outlines the management plane challenges and use cases for complex tier-1 optical environments. It discusses how we need to rethink network analytics and embrace streaming telemetry for real-time resource adaptation. It outlines a guiding network telemetry framework being developed by leading operators and the enabling community-driven technologies, and how they may be used to facilitate the programmable management plane for optical transport infrastructure
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