13,156 research outputs found
Tunneling between de Sitter and anti de Sitter black holes in a noncommutative D3-brane formalism
We obtain dS and AdS generalized Reissner-Nordstrom like black hole
geometries in a curved D3-brane frame-work, underlying a noncommutative gauge
theory on the brane-world. The noncommutative scaling limit is explored to
investigate a possible tunneling of an AdS vacuum in string theory to dS vacuum
in its low energy gravity theory. The Hagedorn transition is invoked into its
self-dual gauge theory to decouple the gauge nonlinearity from the dS geometry,
which in turn is shown to describe a pure dS vacuum.Comment: 7-page
Wormholes in spacetime with torsion
Analytical wormhole solutions in theory are presented. It is discussed
whether the extremely short range repulsive forces, related to the spin angular
momentum of matter, could be the ``carrier'' of the exoticity that threads the
wormhole throat.Comment: 10 pages revte
Assessing Globalization's Critics: "Talkers Are No Good Doers???"
This paper is about the critics of the "doers" of globalization. It describes who they are, where they came from, what they want, how economists, policymakers, and others might understand them better, and where globalization might head from here. Many critics are themselves strongly internationalist and want to see globalization proceed, but under different rules. Some, particularly the protesters in the streets, focus mainly on what is wrong with the world. But some of them put forward broad alternative visions and others offer detailed recommendations for alleviating the problems they see arising from status quo globalization. Most of them have roots in long-standing transnational advocacy efforts to protect human rights and the environment and reduce poverty around the world. What brings them together today is their shared concern that the process by which globalization's rules are being written and implemented is undermining democracy and failing to spread the benefits broadly. This paper sketches the key issues and concerns that motivate the critics in a way that is broadly representative and intelligible to economists. It finds more resonance for the critics' agenda in economics than they commonly recognize. And it attempts to capture the concerns of Southern as well as Northern critics and to analyze the issues that divide as well as bring them together. Finally, it evaluates those issues and alternative proposals on which even globalization enthusiasts and the critics might come together cooperatively.globalization
Static Output Feedback: On Essential Feasible Information Patterns
In this paper, for linear time-invariant plants, where a collection of
possible inputs and outputs are known a priori, we address the problem of
determining the communication between outputs and inputs, i.e., information
patterns, such that desired control objectives of the closed-loop system (for
instance, stabilizability) through static output feedback may be ensured.
We address this problem in the structural system theoretic context. To this
end, given a specified structural pattern (locations of zeros/non-zeros) of the
plant matrices, we introduce the concept of essential information patterns,
i.e., communication patterns between outputs and inputs that satisfy the
following conditions: (i) ensure arbitrary spectrum assignment of the
closed-loop system, using static output feedback constrained to the information
pattern, for almost all possible plant instances with the specified structural
pattern; and (ii) any communication failure precludes the resulting information
pattern from attaining the pole placement objective in (i).
Subsequently, we study the problem of determining essential information
patterns. First, we provide several necessary and sufficient conditions to
verify whether a specified information pattern is essential or not. Further, we
show that such conditions can be verified by resorting to algorithms with
polynomial complexity (in the dimensions of the state, input and output).
Although such verification can be performed efficiently, it is shown that the
problem of determining essential information patterns is in general NP-hard.
The main results of the paper are illustrated through examples
Brane-Production and the Neutrino-Nucleon cross section at Ultra High Energies in Low Scale Gravity Models
The origin of the ultra high energy cosmic ray (UHECR) showers has remained
as a mystery among particle physicists and astrophysicists. In low scale
gravity models, where the neutrino-nucleon cross section rises to typical
hadronic values at energies above eV, the neutrino becomes a
candidate for the primary that initiates these showers. We calculate the
neutrino-nucleon cross section at ultra high energies by assuming that it is
dominated by the production of p-branes. We show, using a generalized
Randall-Sundrum model, that the neutrino-nucleon cross-section at neutrino
energies of GeV is of the order of 100 mb, which is required for
explaining UHECR events. Similar result also follows in other models such as
the Lykken-Randall model.Comment: 13 pages, 2 figures, significantly revised version, no change in
conclusion
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