منابع مشابه
Cosmic Acceleration and M-theory
The status of accelerating four-dimensional universes obtained by timedependent compactifications of 10 or 11 dimensional supergravity is reviewed, as is the ‘no-go’ theorem that they evade. All flat cosmologies for a simple exponential potential are found explicitly. It is noted that transient acceleration is generic, and unavoidable for ‘flux’ compactifications. Included is an eternally accel...
متن کاملCosmic acceleration from M theory on twisted spaces
In a recent paper [I. P. Neupane and D. L. Wiltshire, Phys. Lett. B 619, 201 (2005).] we have found a new class of accelerating cosmologies arising from a time–dependent compactification of classical supergravity on product spaces that include one or more geometric twists along with nontrivial curved internal spaces. With such effects, a scalar potential can have a local minimum with positive v...
متن کاملCan the Universe escape eternal acceleration ?
Recent astronomical observations of distant supernovae lightcurves, [1]-[4], suggest that the expansion of the universe has recently begun to accelerate. Acceleration is created by an antigravitational repulsive stress, like that produced by a positive cosmological constant, or universal vacuum energy. It creates a rather bleak eschatological picture. An ever-expanding universe’s future appears...
متن کاملEternal m-security subdivision numbers in graphs
An eternal $m$-secure set of a graph $G = (V,E)$ is aset $S_0subseteq V$ that can defend against any sequence ofsingle-vertex attacks by means of multiple-guard shifts along theedges of $G$. A suitable placement of the guards is called aneternal $m$-secure set. The eternal $m$-security number$sigma_m(G)$ is the minimum cardinality among all eternal$m$-secure sets in $G$. An edge $uvin E(G)$ is ...
متن کاملEternal m- Security Subdivision Numbers in Graphs
Let be a simple graph with vertex set and edges set . A set is a dominating set if every vertex in is adjacent to at least one vertex in . An eternal 1-secure set of a graph G is defined as a dominating set such that for any positive integer k and any sequence of vertices, there exists a sequence of guards with and either or and is a dominating set. If we take a guard on every ver...
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ژورنال
عنوان ژورنال: Advances in Theoretical and Mathematical Physics
سال: 2007
ISSN: 1095-0761,1095-0753
DOI: 10.4310/atmp.2007.v11.n3.a2