21,206 research outputs found
Massive Gravity on a Non-extremal Brane
We consider a brane world scenario which arises as the near-horizon region of
a non-extremal D5-brane. There is a quasi-localized massive graviton mode, as
well as harmonic modes of higher mass which are bound to the brane to a lesser
degree. Lorentz invariance is slightly broken, which may have observable
effects due to the leakage of the metastable graviton states into the bulk.
Unlike a brane world arising from an extremal D5-brane, there is no mass gap.
We also find that a brane world arising from a non-extremal M5/M5-brane
intersection has the same graviton dynamics as that of a non-extremal D5-brane.
This is evidence that a previously conjectured duality relation between the
dual quantum field theories of each p-brane background may hold away from
extremality.Comment: 10 pages, 4 figures, LaTe
Ultimate Fate of Constrained Voters
We determine the ultimate fate of individual opinions in a
socially-interacting population of leftists, centrists, and rightists. In an
elemental interaction between agents, a centrist and a leftist can become both
centrists or both become leftists with equal rates (and similarly for a
centrist and a rightist). However leftists and rightists do not interact. This
interaction step between pairs of agents is applied repeatedly until the system
can no longer evolve. In the mean-field limit, we determine the exact
probability that the system reaches consensus (either leftist, rightist, or
centrist) or a frozen mixture of leftists and rightists as a function of the
initial composition of the population. We also determine the mean time until
the final state is reached. Some implications of our results for the ultimate
fate in a limit of the Axelrod model are discussed.Comment: 10 pages, 6 figures, 2-column revtex format; for submission to J.
Phys. A. Final version for JPA; very minor change
S^1-wrapped D3-branes on Conifolds
We construct a D3-brane wrapped on S^1, which is fibred over the resolved
conifold as its transverse space. Whereas a fractional D3-brane on the resolved
conifold is not supersymmetric and has a naked singularity, our solution is
supersymmetric and regular everywhere. We also consider an -wrapped
D3-brane on the resolved cone over T^{1,1}/Z_2, as well as on the deformed
conifold. In the former case, we obtain a regular supergravity dual to a
certain four-dimensional field theory whose Lorentz and conformal symmetries
are broken in the IR region and restored in the UV limit.Comment: Latex, 14 pages, minor correction
Penrose Limits of Non-standard Brane Intersections
The non-standard intersection of two 5-branes and a string can give rise to
AdS_3\times S^3\times S^3\times S^1. We consider the Penrose limit of this
geometry and study the supersymmetry of the resulting pp-wave solution. There
is a one-parameter family of Penrose limits associated with the orthogonal
rotation of the two foliating circles within the two 3-spheres. Supernumerary
Killing spinors arise only when the rotation angle is 45 degrees, for which
case we obtain the corresponding light-cone string action that has
linearly-realised supersymmetry. We also obtain Penrose limits of other
non-standard intersections that give rise to the product of AdS_3 or AdS_2 and
two spheres. The resulting pp-waves are supported by multiple constant field
strengths.Comment: Latex, 15 pages, references adde
Smooth Cosmologies from M-theory
We review two ways in which smooth cosmological evolution between two de
Sitter phases can be obtained from M/string-theory. Firstly, we perform a
hyperbolic reduction of massive IIA* theory to D=6 N=(1,1) SU(2)xU(1) gauged de
Sitter supergravity, which supports smooth cosmological evolution between dS_4
x S^2 and a dS_6-type geometry. Secondly, we obtain four-dimensional de Sitter
gravity with SU(2) Yang-Mills gauge fields from a hyperbolic reduction of
standard eleven-dimensional supergravity. The four-dimensional theory supports
smooth cosmological evolution between dS_2 x S^2 and a dS_4-type geometry.
Although time-dependent, these solutions arise from a first-order system via a
superpotential construction. For appropriate choices of charges, these
solutions describe an expanding universe whose expansion rate is significantly
larger in the past than in the future, as required for an inflationary model.Comment: Latex, 7 pages, Contribution to Quantum Theory and Symmetries
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