5,670 research outputs found
Dodecahedral topology fails to explain quadrupole-octupole alignment
The CMB quadrupole and octupole, as well as being weaker than expected, align
suspiciously well with each other. Non-trivial spatial topology can explain the
weakness. Might it also explain the alignment? The answer, at least in the case
of the Poincare dodecahedral space, is a resounding no.Comment: 5 pages, 1 figur
Density fluctuations and the structure of a nonuniform hard sphere fluid
We derive an exact equation for density changes induced by a general external
field that corrects the hydrostatic approximation where the local value of the
field is adsorbed into a modified chemical potential. Using linear response
theory to relate density changes self-consistently in different regions of
space, we arrive at an integral equation for a hard sphere fluid that is exact
in the limit of a slowly varying field or at low density and reduces to the
accurate Percus-Yevick equation for a hard core field. This and related
equations give accurate results for a wide variety of fields
Experimental verification of democratic particle motions by direct imaging of glassy colloidal systems
We analyze data from confocal microscopy experiments of a colloidal
suspension to validate predictions of rapid sporadic events responsible for
structural relaxation in a glassy sample. The trajectories of several thousand
colloidal particles are analyzed, confirming the existence of rapid sporadic
events responsible for the structural relaxation of significant regions of the
sample, and complementing prior observations of dynamical heterogeneity. The
emergence of relatively compact clusters of mobility allows the dynamics to
transition between the large periods of local confinement within its potential
energy surface, in good agreement with the picture envisioned long ago by Adam
and Gibbs and Goldstein.Comment: 4 pages, 5 figure
Environmental legislation as a driver of design
and other research output
Vacuum Energy Density for Massless Scalar Fields in Flat Homogeneous Spacetime Manifolds with Nontrivial Topology
Although the observed universe appears to be geometrically flat, it could
have one of 18 global topologies. A constant-time slice of the spacetime
manifold could be a torus, Mobius strip, Klein bottle, or others. This global
topology of the universe imposes boundary conditions on quantum fields and
affects the vacuum energy density via Casimir effect. In a spacetime with such
a nontrivial topology, the vacuum energy density is shifted from its value in a
simply-connected spacetime. In this paper, the vacuum expectation value of the
stress-energy tensor for a massless scalar field is calculated in all 17
multiply-connected, flat and homogeneous spacetimes with different global
topologies. It is found that the vacuum energy density is lowered relative to
the Minkowski vacuum level in all spacetimes and that the stress-energy tensor
becomes position-dependent in spacetimes that involve reflections and
rotations.Comment: 25 pages, 11 figure
Circles in the Sky: Finding Topology with the Microwave Background Radiation
If the universe is finite and smaller than the distance to the surface of
last scatter, then the signature of the topology of the universe is writ large
on the microwave background sky. We show that the microwave background will be
identified at the intersections of the surface of last scattering as seen by
different ``copies'' of the observer. Since the surface of last scattering is a
two-sphere, these intersections will be circles, regardless of the background
geometry or topology. We therefore propose a statistic that is sensitive to all
small, locally homogeneous topologies. Here, small means that the distance to
the surface of last scatter is smaller than the ``topology scale'' of the
universe.Comment: 14 pages, 10 figures, IOP format. This paper is a direct descendant
of gr-qc/9602039. To appear in a special proceedings issue of Class. Quant.
Grav. covering the Cleveland Topology & Cosmology Worksho
Exact Polynomial Eigenmodes for Homogeneous Spherical 3-Manifolds
Observational data hints at a finite universe, with spherical manifolds such
as the Poincare dodecahedral space tentatively providing the best fit.
Simulating the physics of a model universe requires knowing the eigenmodes of
the Laplace operator on the space. The present article provides explicit
polynomial eigenmodes for all globally homogeneous 3-manifolds: the Poincare
dodecahedral space S3/I*, the binary octahedral space S3/O*, the binary
tetrahedral space S3/T*, the prism manifolds S3/D_m* and the lens spaces
L(p,1).Comment: v3. Final published version. 27 pages, 1 figur
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