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Four-Dimensional Twisted Group Lattices
Four-dimensional twisted group lattices are used as models for space-time
structure. Compared to other attempts at space-time deformation, they have two
main advantages: They have a physical interpretation and there is no difficulty
in putting field theories on these structures. We present and discuss ordinary
and gauge theories on twisted group lattices. We solve the free field theory
case by finding all the irreducible representations. The non-abelian gauge
theory on the two-dimensional twisted group lattice is also solved. On twisted
group lattices, continuous space-time translational and rotational symmetries
are replaced by discrete counterparts. We discuss these symmetries in detail.
Four-dimensional twisted group lattices can also be used as models for
non-trivial discrete compactifactions of certain ten-dimensional spaces.Comment: 31 pages (no figures) in Late
On the Speed of Gravity and the Corrections to the Shapiro Time Delay
Using a relatively simple method, I compute the v/c correction to the
gravitational time delay for light passing by a massive object moving with
speed v. It turns out that the v/c effects are too small to have been measured
in the recent experiment involving Jupiter and quasar J0842+1845 that was used
to measure the speed of gravity.Comment: 8 pages, LaTeX (or Latex, etc), one figure, which is also available
at http://www-theory.lbl.gov/~samuel/sog_figure.pdf; Revised version is the
one to appear in Phys. Rev. Lett
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