Noncommutative Field Theory and Lorentz Violation

The role of Lorentz symmetry in noncommutative field theory is considered. Any realistic noncommutative theory is found to be physically equivalent to a subset of a general Lorentz-violating standard-model extension involving ordinary fields. Some theoretical consequences are discussed. Existing experiments bound the scale of the noncommutativity parameter to (10 TeV)^{-2}.Comment: 4 page

The z=0.0912 and z=0.2212 Damped Lyman Alpha Galaxies Along the Sight-Line Toward the Quasar OI 363

New optical and infrared observations along the sight-line toward the quasar OI 363 (0738+313) are presented and discussed. Excluding systems which lack confirming UV spectroscopic observations of the actual Lyman alpha line, this sight-line presently contains the two lowest-redshift classical damped Lyman alpha (DLA) quasar absorption line systems known (i.e. with N(HI) \ge 2 x 10^{20} atoms cm^{-2}), one at z(abs)=0.0912 and the other at z(abs)=0.2212. The z=0.09 DLA galaxy appears to be an extended low surface brightness galaxy which is easily visible only in infrared images and shows rich morphological structure. Subtraction of the quasar nuclear and host light yields L_K \approx 0.08L_K* at z=0.09. The impact parameter between the galaxy and quasar sight-line is very small, b<3.6 kpc (<2 arcsec), which makes measurements difficult. The z=0.22 DLA galaxy is an early-type dwarf with a K-band luminosity of L_K \approx 0.1L_K* at impact parameter b=20 kpc. In general, these results serve to support mounting evidence that DLA galaxies are drawn from a wide variety of gas-rich galaxy types. (Abridged)Comment: 27 pages, 6 figures, 2 in color. Submitted to Ap

Nonrelativistic Quantum Hamiltonian for Lorentz Violation

A method is presented for deriving the nonrelativistic quantum hamiltonian of a free massive fermion from the relativistic lagrangian of the Lorentz-violating standard-model extension. It permits the extraction of terms at arbitrary order in a Foldy-Wouthuysen expansion in inverse powers of the mass. The quantum particle hamiltonian is obtained and its nonrelativistic limit is given explicitly to third order