27,384 research outputs found
Sim(2) and SUSY
The proposal of hep-ph/0601236, that the laws of physics in flat spacetime
need be invariant only under a SIM(2) subgroup of the Lorentz group, is
extended to include supersymmetry. SUSY gauge theories which
include SIM(2) couplings for the fermions in chiral multiplets are formulated.
These theories contain two conserved supercharges rather than the usual four.Comment: 10 pages, revtex4. Note added and sign correcte
Nonlinear Properties of the Semiregular Variable Stars
We demonstrate how, with a purely empirical analysis of the irregular
lightcurve data, one can extract a great deal of information about the stellar
pulsation mechanism. An application to R Sct thus shows that the irregular
lightcurve is the result of the nonlinear interaction of two highly
nonadiabatic pulsation modes, namely a linearly unstable, low frequency mode,
and the second mode that, although linearly stable, gets entrained through a
2:1 resonance. In the parlance of nonlinear dynamics the pulsation is the
result of a 4 dimensional chaotic dynamics.Comment: 8 pages to appear in "Mass-Losing Pulsating Stars and Their
Circumstellar Matter", Eds. Y. Nakada & M.Honma, ASSL Ser. (in press). a
version with better quality figures is available from
http://www.phys.ufl.edu/~buchler
Thermal effects on lattice strain in hcp Fe under pressure
We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron
at high pressures using both first-principles linear response quasiharmonic
calculations based on the full potential linear-muffin-tin-orbital (LMTO)
method and the particle-in-cell (PIC) model for the vibrational partition
function using a tight-binding total-energy method. The tight-binding model
shows excellent agreement with the all-electron LMTO method. When hcp structure
is stable, the calculated geometric mean frequency and Helmholtz free energy of
hcp Fe from PIC and linear response lattice dynamics agree very well, as does
the axial ratio as a function of temperature and pressure. On-site
anharmonicity proves to be small up to the melting temperature, and PIC gives a
good estimate of its sign and magnitude. At low pressures, hcp Fe becomes
dynamically unstable at large c/a ratios, and the PIC model might fail where
the structure approaches lattice instability. The PIC approximation describes
well the vibrational behavior away from the instability, and thus is a
reasonable approach to compute high temperature properties of materials. Our
results show significant differences from earlier PIC studies, which gave much
larger axial ratio increases with increasing temperature, or reported large
differences between PIC and lattice dynamics results.Comment: 9 figure
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