27,916 research outputs found
The action for the (propagating) torsion and the limits on the torsion parameters from present experimental data
Starting from the well established form of the Dirac action coupled to the
electromagnetic and torsion field we find that there is some additional softly
broken local symmetry associated with torsion. This symmetry fixes the form of
divergences of the effective action after the spinor fields are integrated out.
Then the requirement of renormalizability fixes the torsion field to be
equivalent to some massive pseudovector and its action is fixed with accuracy
to the values of coupling constant of torsion-spinor interaction, mass of the
torsion and higher derivative terms. Implementing this action into the abelian
sector of the Standard Model we establish the upper bounds on the torsion mass
and coupling. In our study we used results of present experimental limits on
four-fermion contact interaction (LEP, HERA, SLAC, SLD, CCFR) and TEVATRON
limits on the cross section of new gauge boson, which could be produced as a
resonance at high energy collisions.Comment: 12 pages, LaTeX, 5 figures include
Hydrodynamics of Binary Coalescence.I. Polytropes with Stiff Equations of State
We have performed a series of three-dimensional hydrodynamic calculations of
binary coalescence using the smoothed particle hydrodynamics (SPH) method. The
initial conditions are exact polytropic equilibrium configurations with \gam >
5/3, on the verge of dynamical instability. We calculate the emission of
gravitational radiation in the quadrupole approximation. The fully nonlinear
development of the instability is followed until a new equilibrium
configuration is reached. We find that the properties of this final
configuration depend sensitively on both the compressibility and mass ratio. An
{\em axisymmetric} merged configuration is always produced when \gam\lo2.3.
As a consequence, the emission of gravitational radiation shuts off abruptly
right after the onset of dynamical instability. In contrast, {\em triaxial\/}
merged configurations are obtained when \gam\go2.3, and the system continues
to emit gravitational waves after the final coalescence. Systems with mass
ratios typically become dynamically unstable before the onset of mass
transfer. Stable mass transfer from one neutron star to another in a close
binary is therefore probably ruled out. The maximum amplitude and
peak luminosity of the gravitational waves emitted during the final
coalescence are nearly independent of \gam, but depend very sensitively on
the mass ratio .Comment: 27 pages, uuencoded compressed postscript, 16 figures upon request
from [email protected], IAS-AST-94-
Piecewise adiabatic population transfer in a molecule via a wave packet
We propose a class of schemes for robust population transfer between quantum
states that utilize trains of coherent pulses and represent a generalized
adiabatic passage via a wave packet. We study piecewise Stimulated Raman
Adiabatic Passage with pulse-to-pulse amplitude variation, and piecewise
chirped Raman passage with pulse-to-pulse phase variation, implemented with an
optical frequency comb. In the context of production of ultracold ground-state
molecules, we show that with almost no knowledge of the excited potential,
robust high-efficiency transfer is possibleComment: 4 pages, 5 figures. Submitted to Phys. Rev. Let
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