37,040 research outputs found
Decay widths and scattering processes in massive QED
Using mass perturbation theory, we infer the bound-state spectrum of massive
QED and compute some decay widths of unstable bound states. Further, we
discuss scattering processes, where all the resonances and particle production
thresholds are properly taken into account by our methods.Comment: Latex file, 5 pages, 8 ps-figures & 1 style-file; written version of
a talk given at the QCD97 conference in Montpellier, Franc
Ribbons Around Mexican Hats
We analyze quasi-topological solitons winding around a mexican-hat potential
in two space-time dimensions.
They are prototypes for a large number of physical excitations, including
Skyrmions of the Higgs sector of the standard electroweak model, magnetic
bubbles in thin ferromagnetic films, and strings in certain non-trivial
backgrounds.
We present explicit solutions, derive the conditions for classical stability,
and show that contrary to the naive expectation these can be satisfied in the
weak-coupling limit. In this limit we can calculate the soliton properties
reliably, and estimate their lifetime semiclassically. We explain why gauge
interactions destabilize these solitons, unless the scalar sector is extended.Comment: 12p. Latex , Ecole Polytechnique preprint A295.02.94 and Crete
preprint 94-1
Kondo resonance narrowing in d- and f-electron systems
By developing a simple scaling theory for the effect of Hund's interactions
on the Kondo effect, we show how an exponential narrowing of the Kondo
resonance develops in magnetic ions with large Hund's interaction. Our theory
predicts an exponential reduction of the Kondo temperature with spin S of the
Hund's coupled moment, a little-known effect first observed in d-electron
alloys in the 1960's, and more recently encountered in numerical calculations
on multi-band Hubbard models with Hund's interactions. We discuss the
consequences of Kondo resonance narrowing for the Mott transition in d-band
materials, particularly iron pnictides, and the narrow ESR linewidth recently
observed in ferromagnetically correlated f-electron materials.Comment: 4 pages, 3 figure
Federal incentives for industrial modernization: Historical review and future opportunities
Concerns over the aging of the U.S. aerospace industrial base led DOD to introduce first its Technology Modernization (Tech Mod) Program, and more recently the Industrial Modernization Incentive Program (IMIP). These incentives include productivity shared savings rewards, contractor investment protection to allow for amortization of plant and equipment, and subcontractor/vendor participation. The purpose here is to review DOD IMIP and to evaluate whether a similar program is feasible for NASA and other non-DOD agencies. The IMIP methodology is of interest to industrial engineers because it provides a structured, disciplined approach to identifying productivity improvement opportunities and documenting their expected benefit. However, it is shown that more research on predicting and validating cost avoidance is needed
Atomic Model of Susy Hubbard Operators
We apply the recently proposed susy Hubbard operators to an atomic model. In
the limiting case of free spins, we derive exact results for the entropy which
are compared with a mean field + gaussian corrections description. We show how
these results can be extended to the case of charge fluctuations and calculate
exact results for the partition function, free energy and heat capacity of an
atomic model for some simple examples. Wavefunctions of possible states are
listed. We compare the accuracy of large N expansions of the susy spin
operators with those obtained using `Schwinger bosons' and `Abrikosov
pseudo-fermions'. For the atomic model, we compare results of slave boson,
slave fermion, and susy Hubbard operator approximations in the physically
interesting but uncontrolled limiting case of N->2. For a mixed representation
of spins we estimate the accuracy of large N expansions of the atomic model. In
the single box limit, we find that the lowest energy saddle-point solution
reduces to simply either slave bosons or slave fermions, while for higher boxes
this is not the case. The highest energy saddle-point solution has the
interesting feature that it admits a small region of a mixed representation,
which bears a superficial resemblance to that seen experimentally close to an
antiferromagnetic quantum critical point.Comment: 17 pages + 7 pages Appendices, 14 figures. Substantial revision
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