4,368 research outputs found
Maximizing phonon thermal conductance for ballistic membranes
At low temperatures, phonon scattering can become so weak that phonon
transport becomes ballistic. We calculate the ballistic phonon conductance G
for membranes using elasticity theory, considering the transition from three to
two dimensions. We discuss the temperature and thickness dependence and
especially concentrate on the issue of material parameters. For all membrane
thicknesses, the best conductors have, counter-intuitively, the lowest speed of
sound.Comment: 4 pages, 4 figures, proceedings to phonons 2007 conferenc
Comment on the Average Momentum of Top Quarks in the Threshold Region
The behavior of the momentum distribution of top quarks in the threshold
region is investigated. The qualitative behavior, in particular the dependence
of the average momentum on the strong coupling constant can be understood from
analytical calculations for the Coulomb potential. Ambiguities in the relation
between the excitation curve and the top mass are addressed.Comment: Univ. of Karlsruhe preprint TTP93-31, LaTeX, 6 pages including two
figures (uses epsf) appended as uuencoded postscript fil
Hadron Radiation in Leptonic Decays
The rate for the final state radiation of hadrons in leptonic decays is
evaluated, using as input experimental data for in
the low energy region. Configurations with a lepton pair of large and a
hadronic state of low invariant mass are dominant. A relative rate
is calculated. This
result is about twice the prediction based on a parton model calculation with a
quark mass of MeV. The rate for secondary production of heavy quarks is
calculated in the same formalism.Comment: 7 pages, LaTex (uses epsf.sty, 2 figures appended as uuencoded eps
files). Errors of some numerical values corrected. Conclusions are not
affected by these modification
Polarization in Top Quark Pair Production near Threshold
The polarization dependent momentum distributions of top quarks and their
decay products are calculated for production at future
colliders with polarized beams. The Green function formalism is applied to this
reaction near energy threshold. The Lippmann--Schwinger equations for the
-wave and -wave Green functions are solved numerically for the QCD
chromostatic potential given by the two-loop formula at large momentum
transfers and Richardson ansatz at intermediate and small ones. It is
demonstrated that for the longitudinally polarized electron beam an optimally
polarized sample of top quarks can be produced.Comment: 11 pages, LaTex (uses epsf.sty, 3 ps-figures appended as extra
uuencoded file). The complete paper, including figures, is also available via
anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp94-28/ttp94-28.ps,
or via www at http://ttpux2.physik.uni-karlsruhe.de/preprints.htm
Polarization in Top Quark Production and Decay near Threshold
Theoretical results are presented for top quarks produced in annihilation of
polarized electrons on positrons. Polarization studies for pairs near
threshold are free from hadronization ambiguities. This is due to the short
lifetime of the top quark. Semileptonic decays are discussed as well as their
applications in studying polarization dependent processes involving top quarks.
The Green function formalism is applied to production at future
colliders with polarized beams. Lippmann--Schwinger equation is solved
numerically for the QCD chromostatic potential given by the two-loop formula at
large momentum transfers and Richardson ansatz at intermediate and small ones.
The polarization dependent momentum distributions of top quarks and their decay
products are calculated.Comment: 6 pages, LaTex (uses epsf.sty, 2 figures appended as uuencoded ps
files). The complete paper, including figures, is also available via
anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as
/ttp94-24/ttp94-24.ps, or via www at
http://ttpux2.physik.uni-karlsruhe.de/preprints.html
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