1,872 research outputs found
Excitated state properties of 20-chloro-chlorophyll a
The excited-state and lasing properties of 20-chloro-chlorophyll a in ether solution were compared to those of chlorophyll a. Desactivation parameters and cross-sections were obtained from non-linear absorption spectroscopy in combination with a physico-mathematical methods package. The Cl substituent at C-20 (1) increases both intersystem crossing and internal conversion, (2) produces a blue-shift of the S1 absorption spectrum, and (3) leads to pronounced photochemistry
Test particle description of transport processes for states with a continuous mass spectrum
Aiming at a description of transport processes where the dynamically
generated width of the states is potentially large a transport equation beyond
the quasiparticle approximation is derived in first order gradient expansion.
An effective particle number is identified which is exactly conserved by the
coarse grained transport equation. Using a test particle ansatz for this
conserved quantity allows to rewrite the transport equation into equations of
motion for test particles. The two-body collision terms are formulated in terms
of the test particles which gain non-trivial renormalization factors due to the
coarse graining process.Comment: 10 pages, LaTeX, no figures, Talk given at the workshop
``Kadanoff-Baym Equations --- Progress and Perspectives for Many-Body
Physics'', Rostock, Germany, 20.-24. September 199
Determination of vector meson properties by matching resonance saturation to a constituent quark model
The properties of mesonic resonances can be calculated in terms of the
low-energy coefficients of chiral perturbation theory (chiPT) by extending
unitarized chiPT to higher energies. On the other hand these low-energy
coefficients can be calculated in two different models, namely (i) by assuming
resonance saturation and (ii) within a constituent quark model. By matching the
expressions of the two models combined with the results of unitarized chiPT and
the Weinberg sum rules the properties of vector and axial-vector mesons can be
calculated in the combined large-N_c and chiral limit.Comment: completely rewritten, 3 pages, 1 figure, contribution for QNP 2002:
Quarks and Nuclear Physics, June 9-14, 2002, Juelich, German
Medium Modifcations of Mesons in Elementary Reactions and Heavy-Ion Collisions
Experimental searches for modifications of vector mesons in the nuclear
medium are reviewed. Data on and mesons are presented. The
results have been obtained in elementary reactions with proton and photon beams
as well as in heavy-ion collisions. Compared to the free particle properties,
the and meson are found to drop in mass at normal nuclear
matter density by 9-14% and 3.5% whereas their widths are reported to increase
by factors of about 16 and 3.6, respectively. For the meson, conflicting
results on in-medium mass shifts and broadening have been published. The
experimental data are compared to recent model calculations.Comment: Erice 2007 Proceeding
Towards an effective field theory for vector mesons
The assumption that vector mesons dominate the interactions of hadrons with
electromagnetism (vector-meson dominance - VMD) provides an important
phenomenological concept. On the other hand, a clear microscopic derivation is
still missing and there are cases where VMD drastically fails, e.g. for the
omega transition form factor. In principle, effective field theories with their
systematic expansion and power counting could provide a tool to assess the
validity of VMD and more generally to describe the interactions of vector
mesons at low energies. Though the systematic development is still in an infant
stage we present here a Lagrangian for light pseudoscalar and vector mesons
which is inspired by ideas from effective field theories. The Lagrangian is
used to calculate electromagnetic meson form factors. It turns out that one can
reproduce both the successes of VMD concerning the pion form factors and the
deviations from VMD concerning the omega transition form factor.Comment: Talk presented at the 50th International Winter Meeting on Nuclear
Physics, 23-27 January 2012, Bormio (Italy
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