53 research outputs found
Beyond two-stage models for lung carcinogenesis in the Mayak workers: Implications for Plutonium risk
Mechanistic multi-stage models are used to analyze lung-cancer mortality
after Plutonium exposure in the Mayak-workers cohort, with follow-up until
2008. Besides the established two-stage model with clonal expansion, models
with three mutation stages as well as a model with two distinct pathways to
cancer are studied. The results suggest that three-stage models offer an
improved description of the data. The best-fitting models point to a mechanism
where radiation increases the rate of clonal expansion. This is interpreted in
terms of changes in cell-cycle control mediated by bystander signaling or
repopulation following cell killing. No statistical evidence for a two-pathway
model is found. To elucidate the implications of the different models for
radiation risk, several exposure scenarios are studied. Models with a radiation
effect at an early stage show a delayed response and a pronounced drop-off with
older ages at exposure. Moreover, the dose-response relationship is strongly
nonlinear for all three-stage models, revealing a marked increase above a
critical dose
Charm quark mass from QCD sum rules for the charmonium system
In this work, the charm quark mass is obtained from a QCD sum rule analysis
of the charmonium system. In our investigation we include results from
nonrelativistic QCD at next-to-next-to-leading order. Using the pole mass
scheme, we obtain a value of GeV for the charm pole mass.
The introduction of a potential-subtracted mass leads to an improved scale
dependence. The running -mass is then determined to be
GeV.Comment: 15 pages, 3 figure
Pentaquark and diquark-diquark clustering: a QCD sum rule approach
In this work we study the Theta(1540) in the framework of QCD sum rules based
on (ud)^2\bar{s} diquark clustering as suggested by Jaffe and Wilczek. Within
errors, the mass of the pentaquark is compatible with the experimentally
measured value. The mass difference between the Theta and the pentaquark with
the quantum numbers of the nucleon amounts to 70 MeV, consistent with the
interpretation of the N(1440) as a pentaquark.Comment: 10 pages, 3 figures; discussions extended, references added, version
to appear in Phys. Lett.
The <SPP> Green function and SU(3) breaking in Kl3 decays
Using the 1=/N-C expansion scheme and truncating the hadronic spectrum to the lowest-lying resonances, we match a meromorphic approximation to the Green function onto QCD by imposing the correct large-momentum falloff, both off- shell and on the relevant hadron mass shells. In this way we determine a number of chiral low-energy constants of O(p(6)), in particular the ones governing SU(3) breaking in the K-l3 vector form factor at zero momentum transfer. The main result of our matching procedure is that the known loop contributions largely dominate the corrections of O(p(6)) to f(+)(0). We discuss the implications of our final value f(+)(K0 pi-) (0) = 0.984 +/- 0.012 for the extraction of V-us from K-l3 decays
Quark-hadron-duality in the charmonium and upsilon system
In this work we discuss the practical and conceptual issues related to
quark-hadron-duality in heavy-heavy systems. Recent measurements in the
charmonium region allow a direct test of quark-hadron-duality. We present a
formula for non-resonant background production in e^+ e^- \to D{\bar D} and
extract the resonance parameters of the \psi(3S)-\psi(6S). The obtained results
are used to investigate the upsilon energy range.Comment: 21 pages, 3 figures, references adde
QCD moment sum rules for Coulomb systems: the charm and bottom quark masses
In this work the charm and bottom quark masses are determined from QCD moment
sum rules for the charmonium and upsilon systems. To illustrate the special
character of these sum rules when applied to Coulomb systems we first set up
and study the behaviour of the sum rules in quantum mechanics. In our analysis
we include both the results from nonrelativistic QCD and perturbation theory at
next-next-to-leading order. The moments are evaluated at different values of
q^2 which correspond to different relative influence among the theoretical
contributions. In the numerical analysis we obtain the masses by choosing
central values for all input parameters. The error is estimated from a
variation of these parameters. First, the analysis is performed in the pole
mass scheme. Second, we employ the potential-subtracted mass in intermediate
steps of the calculation to then infer the quark masses in the MS-scheme. Our
final results for the pole- and MS-masses are: M_c = 1.75 \pm 0.15 GeV,
m_c(m_c) = 1.19 \pm 0.11 GeV, M_b = 4.98 \pm 0.125 GeV and m_b(m_b) = 4.24 \pm
0.10 GeV.Comment: 55 pages, 12 figures. References added, discussions extended. To
appear in Phys. Rev.
Towards a consistent estimate of the chiral low-energy constants
Guided by the large-N_C limit of QCD, we construct the most general
chiral resonance Lagrangian that can generate chiral low-energy
constants up to O(p^6). By integrating out the resonance
fields, the low-energy constants are parametrized
in terms of resonance masses and couplings. Information on those
couplings and on the low-energy constants can be extracted by
analysing QCD Green functions of currents both for large and small
momenta. The chiral resonance theory generates
Green functions that interpolate between QCD and
chiral perturbation theory. As specific examples we consider
the VAP and SPP Green
functions.Ministerio de Educación y Ciencia, FPA2004-00996, HU2002-0044,
Generalitat Valenciana, GRUPOS03/013, GV04B-594, GV05/015,
European Commission, HPRN-CT2002-00311 (EURIDICE)Peer reviewe
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