2,374 research outputs found
Isospin breaking in pion-nucleon scattering at threshold by radiative processes
We investigate the dispersive contribution by radiative processes such as
(pi- proton to neutron gamma) and (pi- proton to Delta gamma) to the
pion-nucleon scattering lengths of charged pions in the heavy baryon limit.
They give a large isospin violating contribution in the corresponding isoscalar
scattering length, but only a small violation in the isovector one. These terms
contribute 6.3(3)% to the 1s level shift of pionic hydrogen and give a chiral
constant F_pi^2f_1=-25.8(8) MeV.Comment: 9 pages with 1 figur
Chiral Dynamics of Deeply Bound Pionic Atoms
We present and discuss a systematic calculation, based on two-loop chiral
perturbation theory, of the pion-nuclear s-wave optical potential. A proper
treatment of the explicit energy dependence of the off-shell pion self-energy
together with (electromagnetic) gauge invariance of the Klein-Gordon equation
turns out to be crucial. Accurate data for the binding energies and widths of
the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and
the notorious "missing repulsion" in the pion-nuclear s-wave optical potential
is accounted for. The connection with the in-medium change of the pion decay
constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure
Electron-neutrino scattering off nuclei from two different theoretical perspectives
We analyze charged-current electron-neutrino cross sections on Carbon. We
consider two different theoretical approaches, on one hand the Continuum Random
Phase Approximation (CRPA) which allows a description of giant resonances and
quasielastic excitations, on the other hand the RPA-based calculations which
are able to describe multinucleon emission and coherent and incoherent pion
production as well as quasielastic excitations. We compare the two approaches
in the genuine quasielastic channel, and find a satisfactory agreement between
them at large energies while at low energies the collective giant resonances
show up only in the CRPA approach. We also compare electron-neutrino cross
sections with the corresponding muon-neutrino ones in order to investigate the
impact of the different charged-lepton masses. Finally, restricting to the
RPA-based approach we compare the sum of quasielastic, multinucleon emission,
coherent and incoherent one-pion production cross sections (folded with the
electron-neutrino T2K flux) with the charged-current inclusive
electron-neutrino differential cross sections on Carbon measured by T2K. We
find a good agreement with the data. The multinucleon component is needed in
order to reproduce the T2K electron-neutrino inclusive cross sections
The Pion-Nucleon coupling constant from np charge exchange scattering
A novel extrapolation method has been used to deduce the charged Pion-Nucleon
coupling constant from backward differential scattering cross sections. We
applied it to new measurements performed at 162 MeV at the The Svedberg
Laboratory in Uppsala. In the angular range , the
carefully normalized data are steeper than those of most previous measurements.
The extracted value, , in good agreement with
the classical value, is higher than those determined in recent nucleon-nucleon
partial-wave analyses.Comment: 6 pages, 3 encapsulated figures, epsfig, menu97.cls (included
Quark Condensate in the Deuteron
We study the changes produced by the deuteron on the QCD quark condensate by
means the Feynman-Hellmann theorem and find that the pion mass dependence of
the pion-nucleon coupling could play an important role. We also discuss the
relation between the many body effect of the condensate and the meson exchange
currents, as seen by photons and pions. For pion probes, the many-body term in
the physical amplitude differs significantly from that of soft pions, the one
linked to the condensate. Thus no information about the many-body term of the
condensate can be extracted from the pion-deuteron scattering length. On the
other hand, in the Compton amplitude, the relationship with the condensate is a
more direct one.Comment: to appear in Physics Review C (19 pages, 3 figures
Energy level displacement of excited np states of kaonic hydrogen
We compute the energy level displacement of the excited np states of kaonic
hydrogen within the quantum field theoretic and relativistic covariant model of
strong low-energy bar-KN interactions suggested in EPJA21, 11 (2004). For the
width of the energy level of the excited 2p state of kaonic hydrogen, caused by
strong low-energy interactions, we find Gamma_2p = 2 meV. This result is
important for the theoretical analysis of the X-ray yields in kaonic hydrogen.Comment: 20 pages, no figures, Latex, new references are adde
Chiral -exchange NN-potentials: Results for diagrams proportional to g_A^4 and g_A^6
We calculate in (two-loop) chiral perturbation theory the local NN-potentials
generated by the three-pion exchange diagrams proportional to g_A^4 and g_A^6.
Surprisingly, we find that the total isoscalar central -exchange
potential vanishes identically. The individually largest -exchange
potentials are of isoscalar spin-spin, isovector central and isoscalar tensor
type. For these potentials simple analytical expressions can be given. The
strength of these dominant -exchange potentials at r=1.0 fm is 4.6 MeV,
2.9 MeV and 1.4 MeV, respectively. Furthermore, we observe that the spin-spin
and tensor potentials due to the diagrams proportional to g_A^6 do not exist in
the infinite nucleon mass limit.Comment: 8 pages, 5 figure
Effect of Dose on Serum Pharmacokinetics of Intravenous Ciprofloxacin with Identification and Characterization of Extravascular Compartments Using Noncompartmental and Compartmental Pharmacokinetic Models
The effect of dose on the pharmacokinetics of ciprofloxacin in serum and urine following single intravenous doses of 100, 150, and 200 mg was studied in nine healthy volunteers. Mean peak levels in serum were 1.4, 2.0, and 3.2 mg/liter for the 100-, 150-, and 200-mg doses, respectively. The data on concentrations in serum were best described by a three-compartment pharmacokinetic model. The terminal half-life (from noncompartmental analysis) averaged between 4.2 and 4.6 h. Average urinary recovery ranged between 45.8 and 48.1%. The average renal clearance of ciprofloxacin was 2.9- to 3.4-fold greater than the measured creatinine clearance. Total serum and renal clearances decreased with increasing dose; however, this was not statistically significant (P \u3e 0.05; repeated-measures analysis of variance). Ciprofloxacin was well tolerated by all subjects. In this dose range, ciprofloxacin pharmacokinetics are independent of dose
Electromagnetic Polarisability of the Nucleon in Chiral Perturbation Theory
We compute the polarisability of the nucleon to leading order in chiral
perturbation theory. The contributions from kaons and baryon resonances as
intermediate states are included in addition to the contribution from pions and
nucleons that had been previously computed. The isoscalar operators are
dominated by the infrared behaviour of pion loops giving rise to a
coefficient. In contrast, the isovector operators are dominated by loops
involving kaons, giving a coefficient, and further demonstrates that
the strange quark is an important component of the nucleon. In addition, the
inclusion of the decuplet of baryon resonances as intermediate states
substantially modifies the result found from the octet baryons alone for the
isoscalar polarisability.Comment: 11 pages (uses harvmac, figures available upon request) , UCSD/PTH
92-30, QUSTH-92-0
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