21 research outputs found
Gauge symmetric delta(1232) couplings and the radiative muon capture in hydrogen
Using the difference between the gauge symmetric and standard pi-N-delta
couplings, a contact pi-pi-N-N term, quadratic in the pi-N-delta coupling, is
explicitly constructed. Besides, a contribution from the delta excitation
mechanism to the photon spectrum for the radiative muon capture in hydrogen is
derived from the gauge symmetric pi-N-delta and gamma-N-delta couplings. It is
shown for the photon spectrum, studied recently experimentally, that the new
spectrum is for the photon momentums k > 60 MeV by 4-10 % smaller than the one
obtained from standardly used couplings with the on-shell deltas.Comment: 9 pages, 3 figure
Nuclear muon capture by 3He: meson exchange currents for the triton channel
Exchange current corrections are calculated using currents found from the
hard-pion model and AV14+3BF wavefunctions. Results are given for the rate and
spin observables. Their sensitivity to g_P, the nucleon pseudoscalar form
factor, is reported.Comment: 35 pages, uuencoded gz-compressed tar file 42 Kbyte
Nuclear electron capture rate in stellar interiors and the case of 7Be
Nuclear electron capture rate from continuum in an astrophysical plasma
environment (like solar core) is calculated using a modified Debye-Huckel
screening potential and the related non-Gaussian q-distribution of electron
momenta. For q=1 the well-known Debye-Huckel results are recovered. The value
of q can be derived from the fluctuation of number of particles and temperature
inside the Debye sphere. For 7Be continuum electron capture in solar core, we
find an increase of 7 -- 10 percent over the rate calculated with standard
Debye-Huckel potential. The consequence of this results is a reduction of the
same percentage of the SSM 8B solar neutrino flux, leaving unchanged the SSM
7Be flux.Comment: 8 pages, 1 figure, IOP macro style, submitted to JP
On the pion electroproduction amplitude
We analyze amplitudes for the pion electroproduction on proton derived from
Lagrangians based on the local chiral SU(2) x SU(2) symmetries. We show that
such amplitudes do contain information on the nucleon axial form factor F_A in
both soft and hard pion regimes. This result invalidates recent Haberzettl's
claim that the pion electroproduction at threshold cannot be used to extract
any information regarding F_A.Comment: 14 pages, 6 figures, revised version, accepted for publication in
Phys. Rev.
Weak axial nuclear heavy meson exchange currents and interactions of solar neutrinos with deuterons
Starting from the axial heavy meson exchange currents, constructed earlier in
conjunction with the Bethe--Salpeter equation, we first present the axial
--, -- and meson exchange Feynman amplitudes that satisfy
the partial conservation of the axial current. Employing these amplitudes, we
derive the corresponding weak axial heavy meson exchange currents in the
leading order in the 1/M expansion ( is the nucleon mass), suitable for the
nuclear physics calculations beyond the threshold energies and with wave
functions obtained by solving the Schr\"odinger equation with one--boson
exchange potentials. The constructed currents obey the nuclear form of the
partial conservation of the axial current. We apply the space component of
these currents in calculations of the cross sections for the disintegration of
deuterons by low energy (anti)neutrinos. The deuteron and the final state
nucleon--nucleon wave functions are derived (i) from a variant of the OBEPQB
potential, and (ii) from the Nijmegen 93 and Nijmegen I nucleon-nucleon
interaction. The extracted values of the constant , entering the
axial exchange currents of the pionless effective field theory, are in a
reasonable agreement with its value predicted by the dimensional analysis.Comment: 34 pages, 3 figures, 11 table