Search results for "Self-energy"
showing 10 items of 25 documents
Semiphenomenological approach to nucleon properties in nuclear-matter
1992
We have evaluated the nucleon self-energy in a model that has proper analytical properties, satisfies the low density theorem and provides values of Im \ensuremath{\Sigma} for high densities comparable to those of realistic microscopic approaches. The model, however, relies only upon the NN experimental cross sections and the empirical spin-isospin interaction, which induces an important polarization of the medium. The results obtained for the spectral functions, occupation numbers, and effective masses are quite reasonable. The model does not give the absolute value of the nucleon self-energy but only differences with respect to the Fermi energy. On the other hand, it provides an easy and …
Short range correlations in the pion s-wave self-energy of pionic atoms
1995
We evaluate the contribution of second order terms to the pion-nucleus s-wave optical potential of pionic atoms generated by short range nuclear correlation. The corrections are sizeable because they involve the isoscalar s-wave $\pi N$ amplitude for half off-shell situations where the amplitude is considerably larger than the on-shell one. In addition, the s-wave optical potential is reanalyzed by looking at all the different conventional contributions together lowest order, Pauli corrected rescattering term, second order absorptive effects, terms from the interaction of pions with the virtual pion cloud (chiral corrections) and correlation effects. Different off-shell extrapolations for t…
Theoretical study of neutrino-induced coherent pion production off nuclei at T2K and MiniBooNE energies
2009
19 latex pages, 10 figures, 2 tables.--ISI Article Identifier:000262979700013
On relativistic approaches to pion self-energy in nuclear matter
2003
We argue that, in contrast to the non-relativistic approach, a relativistic evaluation of the nucleon--hole and delta-isobar--nucleon hole contributions to the pion self-energy incorporates the s-wave scattering, which requires a more accurate evaluation. Therefore relativistic approach containing only these diagrams does not describe appropriately the pion self-energy in isospin symmetric nuclear matter. We conclude that, a correct relativistic approach to the pion self-energy should involve a more sophisticated calculation in order to satisfy the known experimental results on the near-threshold behaviour of the pion-nucleon (forward) scattering amplitude.
On the CP asymmetries in Majorana neutrino decays
1997
We study the CP asymmetries in lepton number violating two body scattering processes and show explicitly how they vanish, in agreement with unitarity constraints. We relate these cross section asymmetries to the CP decay rate asymmetries of the intermediate massive neutrinos and show how the inclusion of the Universe expansion via Boltzmann equations is the key ingredient to allow the production of a non-vanishing asymmetry in spite of the unitarity constraint on the cross sections. We then show that the absorptive parts of both the one loop vertex and self energy corrections do contribute to the CP decay asymmetries.
Infrared finite ghost propagator in the Feynman gauge
2007
We demonstrate how to obtain from the Schwinger-Dyson equations of QCD an infrared finite ghost propagator in the Feynman gauge. The key ingredient in this construction is the longitudinal form factor of the non-perturbative gluon-ghost vertex, which, contrary to what happens in the Landau gauge, contributes non-trivially to the gap equation of the ghost. The detailed study of the corresponding vertex equation reveals that in the presence of a dynamical infrared cutoff this form factor remains finite in the limit of vanishing ghost momentum. This, in turn, allows the ghost self-energy to reach a finite value in the infrared, without having to assume any additional properties for the gluon-g…
Nonperturbative comparison of QCD effective charges
2009
We study the non-perturbative behavior of two versions of the QCD effective charge, one obtained from the pinch technique gluon self-energy, and one from the ghost-gluon vertex. Despite their distinct theoretical origin, due to a fundamental identity relating various of the ingredients appearing in their respective definitions, the two effective charges are almost identical in the entire range of physical momenta, and coincide exactly in the deep infrared, where they freeze at a common finite value. Specifically, the dressing function of the ghost propagator is related to the two form factors in the Lorentz decomposition of a certain Green's function, appearing in a variety of field-theoret…
Connection between the pinch technique and the background field method
1995
The connection between the pinch technique and the background field method is further explored. We show by explicit calculations that the application of the pinch technique in the framework of the background field method gives rise to exactly the same results as in the linear renormalizable gauges. The general method for extending the pinch technique to the case of Green's functions with off-shell fermions as incoming particles is presented. As an example, the one-loop gauge independent quark self-energy is constructed. We briefly discuss the possibility that the gluonic Green's functions, obtained by either method, correspond to physical quantities.
Gauge-invariant truncation scheme for the Schwinger-Dyson equations of QCD
2008
We present a new truncation scheme for the Schwinger-Dyson equations of QCD that respects gauge invariance at any level of the dressed loop expansion. When applied to the gluon self-energy, it allows for its non-perturbative treatment without compromising the transversality of the solution, even when entire sets of diagrams (most notably the ghost loops) are omitted, or treated perturbatively.
One-Loop Self Energy and Renormalization of the Speed of Light for some Anisotropic Improved Quark Actions
2000
One-loop corrections to the fermion rest mass M_1, wave function renormalization Z_2 and speed of light renormalization C_0 are presented for lattice actions that combine improved glue with clover or D234 quark actions and keep the temporal and spatial lattice spacings, a_t and a_s, distinct. We explore a range of values for the anisotropy parameter \chi = a_s/a_t and treat both massive and massless fermions.