Search results for "Self-energy"
showing 5 items of 25 documents
Heavy quark decomposition of the S matrix and its relation to the pinch technique.
1995
We propose a decomposition of the S-matrix into individually gauge invariant sub-amplitudes, which are kinematically akin to propagators, vertices, boxes, etc. This decompsition is obtained by considering limits of the S-matrix when some or all of the external particles have masses larger than any other physical scale. We show at the one-loop level that the effective gluon self-energy so defined is physically equivalent to the corresponding gauge independent self-energy obtained in the framework of the pinch technique. The generalization of this procedure to arbitrary gluonic $n$-point functions is briefly discussed.
Top quark mass definition andtt¯production near threshold at the Next Linear Collider
2001
We suggest an infrared-insensitive quark mass, defined by subtracting the soft part of the quark self energy from the pole mass. We demonstrate the deep relation of this definition with the static quark-antiquark potential. At leading order in 1/m this mass coincides with the PS mass which is defined in a completely different manner. Going beyond static limit, the small normalization point introduces recoil corrections which are calculated here as well. Using this mass concept and other concepts for the quark mass we calculate the cross section of e+ e- -> t t-bar near threshold at NNLO accuracy adopting three alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS mass, …
Calculation of the first-orders-wave optical potential in pionic atoms
1989
A microscopic calculation of the first-order s-wave optical potential in pionic atoms which allows the inclusion of the off-shell dependence in momentum of the s-wave \ensuremath{\pi}N amplitude is carried out. Binding effects are also properly taken into account. The results obtained, together with those of the second-order optical potential, are in disagreement with phenomenological optical potentials. The results of the paper suggest the need of new and precise experiments on \ensuremath{\pi}N scattering at low energies and other experiments which can provide precise values of the \ensuremath{\pi}N scattering lengths.
Mesonic exchange current contribution to K+ nucleus scattering.
1993
A microscopical many-body calculation of the self-energy of a positive kaon interacting with a nucleus is carried out of kinetic energies Tk up to 500MeV. On top of the well know contribution of the impulse approximation, we have considered the kaon coupling to the pions in the nucleus. Previous approximations for the pionic cloud contribution, specially on the imaginary part from the pionic cloud wich were not previously considered. The results for the total and differential cross sections are satisfactory after these new contributions are included, but uncertainties remain in the real part. Nieves Pamplona, Juan Miguel, Juan.M.Nieves@ific.uv.es ; Oset Baguena, Eulogio, Eulogio.Oset@ific.u…
Many-particle theory for time-dependent quantum transport in nanostructures
2012
During the recent decades, molecular electronics has established its place as one of the promising fields in the nanoscience. The possibility to manufacture and control molecular junctions where single molecules are squeezed between the conducing electrodes has opened up new possibilities to develop nanoscale devices which could be employed as building blocks for future nanoelectronic applications. The driving force for this new branch of physics has been the experimental advances but also theoretical methods have been under intensive study and many theoretical tools have been developed to understand the electron transport processes in the nanoscale systems. This thesis focuses on developin…