2,093 research outputs found
Solving the inhomogeneous Bethe-Salpeter Equation in Minkowski space: the zero-energy limit
For the first time, the inhomogeneous Bethe-Salpeter Equation for an
interacting system, composed by two massive scalars exchanging a massive
scalar, is numerically investigated in ladder approximation, directly in
Minkowski space, by using an approach based on the Nakanishi integral
representation. In this paper, the limiting case of zero-energy states is
considered, extending the approach successfully applied to bound states. The
numerical values of scattering lengths, are calculated for several values of
the Yukawa coupling constant, by using two different integral equations that
stem within the Nakanishi framework. Those low-energy observables are compared
with (i) the analogous quantities recently obtained in literature, within a
totally different framework and (ii) the non relativistic evaluations, for
illustrating the relevance of a non perturbative, genuine field theoretical
treatment in Minkowski space, even in the low-energy regime. Moreover,
dynamical functions, like the Nakanishi weight functions and the distorted part
of the zero-energy Light-front wave functions are also presented.
Interestingly, a highly non trivial issue related to the abrupt change in the
width of the support of the Nakanishi weight function, when the zero-energy
limit is approached, is elucidated, ensuring a sound basis to the forthcoming
evaluation of phase-shifts.Comment: 23 pages and 4 figures. Minor changes in the abstract, typos fixed
and added a figure. Submitted for publicatio
Neutron electromagnetic form factors and inclusive scattering of polarized electrons by polarized He and H targets
The electromagnetic inclusive responses of polarized He and H are
thoroughly investigated at the quasielastic peak for squared momentum transfers
up to , within the plane wave impulse approximation. Great
emphasys is put on the effects in the bound-state due to different two- and
three-body nuclear forces, and to the Coulomb interaction as well. A careful
analysis of the polarized responses allows to select possible experiments for
minimizing the model dependence in the extraction of the neutron
electromagnetic form factors. In particular, the relevant role played by the
proton in the transverse-longitudinal response of polarized He, at low
momentum transfer, can be utilized for obtaining valuable information on the
proton contribution to the total polarized response and eventually on the
neutron charge form factor.Comment: 27 pages, Latex, 9 Postscript figures. To appear in Phys. Rev. C
(July '97
Implication of the proton-deuteron radiative capture for Big Bang Nucleosynthesis
The astrophysical -factor for the radiative capture He in
the energy-range of interest for Big Bang Nucleosynthesis (BBN) is calculated
using an {\it ab-initio} approach. The nuclear Hamiltonian retains both two-
and three-nucleon interactions - the Argonne and the Urbana IX,
respectively. Both one- and many-body contributions to the nuclear current
operator are included. The former retain for the first time, besides the
leading order contribution ( is the nucleon mass), also the next-to-leading
order term, proportional to . The many-body currents are constructed in
order to satisfy the current conservation relation with the adopted Hamiltonian
model. The hyperspherical harmonics technique is applied to solve the
bound and scattering states. A particular attention is used in this second case
in order to obtain, in the energy range of BBN, an uncertainty on the
astrophysical -factor of the order or below 1 %. Then, in this energy
range, the -factor is found to be 10 % larger than the currently
adopted values.Part of this increase (1-3 %) is due to the one-body
operator, while the remaining is due to the new more accurate scattering wave
functions. We have studied the implication of this new determination for the
He -factor on deuterium primordial abundance. We find that
the predicted theoretical value for H/H is in excellent agreement with its
experimental determination, using the most recent determination of baryon
density of Planck experiment, and with a standard number of relativistic
degrees of freedom during primordial nucleosynthesis.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let
Fermionic bound states in Minkowski-space: Light-cone singularities and structure
The Bethe-Salpeter equation for two-body bound system with spin
constituent is addressed directly in the Minkowski space. In order to
accomplish this aim we use the Nakanishi integral representation of the
Bethe-Salpeter amplitude and exploit the formal tool represented by the exact
projection onto the null-plane. This formal step allows one i) to deal with
end-point singularities one meets and ii) to find stable results, up to
strongly relativistic regimes, that settles in strongly bound systems. We apply
this technique to obtain the numerical dependence of the binding energies upon
the coupling constants and the light-front amplitudes for a fermion-fermion
state with interaction kernels, in ladder approximation, corresponding to
scalar-, pseudoscalar- and vector boson exchanges, respectively. After
completing the numerical survey of the previous cases, we extend our approach
to a quark-antiquark system in state, taking both constituent-fermion and
exchanged boson masses, from lattice calculations. Interestingly, the
calculated light-front amplitudes for such a mock pion show peculiar signatures
of the spin degrees of freedom.Comment: 22 pages, 7 figures, bst file include
Restricted infinitesimal deformations of restricted simple Lie algebras
We compute the restricted infinitesimal deformations of the restricted simple
Lie algebras over an algebraically closed field of characteristic different
from 2 and 3.Comment: 15 pages; final version, to appear in Journal of Algebra and Its
Application
Micropollutants throughout an integrated urban drainage model: Sensitivity and uncertainty analysis
The paper presents the sensitivity and uncertainty analysis of an integrated urban drainage model which includes micropollutants. Specifically, a bespoke integrated model developed in previous studies has been modified in order to include the micropollutant assessment (namely, sulfamethoxazole \ue2\u80\u93 SMX). The model takes into account also the interactions between the three components of the system: sewer system (SS), wastewater treatment plant (WWTP) and receiving water body (RWB). The analysis has been applied to an experimental catchment nearby Palermo (Italy): the Nocella catchment. Overall, five scenarios, each characterized by different uncertainty combinations of sub-systems (i.e., SS, WWTP and RWB), have been considered applying, for the sensitivity analysis, the Extended-FAST method in order to select the key factors affecting the RWB quality and to design a reliable/useful experimental campaign. Results have demonstrated that sensitivity analysis is a powerful tool for increasing operator confidence in the modelling results. The approach adopted here can be used for blocking some non-identifiable factors, thus wisely modifying the structure of the model and reducing the related uncertainty. The model factors related to the SS have been found to be the most relevant factors affecting the SMX modeling in the RWB when all model factors (scenario 1) or model factors of SS (scenarios 2 and 3) are varied. If the only factors related to the WWTP are changed (scenarios 4 and 5), the SMX concentration in the RWB is mainly influenced (till to 95% influence of the total variance for SSMX,max) by the aerobic sorption coefficient. A progressive uncertainty reduction from the upstream to downstream was found for the soluble fraction of SMX in the RWB
BioMAc 2016 Bioreattori a membrane (MBR) e trattamenti avanzati per la depurazione delle acque
Questo volume raccoglie i contributi presentati nella manifestazione BioMAc 2016: Bioreattori a
Membrane (MBR) e trattamenti avanzati per la depurazione delle Acque, che ha avuto luogo presso
il Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale, dei Materiali dell'Universit\ue0 degli Studi
di Palermo, Aula G. Capit\uf2, nei giorni 27 e 28 ottobre 2016
Bethe-Salpeter bound-state structure in Minkowski space
The quantitative investigation of the scalar Bethe-Salpeter equation in
Minkowski space, within the ladder-approximation framework, is extended to
include the excited states. This study has been carried out for an interacting
system composed by two massive bosons exchanging a massive scalar, by adopting
(i) the Nakanishi integral representation of the Bethe-Salpeter amplitude, and
(ii) the formally exact projection onto the null plane. Our analysis, on one
hand, confirms the reliability of the method already applied to the ground
state and, on the other one, extends the investigation from the valence
distribution in momentum space to the corresponding quantity in the
impact-parameter space, pointing out some relevant features, like (i) the
equivalence between Minkowski and Euclidean transverse-momentum amplitudes, and
(ii) the leading exponential fall-off of the valence wave function in the
impact-parameter space.Comment: 15 pages, 7 figure
Simplified model to evaluate the fate of micropollutants in an integrated urban drainage system: sensitivity analysis
The paper presents the sensitivity analysis of an integrated urban water quality system by means of the global sensitivity analysis (GSA). Specifically, an home-made integrated model developed in previous studies has been modified in order to include the micropollutant assessment (namely, sulfamethoxazole - SMX). The model takes into account also the interactions between the three components of the system: sewer system (SS), wastewater treatment plant (WWTP) and the receiving water body (RWB). The analysis has been applied to an experimental catchment nearby Palermo (Italy): the Nocella catchment. Five scenarios each characterized by different combinations of sub-systems (i.e., SS, WWTP and RWB) have been considered applying the Extended-FAST method in order to select the key factors affecting the RWB quality and to design a reliable/useful experimental campaign. Results demonstrated that GSA is a powerful tool for increasing operator confidence in the modelling results; the approach can be used for blocking some non-identifiable parameters thus wisely modifying the structure of the model and reducing the related uncertainty. The model factors related to the SS have been found to be the most relevant factors affecting the SMX modelin
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