Victoria E. Herscovitz

Uma proposta para o ensino de mecânica quântica

As a consequence of the advances of quantum technology, how to help science and engineering majors to get a better undersctanding of key quantum mechanical concepts has became a contemporary research topic in science teaching at international level. In this paper we present the theoretical framework of a didactical approach in this direction as well as the results of its implementation with engineering students.

On the momentum distribution of short-lived nuclear hole states

Abstract The influence of the lifetime of internal hole states, resulting from nuclear quasi-free scattering, on the corresponding momentum distributions is studied. The Schrodinger equation for bound states in complex potentials is solved by an iteration procedure. The momentum distribution of 1s hole states in lp and 2s-1d shell nuclei is determined for some complex interactions, and leads to strongly model-dependent results. For imaginary potentials proportional to the density distributions of the shells less bound than the hole, the influence on the momentum distributions is very small, but sizable modifications result for potentials acting predominantly at the centre or at the surface.

A remark on nuclear hole states in quasi-free scattering

Abstract Without adding basic complications, an improvement in the usual approximation of the overlap integral occuring in the cross section for quasi-free scattering is achieved by replacing the single-particle state by a hole state bound in a complex potential. The effect of the finite lifetime of hole states on the angular correlation distributions is estimated.

Broken symmetries and the electron-muon problem

SummaryThe fermion propagators in the quantum electrodynamics of the combined fields of electrons and muons with zero bare masses have been investigated. The basic theory possesses various symmetry properties which are not present in the vacuum. This results in a non-uniqueness of the mathematical description, and equivalence classes for the fermion propagators have been defined. In the approximation used it has been shown that a meaningful vacnum correlation of the two lepton fields is incompatible with an exactly parity invariant vacuum.RiassuntoSi sono studiati i propagatori fermionici nell’elettrodinamica quantistica dei campi combinati degli elettroni e dei muoni con masse nude nulle. La teoria fondamentale possiede varie proprietà di simmetria che non sono presenti nel vuoto. Ne risulta una non unicità della descrizione matematica, e si sono quindi definite le classi di equivalenza dei propagatori fermionici. Si è dimostrato, nell’approssimazione usata, che una significativa correlazione del vuoto dei due campi leptonici è incompatibile con un vuoto esattamente invariante rispetto alla parità.

A GENERALIZATION OF THE LANDAU GAUGE

SummaryA gauge has been derived in which the γp-part of the self-energy integral for the electron, with Гώ = constant · γώ but with arbitrary photon and electron propagators, vanishes identically. For the special case of the free photon propagator this diagonalizing gauge is the Landau gauge. Using this generalized Landau gauge the Dyson equation for the electron propagator, in which only the approximation Г = constant · γώ has been made, reduces to an integral equation for one scalar function.RiassuntoSi è dedotta vina gauge in oui la parte γp dell’integrale dell’autoenergia dell’elettrone, conTώ = const · γώ ma con propagatori fotonici ed elettronici arbitrari, si annulla identicamente. Nel caso speciale del propagatore del fotone libero questa gauge diagonale è la gauge di Landau. Facendo uso di questa gauge di Landau generalizzata l’equazione di Dyson per il propagatore elettronico, in oui si è fatta solo l’approssimazione Гώ = cost · γώ, si riduce ad un’equazione integrale per una funzione scalare.

Quasi-free scattering of polarized electrons by polarized nuclear protons

Abstract It is shown that quasi-free electron scattering in a suitable geometry takes place on strongly polarized nuclear protons. A calculation for the single particle model of 16 O predicts large asymmetries for the scattering of polarized electrons.

Introdução à Mecânica Quântica: uma proposta de minicurso para o ensino de conceitos e postulados fundamentais

We analyze the viability of a short-term pedagogical proposal about Quantum Mechanics teaching at an introductory level. The course was intended to create situations to enhance the acquisition and retention of the fundamental

Mean-field approach to Λ and Σ hypernuclei

The Lambda -nucleus and the Sigma -nucleus potentials are compared in the relativistic, zero-range mean-field model. The authors find the relative strength of the spin-orbit interaction RSigma Lambda =VLSSigma /VLSLambda to be particularly sensitive to the various model assumptions; an experimental ratio RSigma Lambda approximately=1 would support strong SU(3) symmetry breaking as the major source for a small spin-orbit interaction in hypernuclei, whereas a ratio RSigma Lambda >>1 supports predictions based on a good SU(3) symmetry in combination with a large tensor coupling of the omega meson and from the quark model.

The length scale in quantum electrodynamics without a bare mass

SummaryA definite length scale in Quantum Electrodynamics without a bare mass can only be induced by a coupling with another system. This problem is studied in a model consisting of one charged « neutrino » field and charged strongly interacting particle fields. A criterion is derived which is similar to the principle of extremalization of the energy in Mechanics. The approximation used allows only the conclusion that the ratio between the lepton mass and the strongly interacting particle masses is not of zeroth order in the renormalized electromagnetic coupling. constant.RiassuntoNell’elettrodinamica quantistica con massa nuda zero, si può indurre uua scala di lunghezze deflnita solo con l’accoppiamento ad un altro sistema. Si studia il problema su un modello costituito da un campo di« neutrini » carico e da campi di particelle cariche fortemente interagenti. Si ricava un criterio simile all’estrazione dell’energia in meccanica. L’approssimazione usata permette solo la conclusione che il rapporte tra la massa del leptone e le masse delle particelle fortemente interagenti non è d’ordine zero nella costante d’accoppiamento elettromagnetico rinormalizzata.

The hyperon-nucleon interaction potential in the bound-state soliton model: the ΛN case

Abstract We develop the formalism to study the hyperon-nucleon interaction potential within the bound-state approach to the SU (3) Skyrme model. The general framework is illustrated by applying it to the diagonal ΛN potential. The central, spin-spin and tensor components of this interaction are obtained and compared with those derived using alternative schemes.