Showing papers in "Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields in 1987"
TL;DR: In this article, the authors formulate a general-relativistic concept of quantum geometry capable of describing the behaviour of quantum Lorentz frames in free fall in arbitrary external gravitational fields.
Abstract: We formulate a general-relativistic concept of quantum geometry capable of describing the behaviour of quantum Lorentz frames in free fall in arbitrary external gravitational fields. The mathematical framework suited to this task turns out to be that of Hilbert bundles over a space-time manifold of mean stochastic locations of quantum test particles, with fibres soldered to the base manifold at each given mean space-time location. Furthermore, these fibre bundles incorporate connections compatible with the Hermitian structure. Quantum propagation results from the parallel transport governed by these connections and applied to generalized coherent states, whereas the Hermitian structure supplies the transition probabilities required for the construction of quantum frame and particle propagators. All resulting fibre bundles are shown to possess nonzero curvature forms, which in the generic case incorporate the symplectic 2-form of the cotangent bundle of the base manifold, the pseudo-Riemannian curvature of that manifold and additional components resulting from Maxwell and Yang-Mills connections. In addition, their structure groups incorporate stochastic phase space representations of the Poincare group in a manner that supplies manifest Poincare gauge invariance of the resulting quantum space-time framework.
24 citations
TL;DR: In this article, the Coulomb barrier energy was used to obtain the subbarrier fusion cross-section, which depends on two parameters which are energy independent and which are different for different reactions.
Abstract: The elastic model is applied to the subbarrier fusion. The fusion cross-section so obtained depends on two parameters which are energy independent and which are different for different reactions. These parameters are connected with the Coulomb barrier energy. It is shown, also, that the ratioσf/σ0 (σ0 is a geometrical cross-section) is the same for all the systems. For the considered systems is 24≤A≤194.
21 citations
TL;DR: In this paper, the role of quantum Lorentz frame is taken over by second-quantized frames constructed out of coherent exciton states, whose structure groups contain unitary representations of the Poincare group, with the latter emerging as a gauge group for the internal degrees of freedom of the considered quantum particles.
Abstract: It is shown that an earlier introduced concept of quantum geometry, given by a Hilbert bundle over a base space whose elements constitute a generic curved space-time and represent the mean locations of quantum frames, can be generalized to the case of Fock bundles, whose Fock fibres are the carriers of multiparticle states In this new context, the role of quantum Lorentz frame is taken over by second-quantized frames constructed out of coherent exciton states The structure groups of the considered bundles contain unitary representations of the Poincare group, with the latter emerging as a gauge group for the internal degrees of freedom of the considered quantum particles Connections compatible with the Hermitian structure are introduced on bundles of second-quantized frames that are associated to principal bundles of affine Lorentz frames The corresponding parallel transport is expressed in terms of path integrals for quantum frame propagators It is shown that the resulting geometro-stochastic quantum field theory in curved space-time does not give rise to the foundational difficulties with the particle concept, with normal ordering and with the definition of the stress-energy tensor, that are inherent in more conventional approaches to quantum field theory in curved space-time Hence, the derived path integral formulae for the propagation of systems of quantum field particles display in the present framework none of the ambiguities encountered by those approaches
14 citations
TL;DR: By introducing an elementary Δ and by treating perturbatively the background, a simple model for πNΔ dynamics is constructed in this article, and the resulting unitarized amplitudes turn out to be parametrized in a simple way in terms of the renormalized quantities of the theory.
Abstract: By introducing an elementary Δ and by treating perturbatively the background, a simple model for πNΔ dynamics is constructed It accounts for πN scattering as well as for π-photoproduction The resulting unitarized amplitudes turn out to be parametrized in a simple way in terms of the renormalized quantities of the theory Comparisons with earlier parametrizations are made The present microscopical description provides a consistent framework for extension to nuclei
13 citations
TL;DR: In this paper, an unambiguous geometrical representation of nuclear quantum space, analogous to the electron orbitals of the hydrogen atom, is presented, where the position of each fermion relative to the axes of quantum space is dependent upon the particle's eigenvalues.
Abstract: There is an unambiguous geometrical representation of nuclear « quantum space » which is analogous to the electron orbitals of the hydrogen atom. In both the atom and the nucleus, the position of each fermion relative to the axes of « quantum space » is dependent upon the particle’s eigenvalues. In the nuclear realm, the geometry of eigenstates corresponds precisely with the symmetries of an antiferromagnetic face-centred cubic (FCC) lattice with alternating isospin layers. The correspondence between the eigenstates of the Schrodinger equation and the FCC lattice is demonstrated and the relationship between the spin-orbit model and the FCC model is discussed. The random-phase-approximation (RPA) technique is used to examine the ground and excited states of the FCC lattice.
10 citations
TL;DR: The dependence of Kβ/Kα values on the mode of excitation in the case of Mn and Fe is attributed to chemical effects, while no such dependence is found for the high-Z elements.
Abstract: TheKβ/Kα X-ray intensity ratios are measured for Mn and Fe and for six other elements withZ lying in the range 49⩽Z⩽82 following electron capture decay and photon excitation using241Am and57Co sources High-resolution Si(Li) and HpGe detector systems were used in the experiments The dependence ofKβ/Kα values on the mode of excitation in the case of Mn and Fe is attributed to chemical effects, while no such dependence is found for the high-Z elements
8 citations
TL;DR: In this article, the integrability conditions of a time-dependent Hartree-Bogolubov (TDHB) equation were studied from a group-theoretical viewpoint.
Abstract: We study the integrability conditions of a time-dependent Hartree-Bogolubov (TDHB) equation to determine collective submanifolds from the group-theoretical viewpoint. The basic idea lies in the introduction of a sort of Lagrange manner familiar to fluid dynamics to describe collective co-ordinates. This manner enables us to take a one-form Ω which is linearly composed of a TDHB Hamiltonian and infinitesimal generators induced by collective variable differentials of aSO2N (Bogolubov) canonical transformation. The integrability conditions of our system read dΩ−ΩΛΩ=0, which is a fundamental equation to determine the collective submanifolds in the TDHB method. This equation may work wellin the large scale beyond aSO2N RPA as the small-amplitude limit, with an appropriate boundary condition.
8 citations
TL;DR: In this paper, the natural orbital representation in the singleparticle potential method is applied to calculate the proton momentum distribution in 40Ca and the dependence of the momentum and density distributions on different sets of occupation numbers is examined, and results are compared with calculations using other theoretical models including nucleon-nucleon correlations.
Abstract: The natural orbital representation in the single-particle potential method is applied to calculate the proton momentum distribution in40Ca. The dependence of the momentum and density distributions on different sets of occupation numbers is examined, and the results are compared with calculations using other theoretical models including nucleon-nucleon correlations.
8 citations
TL;DR: In this paper, the 12C(4He, HI) reaction at (33.8±0.2) MeV alpha energy using CR-39 passive solid-state nuclear track detectors was studied at a laboratory angle of 35°.
Abstract: The12C(4He, HI) reaction has been studied at (33.8±0.2) MeV alpha energy using CR-39 passive solid-state nuclear track detectors. The differential cross-sections for12C(4He,5Li)11B and12C(4He,6Li)10B at a laboratory angle of 35° have been measured to be (12.9±2.6) mb/sr and (12.0±2.4) mb/sr, respectively.
8 citations
TL;DR: The action-dynamical principle for closed-time paths is derived in field theory directly from the integrated form of Schrodinger's equation in a general form applicable to theories with dependent fields, higher-spin fields and, in particular, to gauge theories as mentioned in this paper.
Abstract: The action (dynamical) principle for closed-time paths is derived in field theory directly from the integrated form of Schrodinger's equation in a general form applicable to theories with dependent fields, higher-spin fields and, in particular, to gauge theories. In general, the derived action principle leads to extra vertices from what one expects naively from the interaction Lagrangian alone. As an application, the formalism is applied to gauge theories with Yang-Mills fields (including a matter field) and a Faddeev-Popov factor is explicitly shown to arise without the recourse to path integrals, without the use of canonical commutation relations and without the need of going to the complicated structure of the Hamiltonian.
8 citations
TL;DR: In this article, a complete expansion up to order 1/m2 for one-and two-photon matrix elements is derived keeping also into account the behaviour of the wave functions under Lorentz transformations.
Abstract: A complete expansion up to order 1/m2 for one- and two-photon matrix elements is derived keeping also into account the behaviour of the wave functions under Lorentz transformations. Lowest-order binding-energy corrections are inserted in the verification of the low-energy theorem for Compton scattering. Gauge invariance is ensured by extensive use of the minimal substitution.
TL;DR: In this paper, the authors obtained a lifetime of (142.22±0.14) ns, which is in fair agreement with the theoretical value of 142.07 ns but larger than previous experimental determinations.
Abstract: Moderated positrons from a22Na source form positronium atoms at the surface of a channel plate multiplier in a weak magnetic field. They decay inside a finite volume and the decay quanta are registered by ten plastic scintillation detectors and counted in a fast data acquisition system with zero deadtime. After corrections for the escape of atoms from the observation volume and for prompt annihilation back-ground we obtain a lifetime of (142.22±0.14) ns. This is in fair agreement with the theoretical value of 142.07 ns but larger than previous experimental determinations. A possible correction from annihilation at the walls of the decay chamber would further increase the lifetime.
TL;DR: In this paper, the authors use the technique of dimensional regularization with Wilson loops to do explicitly the calculations of the renormalization of the charge in the Yang-Mills theory up to fourth order.
Abstract: We use the technique of dimensional regularization with Wilson loops to do explicitly the calculations of the renormalization of the charge in the Yang-Mills theory up to fourth order. We show that in dimensions different from four the results cannot be interpreted as charge renormalization.
TL;DR: In this article, the α-Kx coincidence technique was used to measure the probability of K-shell ionization of lead and polonium atoms by the alpha-decay of the 210,218,214Po and222Rn isotopes from the decay chain of226Ra.
Abstract: The probabilities ofK-shell ionization of lead and polonium atoms by the alpha-decay of the210,218,214Po and222Rn isotopes from the decay chain of226Ra are measured by theα-Kx coincidence technique. The experimentalK-shell ionization probabilitiesPK=(2.15±0.22, 3.73±0.25, 5.82±0.19, 2.36±0.22)·10−6, respectively, are compared with the latest theoretical predictions.
TL;DR: In this article, the internal bremsstrahlung (IB) spectra emitted in the beta-decays of 89Sr and 90Sr were measured with a HPGe detector and a multichannel analyser along with a standard geometrical set-up.
Abstract: The internal bremsstrahlung (IB) spectra emitted in the beta-decays of89Sr and90Sr were measured with a HPGe detector and a multichannel analyser along with a standard geometrical set-up Sufficient care has been taken to avoid spurious effects After making all the necessary corrections, the experimental results were compared with the corresponding theoretical distributions due to Knipp and Uhlenbeck and Bloch (KUB), Lewis and Ford, Nilsson, and also due to Ford and Martin (detour theory) The total IB yields of intensity and energy from each of the isotopes in the investigated energy regions are also determined and compared with the corresponding theoretical values The present results of IB from89Sr are satisfactorily accounted for by the KUB theory In the case of90Sr the experimental results of IB coincide with the Coulomb-corrected theoretical distribution due to Nilsson in the energy range from 60 keV to 110 keV and beyond 110 keV, they are found to be in excess over Nilsson’s theory as well as the detour theory due to Ford and Martin up to the maximum photon energy studied, namely 350 keV
TL;DR: In this article, shape transitions in Sr isotopes are studied in the conventional shell model and the single-neutron energies are varied linearly in the isotope string to absorb the n-p interactions.
Abstract: Shape transitions in Sr isotopes are studied in the conventional shell model. The single-neutron energies are varied linearly in the isotope string to absorb the n-p interactions. It is found that the gross features of the energy spectra and the onset of deformation of98Sr and100Sr can be reproduced. However, the details of the rotational-band behaviour of the energy spectra of98Sr and100Sr cannot be reproduced.
TL;DR: In this paper, the three-parameter strong-absorption model of Frahn and Venter was used to analyze the inelastic scattering from a number of nuclei, and best-fit parameter values were obtained which gave the nuclear interaction radius and surface diffuseness.
Abstract: Angular distributions of 25 and 41 MeV3He particles elastically scattered from a number of nuclei are analysed in terms of the three-parameter strong-absorption model of Frahn and Venter. Best-fit parameter values are obtained which give the nuclear interaction radius and surface diffuseness. Data on inelastic scattering leading to the lowest 2+ state in a few nuclei are studied giving the quadrupole deformation parameter β2.
TL;DR: In this paper, it was shown that the minimal coupling interaction is the only possible way to give a Lagrangian description for the electron-monopole system, and that this is the case even for the case of a single electron.
Abstract: The usual Lagrangian description for a charged particle in a magnetic-field force is shown to be, generically, unique. In particular, this turns out to be true for the electron-monopole system. This leads to the conclusion that the «minimal coupling interaction» is the only possible way to give a Lagrangian description for this system.
TL;DR: In this paper, a nonrelativistic potential model was proposed to predict the spectrum of heavy and light mesons and the leptonic-decay width of vector mesons.
Abstract: Using a new nonrelativistic potential model we predict the spectrum of heavy and light mesons and the leptonic-decay width of vector mesons. The potential contains a regularized Coulomb part which allows a nonperturbative treatment of the spin-dependent interaction. In addition, we calculate the electromagnetic mass differences of pseudoscalar and vector mesons. The influence of themd-mu mass difference on the strong interaction can be larger than the electromagnetic effect itself. The mass dependence of this effect is discussed in some detail.
TL;DR: In this paper, a new approach to the multichannel scattering problem with realistic local or nonlocal interactions is developed by employing the negative energy solutions of uncoupled Sturmian eigenvalue problems referring to simple auxiliary potentials.
Abstract: A new approach to the multichannel scattering problem with realistic local or nonlocal interactions is developed. By employing the negative-energy solutions of uncoupled Sturmian eigenvalue problems referring to simple auxiliary potentials, the coupling interactions appearing in the original multichannel problem are approximated by finite-rank potentials. By resorting to integral-equation techniques the coupled-channel equations are then reduced to linear algebraic equations which can be straightforwardly solved. Compact algebraic expressions for the relevant scattering matrix elements are thus obtained. The convergence of the method is tested in the single-channel case with realistic optical potentials. Excellent agreement is obtained with a few terms in the separable expansion for both real and absorptive interactions.
TL;DR: In this article, the Dyson-Schwinger equation for the quark propagator in quantum chromodynamics was examined by employing the gauge technique with the object of investigating spontaneously broken flavor symmetry in the chiral limit of vanishing current quark masses.
Abstract: We examine the Dyson-Schwinger equation for the quark propagator in quantum chromodynamics by employing the gauge technique with the object of investigating spontaneously broken flavor symmetry in the chiral limit of vanishing current quark masses. We show that dynamical breakdown of flavorSU V (N F ) symmetry does not occur, thus reiterating an assertion by Vafa and Witten. Our analysis is limited to three flavors but is generalizable to an arbitrary number of flavors,N F>3.
TL;DR: From binding energy systematics, confirmations of subshell closures at neutron numbersN = 6, 14, 16, 56 and proton numbersZ=6, 14 and 16 as discussed by the authors.
Abstract: From binding-energy systematics, confirmations of subshell closures at neutron numbersN=6, 14, 16, 56 and proton numbersZ=6, 14, 16 and 38 are proposed. Irregularities due to shell and sub-shell closures at mass numbersA=4, 8, 12, 16 and 208 are confirmed from a plot of binding energy per nucleonvs. A. The energy ratios of the second and the first excited levels of doubly even nuclei confirm shell closures atN=56 andZ=64.
TL;DR: In this paper, the authors discuss the phenomenological consequences of implementing intermediate-mass scales in E6 superstring-inspired models, and perform quantitatively the minimization of the low-energy effective potential and the renormalization group analysis, yielding a viable set of mass spectra.
Abstract: We discuss the phenomenological consequences of implementing intermediate-mass scales inE6 superstring-inspired models. Starting from a suitable Calabi-Yau compactification withb1,1>1, one gets, after Hosotani breaking, the rankr=5 gauge groupSU(3)c×SU(2)L×U(1)Y×U(1)E, that is broken at an intermediate-mass scale down to the standard-model group. The analysis of both the intermediate and the electroweak breaking is performed in the two cases Λc=Mx and Λc
TL;DR: In this article, a density functional approach for describing properties of nuclear systems at finite temperatures is developed by using local-scale point transformations, which leads to a fully practical procedure for solving the temperature-dependent Hartree-Fock problem in terms of the nuclear local density distribution.
Abstract: A density functional approach for describing properties of nuclear systems at finite temperatures is developed by using local-scale point transformations. Within a mean-field approximation it leads to a fully practical procedure for solving the temperature-dependent Hartree-Fock problem in terms of the nuclear local-density distribution. The numerical results obtained in a large scale of temperatures for the nucleus,208Pb with Skyrme-type forces SkM are seen to reproduce quite accurately the average as well as the microscopic temperature-dependent Hartree-Fock results. Finite-temperature random-phase approximation sum rule expressions are applied for investigating nuclear scaling incompressibility and giant-monopole isoscalar and isovector energies as functions of temperature.
TL;DR: In this paper, an expression for the nuclear part of the nucleus-nucleus potential which arises in a natural way in the framework of the elastic model for the heavy-ion fusion was proposed.
Abstract: In the present work we suggest an expression for the real part of the nuclear part of the nucleus-nucleus potential which arises in a natural way in the framework of the elastic model for the heavy-ion fusion. This potentialVN is energy dependent and it is such thatVN+VC
TL;DR: In this paper, the authors derived an explicitly supersymmetric expression for the chiral anomaly of the Yang-Mills theory in two dimensions using the descent equations in constrained (1, 1)-superspace.
Abstract: We derive an explicitly supersymmetric expression for the chiral anomaly of a supersymmetric Yang-Mills theory in two dimensions. For this we use the descent equations in constrained (1, 1)-superspace. The anomaly is polynomial in the vector superfield.
TL;DR: In this paper, the Komar-Todorov and Kim-Noz families of spinless spinless particle models have been studied and the transition matrix elements for the scattering of the two-particle bound states by an external object, interacting separately with each component particle.
Abstract: We make a study of the problem of two interacting relativistic spinless particles: classical motion in the Lagrangian formalism, quantization in Dirac's constrained Hamiltonian formalism, properties of the resulting quantum equations and solutions. Introducing slight modifications related to the treatment of the unphysical degree of freedom «centre-of-mass relative time and energy», we obtain the Komar-Todorov and Kim-Noz families of models. Though more artificial, these models use a phase space which remains connected to the free-particle phase space, in contrast with the reduced phase space used in Dirac's quantization. This enables us to compute the transition matrix elements for the scattering of the two-particle bound states by an external object, interacting separately with each component particle.
TL;DR: In this paper, a new form for the propagator of a spin-3/2 particle has been proposed, which differs from the one normally used in the literature, and the new propagator gives unique predictions for the contributions to the processes π n → πN, γ n → pn from tree diagrams with a Δ(1231) intermediate state.
Abstract: Recently a form for the propagator of a spin-3/2 particle has been proposed, which differs from the one normally used in the literature. We show that the new propagator gives unique predictions for the contributions to the processes πN → πN, γN → πN, γd → pn from tree diagrams with a Δ(1231) intermediate state, whereas the old propagator gives results which depend on unknown parametersy, z arising from off-mass-shell γNΔ, πNΔ couplings. We show further that, with the new propagator, one obtains a very simple model of low-energy pion-nucleon scattering, while the contributions to pion photoproduction and deuteron photodisintegration fit very well into models for these processes. These properties of the new propagator lead to the conclusion that it should be used in an effective treatment of Δ exchange, in preference to the usual treatment.
TL;DR: The problem of the missing strength in (e, e′p) reactions is investigated with special attention to the nonlocality of the nucleon-nucleus optical potential.
Abstract: The problem of the missing strength in (e, e′p) reactions is investigated with special attention to the nonlocality of the nucleon-nucleus optical potential. Some consequences for the extracted occupation numbers are illustrated.