Showing papers in "Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields in 1977"

Lattice supersymmetry@@@Суперсимметрия рещетки

Abstract: SummaryIt is shown that supersymmetry can be formulated on a space-time lattice. The transformation properties of superfields are demonstrated and the simplest action that gives the Wess-Zumino model in the continuous limit is discussed.RiassuntoSi mostra che la supersimmetria può essere formulata in un reticolo dello spazio-tempo. Si dimostrano le proprietà di trasformazione dei supercampi e si discute l’azione più semplice che dà il modello di Wess-Zumino nel limite continuo.РеэюмеПокаэывается, что суперсимметрия может быть сформулирована на пространственно-вре менной рещетке. Демонстрируются свойства преобраэований суперполей. Обсуждается простейщий способ, который дает модель Весса-Зумино в непрерывном пределе.

Determination of the branching fractions for K--meson absorptions at rest in carbon nuclei

Abstract: The branching ratios for the primary interactions of K−-mesons at rest with carbon nuclei have been determined by means of a heavy-liquid bubble chamber filled with a mixture of hydrocarbons. The results are compared with those obtained in other absorbing media, and the question of the existence of a halo of neutrons at the surface of heavy nuclei is discussed in the light of these new results.

Study of quasi-elastic reactions of ν and\overline v in gargamellein gargamelle

Abstract: The quasi-elastic cross-sectionsσeltot and dσ/dq2 for the reactions 1) νn → μ−p and 2)\(\overline v \) → μ+n have been measured by using the data of the ν Gargamelle collaboration. 687 ν events, candidates for reaction 1), and 476\(\overline v \) events, candidates for the reactions 2), have been used for the analysis. Because the ν and\(\overline v \) interactions are on nuclei, suitable corrections for nuclear effects have been taken into account. In the framework of the «usual»V −A theory, by assuming for the axial form factor the dipolar formFA(q2)=1.23/(1 +q2/MA/2)2, our data have been fitted to the differential cross-section dσ/dq2 integrated over the ν and\(\overline v \) energy spectra and to the total cross-sectionσeltot as a function of the ν,\(\overline v \) energy to determine the best value for the parameterMA.

Non-abelian gauge theories and triangle anomalies

Abstract: Conditions for the validity of (a weak version of) the Adler-Bardeen theorem for non-Abelian gauge theories are obtained. Its validity ensures that those theories in which the coefficient of the triangle anomaly vanishes at the one-loop level are anomaly free and therefore they are renormalizable and unitary. This result is based on the derivation of Slavnov-Taylor identities modified by the presence of anomalous terms and on a renormalization-group-like equation for the anomaly coefficient. In the derivation, the dimensional regularization scheme has been followed.

Superluminal transformations using either complex space-time or real space-time symmetry

Abstract: In order to adequately discuss the transformations between the space-time co-ordinates of two inertial frames moving superluminally relative to each other, it is necessary to use either four complex space-time co-ordinates or six real space-time co-ordinates—three of space and three of time. A major difficulty then arises in the physical understanding of the extra parameters. In these two cases, considered separately, specific transformations are found for both the superluminal and the subluminal cases. It is found that in the subluminal cases the extra co-ordinates are completely uncoupled from the original ones, while in the superluminal cases there is a necessary coupling.

A simple model for proton-antiproton scattering at low energies

Abstract: The\(\bar pp\) scattering data at low energies are very well reproduced with the one-boson exchange potential (OBEP) and with the annihilation described by a boundary condition at a certain radius. Our only free parameter is the boundary radius. We show that the elastic\(\bar pp\) forward peak is not a diffractive peak. Its slope as well as the antishrinkage are explained by the OBEP alone.

Some aspects of instantons

Abstract: We study various effects associated with Euclidean instanton solutions. By means of an instructive example, we discuss how the probability of tunnelling among vacuum states in Minkowski space is connected with stationary (instanton) solutions in Euclidean space. Next we examine the cluster decomposition properties of non-Abelian gauge theories and indicate how these are recovered in the presence of instanton solutions. The validity of perturbation theory in these field theories is discussed. We show that perturbative analyses are only tenable in the deep Euclidean region, unless there is an intrinsic scale. Finally, we examine the role that instantons have in providing violations of otherwise conserved quantum numbers. We study, in particular, how fermion number nonconservation results by a careful examination of the path integral for the fermion-generating functional.

A study of π+, π− and proton production in pp interactions at 69 GeV/c

Abstract: We present the inclusive and semi-inclusive production of protons, π+, π−, for the full range of kinematic variables, from 7850 inelastic interactions obtained in the 4.7 m liquid-hydrogen bubble chamber Mirabelle at the Serpukhov accelerator and with an incident proton beam of 69 GeV/c. We compare the data with those at other energies, and we give the results of different phenomenological fits.

Photodisintegration of4He in the giant-resonance region

Abstract: Total and differential cross-sections for the photodisintegration reactions of4He have been measured for excitation energies up to about 80 MeV with a diffusion cloud chamber in magnetic field. The dipole and quadrupole absorption contributions are deduced for two-body photodisintegration reactions. The different behaviour with the energy of the interference term for photoproton and photoneutron emission is confirmed. The ratio σ(γ, p)/σ(γ, n) is higher than 1, for photon energies lower than about 27 MeV, in agreement with some theoretical predictions. The results of the σ(γ, np) and σ(γ, 2n2p) cross-section measurements have been also analysed.

One-boson exchange potentials and nucleon-antinucleon scattering

Abstract: Recently, there have been several suggestions that low-energy nucleon-antinucleon (NN) resonances might exist. They were based on the real part of the Bryan-Phillips potential, while the absorptive part was taken as a small perturbation. We re-examine theNN scattering, taking into account the whole Bryan-Phillips potential. We find, as others, that the real part, the one-boson exchange potential (OBEP), produces many resonances. However, the inclusion of the dominant absorptive part eliminates all of them. In addition, we find that theNN scattering is sensitive to the unknown, short-range behaviour of this OBEP and, therefore, we question its predictive reliability. We argue that, if experimentally one findsNN low-energy resonances, we would be able to learn more about the short-range behaviour of the OBEP.

Local Operators and Charged States in Quantum Electrodynamics

Abstract: It is proved that in any local gauge physical charged states cannot be obtained by applying local operators to the vacuum state.c-number gauge transformations of the second kind are discussed and in terms of them conditions are given for operators to map physical states into physical states.

The complete field of a general static spherically symmetric distribution of charge

Abstract: The exact solution of the combined Einstein-Maxwell field equations is presented which describes the complete field, interior and exterior, of a general static spherically symmetric distribution of charge. The solution is a functional of the charge density σ and of the componentsM11 andM44 of the matter energy tensorMji; the componentsM22 andM33 are given in terms of σ,M11 andM44. The solution is well behaved everywhere and satisfies all the necessary junction conditions across the surface of the distribution. Outside the distribution, the solution reduces to the exterior Nordstrom solution with the gravitational massm explicitly defined in terms of σ and of the matter density ϱ(= −M44). In the special case of charged dust, that is when all the matter stresses are zero, it is shown that σ=± ϱ inside the distribution andm=|e| outside the distribution, wheree is the total charge of the dust. A class of explicit solutions is also given in this case, and a theorem is proved which establishes a particularly simple form of the line element for the most general spherically symmetric charged dust.

Low-energy properties of a relativistic quark model with linear scalar potential

Abstract: A simple quark model with a linear rising scalar confining potential and an additional Coulomb potential is discussed. The eigenvalues of the appropriate Dirac equation are studied with respect to variations of the quark bare mass and to the potential parameters. The model is able to account for the static properties of the nucleon.

Some remarks on finite-difference equations of physical interest

Abstract: In this paper, the properties of mixed finite-difference and differential equations arising in various physical problems are investigated. First, a prescription for the correct transition to the continuum limit is given and illustrated in some concrete cases. It is further found that, by introducing a suitable generating function associated with a mixed equation, Cauchy's problem for a class of partial differential operators can be solved in a quite simple way.

About low-energy expansion of two-current amplitudes

Abstract: An alternative technique to deal with processes in which two isospin-carrying electromagnetic or weak currents appear is developed to predict the amplitude up to nontrivial structure terms by means of the divergence conditions. Applications are made to isovector Compton scattering and radiative muon capture by a free proton.

Čerenkov radiation from computer simulations of the γ-ray-initiated atmospheric showers

Abstract: Computer simulations have been made of the spatial and temporal characteristics of the Cerenkov radiation produced in the atmosphere by showers initiated by γ-rays of energy (10÷300) GeV. The simulations contain improvements in detail over those previously available and allowance was made for the effects of the geomagnetic field on the electron cascade development and absorption in the atmosphere of the Cerenkov light. The results are appropriate to a range of detectors at an altitude of 2380 m and at sea-level. Details are given of the average spatial and temporal characteristics of the light flux including isophote plots. The fluctuations in these quantities are specified and the origin of the fluctuations identified.

Bose-Einstein Clustering and Critical Hadron Temperatures

Abstract: It is shown that a relativistic quantum gas of pions, due to Bose-Einstein statistics and the resulting possibility of condensation, exhibits a structure similar to that obtained in the statistical bootstrap model, with clusters of condensed pions taking the place of fireballs. The critical temperatureT* of the BE system is, however, associated with a first-order phase transition from a gas of pions and clusters at low energy density to a system of condensed pions at high energy density. The phase transition and the nature of the two phases are investigated.

K-shell internal ionization and excitation in beta-decay: Theoretical study

Abstract: The total probability of aK-shake-off process in β-decay has been reformulated by correcting the theory by Law and Campbell. By means of the improved formulation and by adding simple corrections for theK-shake-up contribution and for the correlation effect betweenK electron and other bound electrons, the totalK hole creation probability per β-decay has been evaluated for 24 interesting nuclides. There exist distinct disagreements between our calculated values and recent experimental data; the measured probabilities are systematically larger than our calculated ones for medium- and high-Z nuclides. This clearly indicates that the theory ofK shake-off, as here corrected, is not sufficient to explain the recent experimental data. This is contrary to the conclusion recently presented by many other workers that theK-shake-off plus shake-up process is the predominant mechanism ofK-shell internal ionization and excitation in β-decay. It will be necessary to introduce the β-particleelectron correlation in future theoretical treatments.

A model for the supersymmetric relativistic oscillator

Abstract: By following the ideas suggested by the supersymmetric theories, a model for a pseudoclassical relativistic oscillator is studied. It is shown how it is possible to construct a (pseudoclassical) supersymmetric Lagrangian for the harmonic oscillator from the classical one. The quantization of the theory is different in the two cases: in the Bose sector we have a mass spectrum for particles with integer spin, whereas in the supersymmetric sector we have a tower of particles with half-integer spin and degenerate in mass.

Analysis of a nondegenerate decay system

Abstract: Recently developed analytic techniques are introduced for the treatment of decay problems. The one-channel decay problem is treated in detail; the pole and nonexponential contributions are calculated both by numerical techniques and analytically. Conditions for the dominance of the pole contribution are specified. The asymptotic procedures used are developed systematically in a mathematical appendix.

Inclusive and exclusive cross-sections in K−p interactions at 14.3 GeV/c

Abstract: The inclusive cross-sections for the production of 0− mesons, 1/2+ and 3/2+ baryons, as well as for some other baryon and meson resonances (Λ(1405), Λ(1520), K*(890), Φ and f′) in 14.3 GeV/c K−p interactions are given. The cross-sections for exclusive 4C and 1C reactions representing altogether about half of the total cross-section are also presented and discussed.

Appropriate linearizations of interacting theories with spontaneous symmetry breaking

Abstract: Spontaneous breakdown of a symmetry group in a dynamical theory is connected with a rearrangement of group properties between quantized and classical degrees of freedom enforced by the classical asymmetry properties of the ground state. By disentangling the classical and quantized parts in the original basic field operators, designed for describing the short-distance behaviour, and by rearranging them in various ways, new dressed field operators with different symmetry properties, adapted to the description in the asymptotic region, can be constructed which, in general, admit more appropriate linearizations of the theory and hence offer better starting points for a perturbative treatment of the interaction. There are essentially two different dressing mechanisms of the basic field by which fields with particle interpretation are generated: an asymmetric dressing which relies strongly on the asymmetry of the ground state and a symmetric dressing which is only triggered by it. The formalism is exemplified for the nonlinear chiral model of Nambu and Jona-Lasinio. The main purpose of the paper, however, does not aim at improving the approximations in this model, but is thought of as a preparation for a similar treatment of more realistic theories with a spontaneous breakdown of a non-Abelian symmetry group and of the dilatation group in which these considerations may offer natural explanations for the occurrence of approximate higher symmetries and for the mysterious coexistence of two types of particles, the leptons and gauge particles on the one hand and the hadrons on the other hand.

Covariant loops and strings in a positive definite Hilbert space

Abstract: Relativistic loops and strings are defined in the conventional way as solutions of a one-dimensional wave equation with certain boundary conditions and satisfying the orthogonal gauge conditions. Conventional pseudo-Cartesian co-ordinates (rather than null-plane co-ordinates) are used. The creation and annihilation operator four-vector α † anda μ are required to be spacelike (orthogonal to the total momentumP μ), so that the resulting Fock spaceH + is positive definite. This requirement is shown to be mathematically consistent with Poincare invariance and to impose no additional physical constraints on the system. It can be implemented in a canonical realization of the Poincare algebra as a condition on state vectors, or in a noncanonical realization as an operator equation, as is done here. The spaceH + is further restricted by the Virasoro conditions to a physical subspace Φ which is of course also positive definite. In this way there arises no critical-dimension problem and Poincare invariance holds also in 3+1 dimensions. The energy and spin spectra are the same as usual, leading to linear Regge trajectories, except that there are no tachyons and no zero-mass states. The leading Regge trajectory has negative intercept.

A higher conserved current in the quantized massive thirring model

Abstract: A higher conserved current in the quantized massive Thirring model is explicitly constructed.

Search for fractionally charged particles produced in proton-proton collisions at the highest ISR energy

Abstract: The results of an experiment to search for quarks at the CERN ISR, at a total centre-of-mass energy √s=62.2 GeV, are reported. The experiment was sensitive to fractionally charged particles with 0.035e≤|Q|≤0.67e, β=v/c≥0.1 and masses up to 26 GeV/c2. The 90% confidence level on the ratio «quark flux/charged flux» is 1.78·10−9 forQ=+(1/3)e and 1.05·10−9 forQ=−(1/3)e. These values hold true for production processes with transverse momentap⊥≃0.4 GeV/c.

Quantized metric on locally flat space-time and spontaneous dilatation asymmetry

Abstract: The existence of a uniquely defined possibly nontrivial metric on a locally flat space-time with quantum structure can be related to the existence of aSL2,C ×U2 spinor field Ψ with spin 1/2, two internal degrees of freedom and noncanonical dimension 1/2. The simplestSU2 connexion of space-time is expressed by a uniquely defined nonlinear field equation for the basic field Ψ. A canonical formulation of the basic equation including the quantization is possible by a rear-rangement of the dimension properties of the basic equation which can be interpreted as a consequence of a spontaneous dilatation asymmetry. In the canonical formulation a particle interpretation of the basic law of motion seems possible.

Quark interactions and universal multihadron jets

Abstract: The constituent approach to strong and electromagnetic hadron interactions requires weak coupling at large momentum transfer, to obtain scaling, and strong coupling at low momentum transfer, to permit quark confinement. Asymptotically free or weakly coupled hard interactions do not provide multiparticle production. Thus soft high-energy quark-quark interactions constitute a universal jet mechanism for multihadron production in soft and in hard hadron-hadron collisions, as well as in deep inelastic lepton-hadron scattering and in e+e− annihilation.

Some quantitative estimates about final-state polarization in deep inelastic lepton-nucleon scattering

Abstract: We discuss the reaction polarized lepton + unpolarized nucleon\( \to _{\Sigma + }^\Lambda + \) anything and give some quantitative estimates on the polarization of the hyperons to be expected in a naive parton model. We find large polarizations for hyperons produced in the parton fragmentation region — of the order 30% for Λ and 60% for Σ+. For hyperons from the target fragmentation almost as large polarizations are predicted and a relatively large yield is expected.

A microscopic evaluation of the nuclear dipole polarizability

Abstract: The dipole polarizability sum rule has been evaluated by means of a restricted Hartree-Fock approach. The method leads to a simple and analytical expression for the dipole polarizability. Explicit calculations have been performed in16O and40Ca with different types of interaction.

A new treatment of radiative decays of mesons

Abstract: Motivated by the remarkably good agreement in the descriptions of deep inelastic processes and some radiative meson decays by the quark model and the method of infinite vector-meson saturation, we argue in general that these two approaches are equivalent. We explicit the nature of this equivalence by endowing vector-mesondominated vertices with the asymptotics implied by quark current algebra. With this leverage we obtain satisfactory predictions forSU3 meson decays, including those for which the quark model by itself fails, excepting the ρ → πγ decay. Applied to the radiative decays of the new mesons, this scheme avoids the difficulties of nonrelativistic calculations and predicts considerably smaller widths.