Kinematical and nonlocality effects on the nonmesonic weak hypernuclear decay

We make a careful study about the nonrelativistic reduction of one-meson-exchange models for the nonmesonic weak hypernuclear decay. Starting from a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (pi, eta, K, rho, omega, K*), the strangeness-changing weak LambdaN --> NN transition potential is derived, including two effects that have been systematically omitted in the literature, or, at best, only partly considered. These are the kinematical effects due to the difference between the lambda and nucleon masses, and the first-order nonlocality corrections, i.e., those involving up to first-order differential operators. Our analysis clearly shows that the main kinematical effect on the local contributions is the reduction of the effective pion mass. The kinematical effect on the nonlocal contributions is more complicated, since it activates several new terms that would otherwise remain dormant. Numerical results for C-12(Lambda) and He-5(Lambda) are presented and they show that the combined kinematical plus nonlocal corrections have an appreciable influence on the partial decay rates. However, this is somewhat diminished in the main decay observables: the total nonmesonic rate, Gamma(nm), the neutron-to-proton branching ratio, Gamma(n)/Gamma(p), and the asymmetry parameter, a(Lambda). The latter two still cannot be reconciled with the available experimental data. The existing theoretical predictions for the sign of a(Lambda) in He-5(Lambda) are confirmed. (C) 2003 Elsevier B.V. All rights reserved.

The two-loop massless (lambda/4!)phi(4) model in nontranslational invariant domain

We study the (lambda/4!)phi(4) massless scalar field theory in a four-dimensional Euclidean space, where all but one of the coordinates are unbounded. We are considering Dirichlet boundary conditions in two hyperplanes, breaking the translation invariance of the system. We show how to implement the perturbative renormalization up to two-loop level of the theory. First, analyzing the full two and four-point functions at the one-loop level, we show that the bulk counterterms are sufficient to render the theory finite. Meanwhile, at the two-loop level, we must also introduce surface counterterms in the bare Lagrangian in order to make finite the full two and also four-point Schwinger functions. (c) 2006 American Institute of Physics.

The reaction (p)over-barp -> (Lambda)over-bar(c)(-)Lambda(+)(c) close to threshold

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

De sitter relativity: a natural scenario for an evolving Lambda

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A statistical law for multiplicities of SU(3) irreps (lambda, mu) in the plethysm {eta} circle times(3) {m} -> (lambda, mu)

A statistical law for the multiplicities of the SU(3) irreps (lambda, mu) in the reduction of totally symmetric irreducible representations {m} of U(N), N = (eta + 1) (eta + 2)/2 with eta being the three-dimensional oscillator major shell quantum number, is derived in terms of the quadratic and cubic invariants of SU(3), by determining the first three terms of an asymptotic expansion for the multiplicities. To this end, the bivariate Edgeworth expansion known in statistics is used. Simple formulae, in terms of m and eta, for all the parameters in the expansion are derived. Numerical tests with large m and eta = 4, 5 and 6 show good agreement with the statistical formula for the SU(3) multiplicities.

Measurement of the Lambda(b) cross section and the (Lambda)over-bar(b) to Lambda(b) ratio with J/psi Lambda decays in pp collisions at root s=7 TeV CMS Collaboration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Weak nonmesonic decay spectra of hypernuclei

We compute one- and two-nucleon kinetic-energy spectra and opening-angle distributions for the nonmesonic weak decay of several hypernuclei, and compare our results with some recent data. The decay dynamics is described by transition potentials of the one-meson-exchange type, and the nuclear structure aspects by two versions of the independent-particle shell model (IPSM). In version IPSM-a, the bole states are treated as stationary, while in version IPSM-b the deep-hole ones are considered to be quasi-stationary and are described by Breit-Wigner distributions.

Applicability of the linear delta expansion for the lambda phi(4) field theory at finite temperature in the symmetric and broken phases

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the production fraction times branching fraction f(b -> Lambda(b)) . B(Lambda(b) -> J/psi Lambda)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Asymmetry parameter for nonmesonic hypernuclear decay

We give general expressions for the vector asymmetry in the angular distribution of protons in the nonmesonic weak decay of polarized hypernuclei. From these we derive an explicit expression for the calculation of the asymmetry parameter, a(Lambda), which is applicable to the specific cases of He-5(Lambda) and C-12(Lambda) described within the extreme shell model. In contrast to the approximate formula widely used in the literature, it includes the effects of three-body kinematics in the final states of the decay and correctly treats the contribution of transitions originating from single-proton states beyond the s-shell. This expression is then used for the corresponding numerical computation of a(Lambda) within several one-meson-exchange models. Besides the strictly local approximation usually adopted for the transition potential, we also consider the addition of the first-order nonlocality terms. We find values for a(Lambda) ranging from -0.62 to -0.24, in qualitative agreement with other theoretical estimates but in contradiction with some recent experimental determinations.

Infrared laser photobiomodulation (lambda 830 nm) on bone tissue around dental implants: A Raman spectroscopy and scanning electronic microscopy study in rabbits

Objective: the aim of this study was to assess, through Raman spectroscopy, the incorporation of calcium hydroxyapatite (CHA; similar to 960 cm(-1)), and scanning electron microscopy (SEM), the bone quality on the healing bone around dental implants after laser photobiomodulation ( lambda 830 nm). Background Data: Laser photobiomodulation has been successfully used to improve bone quality around dental implants, allowing early wearing of prostheses. Methods: Fourteen rabbits received a titanium implant on the tibia; eight of them were irradiated with lambda 830 nm laser ( seven sessions at 48-h intervals, 21.5 J/cm(2) per point, 10 mW, phi similar to 0.0028 cm(2), 86 J per session), and six acted as control. The animals were sacrificed 15, 30, and 45 days after surgery. Specimens were routinely prepared for Raman spectroscopy and SEM. Eight readings were taken on the bone around the implant. Results: the results showed significant differences on the concentration of CHA on irradiated and control specimens at both 30 and 45 days after surgery ( p < 0.001). Conclusion: It is concluded that infrared laser photobiomodulation does improve bone healing, and this may be safely assessed by Raman spectroscopy or SEM.

CLASSICAL EQUIVALENCE OF LAMBDA-R-PHI-2 THEORIES

It is shown that the action functional S[g, phi] = integral d4 x square-root -g[R/k(1 + klambdaphi2) + partial derivative(mu)phi partial derivative(mu)phi] describes, in general, one and the same classical theory whatever may be the value of the coupling constant lambda.

Analytic solutions for the Lambda-FRW model

The high precision attained by cosmological data in the last few years has increased the interest in exact solutions. Analytic expressions for solutions in the Standard Model are presented here for all combinations of Lambda = 0, Lambda not equal 0, kappa = 0, and kappa = 0, in the presence and absence of radiation and nonrelativistic matter. The most complete case (here called the Lambda gamma CDM Model) has Lambda not equal 0, kappa not equal 0, and supposes the presence of radiation and dust. It exhibits clearly the recent onset of acceleration. The treatment includes particular models of interest such as the Lambda CDM Model (which includes the cosmological constant plus cold dark matter as source constituents).

Nonmesonic weak decay of Λ-hypernuclei within independent-particle shell-model

After a short introduction to the nonmesonic weak decay (NMWD) ΛN→nN of Λ-hypernuclei we discuss the long-standing puzzle on the ratio Γn/Γp, and some recent experimental evidences that signalized towards its final solution. Two versions of the Independent-Particle-Shell-Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account, and (b) IPSM-b, where the highly excited hole states are considered to be quasi-stationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. We evaluate the coincidence spectra in Λ 4He, Λ 5He, Λ 12C, Λ 16O, and Λ 28Si, as a function of the sum of kinetic energies EnN=En+EN for N=n, p. The recent Brookhaven National Laboratory experiment E788 on Λ 4He, is interpreted within the IPSM. We found that the shapes of all the spectra are basically tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange- potential. In spite of the straightforwardness of the approach a good agreement with data is achieved. This might be an indication that the final-state- interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the π+K exchange potential with soft vertex-form-factor cutoffs (Λπ≈0. 7GeV, ΛK≈0.9GeV), is able to account simultaneously for the available experimental data related to Γp and Γn for Λ 4H, and Λ 5He. © 2010 American Institute of Physics.

Nonmesonic Weak Decay Spectra of Light Hypernuclei

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)