Systematic description of COVID-19 pandemic using exact SIR solutions and Gumbel distributions.

An epidemiological study is carried out in several countries analyzing the first wave of the COVID-19 pandemic using the SIR model and Gumbel distribution. The equations of the SIR model are solved exactly using the proper time as a parameter. The physical time is obtained by integration of the inverse of the infected function over proper time. Some properties of the solutions of the SIR model are studied such as time scaling and the asymmetry, which allows to obtain the basic reproduction number from the data. Approximations to the solutions of the SIR model are studied using Gumbel distributions by least squares fit or by adjusting the maximum of the infected function. Finally, the parameters of the SIR model and the Gumbel function are extracted from the death data and compared for the different countries. It is found that ten of the selected countries are very well described by the solutions of the SIR model, with a basic reproduction number between 3 and 8.

Meson-exchange currents and quasielastic antineutrino cross sections in the superscaling approximation.

We evaluate quasielastic double-differential antineutrino cross sections obtained in a phenomenological model based on the superscaling behavior of electron scattering data and estimate the contribution of the vector meson-exchange currents in the two-particle-two-hole sector. We show that the impact of meson-exchange currents for charge-changing antineutrino reactions is much larger than in the neutrino case.

Quasielastic charged-current neutrino-nucleus scattering.

We provide integrated cross sections for quasielastic charged-current neutrino-nucleus scattering. Results evaluated using the phenomenological scaling function extracted from the analysis of experimental (e, e') data are compared with those obtained within the framework of the relativistic impulse approximation. We show that very reasonable agreement is reached when a description of final-state interactions based on the relativistic mean field is included. This is consistent with previous studies of differential cross sections which are in accord with the universality property of the superscaling function.

Superscaling in charged current neutrino quasielastic scattering in the relativistic impulse approximation.

Superscaling of the quasielastic cross section in charged-current neutrino-nucleus reactions at energies of a few GeV is investigated within the framework of the relativistic impulse approximation. Several approaches are used to describe final-state interactions and comparisons are made with the plane-wave approximation. Superscaling is very successful in all cases. The scaling function obtained using a relativistic mean field for the final states shows an asymmetric shape with a long tail extending towards positive values of the scaling variable, in excellent agreement with the behavior presented by the experimental scaling function.

What does the free space Lambda Lambda interaction predict for Lambda Lambda hypernuclei?

Data on LambdaLambda hypernuclei provide a unique method to learn details about the strangeness S = -2 sector of the baryon-baryon interaction. From the free space Bonn-Jülich potentials, determined from data on baryon-baryon scattering in the S = 0,-1 channels, we construct an interaction in the S = -2 sector to describe the experimentally known LambdaLambda hypernuclei. After including short-range (Jastrow) and RPA correlations, we find masses for these LambdaLambda hypernuclei in a reasonable agreement with data, taking into account theoretical and experimental uncertainties. Thus, we provide a natural extension, at low energies, of the Bonn-Jülich one-boson exchange potentials to the S = -2 channel.