Constraining the GENIE model of neutrino-induced single pion production using reanalyzed bubble chamber data

A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the Standard Model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, \(\eta\), corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of \(\eta\) from observations of anisotropies in the cosmic microwave background. However the primordial abundance of lithium-7 inferred from observations is significantly below its expected value. Taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range \(\eta = (5.7-6.7)\times 10^{-10}\) at 95% CL (corresponding to a cosmological baryon density \(\Omega_B h^2 = 0.021 - 0.025\)). The D and He-4 abundances, when combined with the CMB determination of \(\eta\), provide the bound \(N_\nu=3.28 \pm 0.28\) on the effective number of neutrino species. Other constraints on new physics are discussed briefly.

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.