I'm reading Carroll and Ostlie's "An Introduction to Modern Astrophysics". In the BBN section, they describe that the universe contains a mixture of photons, electron-positron pairs, and electron and muon neutrinos and their antiparticles. They also mention that there was a small number of protons and neutrons and that protons and neutrons were constantly being transformed into each other from various reactions. From my understanding (not C & O necessarily), the Heisenberg Uncertainty Principle permits matter to spontaneously appear because there is some uncertainty as to how much mass there is in a vacuum; however, these particles must appear in "pairs" (ie. positron and an electron). If we assume inflation is correct, it is thought that these particles would become diluted after this process. So I guess I'm wondering how are these particles predicted in general (during the radiation era)? Is the energy released during inflation thought to have created these particles or something else?