The light element abundance for He3/H is an important parameter in understanding the Schram plot and the cosmological lithium problem. The Schram plot is a graph that compares the observed abundances of light elements, such as lithium, helium, and deuterium, with the predictions of Big Bang nucleosynthesis.
The yellow box in the Schram plot represents the observed abundances of light elements, and the red stripe represents the predicted abundances based on Big Bang nucleosynthesis. The absence of the yellow box for He3/H indicates that there is currently no direct observational data for this ratio.
This is due to the difficulty in measuring the abundance of He3 in the universe. He3 is a rare isotope of helium and is not as abundant as He4. The abundance of He3 in the universe is also affected by various astrophysical processes, such as stellar nucleosynthesis and cosmic ray interactions.
Therefore, while the observed abundances of other light elements, such as lithium and deuterium, have been measured and are included in the yellow box, the abundance of He3 is still uncertain and is not included in the Schram plot. However, ongoing research and advancements in technology may provide more accurate measurements of the He3 abundance in the future, which could help to further understand the cosmological lithium problem.
