Review Questions

1. What is the physical reason the electron binding energy differs between the deuterium (D) isotope and the hydrogen (H) isotope? What is wavelength/energy difference between the neutral deuterium (DI) Ly⍺ transition and neutral hydrogen (HI) Ly⍺ transition called? How many angströms is this difference? 

2. Explain why the measured deuterium to hydrogen abundance ratio, denoted D/H, can be determined, to a high degree of approximation, directly from the ratio of the DI to the HI column densities.

3. In the 1970s, several teams measured D/H in the ISM of the Galaxy.  What instrument did they use and in what type of objects did they measure the absorption lines? What is the approximate average value that they measured?

4. Briefly describe the "Deuterium Wars" of the late 1990s. In your answer include (i) the major players (or combatants!), (ii) the numerical value of a "low" and "high" D/H measurement, (iii) what possible "data analysis" tribulations were thought to give rise to the "low" and "high" disagreements, and (iv), which value, "low" or "high", won the battle.

5. Briefly describe the era of FUSE D/H measurements in the Galactic ISM, including the scatter in the measurements and speculations as to what gave rise to that scatter. A decade later, why and how did incorporating the COS instrument on HST help improve those D/H measurements? 

6. Briefly explain/describe the breakthrough(s) that occurred such that the team led by Ryan Cooke and Max Pettini were able to achieve high precision measurements of D/H. What is their mean measured value of D/H? What are (simply list) the four higher-order effects that, if treated in the analysis, might further improve D/H measurements.

7. After a quarter century of extragalactic D/H studies, for how many total absorbers has D/H been measured? Even with this relatively small number, the precision is so high that Big Bang Nucleosynthesis (BBN) theory is being challenged.  What aspects of their codes do BBN theorists think need improving if they are to obtain higher accuracy in their theoretical predictions?

8. Describe the tension between D/H measured using quasar absorption line systems and D/H values obtained from analysis of the cosmic microwave background, i.e. Planck data.

9. What is Gamow's "Devine Creation Curve" and what were his assumptions?  What is a Schramm plot showing and what is its usefulness (how is it applied)?

10. In a few short words, what is the deuterium bottleneck? Explain the primary competing physical processes that cause the deuterium bottleneck.  

11. According to arguments first presented by Peebles (1966), do you expect a higher or a lower D/H if the baryon to photon ratio were higher?  Explain the physical reason(s).  What if the free neutrino half-life were longer?  Explain.

12. What is the lithium problem? What possible solutions exist?

13. Briefly describe and explain how BBN theorists explore the various dependencies in their codes to obtain the best predictions of D/H and to understand the web of uncertainties in their calculations.

Problems

1. Under construction