On electrostatic screening of ions in astrophysical plasmas

There has been some controversy over the expression for the so-called `interaction energy' due to screening of charged particles in a plasma. Even in the relatively simple case of weak screening, first discussed in the context of astrophysical plasmas by Salpeter (1954), there is disagreement. In particular, Shaviv and Shaviv (1996) have claimed recently that by not considering explicitly in his calculation the complete screening cloud, Salpeter obtained a result for the interaction energy between two nuclei separated by a distance $r$ which in the limit $r \to 0$ is only 2/3 the correct value. It appears that this claim has arisen from a fundamental misconception concerning the dynamics of the interaction. We rectify this misconception, and show that Salpeter's formula is indeed correct.Comment: 17 pages, no figures, AAS Latex, to appear in The Astrophysical Journa

Systematic quantum corrections to screening in thermonuclear fusion

We develop a series expansion of the plasma screening length away from the classical limit in powers of $\hbar^{2}$. It is shown that the leading order quantum correction increases the screening length in solar conditions by approximately 2% while it decreases the fusion rate by approximately $0.34$. We also calculate the next higher order quantum correction which turns out to be approximately 0.05%

Competition between Pressure and Gravity Confinement in Lyman-Alpha Forest Observations

A break in the distribution function of Ly$\alpha$ clouds (at a typical redshift of $2.5$) has been reported by Petitjean et al. (1993). This feature is what would be expected from a transition between pressure confinement and gravity confinement (as predicted in Charlton, Salpeter, and Hogan (1993)). The column density at which the feature occurs has been used to determine the external confining pressure, $\sim 10 {\rm cm}^{-3} {\rm K}$, which could be due to a hot, intergalactic medium. For models that provide a good fit to the data, the contribution of the gas in clouds to $\Omega$ is small. The specific shape of the distribution function at the transition (predicted by models to have a non-monotonic slope) can serve as a diagnostic of the distribution of dark matter around Ly$\alpha$ forest clouds, and the present data already eliminate certain models.Comment: 10 pages plain TeX, 2 figures available upon request, submitted to ApJ Letters, PSU-jc-