English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We consider the effect of interactions on the line shape of the two-photon1s-2s transition in a (doubly) spin-polarized atomic hydrogen gas in terms ofthe interatomic interaction potentials. We show that the frequency-weighted sumrule for the intensity of the line is not given simply in terms of thepseudopotentials that describe the interactions between low-energy atoms. Theorigin of the departures from the simple pseudopotential result for thefrequency-weighted sum rule is traced to what we refer to as incoherentcontributions to the spectral weight. These arise from more complicated finalstates of the many-body system than the ones usually considered. In particular,we show how the relevant response function may be treated in a manner similarto the density-density response function for Fermi liquids, and express it as acoherent part coming from single particle-hole pairs, and an incoherent partcoming from other excitations. We argue that in experiments only the coherentpart of the response of the system is observed, and its contribution to thefrequency-weighted sum rule is shown to be given correctly by thepseudopotential approximation. Finally we calculate the width of the coherentpart of the line due to collisional damping.Comment: 15 pages of ReVTeX containing 3 postscript figure

Collisional frequency shifts of absorption lines in an atomic hydrogen gas