Coulomb expectation values in $D=3$ and $D=3-2\epsilon$ dimensions

Abstract

We explore the quantum Coulomb problem for two-body bound states, in $D=3$ and $D=3-2\epsilon$ dimensions, in detail, and give an extensive list of expectation values that arise in the evaluation of QED corrections to bound state energies. We describe the techniques used to obtain these expectation values and give general formulas for the evaluation of integrals involving associated Laguerre polynomials. In addition, we give formulas for the evaluation of integrals involving subtracted associated Laguerre polynomials--those with low powers of the variable subtracted off--that arise when evaluating divergent expectation values. We present perturbative results (in the parameter $\epsilon$) that show how bound state energies and wave functions in $D=3-2\epsilon$ dimensions differ from their $D=3$ dimensional counterparts and use these formulas to find regularized expressions for divergent expectation values such as $⟨{\bar{V}}^3⟩$ and $⟨({\bar{V}}^{\prime }{)}^2⟩$ where $\bar{V}$ is the $D$-dimensional Coulomb potential. We evaluate a number of finite $D$-dimensional expectation values such as $⟨r^{-2+4\epsilon }{\partial }_r^2⟩$ and $⟨r^{4\epsilon }{p}^4⟩$ that have $\epsilon \to 0$ limits that differ from their three-dimensional counterparts $⟨r^{-2}{\partial }_r^2⟩$ and $⟨p^4⟩$. We explore the use of recursion relations, the Feynman-Hellmann theorem, and momentum space brackets combined with $D$-dimensional Fourier transformation for the evaluation of $D$-dimensional expectation values. The results of this paper are useful when using dimensional regularization in the calculation of properties of Coulomb bound systems.

arXiv comment41 pages, 2 figures; v2 includes a sample calculation

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