Integral over spherical Bessel function

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Discussion Overview

The discussion revolves around solving the integral of a spherical Bessel function multiplied by a polynomial and an exponential decay term. The focus includes theoretical approaches, mathematical reasoning, and potential computational methods.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant requests assistance in solving the integral \(\int_{0}^{+\infty} dr r^{n+1} e^{-\alpha r} j_l(kr)\).
  • Another participant humorously suggests that if the integral is not found in established references, it may require original discovery.
  • A third participant shares a solution provided by Mathematica, detailing conditions under which the solution holds, including constraints on the real and imaginary parts of parameters.
  • One participant proposes relating the spherical Bessel function to the standard Bessel function using a specific definition and references a formula from Gradshteyn and Ryzhik.
  • A later reply expresses concern about a potential error in the formula related to the variable of differentiation, emphasizing the importance of understanding the process of obtaining the solution.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of the formula and its derivation, indicating that the discussion remains unresolved with multiple competing perspectives on the approach to solving the integral.

Contextual Notes

There are limitations regarding the assumptions made in the proposed solutions, particularly concerning the conditions under which the Mathematica output is valid and the relationship between spherical and standard Bessel functions.

hmhm696
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Is there somebody who can help me how to solve this integral

<br /> \int_{0}^{+\infty} dr r^{^{n+1}} e^{-\alpha r} j_l(kr)<br />
 
Last edited:
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I have a saying for this type of questions. If it's not in one of the Gradshteyn-Rytzhik editions of their famous book, then it must be discovered. :)
 
This is the answer Mathematica gives:
If[Re[a] >
0 && (Abs[Im[k]] <
Re[a] || (Abs[Im[k]] == Re[a] && Re[n] < 0)) && (Re[k] >
0 || (Im[k] > 0 && Re[k] == 0)),
2^(-1 - l) a^(-2 - n) (k^2/a^2)^(l/2) Sqrt[\[Pi]]
Gamma[2 + l + n] Hypergeometric2F1Regularized[1/2 (2 + l + n),
1/2 (3 + l + n), 3/2 + l, -(k^2/a^2)],
Integrate[
E^(-a r) r^(1 + n) SphericalBesselJ[l, k r], {r, 0, \[Infinity]},
Assumptions ->
Abs[Im[k]] > Re[a] || (Abs[Im[k]] >= Re[a] && Re[n] >= 0) ||
Re[k] < 0 || (Re[k] <= 0 && Im[k] <= 0) || Re[a] <= 0]]
 
I think you can relate the spherical Besselfunction to the normal J Bessel function by the definition:

http://functions.wolfram.com/Bessel-TypeFunctions/SphericalBesselJ/02/

and then use formula attached below which is taken from G & R

G_R.jpg
 
Thanks guys.
I think that given formula has error in the part where it derivative by alpha instead of betha.
For me is important a process, how i can get it.
 

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