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calculus and analysis - Calculation of an integral with a Bessel function


How can I calculate below integral? Is it possible to calculate it in Mathematica? If yes, how? Am I doing something wrong?


Integrate[BesselJ[1, q x] x /(x^2 + a^2)^(5/2), {x, a, Infinity}]

Answer




It seems that for some values of a greater for some value, the integral value is complex. I have done the following:


∫∞axJ1(qx)(x2+a2)5/2dx=∫∞0xJ1(qx)(x2+a2)5/2dx−∫a0xJ1(qx)(x2+a2)5/2dx


The first term is a Hankel transform of order 1, the other can be done substituting the Bessel function by its series equivalent. Thus:


HankelTransform[1/(x^2 + a^2)^(5/2), x, q, 1]

8G1,23,1(4q2a2|−32,−12,120)3√π(a2)5/2q2


and


Assuming[a > 0 && a \[Element] Reals && m \[Element] Integers && m >= 0, 
Integrate[(q x)^(2 (m + 1)) (-1)^m/(2^(2 m + 1) Gamma[m + 2] m! (x^2 + a^2)^(5/2)), {x, 0, a}]]


with finaly:


∑∞m=0i2−2(m+2)q2(m+1)(−a)2(m−1)((4m(4m+5)−1)B−1(m+32,12)−2(m+2)(4m−1)B−1(m+32,32))3m!Γ(m+2)


Plotting the real part of their difference, with m=80 and q=1:


enter image description here enter image description here


which agrees with the other approaches.


You can modify the value of m to the required accuracy.


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