Step 1. The expression provided by OP can be cleaned up a bit. For example, this is a subexpression of the expression provided by OP, with the exception that I put an Inactive
in to get Mathematica to exploit the fact that there is derivative D
just outside:
D[ρ*(((155*2)/ρ)*Inactive[Integrate][BesselJ[l,23*y]^2*y,{y,0,ρ}]),ρ]
This simplifies to
310*ρ*BesselJ[l,23*ρ]^2
Step 2. Doing Step 1 for the entire integrand that OP has provided, I get the following simpler formula for the integrand, where I also replaced 41.85
by 4185/100
to avoid problems with floating point numbers:
integrand[l_]:=integrand[l]=Assuming[ρ>0, 4185/100 l BesselJ[l, 23 ρ]^2 (
ρ^2 Integrate[BesselJ[l, 23 y]^2/y, {y, ρ, \[Infinity]}]
+ Integrate[y BesselJ[l, 23 y]^2, {y, 0, ρ}])/ρ//Simplify];
This can be evaluated. For example, taking the value l==5
in the question:
integrand[5]
(* (1/(1566219705620 ρ^7))837 (529 ρ^2 (-4608 +
101568 ρ^2 - 5596820 ρ^4 +
740179445 ρ^6) BesselJ[0, 23 ρ]^2 -
23 ρ (-18432 + 1625088 ρ^2 - 22387280 ρ^4 +
740179445 ρ^6) BesselJ[0, 23 ρ] BesselJ[1,
23 ρ] + (-18432 + 2843904 ρ^2 - 102981488 ρ^4 -
2960717780 ρ^6 + 391554926405 ρ^8) BesselJ[1,
23 ρ]^2) BesselJ[5, 23 ρ]^2 *)
Step 3. Let us plot this:
Plot[integrand[5],{ρ,0,5},PlotRange->All]
This gives
Looks nice, but decay seems slow. In fact, let us also plot ρ
times the integrand:
Plot[integrand[5]*ρ,{ρ,0,5},PlotRange->All]
This gives
It seems likely that this oscillates forever with some fixed amplitude (could be checkedsee remark below). Thus integrand[5]
is 1/ρ
times this oscillation. That is too slow for convergence of the integral over {ρ,0,\[Infinity]}
. Hence the integral does in fact not converge, it is $+\infty$.
The divergence is not due to the behavior near ρ==0
, in fact the integrand decays quickly towards ρ==0
. Rather, the divergence is due to slow decay as ρ
goes to infinity.
Remark. The 1/ρ
decay is due to the following terms in integrand[5]//Expand
:
ρ BesselJ[0, 23 ρ]^2 BesselJ[5, 23 ρ]^2
ρ BesselJ[1, 23 ρ]^2 BesselJ[5, 23 ρ]^2