Compute $\int_0^{+\infty} \frac{e^{-t}}{t^4+1}dt$

calculuscomplex-analysisdefinite integralsimproper-integralsintegration

Problem:

Compute $\int_0^{+\infty} \frac{e^{-t}}{t^4+1}dt$ possibly using Residue Theorem. I got this problem solving and understanding the following:

Compute $\int_0^{+\infty}\frac{\sin x + \cos x}{x^4+1}dx$

My attempt:

I tried defining $f(z)=\frac{e^{-z}}{z^4+1}$ and integrating in the first quadrant in an opportune slice, but I cannot reach any results. Is there a way to compute this integral?

Best Answer

Without complex analysis or residues, you can compute the antiderivative.

Use the roots of unity and then partial fraction decomposition to face four integrals looking like $$I_a=\int \frac {e^{-t}}{t+a}$$ where $a$ is a complex number. This makes $$I_a=e^a\, \text{Ei}(-(t+a))$$

For sure, the final result is not very pretty $$\int_0^{+\infty} \frac{e^{-t}}{t^4+1}dt=\frac{1}{4 \sqrt{2} \pi ^{3/2}}\,\,G_{1,5}^{5,1}\left(\frac{1}{256}\right.\left| \begin{array}{c} \frac{3}{4} \\ 0,\frac{1}{4},\frac{2}{4},\frac{3}{4},\frac{3}{4} \end{array} \right)$$ where appears the Meijer G function.

Numerically, this is $0.63047783491849835735$ which is not recognized by inverse symbolic calculators.

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