I have to show that for $\Re(\mu)>0$, $$\int_0^\infty x^2e^{-\mu x^2}\ln x\, \mathrm dx=\frac{1}{8\mu}(2-\ln 4\mu-C)\sqrt{\frac{\pi}{\mu}}$$
Source - Table of integrals, series, and products by I S Gradshteĭn on page number $605$
My attempt - \begin{align}\int_0^\infty x^2 e^{-\mu x^2}\ln x\, \mathrm dx&=\frac{1}{2}\int_0^\infty \sqrt{x}e^{-\mu x}\ln x\, \mathrm dx\, \text{ ,via substituting $x^2\mapsto x$}\end{align} Now, the Laplace Transform of $\ln x$ is $f(\mu)=-\frac{\ln(\mu)+\gamma}{\mu}$. And we have the result that $$\mathcal{L}(x^n \ln x)=(-1)^n f^n(\mu)$$ And here $n=\frac{1}{2}$. So, $$\mathcal{L}(x^{1/2}\ln x)=(-1)^{1/2}f^{1/2}(\mu)$$ How can I find the half derivative? It seems extremely absurd. Wolfram Alpha nth derivative calculator also says 'input not valid'.
Questions :
$1.$ Is my approach valid? Is my approach not yielding something?
$2.$ Are there any other approaches to solve this question?
The method chosen by the author of the problem is valid, makes use of transforms, and leads to having to use fractional calculus. This solution is more straight forward.
Also note that older books, like I S Gradshteĭn's tome, uses $C$ as the Euler-gamma constant while others use the more common $\gamma$.
Consider the integral $$ I(s, \alpha) = \int_{0}^{\infty} e^{- s \, t} \, t^{\alpha -1} \, dt = \frac{\Gamma(\alpha)}{s^\alpha}. $$ Differentiate the integral with respect to $\alpha$ to obtain \begin{align} \int_{0}^{\infty} e^{-s \, t} \, \partial_{\alpha} (t^{\alpha -1}) \, dt &= \partial_{\alpha} \left(\frac{\Gamma(\alpha)}{s^\alpha}\right) \\ \int_{0}^{\infty} e^{-s \, t} \, t^{\alpha -1} \, \ln(t) \, dt &= \frac{\Gamma(\alpha)}{s^{\alpha}} \, (\psi(\alpha) - \ln(s)). \end{align} Now let $ t = x^2$ to obtain $$ \int_{0}^{\infty} e^{-s \, x^2} \, x^{2 \alpha -1} \, \ln(x) \, dx = \frac{\Gamma(\alpha)}{4 \, s^{\alpha}} \, (\psi(\alpha) - \ln(s)). $$ When $\alpha = 3/2$ the integral reduces to $$ \int_{0}^{\infty} e^{-s \, x^2} \, x^{2} \, \ln(x) \, dx = \frac{\Gamma(3/2)}{4 \, s^{3/2}} \, (\psi(3/2) - \ln(s)). $$ Since $\psi(3/2) = 2 - \gamma - \ln(4)$, where $\gamma$ is the Euler-gamma constant, then $$ \int_{0}^{\infty} e^{-s \, x^2} \, x^{2} \, \ln(x) \, dx = \frac{1}{8 \, s} \, \sqrt{\frac{\pi}{s}} \, (2 - \gamma - \ln(4s)). $$