I'm looking for the following second derivative
$$ \kappa_2 := \left . \frac{d^2}{d\lambda^2} \ln \left({_2F_1}\!\left(\tfrac{1}{2},\,- \lambda;\,1;\,\alpha\right)\right) \right \vert_{\lambda = 0} , $$
where $\alpha$ is a real parameter in $[0,1]$. As you may have guessed I'm trying to compute the variance of a certain probability distribution.
The first moment is simple and is given by
$$ m_1 = 2 \ln \frac{1 + \sqrt{1-\alpha}}{2}. $$
The second moment can be shown to be equal to the following
$$ m_2 = \frac{2}{\pi} \int_{0}^{1} \frac{\left [ \ln(1-\alpha y^2) \right ]^2}{\sqrt{1-y^2}} dy $$
Mathematica can evaluate the above integral in terms of various function and polylogarithms (in fact dilogarithms). However the resulting expression is not even manifestly real. The above integral expression for $m_2$ is so far the best I found to deal with but there are many others. In essence I am trying to find a "nice" expression for that integral ($m_2$).
I'd be happy if I'm given an expression which is manifestly real. I suspect that the combination $\kappa_2 = m_2 - (m_1)^2 $ (which is equal to the first equation) might look nicer and that some identity involving dilogarithms should be used.
Added
An alternative representation for $m_2$ (obtained using the series of the Hypergeometric) is the following
$$ m_{2}=2\sum_{n=2}^{\infty}\left(\begin{array}{c} -1/2\\ n \end{array}\right)\frac{H_{n-1}}{n}\left(-\alpha\right)^{n} \, , $$
where $H_n$ are the Harmonic numbers, i.e.
$$ H_n \, = \, \sum_{p=1}^n \frac{1}{p} $$
So far this is the best I could get:
$$ \kappa_2 \,=\, -4 \log ^2\left(\sqrt{1-\alpha }+1\right)+4 \log \left(4-4 \sqrt{1-\alpha }\right) \log \left(\sqrt{1-\alpha }+1\right)+4 i \pi \log \left(\frac{2}{\sqrt{1-\alpha }+1}\right)+4 \log (2) \log \left(\frac{1}{\alpha }\right)+4 \text{Li}_2\left(\frac{2 \left(\sqrt{1-\alpha }+1\right)}{\alpha }\right)-4 \text{Li}_2\left(\frac{-\alpha +2 \sqrt{1-\alpha }+2}{\alpha }\right) $$
I would like to avoid the explicitly imaginary (third) term which is compensated by the dilogarithm to produce a real result. Does anybody know an identity for dilogarithm that can be used here?