Let $\phi:\mathbb{R}\to\mathbb{R}$ be an even function with support on $[-1,1]$. Assume that it is in $L^1\cap L^2$ and that its Fourier transform is also in $L^1\cap L^2$. Assume as well that $|\phi|_\infty = \phi(0)=1$. Define $F(x) = \int_x^\infty \widehat{\phi}(t) dt$. 

Given these constraints, what is the choice of $\phi$ that minimizes
$$\int_0^\infty |F(x)| dx?$$

(a) What is the value of that minimum?

(b) A possibly easier problem is to minimize
$$\int_0^\infty F(x) dx,$$
which of course equals
$$\int_0^\infty t \widehat{\phi}(t) dt.$$

(c) A possibly easier problem (in some sense a special case of (b)) is the following: let $g:\mathbb{R}\to \mathbb{R}$ be an even function with $L^2$-norm $|g|_2=1$ and support on $[-1/2,1/2]$. Choose $g$ so as to minimize $$\int_{\mathbb{R}} |x| |\widehat{g}(x)|^2 dx.$$

These are clearly questions of uncertainty-principle type.