Abstract:
Let $X$ be a random variable. For any $r>0$, we set $\beta_r=\mathbf E|X|^r$. The following inequality is proved:
$$
\beta_r^{1/r}\le\gamma^{1/r-1/s}\beta_s^{1/s}\quad(r<s)
$$
where $\gamma=\mathbf P(X\ne0)$. This inequality is optimal in a certain sense.