Signed martingale measure
= Signed martingale measure
{title2=$\mathbb E Z=1,\quad\mathbb E[ZY]=0$}
A finite <signed measure> with total mass one under which discounted asset gains have zero integrals. Its density can be negative, so it need not be a <probability measure> or give arbitrage-free prices to every nonnegative <contingent claim>. A square-integrable signed density is useful in <one-period least-squares hedging>, even when it is not an <equivalent martingale measure>.