Security Market Line
Also called: SML, CAPM line
The security market line plots expected return against beta, and under CAPM every fairly priced asset sits exactly on it. Assets above the line are underpriced, below it overpriced — which is the formal definition of alpha. Empirically the real line is flatter than theory predicts: low-beta stocks have earned more and high-beta stocks less than CAPM says, the low-volatility anomaly that leverage constraints are thought to cause.
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