Abstract :
Extremal BPS-saturated black holes in N = 2, d = 4 supergravity can carry electric and magnetic charges (q(m)Λ, qΛ(e)). It is shown that in smooth cases the moduli fields at the horizon take a fixed “rational” value XΛ(q(m), q(e)) which is determined by the charges and is independent of the asymptotic values of the moduli fields. A universal formula for the Bekenstein-Hawking entropy is derived in terms of the charges and the moduli space geometry at XΛ(q(m), q(e)). This work extends previous results of Ferrara, Kallosh and the author for the pure magnetic case.
