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Extremal single-charge small black holes: Entropy function analysis
We study stretched horizons of the type AdS_2 x S^8 for certain spherically
symmetric extremal small black holes in type IIA carrying only D0-brane charge
making use of Sen's entropy function formalism for higher derivative gravity. A
scaling argument is given to show that the entropy of this class of black holes
for large charge behaves as \sqrt{|q|} where q is the electric charge. The
leading order result arises from IIA string loop corrections. We find that for
solutions to exist the force on a probe D0-brane has to vanish and we prove
that this feature persists to all higher derivative orders. We comment on the
nature of the extremum of these solutions and on the sub-leading corrections to
the entropy. The entropy of other small black holes related by dualities to our
case is also discussed.Comment: 19 pages, v2:typos corrected and references adde