Global solutions for higher-dimensional stretched small black holes

Understand

Small black holes in heterotic string theory have vanishing horizon area at the supergravity level, but the horizon is stretched to the finite radius $AdS_2 \times S^{D-2}$ geometry once higher curvature corrections are turned on.

• This has been demonstrated to give good agreement with microscopic entropy counting.
• Previous considerations, however, were based on the classical local solutions valid only in the vicinity of the event horizon.
• Here we address the question of global existence of extremal black holes in the $D$-dimensional Einstein-Maxwell-Dilaton theory with the Gauss-Bonnet term introducing a variable dilaton coupling $a$ as a parameter.