Fuzzball geometries and higher derivative corrections for extremal holes Original Research Article

2-charge D1–D5 microstates are described by geometries which end in ‘caps’ near image; these caps reflect infalling quanta back in finite time. We estimate the travel time for 3-charge geometries in 4D, and find agreement with the dual CFT. This agreement supports a picture of ‘caps’ for 3-charge geometries. We argue that higher derivative corrections to such geometries arise from string winding modes. We then observe that the ‘capped’ geometries have no non-contractible circles, so these corrections remain bounded everywhere and cannot create a horizon or singularity.