# Extremal Limits and Black Hole Entropy

 Title: Extremal Limits and Black Hole Entropy Author: Randall, Lisa; Johnson, Matthew; Carroll, Sean Note: Order does not necessarily reflect citation order of authors. Citation: Carroll, Sean, Matthew C. Johnson, and Lisa Randall. 2009. Extremal limits and black hole entropy. Journal of High Energy Physics 2009(11): 109. Full Text & Related Files: 0901.0931v2.pdf (215.6Kb; PDF) Abstract: Taking the extremal limit of a non-extremal Reissner-Nordstrom black hole (by externally varying the mass or charge), the region between the inner and outer event horizons experiences an interesting fate--while this region is absent in the extremal case, it does not disappear in the extremal limit but rather approaches a patch of $$AdS_2 \times S^2$$. In other words, the approach to extremality is not continuous, as the non-extremal Reissner-Nordstrom solution splits into two spacetimes at extremality: an extremal black hole and a disconnected $$AdS$$ space. We suggest that the unusual nature of this limit may help in understanding the entropy of extremal black holes. Published Version: doi:10.1088/1126-6708/2009/11/109 Other Sources: http://arxiv.org/abs/0901.0931 Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:8015828 Downloads of this work: