Small Schwarzschild de Sitter black holes, quantum extremal surfaces and islands

We study 4-dimensional Schwarzschild de Sitter black holes in the regime where the black hole mass is small compared with the de Sitter scale. Then the de Sitter temperature is very low compared with that of the black hole and we study the black hole, approximating the ambient de Sitter space as a frozen classical background. We consider distant observers in the static diamond, far from the black hole but within the cosmological horizon. Using 2-dimensional tools, we find that the entanglement entropy of radiation exhibits linear growth in time, indicative of the information paradox for the black hole. Self-consistently including an appropriate island emerging at late times near the black hole horizon leads to a reasonable Page curve. There are close parallels with flat space Schwarzschild black holes in the regime we consider.

Automated summary

We study 4-dimensional Schwarzschild de Sitter black holes in the regime where the black hole mass is small compared with the de Sitter scale. Then the de Sitter temperature is very low compared with that of the black hole. We find that the entanglement entropy of radiation exhibits linear growth in time, indicative of the information paradox for the black hole. Self-consistently including an appropriate island emerging at late times near the black hole horizon leads to a reasonable Page curve. There are close parallels with flat space Schwarzschild black holes in the regime we consider.