We study classical closed bosonic strings probing the near-horizon region of a non-extremal black hole and show that this corresponds to understanding string theory in the Carroll regime. This is done by first performing a Carroll expansion and then a near-horizon expansion of a closed relativistic string, subsequently showing that they agree. Concretely, we expand the phase space action in powers of $c^2$, where $c$ is the speed of light, assuming that the target space admits a string Carroll expansion (where two directions are singled out) and show that there exist two different Carroll strings: a magnetic and an electric string. The magnetic string has a Lorentzian worldsheet, whereas the worldsheet of the electric string is Carrollian. The geometry near the horizon of a four-dimensional (4D) Schwarzschild black hole takes the form of a string Carroll expansion (a 2D Rindler space fibred over a 2-sphere). We show that the solution space of relativistic strings near the horizon bifurcates and the two sectors precisely match with the magnetic/electric Carroll strings with an appropriate target space. Magnetic Carroll strings near a black hole shrink to a point on the two-sphere and either follow null geodesics or turn into folded strings on the 2D Rindler spacetime. Electric Carroll strings wrap the two-sphere and follow a massive geodesic in the Rindler space. Finally, we show that 4D non-extremal Kerr and Reissner-Nordström black holes also admit string Carroll expansions near their outer horizons, indicating that our formulation extends to generic non-extremal black holes.
Carrollian Worldsheets on Carrollian Targets, When does ILST describe a null string theory?
School of Physics, Institute for Research in Fundamental Sciences (IPM)（基础科学研究所物理学院）；Beijing Institute of Mathematical Sciences and Applications (BIMSA)（北京数学与应用数学研究所）
Strings near BTZ black holes: A Carrollian Chronicle
Birla Institute of Technology and Science, Pilani Campus（比拉理工学院皮拉尼校区）；Indian Institute of Technology Kanpur（坎普尔印度理工学院）；Indian Institute of Science Education and Research, Mohali（莫哈利印度科学教育与研究学院）；Tata Institute of Fundamental Research（塔塔基础研究所）
Null Strings Gauged and Reloaded, II: Consistent Classical Treatment of the Null Strings
School of Physics, Institute for Research in Fundamental Sciences (IPM)（基础科学研究所物理学院）；Beijing Institute of Mathematical Sciences and Applications (BIMSA)（北京国际数学研究中心）
Large-$N$ Carrollian Thermodynamics from AdS Black-Hole Phase-Space Contractions
Zhongtai Securities Institute for Financial Studies, Shandong University（山东大学中泰金融研究院）；Department of Physics, Southern Methodist University（南方卫理公会大学物理系）；School of Statistics, Dongbei University of Finance and Economics（东北财经大学统计学院）
School of Physics, Institute for Research in Fundamental Sciences (IPM)（基础科学研究院物理学院）；Beijing Institute of Mathematical Sciences and Applications (BIMSA)（北京数学科学及应用研究院）
Null Strings Gauged and Reloaded, I: Null Strings Have Carroll-Weyl Gauge Symmetry
School of Physics, Institute for Research in Fundamental Sciences (IPM)（基础科学研究所物理学院）；Beijing Institute of Mathematical Sciences and Applications (BIMSA)（北京数学科学与应用研究院）
Path integral quantization of null bosonic strings with Carroll-Weyl ghosts
Yau Mathematical Sciences Center (YMSC), Tsinghua University（丘成桐数学科学中心，清华大学）；Harish-Chandra Research Institute, A CI of Homi Bhabha National Institute（哈里什-昌德拉研究所，霍米·巴巴国立学院下属机构）
Indian Institute of Technology Kanpur（坎普尔印度理工学院）；Birla Institute of Technology and Science, Pilani Campus（比拉理工科学与技术学院皮拉尼校区）；Asia Pacific Center for Theoretical Physics, Postech（韩国高等科学技术研究所亚太理论物理中心）；University of Victoria（维多利亚大学）；Saha Institute of Nuclear Physics（萨哈核物理研究所）；Homi Bhabha National Institute（霍米·巴巴国立研究所）
