Dimensional Reduction of Four-Dimensional Reissner–Nordström Black Hole Spacetime:
The theoretical description of black hole radiation has long presented a fundamental challenge in gravitational physics. Conventional analyses have relied primarily on the semiclassical approximation, in which quantum fields are treated on a fixed classical background, owing to the considerable difficulties involved in treating gravitational effects at high-energy, near-Planckian scales. While this approach has proven successful in deriving the leading-order behavior of Hawking radiation, it is widely recognized as insufficient for capturing the full quantum-gravitational structure of the emission process, particularly in regimes where backreaction become significant.
Recently, however, [Brown et al. JHEP, vol. 2026, (2026) 109] presented an analysis of Hawking radiation that goes beyond the semiclassical treatment by employing two-dimensional Jackiw–Teitelboim (JT) gravity. JT gravity is a gravitational theory formulated in two spacetime dimensions and characterized by the presence of a dilaton field; it has attracted considerable attention as a tractable model capturing the near-horizon dynamics of nearly extremal black holes, including their quantum-gravitational corrections.
Their study demonstrates that the radiation of neutral particles is substantially modified by the Schwarzian mode, a term characteristic of the JT gravitational action This modification is not merely a small correction but alters the emission spectrum in a qualitatively significant manner, indicating that the semiclassical picture omits physically important contributions. This result therefore suggests that an accurate treatment of gravity in this context must incorporate microscopic, Planck-scale effects that are ordinarily neglected in semiclassical approaches.
To understand this finding, the present work introduces the dimensional reduction procedure that underlies the analysis of the radiation. Specifically, by reducing the four-dimensional gravitational action of the Reissner–Nordström spacetime to two-dimensional one through integration over the angular degrees of freedom, the Schwarzian term, central to the calculation of the radiation is obtained explicitly. This derivation clarifies how the effective two-dimensional dynamics responsible for the modified radiation spectrum emerge directly from the underlying four-dimensional theory of gravity.
In my talk, the dimensional reduction procedure, which provide a foundation for understanding how the quantum-gravitational corrections to black hole radiation arise from, and are constrained by, the geometry of the original four-dimensional spacetime, is presented in detail.
Breaking of the selection rule by non-perturbative effects:
Non-invertible symmetries obey selection rules that cannot be fully described by ordinary group theory. Although these selection rules are known to be violated by perturbative loop effects, their violation by non-perturbative effects has not been sufficiently investigated. In this work, I study how D-brane instanton effects violate the non-invertible selection rule and derive the resulting textures explicitly.