Multiway junction conditions: Jackiw-Teitelboim gravity

TL;DR

This paper systematically analyzes multiway junctions in Jackiw-Teitelboim gravity, classifying dilaton configurations, deriving junction conditions, and determining interface geometries based on dilaton behavior.

Contribution

It provides a complete solution to multiway junction conditions in JT gravity, classifies dilaton solutions, and elucidates the geometric and physical constraints at interfaces.

Findings

Dilaton configurations are classified into three types: attractive, repulsive, neutral.

Sufficient attractive dilaton bulks are required for junctions to be allowed.

Explicit interface shapes and dilaton forms are derived for various configurations.

Abstract

A booklet is a geometric structure formed by gluing multiple bulk spacetimes along a common interface and imposing gravitational consistency conditions at the junction. We have systematically investigated the properties of booklet structures, constructed the booklet geometry, and derived the multiway junction conditions applicable at the interface. In this work, we provide a complete solution to the multiway junction conditions for booklets composed of bulks governed by JT gravity. By constructing invariants of the dilaton solution space, we classify all dilaton configurations into three inequivalent types, each exhibiting attractive, repulsive, or neutral behavior. Through continuous isometric transformations, each type is fixed to a standard form characterized by a single physical parameter, effectively eliminating redundant degrees of freedom. This process selects a distinguished class of Poincar\'e coordinates for each type. Expanding the constraint equations order by order breaks coordinate invariance beyond the leading and subleading orders. By jointly solving the junction and continuity conditions up to subleading order, we find that junctions are only allowed when a sufficient number of bulks carry attractive dilatons, as captured quantitatively by a equilibrium condition. We further analyze all possible combinations of different dilaton types and determine the shape of the interface along with the explicit form of the dilaton defined on it.