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Baby Universes and Worldline Field Theories

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arxiv 2101.12221 v4 pith:NLTZR4BK submitted 2021-01-28 hep-th gr-qc

Baby Universes and Worldline Field Theories

classification hep-th gr-qc
keywords quantumgravityalgebraassociatedchoicescomparisonsfieldpath
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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The quantum gravity path integral involves a sum over topologies that invites comparisons to worldsheet string theory and to Feynman diagrams of quantum field theory. However, the latter are naturally associated with the non-abelian algebra of quantum fields, while the former has been argued to define an abelian algebra of superselected observables associated with partition-function-like quantities at an asymptotic boundary. We resolve this apparent tension by pointing out a variety of discrete choices that must be made in constructing a Hilbert space from such path integrals, and arguing that the natural choices for quantum gravity differ from those used to construct QFTs. We focus on one-dimensional models of quantum gravity in order to make direct comparisons with worldline QFT.

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Cited by 2 Pith papers

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  1. The $\alpha$-states of a string worldsheet

    hep-th 2026-07 conditional novelty 6.0

    The α-states of the Hurwitz worldsheet are symmetric-group characters weighted by the Poissonized Plancherel measure, so string amplitudes are ensemble averages whose weak-coupling limit is Kerov's central limit theorem.

  2. Gravitational Hilbert spaces: invariant and co-invariant states, inner products, gauge-fixing, and BRST

    hep-th 2025-09 unverdicted novelty 4.0

    Reviews construction of physical inner products in canonical quantum gravity via group averaging and BRST formalism, illustrated in mini-superspace models and connected to path integrals.