In General > s.a. 3D manifolds [prime factors]; general relativity solutions; Mapping Class.
* History: A precursor was given by the concept of gravitational bag; The original meaning of the term, as used by Wheeler, referred to non-topological geons.
> Similar concepts: see Defects; Kinks.

Non-Topological > s.a. Boson Stars; Galileon Field; solitons.
* Idea: An object with particle-like properties made out of the spacetime metric, and possibly other fields.
@ General references: Wheeler PR(55); Power & Wheeler RMP(57) [thermal]; Brill & Hartle PR(64) [gravitational waves].
@ Modified gravity: Vollick CQG(08)-a0807, CQG(10)-a1004 [1+1 Jackiw-Teitelboim theory with higher-order corrections]; Afonso et al a1705 [Born-Infeld gravity].
@ Gravity + scalar field: Barreto et al PRD(96)gq/05 [turning point instability]; Sones gq/05 [+ electromagnetism].
@ Related topics: Cooperstock et al MPLA(95) [non-existence], IJMPD(96)gq/95 [critical analysis of Brill-Hartle geon]; Perry & Cooperstock CQG(99)gq/98 [stability]; > s.a. anti-de sitter spacetime [instability].

Topological (More recent meaning) > s.a. CPT symmetry; measurement in quantum theory; spin-statistics theorem.
* Idea: An object with particle-like properties made out of spatial geometry; Part of the motivation is that one may be able to account for some non-gravitational charges (e.g., electric charge) using topology.
* Remark: The concept is similar to that of gravitational "kink", but the latter is used to describe a topologically non-equivalent metric tensor fields defined on a given fixed manifold.
* Types: They can be spinorial, fermionic, possibly chiral; Some can switch between bosonic and fermionic behavior after interactions.
* Question: Can they be preons?
* Example: Wheeler's "single wormhole mouth" (not "quasi-localized").
@ General references: Finkelstein & Misner AP(59); Finkelstein JMP(66); Cohen & Wald JMP(72); Sorkin JPA(77); Shastri et al IJTP(80); Whiston JPA(81) [classification, including fermionic]; Williams & Finkelstein IJTP(84); Bais et al NPB(87); Sorkin in(86), in(89); Bugajska IJTP(87); Dunn et al JMP(91); Williams & Zvengrowski JMP(92); Dunn et al JMP(96) [geodesic incompleteness]; Anderson & Brill PRD(97)gq/96; Balachandran et al GRG(11)-a1009 [and non-commutative spacetimes].
@ Phenomenology: Srivastava PRD(87); Olmo & Rubiera-García JCAP(14) [at particle accelerators].
@ Solutions: Harriott & Williams GRG(03) [4D rotating kink]; Louko et al CQG(05)gq/04 [with spin and charge]; > s.a. black-hole solutions.
@ With cosmological constant: Dunn & Williams JMP(89), et al JMP(94) [locally de Sitter].
@ In 1+1 dimensions: Vasilić & Vukašinac CQG(96); Klösch & Strobl PRD(98)gq/97.
@ In 2+1 dimensions: Harriott & Williams NCB(05) [kink number]; Stevens et al CQG(09)-a0809 [no asymptotically flat ones]; Galloway et al CMP(12)-a1005 [non-existence result].

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