Dynamical Triangulation Approach to Regge Calculus  

In General
* Idea: Fix the edge lengths and vary the triangulation by adding/removing simplices with well-defined moves.
* Motivation: Supposed to be ergodic in the space of geometries, and one expects to be able to get many more.
* Drawbacks: Recovery of EH more problematic, since diffeomorphism invariance is lost.
* Action (4D): Given by I = 2 N2 – 10 N4, with = arcos(1/5), Nn = number of n-simplices.
* 2D: Dynamical triangulations are equivalent to matrix models.
* Phase transition: As one changes the curvature (Newton) coupling, between an elongated and a crumpled phase.

References
@ General: Godfrey & Gross PRD(91) [more than 2D]; Ambjørn & Jurkiewicz PLB(92); Nabutovsky & Ben-Av CMP(93) [4D, non-computability]; Ambjørn CQG(95) [2D]; Ambjørn et al ht/96; Schleich & Witt gq/96-in [quantum]; Bialas et al NPPS(98)gq/97.
@ 3D: Carfora & Marzuoli IJMPA(93) [and Reidemeister torsion]; Egawa & Tsuda PLB(98) [random surfaces].
@ Random surfaces: David et al NPB(87) [critical exponents]; Migdal JGP(88).
@ Related topics: Renken NPB(97)hl/96 [renormalization group]; Catterall et al PLB(98) [singular geometries].
@ Phase structure, transitions: Agishtein & Migdal NPB(92), MPLA(92); Varsted NPB(94) [and continuum limit]; Brügmann & Marinari JMP(95) [no exponential bound]; de Bakker PLB(96) [phase transition, first-order]; Renken et al NPB(98), Warner et al PLB(98) [3D]; Warner & Catterall PLB(00)hl [4D, with boundary].
@ Euclidean: Brügmann PRD(93), & Marinari PRL(95) [4D, measure]; Ambjørn et al JMP(95)ht [2D]; Veselov & Zubkov PLB(04) [10D].

Lorentzian / Causal Dynamical Triangulations > s.a. Potts Model [coupled to gravity].
@ Reviews: Ambjørn et al CP(06)ht/05, ht/06-in; Alpert SA(07)feb; Loll a0711-in; Ambjørn et al SA(08)jul.
@ General references: Markopoulou & Smolin NPB(06)ht/04 [varying lapse]; Benedetti a0707-PhD [analytical].
@ 2D: Ansari & Markopoulou NPB(05)ht [as a spin system]; Loll et al ht/06-in [sum over topologies]; Zohren ht/06-MS [analytic results, rev]; Benedetti & Loll GRG(07)gq/06 [counting graphs, and matter behavior]; Ambjørn et al JHEP(07)-a0709 [with partial lifting of causality constraint] Ambjørn et al PLB(08) [matrix model representation]; > s.a. cosmological constant problem, topology change.
@ 3D: Ambjørn et al NPB(01)ht [and 4D]; Ambjørn et al NPPS(02)hl; Dittrich & Loll PRD(02); Konopka PRD(06)ht/05 [varying lapse]; Benedetti et al PRD(07)-a0704 [continuum limit and Hamiltonian].
@ 4D: Ambjørn et al PRL(04)ht; Ambjørn et al a0712 [birth of quantum de Sitter universe].


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