Boundary Conditions in Quantum Cosmology| Boundary Conditions in Quantum Cosmology |
In General
> s.a. quantum cosmology [Lorentzian].
* Requirements: Existence of a
classical world (the density matrix must 'decohere' to get classical probabilities);
Homogeneity, isotropy, right spectrum of fluctuations, enough inflation.
* Some possibilities: In addition to the
ones below, proposals include Penrose's Weyl Tensor Proposal; Brout, Englert (cooperative
process) Fischler, Susskind; Narlikar-Padmanabhan; Tipler's Explosion from Nothing.
@ General references: Hartle in(86);
Zhuk CQG(88);
Moss & Poletti NPB(90);
Vilenkin AIP(99)gq/98;
Avramidi & Esposito gq/99-conf;
Tipler ap/01 [unique initial state];
Coule CQG(05)gq/04 [rev];
Page ht/06-MGXI;
Maydanyuk EPJC(08)-a0707;
Jalalzadeh & Moniz PRD(14)-a1403 [boundary proposals and the algebra of Dirac observables];
Magueijo PRD(20)-a2005 [equivalence between some boundary conditions in minisuperspace].
@ In lqg: Bojowald GRG(03)gq;
Bojowald & Vandersloot PRD(03)gq,
gq/03-MGX;
Coule gq/03 [comparison];
> s.a. signature change.
@ Phenomenology: Suenobu & Nambu GRG(17)-a1603
[numerical solution of the WDW equation, and inflationary number of e-foldings].
@ For perturbations:
Giovannini CQG(03).
Universe-from-Nothing Proposals
> s.a. hartle-hawking no-boundary proposal.
* Vilenkin's tunneling
wavefunction: Solve the Wheeler-DeWitt equation imposing that the wave
function have only outgoing waves on the singular boundary of superspace.
@ General references:
Vilenkin PLB(82),
PRD(83);
Zel'dovich & Starobinskii (84); Grishchuk (84);
Vilenkin PRD(84),
PRD(86),
PRD(94)gq;
Garriga & Vilenkin PRD(97)gq/96 [black hole pair production];
Berman & Trevisan IJMPD(10)gq/01;
Blanco-Pillado et al JCAP(12);
He et al PRD(14)-a1404 [argument from explicit solution of the Wheeler-DeWitt equation];
Kohli a1405 [comments on Krauss' book];
Battarra & Lehners PLB(15)-a1406 [in ekpyrotic cosmological theories].
@ From tunneling: Kandrup & Mazur IJMPA(91) [semiclassical, rev];
Dąbrowski & Larsen PRD(95)gq [FLRW];
Labraña PRD(12)-a1111;
Feldbrugge et al PRL(17)-a1705 [semi-classical description untenable];
Vilenkin & Yamada PRD(18)-a1808 [three approaches];
Vilenkin & Yamada PRD(19)-a1812 [the backreaction problem];
Matsui a2102 [Lorentzian path integral and WKB approximation];
> s.a. CMB anisotropies.
@ And the cosmological constant: Coule MPLA(95)gq/94;
Barvinsky & Kamenshchik PRD(06)ht;
Ambjørn & Watabiki MPLA(17)-a1709 [based on a W\(_3\) symmetry].
@ And inflation: Vilenkin PRD(98)gq,
gq/02-proc [vs Hartle-Hawking proposal];
Coule & Martin PRD(00) [open universe].
> Related topics: see inflation and
planck-scale physics; gravitational instantons; Nothing.
Other Proposals
> s.a. Penrose's Weyl Curvature Hypothesis.
* Linde's continuous regeneration:
The Hartle-Hawking and tunneling wave functions are seen as approximations valid
in some regimes; a modified inflation with continuous generation of bubbles
(with different dimensionality, physical constants, ...) is the thing.
@ Mixed state from Euclidean quantum gravity:
Barvinsky & Kamenshchik JPA(07) [quasi-thermal state].
@ Related topics: Conradi PRD(92);
Bouhmadi-Lopez & Vargas Moniz gq/07-MGXI [thermal boundary conditions].
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