On the creation of the universe via ekpyrotic instantons

Battarra, Lorenzo; Lehners, Jean-Luc

doi:10.1016/j.physletb.2015.01.028

Cited by 30 publications

(44 citation statements)

References 22 publications

(38 reference statements)

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“…An obvious extension will be the inclusion of other types of matter, such as pressurefree matter and scalar fields with nontrivial potentials. In particular it will be interesting to revisit previous uses of instantons, in both inflationary [4] and ekpyrotic [31,32] cosmologies, as well as attempts to describe quantum transitions between contraction and expansion in such models [33], in the light of Picard-Lefschetz theory. In this context, exactly solvable models such as those of [34,35] may provide useful insight.…”

Section: Discussionmentioning

confidence: 99%

“…In the following sections we concentrate on spherical expanding universes. We study the saddle point approximation (31) in four qualitatively different configurations:…”

Section: Minisuperspace Lorentzian Path Integralmentioning

confidence: 99%

“…Given that the third derivative is real-valued and positive, we can determine the directions of the upward and downward flow, as indicated in Since for the boundary condition q 0 = 3 Λ the function h is not a Morse function, i.e. h has two degenerate critical points, the saddle point approximation of equation (31) does not apply. However, using the integral +∞ 0 dne −k n 3 = Γ( 4 3 )k −1/3 , we can approximate…”

Section: Boundary Conditions At the Classical Limitmentioning

confidence: 99%

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Lorentzian quantum cosmology

2017

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We argue that the Lorentzian path integral is a better starting point for quantum cosmology than the Euclidean version. In particular, we revisit the mini-superspace calculation of the Feynman path integral for quantum gravity with a positive cosmological constant. Instead of rotating to Euclidean time, we deform the contour of integration over metrics into the complex plane, exploiting Picard-Lefschetz theory to transform the path integral from a conditionally convergent integral into an absolutely convergent one. We show that this procedure unambiguously determines which semiclassical saddle point solutions are relevant to the quantum mechanical amplitude. Imposing "no-boundary" initial conditions, i.e., restricting attention to regular, complex metrics with no initial boundary, we find that the dominant saddle contributes a semiclassical exponential factor which is precisely the inverse of the famous Hartle-Hawking result. * Electronic address: jfeldbrugge@perimeterinstitute.ca † Electronic address: jlehners@aei.mpg.de ‡ Electronic address: nturok@perimeterinstitute.ca

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Section: Discussionmentioning

confidence: 99%

“…In the following sections we concentrate on spherical expanding universes. We study the saddle point approximation (31) in four qualitatively different configurations:…”

Section: Minisuperspace Lorentzian Path Integralmentioning

confidence: 99%

Section: Boundary Conditions At the Classical Limitmentioning

confidence: 99%

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Lorentzian quantum cosmology

2017

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“…The visual methods employed here, and which were developed in [18][19][20], have the great advantage of allowing one to see by eye where the singularities are located, and thus clearly show in what manner the choice of contour is crucial. With the right contour, we have been able to construct anisotropic instantons with any desired final anisotropy parameters.…”

Section: A Existence and Basic Features Of Anisotropic Instantonsmentioning

confidence: 99%

“…A non-trivial feature is however that care must be taken in choosing a contour of integration in the complex time plane, as for increasing anisotropies singularities start to appear, and the standard contour (originally employed by Hawking since the earliest works [3]) becomes inappropriate. The visual methods developed in [18][19][20] are well suited to reveal this feature, and readily suggest better contours.…”

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confidence: 99%

Wavefunction of anisotropic inflationary universes with no-boundary conditions

2017

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We study the emergence of anisotropic (Bianchi IX) inflationary universes with noboundary conditions in the path integral approach to quantum gravity. In contrast to previous work, we find no evidence for any limit to how large the anisotropies can become, although for increasing anisotropies the shape of the instantons becomes significantly different from Hawking's original no-boundary instanton. In all cases an inflationary phase is reached, with the anisotropies decaying away. Larger anisotropies are associated with a much larger imaginary part of the action, implying that the highly anisotropic branches of the wavefunction are heavily suppressed. Interestingly, the presence of anisotropies causes the wavefunction to become classical much more slowly than for isotropic inflationary universes. We derive the associated scaling of the WKB classicality conditions both numerically and analytically. a sebastian.bramberger@aei.mpg.de b

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Kerr-NUT-de Sitter as an inhomogeneous non-singular bouncing cosmology

Anabalón

Bramberger

Lehners

2019

J. High Energ. Phys.

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We present exact non-singular bounce solutions of general relativity in the presence of a positive cosmological constant and an electromagnetic field, without any exotic matter. The solutions are distinguished by being spatially inhomogeneous in one direction, while they can also contain non-trivial electromagnetic field lines. The inhomogeneity may be substantial, for instance there can be one bounce in one region of the universe, and two bounces elsewhere.Since the bounces are followed by a phase of accelerated expansion, the metrics described here also permit the study of (geodesically complete) models of inflation with inhomogeneous "initial" conditions. Our solutions admit two Killing vectors, and may be re-interpreted as the pathology-free interior regions of Kerr-de Sitter black holes with non-trivial NUT charge.Remarkably enough, within this cosmological context the NUT parameter does not introduce any string singularity nor closed timelike curves but renders the geometry everywhere regular, eliminating the big bang singularity by means of a bounce.

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On the creation of the universe via ekpyrotic instantons

Cited by 30 publications

References 22 publications

Lorentzian quantum cosmology

Lorentzian quantum cosmology

Wavefunction of anisotropic inflationary universes with no-boundary conditions

Kerr-NUT-de Sitter as an inhomogeneous non-singular bouncing cosmology

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