Zobrazeno 1 - 10
of 56
pro vyhledávání: '"Steffen Gielen"'
Autor:
Steffen Gielen, Lisa Mickel
Publikováno v:
Universe, Vol 9, Iss 1, p 29 (2022)
We study the dynamics of gauge-invariant scalar perturbations in cosmological scenarios with a modified Friedmann equation, such as quantum gravity bouncing cosmologies. We work within a separate universe approximation which captures wavelengths larg
Externí odkaz:
https://doaj.org/article/5b67496d09634d00b9fd2777849da323
Publikováno v:
Universe, Vol 6, Iss 1, p 19 (2020)
This editorial introduces the Special Issue “Progress in Group Field Theory and Related Quantum Gravity Formalisms” which includes a number of research and review articles covering results in the group field theory (GFT) formalism for quantum gra
Externí odkaz:
https://doaj.org/article/f50d494178504baa97c6dd6a1188bb60
Autor:
Steffen Gielen
Publikováno v:
Universe, Vol 4, Iss 10, p 103 (2018)
While the equations of general relativity take the same form in any coordinate system, choosing a suitable set of coordinates is essential in any practical application. This poses a challenge in background-independent quantum gravity, where coordinat
Externí odkaz:
https://doaj.org/article/2b0a4b913b8345359867d41a21e0721e
Autor:
Steffen Gielen, Daniele Oriti
Publikováno v:
New Journal of Physics, Vol 16, Iss 12, p 123004 (2014)
In the context of group field theory condensate cosmology, we clarify the extraction of cosmological variables from the microscopic quantum gravity degrees of freedom. We show that an important implication of the second quantized formalism is the dep
Externí odkaz:
https://doaj.org/article/384b2396afaf4622b45905f9f9e198be
Autor:
Steffen Gielen
Publikováno v:
Symmetry, Integrability and Geometry: Methods and Applications, Vol 7, p 104 (2011)
We review some properties of the space of connections as the natural arena for canonical (quantum) gravity, and compare to the case of the superspace of 3-metrics. We detail how a 1-parameter family of metrics on the space of connections arises from
Externí odkaz:
https://doaj.org/article/c6f0ae5adec54ef786a788ec18ba8891
Autor:
Steffen Gielen, João Magueijo
Publikováno v:
Physical Review D. 107
We formulate the transition from decelerated to accelerated expansion as a bounce in connection space and study its quantum cosmology, knowing that reflections are notorious for bringing quantum effects to the fore. We use a formalism for obtaining a
Autor:
Steffen Gielen, Elliot Nash
We study homogeneous cosmological models in formulations of general relativity with cosmological constant based on a (complexified) connection rather than a spacetime metric, in particular in a first order theory obtained by integrating out the self-
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::bad0292b722c5d7f51b03afef29c5d04
http://arxiv.org/abs/2212.06198
http://arxiv.org/abs/2212.06198
Autor:
Steffen Gielen, Lucía Menéndez-Pidal
We explore the consequences of requiring that quantum theories of gravity be unitary, mostly focusing on simple cosmological models to illustrate the main points. We show that unitarity for a clock that encounters a classical singularity at finite ti
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::6ae63cfdc1e031f7973b474f37f6e2bd
http://arxiv.org/abs/2205.15387
http://arxiv.org/abs/2205.15387
Autor:
Steffen Gielen, João Magueijo
We study a quantum Hot Big Bang in the connection representation, with a matter constant of motion m whose conjugate defines time. Superpositions in m induce a unitary inner product. The wavefunction reveals a resolution of the singularity problem wi
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::8ab46504f2be8c650eb66c64bcf8d7c5
http://arxiv.org/abs/2204.01771
http://arxiv.org/abs/2204.01771
Autor:
Steffen Gielen, Andrea Calcinari
In cosmological group field theory (GFT) models for quantum gravity coupled to a massless scalar field the total volume, seen as a function of the scalar field, follows the classical Friedmann dynamics of a flat Friedmann-Lema\^itre-Robertson-Walker
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::7b8ddc6f5e30db4b6cf388cf992b65d4