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Quantum cosmology from group field theory condensates: a review (2016)
Journal Article
Gielen, S., & Sindoni, L. (2016). Quantum cosmology from group field theory condensates: a review. Symmetry, Integrability and Geometry: Methods and Applications, 12, Article 082. https://doi.org/10.3842/sigma.2016.082

We give, in some detail, a critical overview over recent work towards deriving a cosmological phenomenology from the fundamental quantum dynamics of group field theory (GFT), based on the picture of a macroscopic universe as a “condensate” of a large... Read More about Quantum cosmology from group field theory condensates: a review.

Perfect quantum cosmological bounce (2016)
Journal Article
Gielen, S., & Turok, N. (2016). Perfect quantum cosmological bounce. Physical Review Letters, 117(2), Article 021301. https://doi.org/10.1103/physrevlett.117.021301

We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrou... Read More about Perfect quantum cosmological bounce.

Identifying cosmological perturbations in group field theory condensates (2015)
Journal Article
Gielen, S. (2015). Identifying cosmological perturbations in group field theory condensates. Journal of High Energy Physics, 2015(8), Article 010. https://doi.org/10.1007/jhep08%282015%29010

One proposal for deriving effective cosmological models from theories of quantum gravity is to view the former as a mean-field (hydrodynamic) description of the latter, which describes a universe formed by a ‘condensate’ of quanta of geometry. This i... Read More about Identifying cosmological perturbations in group field theory condensates.

Perturbing a quantum gravity condensate (2015)
Journal Article
Gielen, S. (2015). Perturbing a quantum gravity condensate. Physical Review D - Particles, Fields, Gravitation and Cosmology, 91(4), Article 043526. https://doi.org/10.1103/physrevd.91.043526

In a recent proposal using the group field theory approach, a spatially homogeneous (generally anisotropic) universe is described as a quantum gravity condensate of “atoms of space”, which allows the derivation of an effective cosmological Friedmann... Read More about Perturbing a quantum gravity condensate.

Quantum cosmology from quantum gravity condensates: cosmological variables and lattice-refined dynamics (2014)
Journal Article
Gielen, S., & Oriti, D. (2014). Quantum cosmology from quantum gravity condensates: cosmological variables and lattice-refined dynamics. New Journal of Physics, 16(12), Article 123004. https://doi.org/10.1088/1367-2630/16/12/123004

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... Read More about Quantum cosmology from quantum gravity condensates: cosmological variables and lattice-refined dynamics.

Locally Covariant Quantum Field Theory with External Sources (2014)
Journal Article
Fewster, C. J., & Schenkel, A. (2015). Locally Covariant Quantum Field Theory with External Sources. Annales Henri Poincaré, 16(10), 2303-2365. https://doi.org/10.1007/s00023-014-0372-y

© 2014, Springer Basel. We provide a detailed analysis of the classical and quantized theory of a multiplet of inhomogeneous Klein–Gordon fields, which couple to the spacetime metric and also to an external source term; thus the solutions form an aff... Read More about Locally Covariant Quantum Field Theory with External Sources.

Quantum cosmology of (loop) quantum gravity condensates: an example (2014)
Journal Article
Gielen, S. (2014). Quantum cosmology of (loop) quantum gravity condensates: an example. Classical and Quantum Gravity, 31(15), Article 155009. https://doi.org/10.1088/0264-9381/31/15/155009

Spatially homogeneous universes can be described in (loop) quantum gravity as condensates of elementary excitations of space. Their treatment is easiest in the second-quantized group field theory formalism, which allows the adaptation of techniques f... Read More about Quantum cosmology of (loop) quantum gravity condensates: an example.