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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.

A C ∗ -algebra for quantized principal U(1)-connections on globally hyperbolic lorentzian manifolds (2014)
Journal Article
Benini, M., Dappiaggi, C., Hack, T. P., & Schenkel, A. (2014). A C ∗ -algebra for quantized principal U(1)-connections on globally hyperbolic lorentzian manifolds. Communications in Mathematical Physics, 332(1), 477-504. https://doi.org/10.1007/s00220-014-2100-3

© Springer-Verlag Berlin Heidelberg 2014. The aim of this work is to complete our program on the quantization of connections on arbitrary principal U(1)-bundles over globally hyperbolic Lorentzian manifolds. In particular, we show that one can assig... Read More about A C ∗ -algebra for quantized principal U(1)-connections on globally hyperbolic lorentzian manifolds.

Homogeneous cosmologies as group field theory condensates (2014)
Journal Article
Gielen, S., Oriti, D., & Sindoni, L. (2014). Homogeneous cosmologies as group field theory condensates. Journal of High Energy Physics, 2014(6), Article 013. https://doi.org/10.1007/jhep06%282014%29013

We give a general procedure, in the group field theory (GFT) formalism for quantum gravity, for constructing states that describe macroscopic, spatially homogeneous universes. These states are close to coherent (condensate) states used in the descrip... Read More about Homogeneous cosmologies as group field theory condensates.