The universe as a quantum gravity condensate

Oriti, Daniele

doi:10.1016/j.crhy.2017.02.003

Cited by 91 publications

(134 citation statements)

References 105 publications

(176 reference statements)

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“…In group field theory, zero temperature coherent states have been used to obtain an effective description of flat, homogeneous and isotropic cosmology (flat FLRW), where certain quantum corrections arise naturally and generate a dynamical modification with respect to classical general relativity, preventing the occurrence of a big bang singularity along with cyclic solutions in general [37][38][39][40]. Encouraged by these results, the introduction of coherent thermal states may bring further insight and progress in the understanding and analysis of semiclassical and effective continuum dynamics of GFT models.…”

Section: Discussionmentioning

confidence: 99%

Thermal representations in group field theory: squeezed vacua and quantum gravity condensates

Assanioussi¹,

Kotecha²

2020

J. High Energ. Phys.

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We apply the formalism of thermofield dynamics to group field theory quantum gravity and construct thermal representations associated with generalised equilibrium Gibbs states using Bogoliubov transformations. The newly constructed class of thermal vacua are entangled, two-mode squeezed, thermofield double states. The corresponding finite temperature representations are inequivalent to the standard zero temperature one based on a degenerate vacuum. An interesting class of states, coherent thermal states, are defined and understood as thermal quantum gravity condensates.

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Section: Discussionmentioning

confidence: 99%

Thermal representations in group field theory: squeezed vacua and quantum gravity condensates

Assanioussi¹,

Kotecha²

2020

J. High Energ. Phys.

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“…In the present work, we are concerned also with group field theories which generate discrete spacetimes coupled to (discretised) real scalar matter fields. One way to couple a single real scalar degree of freedom, used in recent GFT literature, in particular for cosmological applications [29][30][31], and detailed in [32], is by extending the original configuration space G d , encoding purely geometrical data, by . By extension, n number of scalar fields can be coupled by considering a model based on G d n  .…”

Section: Group Field Theorymentioning

confidence: 99%

“…Also, as discussed in the previous section, in background independent systems like GFTs, as is wellknown [33], a reasonable way of defining physical quantities is by constructing relational observables using material reference frames. In GFT, such relational reference frames using scalar fields have indeed been used in the context of cosmology [29][30][31]. In the present work, we use them for a different, if related, purpose.…”

Section: Group Field Theorymentioning

confidence: 99%

“…(1) The analysis in [43] is carried out at the mean field, 'hydrodynamic' [29] level in terms of the condensate wavefunction of pure coherent states. On the other hand, here the analysis is directly at the level of the 25 All links incident on an isotropic node are labelled by the same spin.…”

Section: Bose-einstein Condensation To Low-spin Phasementioning

confidence: 99%

“…The grand-canonical Gibbs states 29 that encode equilibrium with respect to internal f-translations separately along the n cartesian directions are…”

Section: Equilibrium In F-translationsmentioning

confidence: 99%

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Statistical equilibrium in quantum gravity: Gibbs states in group field theory

Kotecha

Oriti

2018

New J. Phys.

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Gibbs states are known to play a crucial role in the statistical description of a system with a large number of degrees of freedom. They are expected to be vital also in a quantum gravitational system with many underlying fundamental discrete degrees of freedom. However, due to the absence of welldefined concepts of time and energy in background independent settings, formulating statistical equilibrium in such cases is an open issue. This is even more so in a quantum gravity context that is not based on any of the usual spacetime structures, but on non-spatiotemporal degrees of freedom. In this paper, after having clarified general notions of statistical equilibrium, on which two different construction procedures for Gibbs states can be based, we focus on the group field theory (GFT) formalism for quantum gravity, whose technical features prove advantageous to the task. We use the operator formulation of GFT to define its statistical mechanical framework, based on which we construct three concrete examples of Gibbs states. The first is a Gibbs state with respect to a geometric volume operator, which is shown to support condensation to a low-spin phase. This state is not based on a pre-defined symmetry of the system and its construction is via Jaynes' entropy maximisation principle. The second are Gibbs states encoding structural equilibrium with respect to internal translations on the GFT base manifold, and defined via the KMS condition. The third are Gibbs states encoding relational equilibrium with respect to a clock Hamiltonian, obtained by deparametrization with respect to coupled scalar matter fields. specific model), and in terms of which quantum spacetime is indeed (tentatively) described as a quantum manybody system, albeit of a very exotic nature.One of the foundational concepts in statistical physics is that of equilibrium. Equilibrium configurations are those that are invariant under time evolution (in turn identified, in flat space, with time translations), generated by the Hamiltonian of the system. But how does one define statistical equilibrium when there is no preferred time and Hamiltonian? This is the case in classical constrained systems such as general relativity. This is also the case in quantum gravitational contexts, especially in formalisms that are not based on continuum spacetime structures, like differentiable spacetime manifolds etc. This is the open problem of defining statistical equilibrium in a (non-spatiotemporal) background independent system. Still, since equilibrium states hold a special place in statistical physics, this is where we start, for developing a statistical mechanical formulation of quantum gravity within a GFT formalism.In this work we aim to construct Gibbs equilibrium states for a GFT system. Whether these states provide a truly comprehensive characterisation of statistical equilibrium in quantum gravity in general is a different (and challenging) issue that is not considered here. We also do not analyse here the physical consequences of our results for a descrip...

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Introduction

Kotecha

2022

On Generalised Statistical Equilibrium and Discrete Quantum Gravity

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The universe as a quantum gravity condensate

Cited by 91 publications

References 105 publications

Thermal representations in group field theory: squeezed vacua and quantum gravity condensates

Thermal representations in group field theory: squeezed vacua and quantum gravity condensates

Statistical equilibrium in quantum gravity: Gibbs states in group field theory

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