arXiv subjects

Andrea Calcinari

Publications and source records attributed to Andrea Calcinari.

7 recordsLinked to original sources

arXiv2026

Emergent dark sector in group field theory cosmology

We develop an analytical treatment of the emergent cosmological dynamics induced by local polynomial interactions in a deparametrised group field theory model, moving beyond the usual non-interacting approximation. For a single field mode with quartic and sextic couplings we obtain a closed-form generalised Friedmann equation within a controlled Gaussian regime. The dynamics preserves the quantum bounce while generating effective dark matter and dark energy contributions as collective quantum-geometric phenomena, providing the first derivation of both components from a single model. Matching the resulting dark-energy-to-dark-matter density ratio to observations places concrete phenomenological constraints on the fundamental theory, linking the cosmic coincidence problem directly to the underlying quantum gravity dynamics. Our results extend to arbitrary even polynomial interactions, establishing a systematic dictionary between microscopic interaction orders and effective equations of state.

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arXiv2026

Gauge vs (hidden) physical symmetries of FLRW cosmologies

In generally covariant theories evolution in coordinate time is a gauge transformation, so that a symmetry made manifest in a gauge-fixed description need not be a symmetry of the physical dynamics. Deparametrisation, in turn, removes gauge symmetries but may hide physical symmetries, in particular those dependent on the chosen physical clock. We study the relation between gauge and (hidden) physical symmetries in flat FLRW geometry coupled to an arbitrary number $n$ of free massless scalar fields. We show that conformal Killing vectors of the minisuperspace metric generate conserved charges which are Dirac observables--hence gauge-invariant--and whose Poisson algebra is the maximal conformal algebra $\mathfrak{conf}(n,1)\simeq\mathfrak{so}(n+1,2)$, extending previous single-field results to arbitrary $n$. We then revisit the Eisenhart-Duval lift in a family of gauges and show that the manifest symmetry algebra is gauge dependent, enlarging to the Schr\"odinger algebra (which is thus not a physical symmetry) in the distinguished harmonic gauge where the gauge-fixed minisuperspace metric becomes flat. Further, deparametrisation maps the lifted charges to gauge-invariant Dirac observables, which always realise a subalgebra of the conformal algebra and reproduce it in full in the harmonic gauge. These results establish a framework for separating gauge from physical symmetries in minisuperspace models, recovering charges to which reduced phase-space descriptions are structurally blind, and remaining applicable in the presence of potentials.

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arXiv2026

Collective excitations in quantum gravity condensates

A central open problem in quantum gravity is to understand how continuum spacetime emerges from quantum-geometric degrees of freedom in a background-independent setting. A many-body perspective suggests that spacetime emerges as a hydrodynamic phase of many atoms of quantum geometry. This idea underlies several approaches to quantum gravity, and it has been explicitly realised in the group field theory formalism. However, quantum fluctuations beyond the mean-field regime remain largely unexplored. We fill this gap by importing Bogolyubov theory to quantum gravity condensates, showing that leading beyond-mean-field effects manifest as collective excitations, in direct analogy with phonons in laboratory BECs. We implement the construction in a tractable group field theory model, where condensates of quantum-geometric atoms reproduce nonsingular expanding cosmologies, and derive the leading beyond-mean-field corrections to the emergent Friedmann dynamics. These results identify a new class of quantum-gravity excitations and establish a controlled bridge between microscopic quantum-gravitational dynamics, many-body collective phenomena, and signatures of spacetime emergence.

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arXiv2024

Relational dynamics and Page-Wootters formalism in group field theory

Group field theory posits that spacetime is emergent and is hence defined without any background notion of space or time; dynamical questions are formulated in relational terms, in particular using (scalar) matter degrees of freedom as time. Unlike in canonical quantisation of gravitational systems, there is no obvious notion of coordinate transformations or constraints, and established quantisation methods cannot be directly applied. As a result, different canonical formalisms for group field theory have been discussed in the literature. We address these issues using a parametrised version of group field theory, in which all (geometry and matter) degrees of freedom evolve in a fiducial parameter. There is a constraint associated to the freedom of reparametrisation and the Dirac quantisation programme can be implemented. Using the "trinity of relational dynamics", we show that the resulting "clock-neutral" theory is entirely equivalent to a deparametrised canonical group field theory, interpreted in terms of the Page-Wootters formalism. Our results not only show that the deparametrised quantisation is fully covariant and can be seen as encoding the dynamics of joint quantum matter and geometry degrees of freedom, they also appear to be the first application of the Page-Wootters formalism directly to non-perturbative quantum gravity. We show extensions to a setting in which many independent gauge symmetries are introduced, which connects to the "multi-fingered time" idea in quantum gravity and provides a somewhat novel extension of the Page-Wootters formalism.

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arXiv2023

Generalised Gaussian states in group field theory and $\mathfrak{su(1,1)}$ quantum cosmology

We define generalised Gaussian states for quantum cosmological models based on the $\mathfrak{su(1,1)}$ algebra, with particular emphasis on its realisation in group field theory for a single field mode, and study their semiclassical properties. These states are generalisations of coherent, squeezed and thermal states considered previously. As two possible characterisations of semiclassicality, we contrast the requirement of small relative fluctuations in volume and energy with the saturation of the Robertson--Schr\"odinger uncertainty principle. We find that for the most general class of states the appearance of small relative fluctuations, which we take as the main criterion relevant for the emergence of cosmology, is mostly determined by the amount of displacement used to define the state. We also observe that defining such generalised Gaussian states is less straightforward in the algebraic approach to canonical quantisation of group field theory, and discuss special cases.

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arXiv2023

Towards anisotropic cosmology in group field theory

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-Lemaître-Robertson-Walker (FLRW) Universe at low energies while resolving the Big Bang singularity at high energies. An open question is how to generalise these results to other homogeneous cosmologies. Here we take the first steps towards studying anisotropic Bianchi models in GFT, based on the introduction of a new anisotropy observable analogous to the $β$ variables in Misner's parametrisation. In a classical Bianchi I spacetime, $β$ behaves as a massless scalar field and can be used as a (gravitational) relational clock. We construct a GFT model for which in an expanding Universe $β$ initially behaves like its classical analogue before "decaying" showing a previously studied isotropisation. We support numerical results in GFT by analytical approximations in a toy model. One possible outcome of our work is a definition of relational dynamics in GFT that does not require matter.

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arXiv2020

Twisted Geometries Coherent States for Loop Quantum Gravity

We introduce a new family of coherent states for loop quantum gravity, inspired by the twisted geometry parametrization. We compute their peakedness properties and compare them with the heat-kernel coherent states. They show similar features for the area and the holonomy operators, but improved peakedness in the direction of the flux. At the gauge-invariant level, the new family is built from tensor products of coherent intertwiners. To study the peakedness of the holonomy operator, we introduce a new shift operator based on the harmonic oscillator representation associated with the twisted geometry parametrization. The new shift operator captures the components of the holonomy relevant to disentangle its action into a simple positive shift of the spins.

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