Mathematical Physics and String Theory
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Cosmology and emergent spacetime physics from Quantum Gravity

By combining the main lesson of GR (space, time and geometry are identified with the gravitational field, and are dynamical, physical entities) with the main lesson of Quantum Mechanics (all physical systems possess quantum properties: irreducible uncertainty, probabilistic nature of physical observations, entanglement, contextuality), we expect that spacetime should possess a similar quantum nature. However, this very possibility raises a number of conceptual and technical difficulties of the most profound nature, which we have not overcome fully, yet.

The result is that we lack a framework to describe physical situations featuring both strong gravitational fields and quantum fields. One example of such physical regimes is the very early universe, despite the existing models accounting for the growing amount of cosmological data (e.g. the CMB spectrum of cosmological perturbations). In fact, these cosmological models rely on approximate semi-classical tools and make assumptions about extreme physical regimes that only a full quantum gravity theory could justify (or replace). Another example is the physics of black holes, in particular their interior and microscopic structure, and the way they process information.
In addition, lacking a more fundamental theory of quantum gravity, a number of other aspects of spacetime remains somewhat mysterious, also at large scales and for weak gravitational fields: the thermodynamic properties of horizons, and possibly of more general spacetime regions, or the nature of the cosmological constant and of dark energy, to name a few. Our research aims at providing answers, first of all, to these physical questions.

Publications of the group members in this research direction: 

  • Luca Marchetti, Daniele Oriti, Andreas G. A. Pithis, Johannes Thürigen, Phase transitions in TGFT: a Landau-Ginzburg analysis of Lorentzian quantum geometric models, arXiv:2209.04297.
  • Jan de Boer, Bianca Dittrich, Astrid Eichhorn, Steven B. Giddings, Steffen Gielen, Stefano Liberati, Etera R. Livine, Daniele Oriti, Kyriakos Papadodimas, Antonio D. Pereira, Mairi Sakellariadou, Sumati Surya, Herman Verlinde, Frontiers of Quantum Gravity: shared challenges, converging directions, arXiv:2207.10618 [gr-qc].
  • Jibril Ben Achour, Proper time reparametrization in cosmology: Mobius Symmetry and Kodama charges, https://iopscience.iop.org/article/10.1088/1475-7516/2021/12/005
  • Jibril Ben Achour, Etera R. Livine, Symmetries and conformal bridge in Schwarzschild-(A)dS black hole mechanics, arXiv:2110.01455
  • A. F. Jercher, D. Oriti and A. G. A. Pithis, Emergent cosmology from quantum gravity in the Lorentzian Barrett-Crane tensorial group field theory model, JCAP 01 (2022) no.01, 050, arXiv:2112.00091 [gr-qc]
  • Jibril Ben Achour, Etera R. Livine, Daniele Oriti, Goffredo Piani, Schrödinger symmetry in cosmology and black hole mechanics, arXiv:2207.07312
  • D. Oriti and X. Pang, Phantom-like dark energy from quantum gravity, JCAP 12 (2021) no.12, 040 [arXiv:2105.03751 [gr-qc]]
  • L. Marchetti, D. Oriti, Quantum fluctuations in the effective relational GFT cosmology, submitted, arXiv:2010.09700 [gr-qc]
  • L. Marchetti, D. Oriti, Effective relational cosmological dynamics from quantum gravity, to appear in JHEP, arXiv:2008.02774 [gr-qc]
  • M. Finocchiaro, D. Oriti, Renormalization of simplicial group field theory models of 4d quantum gravity: new numerical results and some suggestions, to appear in Frontiers in Physics, arXiv:2004.07361 [hep-th]