arXiv subjects

Roukaya Dekhil

Publications and source records attributed to Roukaya Dekhil.

7 recordsLinked to original sources

arXiv2026

Emergent scalar field dynamics in a cosmological spacetime from GFT quantum gravity

We derive an effective scalar field theory for matter in group field theory condensate cosmology, starting from the fundamental quantum-gravity dynamics in a fully relational framework and encompassing both early- and late-universe regimes. The collective hydrodynamics of the underlying quantum geometry allows us to reconstruct both the homogeneous cosmological dynamics of matter and geometry and an inhomogeneous local field-theory description. Localization in space and time is defined relationally with respect to a material reference frame. At the homogeneous level, we obtain a modified scalar field theory on the emergent FLRW spacetime selected by the condensate. It recovers the standard dynamics of a massless scalar field in the late-time general-relativistic regime while retaining quantum-gravity corrections near the cosmological bounce. At the perturbative level, scalar inhomogeneities obey an effective wave equation that carries signatures of the underlying quantum-gravity microstructure. In the early-universe regime, this equation exhibits a modified dispersion relation with both dispersive and dissipative contributions. These corrections provide a concrete avenue for identifying phenomenological signatures of quantum gravity directly from a fundamental quantum-gravity framework.

gr-qc↗

arXiv2026

Finite path integrals on stochastic branched structures

In this paper, we present a statistical model of spacetime trajectories based on a finite collection of paths organized into a branched manifold. For each configuration of the branched manifold, we define a Shannon entropy. Given the variational nature of both the action in physics and the entropy in statistical mechanics, we explore the hypothesis that the classical action is proportional to this entropy. Under this assumption, we derive a Wick-rotated version of the path integral that remains finite and exhibits both quantum interference at the microscopic level and classical determinism at the macroscopic scale. In effect, this version of the path integral differs from the standard one because it assigns weights of non-uniform magnitude to different paths. The model suggests that wave function collapse can be interpreted as a consequence of entropy maximization. Although still idealized, this framework provides a possible route toward unifying quantum and classical descriptions within a common finite-entropy structure.

quant-ph↗

arXiv2025

A state sum for four-dimensional Lorentzian quantum geometry in terms of edge vectors

We present the construction of a new state sum model for $4d$ Lorentzian quantum gravity based on the description of quantum simplicial geometry in terms of edge vectors. Quantum states and amplitudes for simplicial geometry are built from irreducible representations of the translation group, then related to the representations of the Lorentz group via expansors, leading to interesting (and intricate) non-commutative structures. We also show how the new model connects to the Lorentzian Barrett-Crane spin foam model, formulated in terms of quantized triangle bivectors.

gr-qc↗

arXiv2024

Scale invariance beyond criticality within the mean-field analysis of tensorial field theories

We continue the series of articles on the application of Landau-Ginzburg mean-field theory to unveil the basic phase structure of tensorial field theories which are characterized by combinatorially non-local interactions. Among others, this class covers tensor field theories (TFT) which lead to a new class of conformal field theories highly relevant for investigations on the AdS/CFT conjecture. Moreover, it also encompasses models within the tensorial group field theory (TGFT) approach to quantum gravity. Crucially, in the infrared we find that the effective mass of the modes relevant for the critical behavior vanishes not only at criticality but also throughout the entire phase of non-vanishing vacuum expectation value due to the non-locality of the interactions. As a consequence, one encounters there the emergence of scale invariance on configuration space which is potentially enhanced to conformal invariance thereon.

hep-th↗

arXiv2024

Phase transitions in TGFT: Landau-Ginzburg analysis of the causally complete Lorentzian Barrett-Crane model

It is expected that continuum spacetime emerges via phase transition in the tensorial group field theory (TGFT) approach to quantum gravity. Recent work on the application of Landau-Ginzburg mean-field theory to progressively realistic TGFT models has demonstrated how phase transitions can be realized therein. Here, we further develop this setting and consider the causally complete Lorentzian Barrett-Crane (BC) model which includes not only spacelike but also timelike and lightlike tetrahedra as quantum geometric building blocks. In addition, we incorporate discretized scalar fields by $\mathbb{R}$-valued variables of the group fields. In this context, we analyze models with an arbitrary single interaction of simplicial and tensor-invariant type, extend it to the model with the two vertices well-known from causal dynamical triangulations, and also consider a model with colored simplicial interactions. As a main result, we demonstrate for all those cases that a mean-field approximation of a phase transition towards a non-trivial condensate state can always be realized. In particular, we show that the critical behavior is entirely driven by spacelike faces which are characterized by the boost part of the Lorentz group. The latter induces an exponential suppression of fluctuations which then stabilizes the mean-field vacuum. In contrast, timelike faces do not play a role in this as they are characterized by the rotational and thus compact part of the Lorentz group. Since such a state is typically populated by a large number of TGFT quanta, our work lends further considerable support to the existence of a sensible continuum gravitational regime for causally complete TGFT models. Our results also indirectly strengthen the derivation of effective cosmological dynamics and the recently improved study of scalar cosmological perturbations within a mean-field approximation.

gr-qc↗

arXiv2023

Black holes in the classical and quantum world

These are the lecture notes for an introductory course on black holes and some aspects of their interaction with the classical and quantum world. The focus is on phenomena of "fundamental physics" in the immediate surroundings of the black hole (classical and quantum fields, with little astrophysics). We aim more at qualitative, intuitive understanding than at quantitative rigor or detail. Accordingly, we only assume previous exposure to a conventional introduction to the elements of General Relativity and a glancing acquaintance with the Schwarzschild solution, but not more. We use many figures for illustrations and provide a set of carefully guided exercises. Topics: (1) The black hole as a tale of light and darkness. (2) The black hole that vibrates. (3) The black hole that rotates. (4) The black hole that evaporates. (A) Guided problems.

gr-qc↗

arXiv2023

Introduction to noncommutative field and gauge theory

These are lecture notes for an introductory course on noncommutative field and gauge theory. We begin by reviewing quantum mechanics as the prototypical noncommutative theory, as well as the geometrical language of standard gauge theory. Then, we review a specific approach to noncommutative field and gauge theory, which relies on the introduction of a derivations-based differential calculus. We focus on the cases of constant and linear noncommutativity, e.g., the Moyal spacetime and the so-called $\mathbb{R}^3_λ$, respectively. In particular, we review the $gφ^4$ scalar field theory and the $U(1)$ gauge theory on such noncommutative spaces. Finally, we discuss noncommutative spacetime symmetries from both the observer and particle point of view. In this context, the twist approach is reviewed and the $λ$-Minkowski $gφ^4$ model is discussed.

hep-th↗