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arXiv · 2506.12499

From Explicit Diffeomorphism Breaking to Spontaneous Unimodularization

Yuri Bonder·Johas D. Morales
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Abstract

This contribution investigates modifications of General Relativity that allow or mimic energy nonconservation. We focus on Unimodular Gravity (UG), a theory that explicitly breaks diffeomorphism invariance, and show that it can lead to particle acceleration, opening the door to experimental constraints. We also argue that UG admits a well-posed initial value formulation, despite the presence of nondynamical structures. Finally, we introduce a simple model that spontaneously mimics UG, but in which a cosmological constant cannot arise as an integration constant.

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Yuri Bonder, Johas D. Morales. 2025-06-14. From Explicit Diffeomorphism Breaking to Spontaneous Unimodularization. https://arxiv.org/abs/2506.12499

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