Chiral Fermions and Quantum Gravity

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The challenge of developing a convincing and consistent theory of quantum gravity is hampered perhaps less by theoretical problems than by the lack of clear observational unambiguous data. The present project suggests to use the well-known observation that the fundamental matter constituents are given by chiral fermions as a probe for possible quantum gravity scenarios.Chiral symmetry is an essential ingredient in elementary particle physics. It ensures that fermions with comparatively small masses can exist in Nature. On the other hand, chirality can be spontaneously broken by quantum fluctuations, as it is the case in the electroweak and strong interactions. As gravity are expected to become relevant near the Planck scale, gravity fluctuations must not break the chiral symmetry of the chiral fermions. Otherwise the observation of light fermions in our universe would not be compatible with such gravity interactions.The main objective of this proposal is to interconnect the observed existence of light (chiral) fermions with generic quantum gravity scenarios. For this, the established theoretical framework of quantum field theory will be used with gravity being treated either as an effective field theory or an asymptotically safe fundamental quantum theory. With this tool the project can address the following questions: Can gravitationally induced chiral symmetry breaking (gravitational catalysis) and fermion mass generation be active in the high-energy quantum gravity regime? Does chiral symmetry breaking through gravitational catalysis put constraints on or even rule out some quantum-gravity scenarios? In turn, is the number of fermion fields (e.g., flavors) constrained through gravitational interactions? Is the existence of non-chiral fermions compatible with specific quantum gravity scenarios? Answers to these questions may provide unprecedented but stringent guidelines to the development to a quantum gravity theory that is not only mathematically convincing but also compatible with physical observations.