The Quantum Gravity Imprint: New Guiding Principles at Low Energies

Project Information

QGuide

Grant agreement ID: 101042568

DOI

10.3030/101042568

EC signature date 20 June 2022

Start date 1 October 2022

End date 30 September 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 382 625,00

EU contribution

€ 1 382 625,00

Coordinated by

ORGANISATION EUROPEENNE POUR LA RECHERCHE NUCLEAIRE
Switzerland

Periodic Reporting for period 1 - QGuide (The Quantum Gravity Imprint: New Guiding Principles at Low Energies)

Reporting period: 2022-10-01 to 2025-03-31

Summary of the context and overall objectives of the project

Quantum physics and Einstein’s theory of general relativity are the two main pillars that underlie much of modern physics. Ordinary quantum field theories, which combine classical field theory, special relativity and quantum mechanics, are an excellent approximation when describing the behaviour of microscopic particles in weak gravitational fields. At high energies, however, not every quantum field theory can be consistently coupled to gravity at quantum level, unless it satisfies some additional novel set of conditions known as Swampland constraints.

The EU-funded QGuide project aims to determine the constraints that quantum gravity imposes at low energies. To this end, the team members will uncover the fundamental principles underlying the Swampland conjectures, and look for new universal constraints in the context of string theory. This can have profound implications for Particle Physics and Cosmology, providing new guiding principles to progress in High Energy Physics.

To achieve this goal, the project uses a novel approach based on cutting edge mathematical techniques of algebraic geometry and the topological cobordism groups that extend the notion of symmetry. Each swampland conjecture is subject to scrutiny such that it gets either disproven or promoted to a sharp statement in the realm of well-established string compactifications.
Specific goals include an in-depth analysis of the mechanisms by which string theory avoids new classes of generalised global symmetries, a complete classification of the field spectra emerging at the large field limits of flat space string compactifications, developing new methods to study the scalar potential at the large field limits and determining whether supersymmetry is a necessary condition to ensure vacuum stability.

These new quantum gravity constraints may trigger a revolution in our understanding of the Quantum Gravity imprint at low energies, addressing questions about axions, neutrino masses, inflation, hierarchy problems, weakly coupled charged matter and the accelerated expansion of the universe.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The ERC project QGuide has made significant contributions to our understanding of quantum gravity constraints on effective field theories (EFTs).

One of the most impactful achievements was the discovery of a universal pattern constraining the scale at which quantum gravitational effects become important in a given effective field theory. This pattern links the variation rate of the quantum gravity cutoff scale with the mass of a tower of states becoming light at perturbative limits of the EFT. It has been verified across diverse string theory compactifications, and can provide a universal sharp bound on the scale of quantum gravity gravity physics. It was published in Physical Review Letters and highlighted at Strings 2023, the field's premier conference.

The project also advanced the classification of infinite distance limits and the associated light towers of states, exploring previously uncharted corners of the landscape and providing strong evidence for the Swampland Distance Conjecture. Moreover, it introduced a bottom-up framework to classify how different duality frames can fit together in the moduli space. This further constrains the possible global behaviour of the asymptotic towers via a finite list of geometric structures, and has gathered significant attention within the theoretical physics community.

Additional studies explored novel symmetry structures in string theory, such as non-invertible symmetries, revealing their generic breaking at loop level in string theory and their implications for effective field theories. For instance, they provide a new mechanism to engineer small couplings in an effective field theory. Moreover, although generically broken, approximate non-invertible symmetries have implications for Swampland constraints: in certain cases, they can be used to prove the existence of towers of states related to the Distance Conjecture, and can sometimes explain the existence of slightly sub-extremal states, which fill in the gaps in the sublattice Weak Gravity Conjecture.

Preliminary work on scalar potentials and bubble-of-nothing instabilities has further enriched the project, setting the stage for future breakthroughs.

These achievements collectively represent significant progress in addressing long-standing challenges in quantum gravity, advancing the field beyond the state-of-the-art.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The results of the QGuide project have the potential to significantly advance our understanding of the imprint of quantum gravity at low energies and provide new guiding principles to construct effective field theories coupled to gravity from requiring quantum consistency.

The discovery of a universal pattern relating the quantum gravity cutoff to the mass of light towers of states provides sharp constraints on the scale at which quantum gravitational effects become important in an EFT. The classification of infinite distance limits and light towers of states also opens new possibilities for exploring the structure of the string theory landscape and has the potential to inform future quantum gravity constraints. These works also provide solid evidence for certain conjectures of the Swampland program.

The work about non-invertible symmetries can also have profound implications for Particle Physics and naturalness issues, as it provides a novel explanation for having small parameters protected by these approximate new type of symmetries. It can also be used to fill a loophole for the Weak Gravity Conjecture arising in certain setups with massive gauge fields, and provides a new notion of approximate non-invertible supersymmetry.

However, further research is needed to fully understand the underlying principles behind these results and to explore their implications for particle physics and cosmology. For example, deeper investigation into the universal pattern constraining the quantum gravity scale may yield profound insights into the possible nature of the quantum gravity UV completion. Additionally, further work on symmetry structures, especially non-invertible and (-1)-form symmetries, could have wide-reaching implications for model-building in particle physics.