Higher Time-derivative Theories

The Higher Time-Derivative Theories Seminar is a regular online seminar series bringing together researchers working on higher time-derivative theories and related topics. The series is open to researchers at all career stages, from PhD students and postdoctoral researchers to established and senior researchers, and aims to provide an inclusive forum for presenting recent developments, discussing open problems, and fostering new interactions and collaborations.

Higher time-derivative theories arise in a wide range of areas of mathematical and theoretical physics, including approaches to renormalisable quantum gravity, modified gravity and cosmology, electrodynamics, integrable systems, geometry, and theories with non-standard symmetry structures. They offer a variety of interesting theoretical possibilities, while at the same time raising fundamental questions concerning stability, quantisation, and physical interpretation.

In their conventional formulation, such theories are often associated with Hamiltonians that are not bounded from below and with the Ostrogradsky instability. Whether these features necessarily render higher time-derivative theories physically unacceptable, or whether they can be avoided, circumvented, or reinterpreted in particular classes of models, remains an active and sometimes controversial area of research. A wide range of approaches has been developed, drawing on ideas from classical and quantum mechanics, constrained systems, non-Hermitian and PT-symmetric theories, integrability, geometry, and gravitational physics.

The seminar aims to bring these different communities and perspectives together, encourage discussion across the various approaches, and provide a welcoming environment in which both established researchers and early-career scientists can exchange ideas and develop new collaborations.

Latest presentation

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