Constraints from high energy completion on low-energy effective field theories.

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Sumer Jaitly's PhD will be centred around physics beyond the standard paradigms of particle physics, cosmology and gravity. Sumer will first derive new types of effective field theories that can describe the dark components of the Universe (dark matter, dark energy) in a way compatible with observations and involving more than just scalar degrees of freedom. An essential aspect of his research will be centred around the question of consistency from an effective field theory viewpoint. He will also focus on the irrelevant operators that describe physics beyond the standard model of particle physics. He will then derive and utilize new types of positivity bounds that allow to impose constraints on the low-energy effective theories. The requirement of causality, Lorentz-invariance, locality and unitarity of the high energy completion imposes strong constraints on the behaviour of the low-energy scattering amplitudes which are by now well-understood for 2-2 processes. Extending those bounds beyond 2-2 scattering and probing a much larger class of higher-order operators has remained a long-standing question which will be an essential part of Sumer's PhD thesis. In particular, he will explore the analyticity of the extended Mandelstram phase space for higher scattering processes which will allow him to understand which positivity conditions can be imposed based on higher scattering amplitudes.