12:30 pm 3rd Floor Atrium
Constraints from causality and unitarity .
Causality and unitarity are two fundamental principles in physics. A natural question is whether these principles impose constraints on interacting quantum field theories. In this colloquium, I will explain how the notions of causality and unitarity can be made precise in quantum field theories (with gravity). Application of these constraints lead to inequalities among Wilson coefficients in low energy effective field theories. Then, I will discuss a new constraint on gravitational theories which lead to equalities, rather than inequalities, on the parameter space. I will also sketch an outline of a (physicist's) proof of the constraint.