Unitarity and microscopic acausality in a nonlocal theory

Understand

We consider unitarity and causality in a higher-derivative theory of infinite order, where propagators fall off more quickly in the ultraviolet due to the presence of a transcendental entire function of the momentum.

• Like Lee-Wick theories, these field theories might provide new avenues for addressing the hierarchy problem; unlike Lee-Wick theories, tree-level propagators do not have additional poles corresponding to unobserved particles with unusual properties.
• We consider microscopic acausality in these nonlocal theories.
• The acausal ordering of production and decay vertices for ordinary resonant particles may provide a phenomenologically distinct signature for these models.