Lecturer: Dr. Yu-Tin Huang
Affiliation: National Taiwan University
Abstract:
Assuming perturbative unitarization of the S-
matrix imposes strong constraints on the
spectrum of the theory's UV completion. The
famous example being upper bound for the
Higgs mass. In this talk we will show that when
applied to theories with massless three-point
interactions, violations of unitarity inevitably
appear at the scale of the newly introduced
particle. This forces the theory to include an
infinite tower of massive particles with integer
spacing of m^2. For gravity this leads to two
solutions for the four-point scattering. For non-
renormalizable scalar theories without a three-
point massless interaction, we will show that
only DBI action can be unitarized. This rules out
perturbative completion for a large class of
effective theories with Galilean symmetry,
including the DGP model.