Extended DBI and its generalizations from graded soft theorems

Understand

We analyze a theory known as extended DBI, which interpolates between DBI and the $U(N)\times U(N)/U(N)$ non-linear sigma model and represents a nontrivial example of theories with mixed power counting.

• We discuss symmetries of the action and their geometrical origin; the special case of SU(2) extended DBI theory is treated in great detail.
• The revealed symmetries lead to a new type of graded soft theorem that allows us to prove on-shell constructibility of the tree-level S-matrix.
• It turns out that the on-shell constructibility of the full extended DBI remains valid, even if its DBI sub-theory is modified in such a way to preserve its own on-shell constructibility.