Speaker
Description
The analytic structure and the unitarity of S-matrix enforces non-trivial constraints (known as positivity bounds) on the space of Wilson coefficients of an EFT. The simplest bounds are derived by setting the coefficient of $s^2$ in the amplitude of $2 \to 2$ elastic scattering process in the forward limit, to zero. Meanwhile stronger bounds can be extracted in some occasions by exploiting the positive-definite structure of the $2 \to 2$ scattering amplitude. In this talk, I will discuss how we employ these methods to constrain Wilson coefficients of the 15 $\mathcal{O}(p^4)$ operators of the HEFT Lagrangian. We compare positivity bounds that we derive, with the recent experimental bounds on the 5 QGC operators and show that positivity bounds rule out most of the parameter space. Only $\sim \mathcal{O}(10\%)$ of the total parameter space is consistent with these positivity bounds.
