Generalized Tsirelson's bound from parity symmetry considerations

Abstract

The Bell experiment is a random game with two binary outcomes whose statistical correlation is given by $E_0(\Theta)=-\cos(\Theta)$, where $\Theta \in [-\pi, \pi)$ is an angular input that parameterizes the game setting. The correlation function $E_0(\Theta)$ belongs to the affine space ${\cal H} \equiv \left\{E(\Theta)\right\}$ of all continuous and differentiable periodic functions $E(\Theta)$ that obey the parity symmetry constraints $E(-\Theta)=E(\Theta)$ and $E(\pi-\Theta)=-E(\Theta)$ with $E(0)=-1$ and, furthermore, are strictly monotonically increasing in the interval $[0, \pi)$. Here we show how to build explicitly local statistical models of hidden variables for random games with two binary outcomes whose correlation function $E(\Theta)$ belongs to the affine space ${\cal H}$. This family of games includes the Bell experiment as a particular case. Within this family of random games, the Bell inequality can be violated beyond the Tsirelson bound of $2\sqrt{2}$ up to the maximally allowed algebraic value of 4. In fact, we show that the amount of violation of the Bell inequality is a purely geometric feature.