Our research is related to testing dark energy/modified gravity theories. We determine the positivity bounds on effective field theories with spontaneously broken Lorentz invariance. We consider...Show moreOur research is related to testing dark energy/modified gravity theories. We determine the positivity bounds on effective field theories with spontaneously broken Lorentz invariance. We consider all the operators in a low-energy — effective field theory (EFT) approach and gain the conditions for EFT coefficients so that a theory is healthy (without instabilities). These conditions are called the positivity bounds, for which a theory works. These positivity bounds can give us constraints about the cosmological model. We mainly follow the paper Positivity bounds on effective field theories with spontaneously broken Lorentz invariance by Paolo Creminelli, Oliver Janssen, and Leonardo Senatore, where the positivity bounds are calculated from the two-point correlation functions of conserved quantities like the Noether current and stress-energy tensor. Then we show how this new mechanism of finding positivity bounds can be used for real cosmological models.Show less
