# Tag Info

For any (local) observable $\mathcal{O}$, its expectation value is defined as $$\langle \mathcal{O} \rangle = \frac{1}{Z}\int \mathcal{D}\Phi\mathcal{O}\mathrm{e}^{-S_E[\Phi]}$$ where $$Z = \int \mathcal{D}\Phi\mathrm{e}^{-S_E[\Phi]}$$ is indeed called the partition function. My writing $S_E$ is intended to show that this is for a Euclidean theory ...