A new construction of non-Gaussian, rotation-invariant and reflection positive probability measures $mu$ associated with the $varphi ^4_3$-model of quantum field theory is presented. Our construction uses a combination of semigroup methods, and methods of stochastic partial differential equations (SPDEs) for finding solutions and stationary measures of the natural stochastic quantization associated with the $varphi ^4_3$-model. Our starting point is a suitable approximation $mu_{M,N}$ of the measure $mu$ we intend to construct. $mu_{M,N}$ is parametrized by an $M$-dependent space cut-off function $rho_M: {mathbb R}^3rightarrow {mathbb R}$ and an $N$-dependent momentum cut-off function $psi_N: widehat{mathbb R}^3 cong {mathbb R}^3 rightarrow {mathbb R}$, that act on the interaction term (nonlinear term and counterterms). The corresponding family of stochastic quantization equations yields solutions $(X_t^{M,N}, tgeq 0)$ that have $mu_{M,N}$ as an invariant probability measure. By a combination of probabilistic and functional analytic methods for singular stochastic differential equations on negative-indices weighted Besov spaces (with rotation invariant weights) we prove the tightness of the family of continuous processes $(X_t^{M,N},t geq 0)_{M,N}$. Limit points in the sense of convergence in law exist, when both $M$ and $N$ diverge to $+infty$. The limit processes $(X_t; tgeq 0)$ are continuous on the intersection of suitable Besov spaces and any limit point $mu$ of the $mu_{M,N}$ is a stationary measure of $X$. $mu$ is shown to be a rotation-invariant and non-Gaussian probability measure and we provide results on its support. It is also proven that $mu$ satisfies a further important property belonging to the family of axioms for Euclidean quantum fields, it is namely reflection positive.
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