Higher integrability near the initial boundary for nonhomogeneous parabolic systems of 𝑝-Laplacian type

We establish a sharp higher integrability near the initial boundary for a weak solution to the following p-Laplacian type system:\left\{\begin{aligned} \displaystyle u_{t}-\operatorname{div}\mathcal{A}(x,t,% \nabla u)&\displaystyle=\operatorname{div}\lvert F\rvert^{p-2}F+f&&% \displaystyle\phantom{}\text{in}\ \Omega_{T},\\ \displaystyle u&\displaystyle=u_{0}&&\displaystyle\phantom{}\text{on}\ \Omega% \times\{0\},\end{aligned}\right.by proving that, for given {\delta\in(0,1)}, there exists {\varepsilon>0} depending on δ and the structural data such that\lvert\nabla u_{0}\rvert^{p+\varepsilon}\in L^{1}_{\operatorname{loc}}(\Omega)% \quad\text{and}\quad\lvert F\rvert^{p+\varepsilon},\lvert f\rvert^{(\frac{% \delta p(n+2)}{n})^{\prime}+\varepsilon}\in L^{1}(0,T;L^{1}_{\operatorname{loc% }}(\Omega))\implies\lvert\nabla u\rvert^{p+\varepsilon}\in L^{1}(0,T;L^{1}_{% \operatorname{loc}}(\Omega)).Our regularity results complement established higher regularity theories near the initial boundary for such a nonhomogeneous problem with {f\not\equiv 0} and we provide an optimal regularity theory in the literature.