Yoshiki Kaiho | Searcharxiv

arXiv2026

Double phase flow under Lavrentiev phenomenon

This paper deals with parabolic equations associated with double phase functionals. It is known that double phase functionals may exhibit the Lavrentiev phenomenon, which indicates an existence of a singular minimizer. Our aim is to investigate the process of the associated double phase flow evolving toward the singular minimizer. For this purpose, we study whether solutions can be approximated by smooth functions. We first observe a phenomenon that we call finite-time loss of smooth approximability; more precisely, we prove that the flow eventually ceases to be smoothly approximable. We also establish quantitative estimates on the time of loss. On the other hand, we investigate a phenomenon that we call short-time persistence of smooth approximability; we prove that the smooth approximability persists for a short time provided that the initial datum is regular and that the functional is nondegenerate with respect to the gradient variable. The results concerning finite-time loss of smooth approximability are derived from the evolution variational inequality, whereas the short-time persistence result is obtained by applying analytic semigroup theory. The novelty of this paper lies in studying the dynamical aspect of the Lavrentiev phenomenon, which is usually regarded as a stationary phenomenon.

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arXiv2026

On very weak solutions of certain elliptic systems with double phase growth

In this paper, we prove a higher integrability result for very weak solutions of higher-order elliptic systems involving a double phase operator as the principal part. As a model case, we consider \begin{equation} \int_Ω \left( |D^m u|^{p-2}D^m u + a(x)|D^m u|^{q-2}D^m u \right) \cdot D^m φ= 0 \quad \text{for any } φ\in C_c^{\infty}(Ω), \end{equation} where $n,m \in \mathbb{N},\ n\ge 2,\,1 < p \le q < \infty,\,Ω\subset \mathbb{R}^n$ is an open set and $a:Ω\rightarrow [0,\infty)$ is a measurable function. The proof is based on a construction of an appropriate test function by the Lipschitz truncation technique, a deduction of a reverse Hölder inequality and an application of Gehring's lemma. Our contributions include estimates for weighted mean value polynomials and sharp Sobolev--Poincaré-type inequalities for the double phase operator. Our result can be viewed as a generalization with respect to the derivative order, the coefficient function and the growth conditions of the recent paper by Baasandorj, Byun and Kim (Trans. Amer. Math. Soc. 376:8733-8768,2023).

math.AP↗