Existence and uniqueness of mild solutions for a class of psi-Caputo time-fractional systems of order from one to two
Hamza Ben Brahim, Fatima-Zahrae El Alaoui, Asmae Tajani, Delfim F. M. Torres
TL;DR
We address existence/uniqueness of mild solutions for a time-fractional evolution system driven by a psi-Caputo derivative of order $1<\alpha\leq 2$ in Banach spaces, i.e. $^{{\mathcal{CD}}}^{\alpha,\psi}_{0^{+}}\Theta(t)=A\Theta(t)+f(t,\Theta(t))$ with $\Theta(0)=\Theta_0$, $\Theta'(0)=\Theta_1$. The authors construct a mild-solution formula using cosine/sine operator families and Mainardi's Wright-type function via the generalized Laplace transform in the variable $\psi$, enabling an explicit integral representation that extends the classical $(0,1)$ case to $(1,2]$. They establish existence and uniqueness through two fixed-point frameworks under different hypotheses (Lipschitz vs growth/compactness), derive a Mittag-Leffler-based expansion for a second-order elliptic operator, and illustrate applicability with a concrete diffusion example. Together, the results extend mild-solution theory to higher-order psi-Caputo dynamics, providing explicit kernels and representations applicable to memory-influenced diffusion and wave-like processes.
Abstract
We prove the existence and uniqueness of mild solutions for a specific class of time-fractional $ψ$-Caputo evolution systems with a derivative order ranging from 1 to 2 in Banach spaces. By using the properties of cosine and sine family operators, along with the generalized Laplace transform, we derive a more concise expression for the mild solution. This expression is formulated as an integral, incorporating Mainardi's Wright-type function. Furthermore, we provide various valuable properties associated with the operators present in the mild solution. Additionally, employing the fixed-point technique and Grönwall's inequality, we establish the existence and uniqueness of the mild solution. To illustrate our results, we conclude with an example of a time-fractional equation, presenting the expression for its corresponding mild solution.
