M'hamed El Omari | Searcharxiv

arXiv2026

Relative Chaos for $C_0$-Semigroups Beyond Topological Notions

We investigate instability phenomena for linear evolution equations within the framework of $C_0$--semigroups on infinite--dimensional spaces. We show that Devaney chaos, being formulated in purely topological terms, may depend on the choice of topology and therefore fail to capture intrinsic dynamical behavior. To address this issue, we introduce a trajectory--based notion of relative chaos, defined with respect to a reference solution and measured in a fixed, physically meaningful norm. This criterion is independent of topological refinements and is shown to be strictly weaker than classical Devaney chaos. Its relevance is illustrated on boundary--driven reaction--diffusion--transport semigroups.

math.DS↗

arXiv2026

Time Reparametrization and Chaotic Dynamics in Conformable $C_0$-Semigroups

Conformable derivatives provide a fractional-looking calculus that remains local and admits a simple representation through classical derivatives with explicit weights. In this paper we develop a systematic operator-theoretic perspective showing that conformable time evolution is, in essence, a classical $C_0$-semigroup observed through a nonlinear clock. We introduce the conformable time map $ψ(t)=t^α/α$ and prove that every $C_0$--$α$-semigroup $\{T_α(t)\}_{t\ge0}$ can be written as $T_α(t)=T(ψ(t))$ for a uniquely determined classical $C_0$-semigroup $\{T(s)\}_{s\ge0}$, with generators agreeing on a common domain. This correspondence yields a one-to-one transfer of mild solutions and shows that orbit-based linear dynamics are invariant under conformable reparametrization. In particular, $α$-hypercyclicity and $α$--chaos coincide with the usual notions for the associated classical semigroup. As a consequence, we obtain a conformable version of the Desch--Schappacher--Webb spectral criterion for chaos. We also place the analysis in the natural functional setting provided by conformable Lebesgue spaces $L^{p,α}$ and their explicit isometric identification with standard $L^p$ spaces, which allows one to transport estimates and spectral arguments without loss. The results clarify which dynamical phenomena in conformable models are genuinely new and which are inherited from classical semigroup dynamics via a nonlinear change of time.

math.AP↗