On Nonperiodic Euler Flows with H\"{o}lder Regularity

In [Isett,13], the first author proposed a strengthening of Onsager's conjecture on the failure of energy conservation for incompressible Euler flows with H\"{o}lder regularity not exceeding $1/3$. This stronger form of the conjecture implies that anomalous dissipation will fail for a generic Euler flow with regularity below the Onsager critical space $L_t^\infty B_{3,\infty}^{1/3}$ due to low regularity of the energy profile. In this paper, we establish two theorems that may be viewed as first steps towards establishing the conjectured failure of energy regularity for generic solutions with H\"{o}lder exponent less than $1/5$. Our first result shows that any non-negative function with compact support and H\"older regularity $1/2$ can be prescribed as the energy profile of an Euler flow in the class $C^{1/5-\epsilon}_{t,x}$. The exponent $1/2$ is sharp in view of a regularity result of [Isett,13]. The proof employs an improved greedy algorithm scheme that builds upon that in [Buckmaster-De Lellis-Sz\'ekelyhidi, 13]. Our second result shows that any given smooth Euler flow can be perturbed in $C^{1/5-\epsilon}_{t,x}$ on any pre-compact subset of ${\mathbb R}\times {\mathbb R}^3$ to violate energy conservation. In particular, there exist nonzero $C^{1/5-\epsilon}_{t,x}$ solutions to Euler with compact space-time support, generalizing previous work of the first author [Isett,12] to the nonperiodic setting.