Abstract
In this paper we study the Cauchy problem for the wave equations for hypoelliptic homogeneous left-invariant operators on graded Lie groups when the time-dependent non-negative propagation speed is regular, Hölder, and distributional. For Hölder coefficients we derive the well-posedness in the spaces of ultradistributions associated to Rockland operators on graded groups. In the case when the propagation speed is a distribution, we employ the notion of “very weak solutions” to the Cauchy problem, that was already successfully used in similar contexts in [12] and [20]. We show that the Cauchy problem for the wave equation with the distributional coefficient has a unique “very weak solution” in an appropriate sense, which coincides with classical or distributional solutions when the latter exist. Examples include the time dependent wave equation for the sub-Laplacian on the Heisenberg group or on general stratified Lie groups, or p-evolution equations for higher order operators on Rn or on groups, the results already being new in all these cases.
Highlights
In this paper we study the Cauchy problem for the wave equations for hypoelliptic homogeneous left-invariant operators on graded Lie groups when the time-dependent non-negative propagation speed is regular, Holder, and distributional
In the case of stratified Lie groups such spaces and their properties have been extensively analysed by Folland in [Fol75] and on general graded Lie groups they have been investigated in [FR16] and [FR17]
Recall that these spaces do not depend on a particular choice of the Rockland operator R used in the definition (1.2), see [FR16, Theorem 4.4.20]
Summary
In this paper we study the Cauchy problem for the wave equations for hypoelliptic homogeneous left-invariant operators on graded Lie groups when the time-dependent non-negative propagation speed is regular, Holder, and distributional. × HRs (G), there exists the unique solution of the homogeneous Cauchy problem (1.1) (when f ≡ 0) in the space
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