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November/December 2021 Non-divergence operators structured on homogeneous Hörmander vector fields: heat kernels and global Gaussian bounds
Stefano Biagi, Marco Bramanti
Adv. Differential Equations 26(11/12): 621-658 (November/December 2021).

Abstract

Let $X_{1},...,X_{m}$ be a family of real smooth vector fields defined in $\mathbb{R}^{n}$, $1$-homogeneous with respect to a nonisotropic family of dilations and satisfying Hörmander's rank condition at $0$ (and therefore at every point of $\mathbb{R}^{n}$). The vector fields are not assumed to be translation invariant with respect to any Lie group structure. Let us consider the nonvariational evolution operator \[ \mathcal{H}:=\sum_{i,j=1}^{m}a_{i,j}(t,x)X_{i}X_{j}-\partial_{t} , \] where $(a_{i,j}(t,x))_{i,j=1}^{m}$ is a symmetric uniformly positive $m\times m$ matrix and the entries $a_{ij}$ are bounded Hölder continuous functions on $\mathbb{R}^{1+n}$, with respect to the ``parabolic'' distance induced by the vector fields. We prove the existence of a global heat kernel $\Gamma(\cdot;s,y)\in C_{X,\mathrm{loc}}^{2,\alpha}(\mathbb{R}^{1+n} \setminus\{(s,y)\})$ for $\mathcal{H}$, such that $\Gamma$ satisfies two-sided Gaussian bounds and $\partial_{t}\Gamma, X_{i}\Gamma,X_{i}X_{j}\Gamma$ satisfy upper Gaussian bounds on every strip $[0,T]\times\mathbb{R}^{n}$. We also prove a scale-invariant parabolic Harnack inequality for $\mathcal{H} $, and a standard Harnack inequality for the corresponding stationary operator \[ \mathcal{L}:=\sum_{i,j=1}^{m}a_{i,j}(x)X_{i}X_{j} \] with Hölder continuous coefficients.

Citation

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Stefano Biagi. Marco Bramanti. "Non-divergence operators structured on homogeneous Hörmander vector fields: heat kernels and global Gaussian bounds." Adv. Differential Equations 26 (11/12) 621 - 658, November/December 2021.

Information

Published: November/December 2021
First available in Project Euclid: 4 November 2021

Subjects:
Primary: 35K08 , 35K15 , 35K65

Rights: Copyright © 2021 Khayyam Publishing, Inc.

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Vol.26 • No. 11/12 • November/December 2021
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