Grand Besov–Bourgain–Morrey spaces and their applications to boundedness of operators

Let \(1<q\le p \le r\le \infty \) and \(\tau \in (0,\infty ]\). Besov–Bourgain–Morrey spaces \({\mathcal {M}}\dot{B}^{p,\tau }_{q,r}({\mathbb {R}}^n)\) in the special case where \(\tau =r\), extending what was introduced by J. Bourgain, have proved useful in the study related to the Strichartz estimate and the non-linear Schrödinger equation. In this article, by cleverly mixing the norm structures of grand Lebesgue spaces and Besov–Bourgain–Morrey spaces and adding an extra exponent \(\theta \in [0,\infty )\), the authors introduce a new class of function spaces, called generalized grand Besov–Bourgain–Morrey spaces \({\mathcal {M}}\dot{B}^{p,\tau }_{q),r,\theta }({\mathbb {R}}^n)\). The authors explore their various real-variable properties including pre-dual spaces and the Gagliardo–Peetre and the ± interpolation theorems. Via establishing some equivalent quasi-norms of \({\mathcal {M}}\dot{B}^{p,\tau }_{q),r,\theta }({\mathbb {R}}^n)\) related to Muckenhoupt \(A_1({\mathbb {R}}^n)\)-weights, the authors then obtain an extrapolation theorem of \({\mathcal {M}}\dot{B}^{p,\tau }_{q),r,\theta }({\mathbb {R}}^n)\). Applying this extrapolation theorem, the Calderón product, and the sparse family of dyadic grids of \({\mathbb {R}}^n\), the authors establish the sharp boundedness on \({\mathcal {M}}\dot{B}^{p,\tau }_{q),r,\theta }({\mathbb {R}}^n)\) of the Hardy–Littlewood maximal operator, the fractional integral, and the Calderón–Zygmund operator.