Motivated by the seminal paper due to Brézis–Nirenberg (in: Commun Pure Appl Math 36:437–477, 1983), we will establish the existence of solutions for the following class of degenerate elliptic equations with critical nonlinearity: -Δγv=λ|v|q-2v+v2γ∗-2vinΩ,v=0on∂Ω,\documentclass[12pt]{minimal}
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\begin{document}$$\begin{aligned} {\left\{ \begin{array}{ll}-\Delta _{\gamma } v= \lambda |v|^{q-2}v+\left| v\right| ^{2_{\gamma }^{*}-2}v &{} \text { in } \Omega , \\ v=0 &{} \text { on } \partial \Omega , \end{array}\right. } \end{aligned}$$\end{document}where Δγ:=Δx+(1+γ)2x2γΔy\documentclass[12pt]{minimal}
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\begin{document}$$\Delta _{\gamma }:=\Delta _{x} + (1+\gamma )^2\left| x\right| ^{2\gamma } \Delta _{y}$$\end{document} is the Grushin operator, z:=(x,y)∈RN\documentclass[12pt]{minimal}
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\begin{document}$$z:=(x, y) \in \mathbb {R}^N$$\end{document}, N=m+n,\documentclass[12pt]{minimal}
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\begin{document}$$N=m+n,$$\end{document}m,n≥1,\documentclass[12pt]{minimal}
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\begin{document}$$m,n \ge 1,$$\end{document}Ω⊂RN\documentclass[12pt]{minimal}
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\begin{document}$$\Omega \subset \mathbb {R}^{N}$$\end{document} is a smooth bounded domain, λ>0\documentclass[12pt]{minimal}
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\begin{document}$$\lambda >0$$\end{document}, q∈[2,2γ∗)\documentclass[12pt]{minimal}
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\begin{document}$$q \in [2,2_\gamma ^*)$$\end{document} and 2γ∗=2NγNγ-2\documentclass[12pt]{minimal}
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\begin{document}$$2_{\gamma }^{*}=\frac{2N_\gamma }{N_\gamma -2}$$\end{document} is the critical Sobolev exponent in this context, where Nγ=m+(1+γ)n\documentclass[12pt]{minimal}
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\begin{document}$$N_\gamma =m+(1+\gamma )n$$\end{document} is the so-called homogeneous dimension attached to the Grushin operatorΔγ\documentclass[12pt]{minimal}
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\begin{document}$$\Delta _\gamma $$\end{document}. In order to prove our main results it was necessary to do a careful study involving the best constant Sγ(m,n)\documentclass[12pt]{minimal}
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\begin{document}$$\mathcal {S}_\gamma (m, n)$$\end{document} of the Sobolev embedding for the spaces associated with Δγ\documentclass[12pt]{minimal}
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\begin{document}$$\Delta _\gamma $$\end{document}. In order to do that, we prove a version of the Lions’ Concentration-Compactness Principle for the Grushin operator. We also provide existence results for a critical problem involving the Grushin operator on the whole space RN\documentclass[12pt]{minimal}
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\begin{document}$$\mathbb {R}^N$$\end{document}.
