In this paper, we consider the existence of nontrivial weak solutions to a double critical problem involving a fractional Laplacian with a Hardy term:
(−Δ)su−γu|x|2s=|u|2∗s(β)−2u|x|β+[Iμ∗Fα(⋅,u)](x)fα(x,u), u∈˙Hs(Rn),(0.1)
where
s∈(0,1),
0≤α,β<2s<n,
μ∈(0,n),
γ<γH,
Iμ(x)=|x|−μ,
Fα(x,u)=|u(x)|2#μ(α)|x|δμ(α),
fα(x,u)=|u(x)|2#μ(α)−2u(x)|x|δμ(α),
2#μ(α)=(1−μ2n)⋅2∗s(α),
δμ(α)=(1−μ2n)α,
2∗s(α)=2(n−α)n−2s and
γH=4sΓ2(n+2s4)Γ2(n−2s4). We show that problem (0.1) admits at least a weak solution under some conditions.
To prove the main result, we develop some useful tools based on a weighted Morrey space. To be precise, we discover the embeddings
˙Hs(Rn)↪L2∗s(α)(Rn,|y|−α)↪Lp,n−2s2p+pr(Rn,|y|−pr),(0.2)
where
s∈(0,1),
0<α<2s<n,
p∈[1,2∗s(α)) and
r=α2∗s(α). We also establish an improved Sobolev inequality,
(∫Rn|u(y)|2∗s(α)|y|αdy)12∗s(α)≤C||u||θ˙Hs(Rn)||u||1−θLp,n−2s2p+pr(Rn,|y|−pr), ∀u∈˙Hs(Rn),(0.3)
where
s∈(0,1),
0<α<2s<n,
p∈[1,2∗s(α)),
r=α2∗s(α),
0<max{22∗s(α),2∗s−12∗s(α)}<θ<1,
2∗s=2nn−2s and
C=C(n,s,α)>0 is a constant. Inequality (0.3) is a more general form of Theorem 1 in Palatucci, Pisante [1].
By using the mountain pass lemma along with (0.2) and (0.3), we obtain a nontrivial weak solution to problem (0.1) in a direct way. It is worth pointing out that (0.2) and 0.3) could be applied to simplify the proof of the existence results in [2] and [3].