In this article, we mainly study the global existence of multiple positive solutions for the logarithmic Schrödinger equation with a Coulomb type potential
−Δu+V(ϵx)u=λ(Iα∗|u|p)|u|p−1+ulogu2 in R3,
where u∈H1(R3), ϵ>0, V is a continuous function with a global minimum, and Coulomb type energies with 0<α<3 and p≥1. We explore the existence of local positive solutions without the functional having to be a combination of a C1 functional and a convex semicontinuous functional, as is required in the global case.
Citation: Fangyuan Dong. Multiple positive solutions for the logarithmic Schrödinger equation with a Coulomb potential[J]. Communications in Analysis and Mechanics, 2024, 16(3): 487-508. doi: 10.3934/cam.2024023
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In this article, we mainly study the global existence of multiple positive solutions for the logarithmic Schrödinger equation with a Coulomb type potential
−Δu+V(ϵx)u=λ(Iα∗|u|p)|u|p−1+ulogu2 in R3,
where u∈H1(R3), ϵ>0, V is a continuous function with a global minimum, and Coulomb type energies with 0<α<3 and p≥1. We explore the existence of local positive solutions without the functional having to be a combination of a C1 functional and a convex semicontinuous functional, as is required in the global case.
Recently, some studies have focused on the nonlinear Schrödinger equation
iϵ∂tΨ=−ϵ2ΔΨ+(V(x)+w)Ψ−λ(Iα∗|Ψ|p)|Ψ|p−1−Ψlog|Ψ|2, | (1.1) |
where Ψ:[0,∞)×RN→C,N≥3, α∈(0,N), p>1, λ is a physical constant and Iα is the Riesz potential, defined for x∈RN∖{0} as
Iα(x)=Aα|x|N−α, Aα=Γ(N−α2)Γ(α2)πN/22α. |
The problem described in equation (1.1) has various practical applications in fields such as quantum mechanics, quantum optics, nuclear physics, transport and diffusion phenomena, open quantum systems, effective quantum gravity, theory of superfluidity, and Bose-Einstein condensation. Notably, periodic potentials V can play a significant role in crystals and artificial crystals formed by light beams. While the logarithmic Schrödinger equation has been excluded as a fundamental quantum wave equation based on precise neutron diffraction experiments, there is ongoing discussion regarding its suitability as a simplified model for certain physical phenomena. The existence and uniqueness of solutions for the associated Cauchy problem have been investigated in an appropriate functional framework [1,2,3], and orbital stability of the ground state solution with respect to radial perturbations has also been studied [4,5,6]. The results regarding the wave equation can be referred to in [7,8,9,10].
In the Schrödinger equation, the convolution term involve the Coulomb interaction between electrons or interactions between other particles. In Schrödinger equations with convolution terms, this term typically represents the potential energy arising from interactions between particles. Physically, it implies that particles are influenced not only by external potential fields but also by the potential fields created by other particles. These interactions could involve electromagnetic forces, gravitational forces, or other types of interactions depending on the nature of the system. The introduction of the convolution term adds complexity to the Schrödinger equation because particle interactions are often non-local, extending across the entire spatial domain[11]. Overall, Schrödinger equations with convolution terms provide a more realistic description of interactions in multi-particle systems, enabling a more accurate understanding and prediction of the behavior of microscopic particles under mutual influences.
Understanding the solutions of the elliptic equation
−Δu+V(ϵx)u=λ(Iα∗|u|p)|u|p−1+ulogu2 in RN | (1.2) |
holds significant significance in the examination of standing wave solutions for equation (1.1). These standing wave solutions, characterized by the form Φ(t,x)=eiwt/ϵu(x), play a crucial role in various contexts and provide valuable insights into the behavior and properties of the equation.
In 2018, C. O. Alves and Daniel C. de Morais Filho [12] focus on investigating the existence and concentration of positive solutions for a logarithmic elliptic equation
{−ϵ2Δu+V(x)u=ulogu2, in RN,u∈H1(RN), |
where ϵ>0, N≥3 and V is a continuous function with a global minimum. To study the problem, the authors utilize a variational method developed by Szulkin for functionals that are a sum of a C1 functional with a convex lower semicontinuous functional.
In 2020, Alves and Ji [13] investigated the existence of multiple positive solutions for a logarithmic Schrödinger equation
{−ϵ2Δu+V(x)u=ulogu2, in RN,u∈H1(RN), |
where ϵ>0, N≥1 and V is a continuous function with a global minimum. By employing the variational method, the study demonstrates that when the parameter ϵ is sufficiently small, the number of nontrivial solutions is influenced by the "shape" of the graph of the function V.
In recent years, many authors have studied the nonlinear Schrödinger equation with the potential V. In 2022, Guo et al. [14] utilized fractional logarithmic Sobolev techniques and the linking theorem to elucidate existence theorems for equations with logarithmic nonlinearity. Further, a recent study [15] delineates conditions for a singular nonnegative solution in bounded Rn domains (n≥2), providing comprehensive insights into its behavior.
Inspired by the outcomes observed in the aforementioned papers, in this paper we aim to investigate the existence of multiple positive solutions for the problem (1.2) when N=3, λ>0 and 1≤p≤2∗. It is noteworthy that the introduction of a convolution term presents a notable aspect. The difficulty arises in analyzing the unique existence of solutions to the energy functional when both the convolution term and the logarithmic term operate concurrently. Addressing this challenge involves employing specialized analytical techniques, setting it apart from the methods utilized in [13], marking a novel approach.
In this paper, we shall prove the existence of solution for (1.2) in H1(R3). The associated energy functional of (1.2) will be defined as Jϵ:H1(R3)→(−∞,+∞),
Jε(u)=12∫R3(|∇u|2+(V(εx)+1)u2)dx−λ2p∫R3∫R3|u(x)|p|u(y)|p|x−y|3−αdxdy−∫R3H(u)dx, | (1.3) |
where
∫R3H(u)dx=∫R3−u22dx+u2logu22dx,∀u∈R3, |
with
H(u)=∫u0slogs2ds=−u22+u2logu22, |
and
L(u)=∫R3∫R3|u(x)|p|u(y)|p|x−y|3−αdxdy. |
Given the infinite character and lack of C1 smoothness of the functional Jε, a new approach is required to find weak solutions since traditional methods are not effective here. In this scenario, the fundamental element of our approach lies in harnessing the groundbreaking minimax method introduced by Szulkin [16]. Furthermore, we will employ the Gagliardo-Nirenberg inequality [17,18], the Brezis-Lieb lemma [19], and other specifically techniques for handling the nonlinear Coulomb potential, culminating in a robust result of strong convergence.
In our research, the potential V is based on the following assumptions[13]:
1∘. V:R3→R is a continuous function such that
lim|x|→+∞V(x)=V∞. |
with 0<V(x)<V∞ for any x∈R3.
2∘. There are l points z1,⋯,zl in R3 with z1=0 such that
1=V(zi)=minx∈R3V(x), for 1≤i≤l. |
By employing the variational method, we can establish the existence of non-trivial solutions for the logarithmic Schrödinger equation with a Coulomb-type potential when ϵ is sufficiently small (ϵ>0). This outcome is contingent upon the distinctive characteristics of the graph of the function V.
A positive solution of problem (1.2) means that there exists a positive function u∈H1(R3)∖{0} satisfy u2logu2<+∞ and
∫R3∇u⋅∇v+V(εx)u⋅vdx=λ∫R3(Iα∗|u|p)|u|p−1vdx+∫R3uvlogu2, for all v∈C∞0(R3). |
The main result is as follows.
Suppose that V satisfies 1∘ and 2∘. There exists ε∗>0 such that problem (1.2) has l positive soutions in H1(R3) for ε∈(0,ε∗).
The paper is organized as follows. In Section 2. we present several preliminary results that will be employed in the proofs of our main theorems. In Section 3. we prove the main result which are in the local case. In Section 4. we generalize the local results to the global space.
Notation: Henceforth, in this paper, unless otherwise specified, we adopt the following notations:
● BR(u) denotes an open ball centered at u with a radius of R>0.
● If g is a measurable function, the integral ∫RNg(x)dx will be denoted by ∫g(x)dx.
● C, C1, C2 etc. will denote positive constants of negligible importance with respect to their exact values.
● LR(u) denotes the function L(u) within the ball BR(0).
● ‖⋅‖p denotes the usual norm of the Lebesgue space Lp(R3), for p∈[1,+∞).
● on(1) denotes a real sequence with on(1)→0 as n→+∞.
● The expression ∬⋅ dxdy denotes ∫RN∫RN⋅ dxdy.
● 2∗=2NN−2.
In this section, we give some results and technical tools used for the main results.
First, we define the effective domain of J,
D(Jϵ):={u∈H1(R3):Jϵ(u)<+∞}. |
Considering the problem
−Δu+V(0)u=λ(Iα∗|u|p)|u|p−1+ulogu2 in R3, | (2.1) |
the corresponding energy functional associated to (2.1) is
J0(u)=12∫(|∇u|2+(V(0)+1)u2)dx−λ2p∬|u(x)|p|u(y)|p|x−y|3−αdxdy−12∫u2logu2dx. |
And define the Nehari manifold
Σ0={u∈D(J0)∖(0):J′0(u)u=0}, |
where
D(J0)={u∈H1(R3):J0(u)<+∞}. |
The problem (2.1) has a positive solution attained at the infimum,
c0:=infu∈Σ0J0(u), |
which will be proved in the Lemma 3. We shall additionally utilize the energy level
c∞:=infu∈Σ∞J∞(u), |
through replacing V(0) by V∞, and
Σ∞={u∈D(J∞)∖(0):J′∞(u)u=0}, |
it is clear that
c0<c∞. |
Regarding to the values of c0 and c∞, it should be noted that they correspond to the critical levels of the functionals J0 and J∞, commonly referred to as the Mountain Pass levels.
Based on the approach discussed in previous studies [12,20,21], we address the issue of J0 and J∞ lacking smoothness by decomposing them into a sum of a differentiable C1 functional and a convex lower semicontinuous functional, respectively. Following by [13], to facilitate this decomposition, for δ>0, we define the following functions:
F1(s)={0,s=0,−12s2logs2,0<|s|<δ,−12s2(logδ2+3)+2δ|s|−12δ2,|s|≥δ, |
and
F2(s)={0,|s|<δ,12s2log(s2/δ2)+2δ|s|−32s2−12δ2,|s|≥δ. |
Therefore
F2(s)−F1(s)=12s2logs2,∀s∈R. | (2.2) |
The functionals J0,J∞:H1(R3)→(−∞,+∞] can be reformulated as an alternative form denoted by
J0(u)=Φ0(u)+Ψ(u) and J∞(u)=Φ∞(u)+Ψ(u),u∈H1(R3) | (2.3) |
where
Φ0(u)=12∫(|∇u|2+(V(0)+1)|u|2)dx−λ2pL(u)−∫F2(u)dx | (2.4) |
Φ∞(u)=12∫(|∇u|2+(V∞+1)|u|2)dx−λ2pL(u)−∫F2(u)dx | (2.5) |
and
Ψ(u)=∫F1(u)dx. | (2.6) |
The properties of F1 and F2, as demonstrated in [20] and [21], can be summarized as follows:
F1,F2∈C1(R,R). | (2.7) |
For δ>0 small enough, F1 is convex, even, F1(s)≥0 for all s∈R and
F′1(s)s≥0, s∈R. | (2.8) |
For each fixed q∈(2,2∗), there is C>0 such that
|F′2(s)|≤C|s|q−1,∀s∈R. | (2.9) |
Utilizing the information provided earlier, it can be deduced that the functional Ψ possesses the properties of convexity and lower semicontinuity. Additionally, we can observe that the function Φ belongs to the class of C1 functions.
As we've discussed earlier, solutions to equation (1.2) within a localized context can be addressed through conventional techniques. However, the situation undergoes a transformation when we expand our scope to encompass the entire space. Within this broader perspective, it becomes apparent that the functional Ψ lacks the characteristic of continuous differentiability (C1). This particular case necessitates the application of a novel and separate critical point theorem. In the subsequent section, dedicated to the global case, it becomes essential to introduce definitions that were originally presented in the work referenced as [16].
Let J be a C1 functional defined on Banach space X, we say that {un} is a Palais-Smale sequence of J at c ((PS)c sequence, for short) if
J(un)→c, and J′(un)→0, as n→+∞ | (2.10) |
Let E be a Banach space, E′ be the dual space of E and ⟨⋅,⋅⟩ be the duality paring between E′ and E. Let J:E→R be a functional of the form J(u)=Φ(u)+Ψ(u), where Φ∈C1(E,R) and Ψ is convex and lower semicontinuous. Let us list some definitions:
1. The sub-differential ∂J(u) of the functional J at a point u∈H1(RN) is the following set
{w∈E′:⟨Φ′(u),v−u⟩+Ψ(v)−Ψ(u)≥⟨w,v−u⟩,∀v∈E} | (2.11) |
2. A critical point of J is a point u∈E such that J(u)<+∞ and 0∈∂J(u), i.e.,
⟨Φ′(u),v−u⟩+Ψ(v)−Ψ(u)≥0,∀v∈E | (2.12) |
3. A PS sequence at level d for J is a sequence (un)⊂E such that J(un)→d and there is a numerical sequence τn→0+ with
⟨Φ′(un),v−un⟩+Ψ(v)−Ψ(un)≥−τn‖v−un‖,∀v∈E | (2.13) |
4. The functional J satisfies the PS condition at level d ((PS)d condition, for short) if all PS sequences at level d has a convergent subsequence.
As [21] Lemma 2.2, J is of class C1 in H1(Ω) with Ω is a bounded domian. Hence we can construct the mountain pass structure and find the boundedness of the (PS) sequence without using the decomposition method in the local case, which is different from [12,13,20,21].
In order to make the subsequent theorem proof involving the whole space situation clearer, we explain some necessary concepts here. Henceforward, for every ω∈D(J0), the functional J10(w):H1c(R3)→R given by
⟨J′0(w),z⟩=⟨Φ′V(w),z⟩+∫F′1(w)z, ∀z∈H1c(R3) |
and
‖J′0(w)‖=sup{⟨J′0(w),z⟩:z∈H1c(R3), and ‖z‖v≤1}. |
If ‖J′0(ω)‖ is finite, then J′0(w) can be extended to a bounded operator in H1(R3) and can be therefore be viewed as an element of (H1(R3))′.
If {un}⊂D(J)∖{0} is a (PS) sequence for Jε, then J′ϵ(un)un=on(1)‖un‖V. If {un} is bounded, we have
Jϵ(un)=Jϵ(un)−12J′ϵ(un)un+on(1)‖un‖V=12∫|un|2dx+λ2(1−1p)L(un)+on(1)‖un‖V,∀n∈N. |
In this section, we provide the proof of the existence of l nontrivial critical points for Jϵ,R to equation (1.2) on a local case, which constitutes the preliminary step necessary for our main result. This serves as the foundational work leading up to our primary outcome.
Fix R0>0 such that zi∈BR0(0) for all i∈{1,⋯,l}. So for all R>R0 and u∈H1(BR(0)),
Jϵ,R(u)=12∫BR(0)(|∇u|2+(V(ϵx)+1)u2)dx−λ2pLR(u)−12∫BR(0)u2logu2dx. |
For any u,v∈H1(BR(0)), it is easy to verify that Jϵ,R∈C1(H1(BR(0)),R) and
J′ϵ,R(u)v=∫BR(0)∇u⋅∇vdx+V(ϵx)uvdx−λ∫BR(0)(Iα∗|u|p)|u|p−1vdx−∫BR(0)uvlogu2dx. |
The local space H1(BR(0)) is endow with the norm
‖u‖V=(∫BR(0)(|∇u|2+(V(ϵx)+1)u2)dx)12 |
which is also a norm in H1(R3).
According to the definition of V-norm and H1-norm, we have the following inequality
C1‖u‖H1≤(∫(|∇u|2+(V(ϵx)+1)u2)dx−λL(u)12)12≤‖u‖V≤C2‖u‖H1. |
One can see that V-norm is equivalent to H1-norm.
In the subsequent analysis, we denote Σϵ,R as the Nehari manifold correspond to Jϵ,R, which can be defined as follows:
Σϵ,R={u∈H1(B)∖{0},J′ϵ,R(u)u=0}={u∈H1(B)∖{0},Jϵ,R(u)=12∫BR(0)u2+λ2(1−1p)LR(u)}. |
For all ϵ>0, R>R0, Jϵ,R has the Mountain Pass geometry.
Proof. (i) Recall that
Jϵ,R(u)=12∫BR(0)(|∇u|2+(V(ϵx)+1)u2)dx−λ2pLR(u)−12∫BR(0)u2logu2dx. | (3.1) |
Following by the Hardy-Littlewood-Sobolev inequality and Sobolev imbedding, we obtain
LB(u)≤∬|u(x)|p|u(y)|p|x−y|N−αdxdy≤(∫|u|2NpN+αdx)N+αN≤C‖u‖2pV, | (3.2) |
where N+αN<p<N+αN−2. And for q>2 small and u>0, we have
∫u2logu2dx≤Cq∫|u|q≤‖u‖qV. | (3.3) |
Hence, by (3.1),(3.2) and (3.3), it follows that
Jϵ,R(u)≥12‖u‖2V−λC1‖u‖2pV−C2‖u‖qV>C>0, |
for a constant C>0, and ‖u‖V>0 small enough.
(ii) Fix u∈D(J)∖{0} with suppu⊂BR(0), and for s>0, λ>0, we have
Jϵ,R(su)=12∫BR(0)(s2|∇u|2+s2(V(εx)+1)u2)dx−λ2ps2pLR(u)−12s2logs2∫BR(0)u2dx−12s2∫BR(0)u2logu2dx≤s2(12∫BR(0)(|∇u|2+(V(εx)+1)u2)dx−logs∫BR(0)u2dx−12∫BR(0)u2logu2dx). |
Because of the boundness of Jϵ,R, there exist three bounded terms in the right side of the above inequality, except for the third term. Therefore, we obtain that Jϵ,R(u)→−∞ as s→+∞. So there exists s0>0 independent of ϵ>0 small enough and R>R0 such that Jϵ,R(s0u)<0.
All (PS) sequence of Jϵ,R are bounded in H1(BR(0)).
Proof. Let {un}⊂H1(BR(0)) be a (PS)d sequaence. Then,
|un|2L2(BR(0))+λ(1−1p)LR(un)≤2Jϵ,R(un)−J′ϵ,R(un)un=2d+on(1)+on(1)‖un‖V≤C+on(1)‖un‖V. | (3.4) |
for some C>0. And we ultilize the following logarithmic Sobolev inequality [11],
∫u2logu2≤a2π‖∇u‖2L2(RN)+(log‖u‖2L2(RN)−N(1+loga))‖u‖2L2(RN) | (3.5) |
for all a>0. By taking a2π=12, ξ∈(0,1) and combining (3.4) and(3.5) we get
∫BR(0)u2nlogu2n≤14‖∇un‖22+C(1+‖un‖V)1+ξ. | (3.6) |
Above all, for some ξ∈(0,1),
d+on(1)=Jϵ,R(un)=12∫BR(0)|∇un|2+12∫BR(0)(V(ϵx)+1)u2n−λ2pLR(un)−12∫BR(0)u2nlogu2n≥C‖un‖2V−(1+‖un‖V)1+ξ−λ2pLR(un). |
By (3.4) we have λ2pLR(un)≤λ2(1−1p)LR(un)≤C+on(1)‖un‖V, α∈(N2,N);p∈(2,N+αN−2) therefore it implies that
C‖un‖2V≤C(1+‖un‖V)1+ξ+C+on(1)‖un‖V, |
which means ‖un‖V≤C, i.e. (un) is bounded in H1(BR(0)).
Fix u0≠0, u0∈H1(BR(0)) and ∫u20logu20dx>−∞. According to
cϵ,R=infγ∈Γsupt∈[0,1]Jϵ,R(γ(t))≤supt>0Jϵ,R(tu0)=D0. |
where the definition of the path set γ is given in the lemma 3 and D0 is a uniform constant. Hence we obtain {un} is also bounded in H1(R3).
Now, for a fixed u∈D(J0)∖{0}, and t>0. Define the function
t→ϕ(t):=Jϵ(tu). |
Via computation, we have
ϕ′(t)=t(∫(|∇u|2+V(ϵx)u2)dx−λt2p−2L(u)−2logt∫u2dx−∫u2logu2dx). |
Setting f(t)=λat2p−1+2blogt, for a,b>0 and p>1. In the following, we prove that there exists an unique critical point ˜t, with ˜t>0, at which the function ϕ attains its maximum positive value.
1∘. According to Mountain Pass Geometry, there exists ˜t>0 such that f(˜t)=0, i.e. ϕ′(˜t)=0.
2∘. Since f′(t)=(2p−1)λat2p−2+2bt>0, we know that the function f is a monotonically increasing function, and furthermore, this means that ϕ reaches a positive maximum at the unique critical point ˜t.
Hence, for any u∈D(Jϵ)∖{0}, the intersection of every path {tu;t>0} forms a set
Σϵ={u∈D(Jϵ)∖{0};Jϵ(u)=12∫u2dx+λ2(1−1p)L(u)} |
exactly at the unique point ˜tu. Moreover, ˜t=1 if and only if
u∈Σϵ (˜t=1 ⟺ϕ′(˜t)=J′ϵ(˜tu)u=J′ϵ(u)u=0). |
Based on the energy levels shown above, the following results are obtained. For ϵ≥0,
cϵ=infu∈ΣϵJϵ(u). | (3.7) |
Proof. Let
Γ:={γ∈C([0,1],H1(R3)):γ(0)=0,J(γ(1))<0} |
we can define the mountain pass energy level
c:=infη∈Γsupt∈[0,1]J(η(t)). |
Let u∈Σϵ, we consider Jϵ(t0u)<0 for some t0>0. Then for the continuous path γϵ(t)=t⋅t0u, we have
infγ∈Γsupt∈[0,1]Jϵ(γϵ(t))=cϵ≤maxt∈[0,1]Jϵ(γϵ(t))≤maxt⩾0Jϵ(tu)=Jϵ(u). |
Hence
cϵ≤infu∈ΣϵJϵ(u). | (3.8) |
On the other hand, we will prove that cϵ≥infu∈ΣϵJϵ(u). Take a (PS) sequence {un}⊂H1(R3) for Jϵ. By Lemma 3, (un) is bounded in H1(R3). We claim ‖un‖2↛0. By contradiction, if ‖un‖2→0, using interpolation, ‖un‖q→0, for any q∈[2,2∗). Because |F′2(s)|≤C|s|q−1, then
∫F′2(un)un→0, |
and using Hardy-Littlewood-Sobolev inequality again, we obtain L(un)→0. Recall that
‖un‖2V+∫F′1(un)undx=J′ϵ(un)un+λL(un)+∫u2ndx+∫F′2(un)undx=on(1)‖un‖V+λL(un)+∫u2ndx+∫F′2(un)undx=on(1), | (3.9) |
from where it follows that ‖un‖V→0 and ∫F′1(un)un→0.
Since F1 is convex, even and F1(t)≥F1(0)=0, for all t∈R, we derive that 0≤F1(t)≤F′1(t)t for all t∈R. Hence F1(un)→0 in L1(R3). Then Jϵ(un)→Jϵ(0)=0, which contradicts to cϵ>0. Our claim is proved. Hence, there are constants b1 and b2 such that
0<b1≤‖un‖2≤b2. | (3.10) |
Next, let tn∈(0,1), tnun∈Σϵ, and recalling that
Jϵ(tnun)=12∫|tnun|2dx+λ2(1−1p)L(tnun)=12t2n∫|∇un|2dx+(V(ϵx)+1)u2ndx−λ2pt2pnL(un)−12t2nlogt2n∫u2ndx−12t2n∫u2nlogu2ndx. | (3.11) |
and
J′ϵ(un)un=∫(|∇un|2+V(ϵx)u2n)dx−λL(un)−∫u2nlogu2ndx. |
Then we get
λ(t2p−2n−1)L(un)+logt2n∫u2ndx=J′ϵ(un)un=on(1)‖un‖V. |
According to (3.10) and L(u)≥0, this equation implies tn→1. In addition, by (3.11) and Remark 2 we have
infu∈ΣϵJϵ(u)≤Jϵ(tnun)=t2n2∫u2ndx+λ2(1−1p)t2pnL(un)≤t2n(12∫u2ndx+λ2(1−1p)L(un))=t2n(Jϵ(un)+on(1)‖un‖V). |
Therefore, taking the limit we get
infu∈ΣϵJϵ(u)≤cϵ. |
The functional Jϵ,R satisfies the (PS) condition.
Proof. Take a (PS) sequence {un}⊂H1(BR(0)), it means that
Jϵ,R(un)→d, |
J′ϵ,R(un)un=on(1)‖un‖V. |
By Lemma 3, we know there exists {un}⊂H1(BR(0)), and a subsequence of un, which still denoted by itself such that ‖un‖V, i.e.
un→u in H1(BR(0)), |
un→u in Lq(BR(0)),∀q∈[1,2∗), |
un→u a.e. in BR(0). |
From [13], we set f(t)=tlogt2, F(t)=∫t0f(s)ds=12(t2logt2−t2) for all t∈R and for p∈(2,2∗), there is C>0 such that
|f(t)|≤C(1+|t|p−1), ∀t∈R |
and
|F(t)|≤C(1+|t|p), ∀t∈R. |
In addition, by definition of the norm in H1(BR(0)), we get
‖un−u‖2V=∫|∇(un−u)|2dx+(V(ϵx)+1)|un−u|2dx, |
J′ϵ,R(un)(un−u)=∫∇un∇(un−u)dx+V(ϵx)un(un−u)dx−λ∫(Iα∗|un|2)|un−u|undx−∫(un−u)unlogu2ndx=∫|∇(un−u)|2dx+V(ϵx)|un−u|2dx−λ∫(Iα∗|un−u|2)|un−u|2dx−∫f(un)|un−u|dx=on(1). |
Hence, it is easy to see that
∫|∇(un−u)|2dx+V(ϵx)|un−u|2dx=λ∫(Iα∗|un−u|2)|un−u|2dx+∫f(un)(un−u)dx+on(1)=on(1). |
It implies that
‖un−u‖V→0, |
which means the sequence {un} satisfies (PS) condition.
In fact, Theorem 3 concerns the existence of multiple solutions for equation (1.2) on a ball, which is crucial for the study of the existence of multiple solutions on the entire space as we desire. In order to prove this crucial result, we first present several lemmas. Next, we use the tricks in [13], by constructing l small balls and finding the center of mass, it plays a key role in the proof of the following theorem.
Fix ρ0>0 so that it satisfies ¯Bρ0(zi)∩¯Bρ0(zj)=ϕ for i≠j,i,j∈{1,⋯,l} and ⋃li=1Bρ0(zi)⊂BR0(0). Denote Kρ02=⋃li=1¯Bρ02(zi), and define the functional Qε:H1(R3)∖{0}→R3 by
Qε(u)=∫χ(εx)g(εx)|u|2dx∫g(εx)|u|2dx |
where χ:R3→R3 is given by χ(x)={x,|x|≤R0.R0x|x|,|x|>R0. and g:R3→R3 is a radial positive continuous function with
g(zi)=1, i∈{1,⋯,l} and g(x)→0, as |x|→+∞. |
The next lemma provides a useful way to generate (PS)c sequence associated with Jϵ. There exist α0>0, ϵ0>0, and R0>0 such that ε1∈(0,ε0) small enough and R1>R0 large enough, if u∈Σε,R and Jε,R(u)≤c0+α0, then Qε(u)∈Kρ02 for any ε∈(0,ε1) and R≥R1.
Proof. We prove this lemma by contradiction. If there is αn→0, εn→0 and Rn→∞, un∈Σεn,Rn satisfies
Jεn,Rn(u)≤c0+αn, |
but
Qε(un)∉Kρ02. |
By definition of c0 and Lemma 3, c0≤cεn,Rn, it is easy to see that
c0≤cεn,Rn≤Jεn,Rn(un)≤c0+αn |
which means JεnRn(un)=cεn,Rn+on(1). Denote the functional Ψεn,Rn:H1(BRn(0))→R by
Ψεn,Rn(u)=Jεn,Rn(u)−12∫BRn(0)|u|2−λ2(1−1p)LR(u). |
It implies that
Σεn,Rn={u∈H1(BR(0))∖{0}:Ψεn,Rn(u)=0}. |
Via computation, we obtain
Ψ′εn,Rn(u)u=−∫|u|2−λ(p−1)L(u)≤−β, ∀n∈N, |
where β>0 to guarantee cεn,Rn>0. Without loss of generality, we have the above conditions. We can then proceed to apply the Ekeland Variational Principle from Theorem 8.5 in [22], assuming that
‖J′εn,Rn(un)‖→∞, as n→∞. |
Now, from Jεn,Rn(un)=12∫BRn(0)|un|2dx+λ2(1−1p)LRn(un)≥c0>0, we have lim infn→∞Rn>0. And according to Section 6 in [12], there are two cases:
1. un→u≠0 in L2(RN), and u∈H1(RN).
2. There exists (yn)⊂RN such that vn=un(⋅+yn)⟶v≠0 in L2(RN), and v∈H1(RN).
For case (1), recall that our assumption ε→0, χ(0)=0 and g(0)=1
Qεn(un)=∫χ(εnx)g(εnx)|un|2dx∫g(εnx)|un|2dx→∫χ(0)g(0)|un|2dx∫g(0)|un|2dx=0∈Kρ02. |
This contradicts to Qεn∉Kρ02.
For case (2), there are two different situations. If |εnyn|→+∞, then J′∞(v)v≤0. Thus, for s∈(0,1] such that sv∈Σ∞,
2c∞≤2J∞(sv)=2J∞(sv)−J′∞(sv)sv=∫|sv|2+λ(1−1p)∬s2p|v|p(x)|v|p(y)|x−y|N−αdxdy≤∫|v|2+λ(1−1p)∬|v|p(x)|v|p(y)|x−y|N−αdxdy≤lim infn→+∞∫|vn|2+λ(1−1p)∬|vn|p(x)|vn|p(y)|x−y|N−αdxdy=lim infn→+∞∫|un|2+λ(1−1p)∬|un|p(x)|un|p(y)|x−y|N−αdxdy=limn→∞2Jεn,Rn(un)=2c0, |
which contradicts c0<c∞. If εnyn→y for some y∈RN, and some subsequence. In this case, the functional JV:H1(RN)→R is given by
JV(u)=12∫(|∇u|2+(V(y)+1)u2)dx−λ2p∬|un|p(x)|un|p(y)|x−y|N−αdxdy−12∫u2logu2dx, |
and cV is the moutain pass level of JV. Similar as before,
cV=infu∈ΣVJV(u), |
where
ΣV={u∈D(JV)∖{0}:JV(u)=12∫u2+λ2(1−1p)∬|u|p(x)|u|p(y)|x−y|N−αdxdy}. |
If V(y)>1=miniV(xi),i∈{1,⋯,l}, then
cV>c0, |
but according to the previous arguments
cV≤c0, |
which is a contradiction. So V(y)=1 and y=zi for i∈{1,⋯,l}.
Qεn(un)=∫χ(εnx)g(εnx)|un|2dx∫g(εnx)|un|2dx=∫χ(εn(x+yn))g(εn(x+yn))|vn|2dx∫g(εn(x+yn))|vn|2dx→∫χ(zi)g(zi)|v|2dx∫g(zi)|v|2dx=zi∈Kρ02. |
This is contrary to our initial hypothesis, and the proof is done.
In the following, for simplicity, we indicate the following notations.
Ωiε,R≜{u∈Σε,R:|Qε(u)−zi|<ρ0},∂Ωiε,R≜{u∈Σε,R:|Qε(u)−zi|=ρ0},αiε,R≜infu∈Ωiε,RJε,R(u),˜αiε,R≜infu∈∂Ωiε,RJε,R(u). |
For γ∈(c∞−c08,c∞−c02), there exists ε2∈(0,ε1) small enough such that
αiε,R<c0+γ and αiε,R<˜αiε,R |
for all ε∈(0,ε2), and R≥R1(ε)>R0.
Proof. Let u∈H1(R3) be a ground state solution of J0, that is for u∈Σ0,
J0(u)=infu∈Σ0J0(u)=c0, and J′0(u)=0. |
For any i∈{1,⋯,l}, there exists ε1>0 such that
|Qε(u(⋅−ziε))−zi|<ρ,∀ε∈(0,ε1). |
Fix R>R1=R1(ε) and tε,R>0 such that uiε,R(x)=tε,RφR(x)u(x−ziε)∈Σε,R,
|Qε(uiε,R)−zi|<ρ,∀ε∈(0,ε1) and R>R1, |
and
Jε,R(uiε,R)≤c0+α08, ∀ε∈(0,ε1),R>R1, | (3.12) |
where φR(x)=φ(xR) with φ∈C∞0(R3), 0≤φ(x)≤1 for all x∈R3,φ(x)=1 for x∈B12(0) and φ(x)=0 for x∈Bc1(0). So
uiε,R∈Ωiε,R∀ε∈(0,ε2) and R>R1. |
Take the infimum for (3.12), thanks to α0<c∞−c02,Jε,R≤c0+α0<c∞+c02, we get
αiε,R<c0+α04<c0+γ. | (3.13) |
Now let c∞−c08<γ<c∞−c02, then the first inequality is done. Next, if u∈∂Ωiε,R, then there is
u∈Σε,R and |Qε(u)−zi|=ρ0>ρ02, |
hence Qε(u)∉Kρ02. By Lemma 3, we have
Jε,R(u)>c0+α0 | (3.14) |
for u∈∂Ωiε,R and ε∈(0,ε2), R≥R1. Take the infimum for (3.14) we obtain
˜αε1R=inf∂Ωε,RJε,R(u)≥c0+α0,∀ε∈(0,ε2), R≥R1. | (3.15) |
Above all, from (3.13) and (3.15)
αiε,R<˜αiε,Rforε∈(0,ε2),andR≥R1, |
where ε2∈(0,ε1).
For ε∗∈(0,ε2) small enough and R1=R1(ε)>R0 large enough, there exist at least l nontrival critical points of Jε,R for ε∈(0,ε0) and R≥R1. Moreover, all of the solutions are positive.
Proof. From Lemma 3, for ε∗∈(0,ε2) small enough and R1>R0 large enough, there is
αiε,R<˜αiε,R for ε∈(0,ε∗) for R≥R1. |
As stated Theorem 2.1 in [23], the inequalities mentioned above enable us to employ Ekeland's variational principle to establish the (PS)αiε,R sequence (uin)⊂Ωiε,R for Jε,R. Following by Lemma 3, since αiε,R<c0+γ, there is ui such that uin→ui in H1(BR(0)). Then
ui∈Ωiε,R,Jε,R(ui)=αiε,R,J′ε,R(ui)=0. |
Recall that
¯Bρ0(zi)∩¯Bρ0(zj)≠ϕ,i≠j, |
and
Qε(ui)∈¯Bρ0(zi)(Qε∈Kρ2=l⋃i=1¯Bρ2(zi)). |
We have ui≠uj,i≠j,i,j∈{1,⋯,l}. If we decrease γ and increase R1 when necessary, we can assume that
2cε,R<c0+γ. |
for ε∈(0,ε∗),R≥R1. So all of the solutions do not charge sign, and because the function f(u)=ulogu2 is odd, we make them nonnegative. The maximum principle implies that any solution to a given equation or system of equations within the open ball BR(0) will necessarily be positive throughout the entire ball, provided that it is positive on the boundary.
In this section, we prove the existence of solution for the original equation (1.2).
For v∈H1(BRn(0)), uin=uiε,Rn be a solution obtained in Theorem 3.
∫BRn∇uin∇v+V(εx)uinv=λ∫BRn(Iα∗|uin|p)|uin|p−1vdx+∫BRnuinlog|uin|2vdx, |
Jε,Rn(uin)=αiε,Rn,∀n∈N. |
There exists ui∈H1(R3) satisfies uin⇀ui in H1(R3) and ui≠0, i∈{1,⋯,l}.
Proof. From Lemma 3, we know that {αiε,Rn} is a bounded sequence,
Jε,Rn(uin)=αiε,Rn<c0+γ |
which implies that {uin} is a bounded sequence. So we can assume that uin⇀ui for some ui∈H1(R3).
Next, we prove ui≠0. In the following, we use {un} and {αn} to denote {uin} and {αiε,Rn} for convenience.
To continue, let us utilize the Concentration Compactness Principle, originally introduced by Lions [13], applied to the following sequence.
ρn(x):=|un(x)|2‖un‖22,∀x∈R3. |
This principle guarantees that one and only one of the following statements is true for a subsequence for {ρn}, which we will still refer to as {ρn}:
(Vanishing) For all K>0, one has:
limn→+∞supy∈RN∫BK(y)ρndx=0; | (4.1) |
(Compactness) There exists a sequence {yn} in R3 with the property that for all ε>0, there exists K>0 such that for all n∈N, one has:
∫BK(yn)ρndx≥1−η; | (4.2) |
(Dichotomy) There exists {yn}⊂RN, α∈(0,1), K1>0, Kn→+∞ such that the functions ρ1,n(x)=χBK1(yn)(x)ρn(x) and ρ2,n(x):=χBcKn(yn)(x)ρn(x) satisfy:
∫ρ1,ndx→α and ∫ρ2,ndx→1−α. | (4.3) |
Our goal is to demonstrate that the sequence {ρn} satisfies the Compactness condition, and to achieve this, we will exclude the other two possibilities. By doing so, we will arrive at a contradiction, thus proving the proposition.
The vanishing case (4.1) can not occur, otherwise we deduce that ‖un‖p→0, and consequently ∫F′2(un)un<∞. By employing the same reasoning as in the previous section, it can be proven that un→0 in H1(R3). However, this contradicts the fact that αn≥c1 for all n∈N, as stated in Lemma 3.
The Dichotomy case (4.3) can not occur. Let us assume that the dichotomy case holds, under this assumption, we claim that the sequence {yn} is unbounded. If this were not the case and {yn} were bounded, then in that situation, utilizing the fact that ‖un‖L2(R3)↛0, the first convergence in (4.3) would lead to
∫BK1(yn)|un|2dx=|un|22∫R3ρ1,ndx⩾δ, |
for some δ>0 and n large enough. Therefore, taking R′>0 such that BK1(yn)⊂BR′(0) for all n∈N, it follows that ∫BR′(0)|un|2dx≥δ, for all n sufficiently large. Becauseun→0 in L2(BR′(0)), the inequality above is impossible. As a result, {yn} is an unbounded sequence. In the following, denote:
vn(x):=un(x+yn),x∈R3. |
Since the boundness of the sequence (vn)⊂H1(R3) and up to subsequence, we may assume that vn⇀v. By the first part of (4.3), v≢0 holds.
Claim4.1. F′1(v)v∈L1(R3) and J′∞(v)v≤0. For η∈C∞0(R3), 0≤η≤1, η≡1 in B1(0) and η≡0 in B2(0)c, we define ηR:=η(⋅R) and v=ηR(⋅−yn)un, we get
∫∇vn∇(ηRvn)dx+(V(ε(x+yn))+1)v2nηRdx+∫F′1(vn)vnηRdx=∫F′2(vn)vnηRdx+λ∫(Iα∗|vn|p)|vn|pηRdx+on(1). |
If we fix R and go to the limit in the above equation when n→∞, we get
∫|∇v|2ηRdx+v∇ηR⋅∇vdx+(V∞+1)v2ηRdx+∫F′1(v)vηRdx≤∫F′2(v)vηRdx+λ∫(Iα∗|v|p)|v|pηRdx |
where |∇ηR|≤2R, using that F′1(t)t≥0 for all t∈R, and Fatou's lemma as R→+∞, we obtain
∫|∇v|2dx+(V∞+1)v2dx−λ∫(Iα∗|v|p)|v|pdx+∫F′1(v)vdx−∫F′2(v)vdx≤0, |
that is J′∞(v)v≤0.
On this account, there exists t∞∈(0,1] such that t∞v∈Σ∞, then
c∞≤J∞(t∞v)=t2∞2∫|v|2dx+λ2(1−1p)t2p∞L(v)≤lim infn→+∞[12∫|vn|2dx+λ2(1−1p)L(vn)]≤lim supn→+∞[12∫|un|2dx+λ2(1−1p)L(un)]=lim supn→+∞Jεn,Rn(un)=lim supn→∞αn≤c0+γ. |
But we have γ<c∞−c0, it is absurd. Hence, there is no dichotomy, and in fact compactness must hold. We make the last requirement to achieve our aim.
Claim4.2. The sequence of points {yn}⊂R3 in (4.2) is bounded.
To establish this claim, we employ a proof by contradiction by assuming that the sequence of {yn} is bounded. However, by considering a subsequence, we observe that |yn|→+∞. Following a similar approach as in the case of the Dichotomy, where {yn} was unbounded, we eventually arrive at the inequality c0+γ≥c∞.
For a given η>0, there is R>0 such that
∫BcR(0)ρndx<η,∀n∈N, |
that is
∫BcR(0)|un|2dx≤η|un|22≤ηsupn∈N|un|22=bη. |
Therefore, for R1≥max{R,R′}, since un→0 in L2(BR1(0)), there is n0∈N large enough such that
∫BR1(0)|un|2dx≤η,∀n≥n0. |
Thereby, we conslude
∫|un|2dx≤η+∫BcR1(0)|un|2dx≤η+bη≤Cη, |
where C≁η. Due to the arbitrary nature of η, we can deduce that un→0 in L2(R3). By interpolation on the Lebesgue spaces and {un} is bounded in H1(R3), it follows that
un→0 in Lp(R3),2≤p<2∗. |
Using the trick that for some p>1 small, tlogt≤Ctp, it implies that
∫u2nlogu2n→0. |
For p∈(3+α3,3+α), the sequence {‖un‖p}n∈N converges to ‖u‖p in the sense of measures, {un}n∈N converges to u almost everywhere, the sequence {Iα∗|un|p}n∈Nis bounded in L2(R3) and u≠0.
From Proposition 4.8 in [24], since un∈D(J)∖{0} then we have
limn→∞∫R3Iα∗|un|p)|un|p−(Iα∗|un−u|p)|un−u|p=∫(Iα∗|u|p)|u|p. | (4.4) |
Above all, Jε,Rn(un)=αn→0, which contradicts αn≥cε>0, for all n∈N.
Proposition 4 yields a direct corollary as follows. For ε∈(0,ε∗) small, considering each sequence {uin}⊂H1(R3) as stated in Proposition 4, we have ui≠0 and J′ε(ui)v=0 for all v∈C∞0(R3), i.e. Jε has a nontrival weak solution ui. Moreover, for i∈{1,⋯,l},
Qε(uin)⟶Qε(ui). | (4.5) |
And since
Qε(uin)∈¯Bρ0(zi),∀n∈N, |
we have
Qε(ui)∈¯Bρ0(zi). | (4.6) |
Proof. By Proposition 4, ui≠0, i∈{1,⋯,l} and uin→ui in Lp1oc(R3) for p∈[2,2∗), we obtain that
∫uinlog|uin|2vdx→∫uilog|ui|2vdx,∀v∈C∞0(R3) |
Besides, as in Proposition 4 and (4.4), we have
limn→∞∫R3(Iα∗|uin|p)|uin|p−1v−(Iα∗|uin−ui|p)|uin−ui|p−1v=∫R3(Iα∗|ui|p)|ui|p−1v, |
for all v∈C∞0(R3). And since
∫(∇uin⋅∇v+(V(εx)+1)uinv)dx→∫(∇ui⋅∇v+V(εx)+1)uiv)dx, |
for all v∈C∞0(R3). We conclude that J′ε(ui)v=0 for all v∈C∞0(R3). By definition of g we have g(x)→0 as |x|→+∞, it is clear that
∫χ(εx)g(εx)|uin|2dx⟶∫χ(εx)g(εx)|ui|2dx |
and
∫g(εx)|uin|2dx→∫g(εx)|ui|2dx. |
Under the condition that these two limits hold, (4.5) and (4.6) are guaranteed.
Next, we give a proof of Theorem 1, that is, there exist l solutions ui∈H1(R3)∖{0}.
Proof of Theorem 1.
According to Corollary 4, for i∈{1,⋯,l} and ε∈(0,ε∗), there exists a solution ui∈H1(R3)∖{0} for problem (1.2) such that
Qε(ui)∈¯Bρ0(zi). |
Because we have
¯Bρ0(zi)∩¯Bρ0(zj)=ϕ,i≠j. |
Then it implies that ui≠uj for i≠j.
The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.
The author declares there is no conflict of interest.
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