## Boundary Value Problems

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# Existence of nontrivial solutions to perturbed p-Laplacian system in ℝ N involving critical nonlinearity

Boundary Value Problems20122012:53

DOI: 10.1186/1687-2770-2012-53

Accepted: 4 May 2012

Published: 4 May 2012

## Abstract

We consider a p-Laplacian system with critical nonlinearity in N . Under the proper assumptions, we obtain the existence of nontrivial solutions to perturbed p-Laplacian system by using the variational approach.

MR Subject Classification: 35B33; 35J60; 35J65.

### Keywords

p-Laplacian system critical nonlinearity variational methods.

## 1 Introduction

(1.1)

where Δ p u = div(|u|p-2u) is the p-Laplacian operator, 1 < p < N and p* = Np/(N − p) is the critical exponent.

Throughout the article, we will assume that:

(V0) V C( N ), V (0) = inf V (x) = 0 and there exists b > 0 such that the set ν b := {x N : V (x) < b} has finite Lebesgue measure;

(K0) K(x) C( N ), 0 < inf K ≤ sup K < ∞;

(H1) H C1(2) and H s , H t = o(|s|p-1+ |t|p-1) as |s| + |t| → 0;

(H2) there exist c > 0 and p < q < p* such that

(H3) There are a0> 0, θ (p, p*) and α, β > p such that H(s, t) ≥ a0(|s| α + |t| β ) and 0 < θH(s, t) ≤ sH s + tH t .

Under the above mentioned conditions, we will get the following result.

Theorem 1. If (V0), (K0) and (H1)-(H3) hold, then for any σ > 0, there is ε σ > 0 such that if ε < ε σ , the problem (1.1) has at least one positive solution (u ε , v ε ) which satisfy
The scalar form of the problem (1.1) is as follows
(1.2)

The Equation (1.2) has been studied in many articles. The case p = 2 was investigated extensively under various hypotheses on the potential and the nonlinearity by many authors including Brézis and Nirenberg [1], Ambrosetti [2] and Guedda and Veron [3] (see also their references) in bounded domains. As far as unbounded domains are concerned, we recall the work by Benci and Cerami [4], Floer and Weistein [5], Oh [6], Clapp [7], Del Pino and Felmer [8], Cingolani and Lazzo [9], Ding and Lin [10]. Especially, in [10], the authors studied the Equation (1.2) in the case p = 2. In that article, they made the following assumptions:

(A1) V C( N ), min V = 0 and there is b > 0 such that the set ν b := {x N : V (x) < b} has finite Lebesgue measure;

(A2) K(x) C( N ), 0 < inf K ≤ sup K <

(B1) h C( N × ) and h(x, u) = o(|u|) uniformly in x as |u| → 0;

(B2) there are c0> 0, q < 2* such that |h(x, u)| ≤ c0(1 + |u|q-1) for all (x, u);

(B3) there are a0> 0, p > 2 and µ > 2 such that H(x, u) = a0|u| p and µH(x, u) ≤ h(x, u)u for all (x, u), where .

That article obtained the existence of at least one positive solution u ε of least energy if the assumptions (A1)-(A2) and (B1)- (B3) hold.

For the Equation (1.2) in the case p ≠ 2, we recall some works. Garcia Azorero and Peral Alonso [11] considered (1.2) with ε ≤ 1, V (x) = µ, K(x) = 1, h(x, u) = 0 and proved that (1.2) has a solution if p2N and µ (0, λ1), where λ1 is the first eigenvalue of the p-Laplacian. In [12], Alves and Ding studied the same problem of [11] and obtained the multiplicity of positive solutions in bounded domain Ω N . Moreover, Liu and Zheng [13] investigated (1.2) in N with ε = 1 and K(x) = 0. Under the sign-changing potential and subcritical p-superlinear nonlinearity, the authors got the existence result.

Motivated by some results found in [10, 11, 13], a natural question arises whether existence of nontrivial solutions continues to hold for the p-Laplacian system with the critical nonlinearity in N .

The main difficulty in the case above mentioned is the lack of compactness of the energy functional associated to the system (1.1) because of unbounded domain N and critical nonlinearity. To overcome this difficulty, we make careful estimates and prove that there is a Palais-Smale sequence that has a strongly convergent sequence. The method or idea here is similar to the one of [10]. We can prove that the functional associated to (1.1) possesses (PS) c condition at some energy level c. Furthermore, we prove the existence result by using the mountain pass theorem due to Rabinowitz [14].

The main result in the present article concentrates on the existence of positive solutions to the system (1.1) and can be seen as a complement of the results developed in [10, 11, 13].

This article is organized as follows. In Section 2, we give the necessary notations and preliminaries. Section 3 is devoted to the behavior of (PS) c sequence and the mountain geometry structure. Finally, in Section 4, we prove the existence of nontrivial solution.

## 2 Notations and preliminaries

Let denote the collection of smooth functions with compact support and D1,p( N ) be the completion of under
We introduce the space
equipped with the norm
and the space
under

Observe that ‖ · ‖ E is equivalent to the one ‖ · ‖ λ for each λ > 0. It follows from (V0) that E( N , V) continuously embeds in W1,p( N ).

Set B = E λ × E λ and for any (u, v) B. Let λ = ε-pin the system (1.1), then (1.1) is changed into
(2.1)

In order to prove Theorem 1, we only need to prove the following result.

Theorem 2. Let (V0), (K0) and (H1)-(H3) be satisfied. Then for any σ > 0, there exists Λ σ > 0 such that if λ ≥ Λ σ , the system (2.1) has at least one least energy solution (u λ , v λ ) satisfying
(2.2)
The energy functional associated with (2.1) is defined by

where .

From the assumptions of Theorem 2, standard arguments [14] show that I λ C1(B, ) and its critical points are the weak solutions of (2.1).

## 3 Technical lemmas

In this section, we will recall and prove some lemmas which are crucial in the proof of the main result.

Lemma 3.1. Let the assumptions of Theorem 2 be satisfied. If the sequence {(u n , v n )} B is a (PS) c sequence for I λ , then we get that c ≥ 0 and {(u n , v n )} is bounded in the space B.

Proof. One has
By the assumptions (K0) and (H3), we have

Together with I λ (u n , v n ) → c and as n → ∞, we easily obtain that the (PS) c sequence is bounded in B and the energy level c ≥ 0. □

From Lemma 3.1, there exists (u, v) B such that (u n , v n ) (u, v) in B. Furthermore, passing to a subsequence, we have u n u and v n v in for any d [p, p*) and u n u, v n v a.e. in N .

Lemma 3.2. Let d [p, p*). There exists a subsequence such that for any ε > 0, there is r ε > 0 with

for any r ≥ r ε , where B r := {x N : |x| ≤ r}.

Proof. The proof of Lemma 3.2 is similar to the one of Lemma 3.2 of [10], so we omit it. □

Let η C(+) be a smooth function satisfying 0 ≤ η(t) 1, η(t) = 1 if t ≤ 1 and η(t) = 0 if t ≥ 2. Define , . It is obvious that
(3.1)
Lemma 3.3. One has
and

uniformly in (φ, ψ) B with ‖(φ, ψ B ≤ 1.

Proof. From the assumptions (H1)-(H2) and Lemma 3.2, we have
(3.2)
By Hölder inequality and Lemma 3.2, it follows that
and
Similarly, we get
and
Thus
From the similar argument, we also get

Lemma 3.4. One has along a subsequence
and
Proof. From the Lemma 2.1 of [15] and the argument of [16], we have
By (3.1) and the similar idea of proving the Brézis-Lieb Lemma [17], it is easy to get
and
In connection with the fact I λ (u n , v n ) → c and , we obtain

In the following, we will verify the fact .

For any (φ, ψ) B, it follows that
Standard argument shows that
and

uniformly in ‖φ, ψ)‖ B 1.

By Lemma 3.3, we have
and
uniformly in ‖(φ, ψ)‖ B 1. From the facts above mentioned, we obtain

Let , , then , . From (3.1), we get (u n , v n ) → (u, v) in B if and only if in B.

Observe that

where .

Thus by Lemma 3.4, we get
(3.3)

Now, we consider the energy level of the functional I λ below which the (PS) c condition hold.

Let V b (x):= max{V (x), b}, where b is the positive constant in the assumption (V0). Since the set ν b has finite measure and , in , we get
(3.4)
From (K0), (H1)-(H3) and Young inequality, there is C b > 0 such that
(3.5)
Let S be the best Sobolev constant of the immersion

Lemma 3.5. Let the assumptions of Theorem 2 be satisfied. There exists α0> 0 independent of λ such that, for any (PS) c sequence {(u n , v n )} B for I λ with (u n , v n ) (u, v), either (u n , v n ) (u, v) or .

Proof. Assume that (u n , v n ) (u, v), then
and
By the Sobolev inequality, (3.4) and (3.5), we get
This, together with and (3.3), gives
Set , then

This proof is completed. □

Since is not compact, I λ does not satisfy the (PS) c condition for all c > 0. But Lemma 3.5 shows that I λ satisfies the following local (PS) c condition.

Lemma 3.6. From the assumptions of Theorem 2, there exists a constant α0> 0 independent of λ such that, if a (PS) c sequence {(u n , v n )} B for I λ satisfies , the sequence {(u n , v n )} has a strongly convergent subsequence in B.

Proof. By the fact , we have

This, together with I λ (u, v) ≥ 0 and Lemma 3.5, gives the desired conclusion. □

Next, we consider λ = 1. From the following standard argument, we get that I λ possesses the mountain-pass structure.

Lemma 3.7. Under the assumptions of Theorem 2, there exist α λ , ρ λ > 0 such that
Proof. By (3.5), we get that for any δ > 0, there is C δ > 0 such that
Thus
Note that . If δ ≤ (2pλC1)-1, then

The fact p* > p implies the desired conclusion. □

Lemma 3.8. Under the assumptions of Lemma 3.7, for any finite dimensional subspace

F B, we have
Proof. By the assumption (H3), it follows that

Since all norms in a finite-dimensional space are equivalent and α, β > p, we prove the result of this Lemma. □

By Lemma 3.6, for λ larger enough and c λ small sufficiently, I λ satisfies (PS) condition.

Thus, we will find special finite-dimensional subspaces by which we establish sufficiently small minimax levels.

Define the functional

It is apparent that Φ λ C1(B) and I λ (u, v) ≤ Φ λ (u, v) for all (u, v) B.

Observe that
and

For any δ> 0, there are φ δ , with and suppφδ, such that .

Let , then . For t ≥ 0, we get
where
We easily prove that
Together with V (0) = 0 and , this implies that there is Λδ> 0 such that for all λ ≥ Λδ, we have
(3.6)

It follows from (3.6) that

Lemma 3.9. Under the assumptions of Lemma 3.7, for any > 0, there is Λσ> 0 such that λ ≥ Λσ, there exists with and

where ρ λ is defined in Lemma 3.7.

Proof. This proof is similar to the one of Lemma 4.3 in [10], it can be easily proved. □

## 4 Proof of the main result

In the following, we will give the proof of Theorem 2.

Proof. From Lemma 3.9, for any σ > 0 with 0 < σ < α0, there is Λ σ > 0 such that for λ ≥ Λ σ , we obtain

where

Furthermore, Lemma 3.6 implies that I λ satisfies (PS) condition. Hence, by the mountain-pass theorem, there is (u λ , v λ ) B satisfying I λ (u λ , v λ ) = c λ and This shows (u λ , v λ ) is a weak solution of (2.1). Similar to the argument in [10], we also get that (u λ , v λ ) is a positive least energy solution.

Finally, we prove (u λ , v λ ) satisfies the estimate (2.2). Observe that and we have

This shows that (u λ , v λ ) satisfies the estimate (2.2). The proof is complete. □

## Declarations

### Acknowledgements

The authors would like to appreciate the referees for their precious comments and suggestions about the original manuscript. This research is supported by the National Natural Science Foundation of China (10771212) and the Fundamental Research Funds for the Central Universities (2010LKSX09).

## Authors’ Affiliations

(1)
Department of Mathematics, China University of Mining and Technology

## References

1. Brézis H, Nirenberg L: Some variational problems with lack of compactness. Proc Symp Pure Math 1986, 45: 165-201.View Article
2. Ambrosetti A, Rabinowitz PH: Dual variational methods in critical point theory and applications. J Funct Anal 1973, 14: 349-381.
3. Guedda M, Veron L: Quasilinear elliptic equations involving critical Sobolev exponents. Non Anal 1989, 12: 879-902.
4. Benci V, Cerami G: Existence of positive solutions of the equation in N . J Funct Anal 1990, 88: 90-117.
5. Floer A, Weinstein A: Nonspreading wave packets for the cubic Schrödinger equation with a bounded potential. J Funct Anal 1986, 69: 397-408.
6. Oh YG: On positive multi-lump bound states of nonlinear Schrödinger equations under multiple well potential. Commun Math Phys 1990, 131: 223-253.
7. Clapp M, Ding YH: Minimal nodal solutions of a Schrödinger equation with critical nonlinearity and symmetric potential. Diff Integr Equ 2003, 16: 981-992.
8. Del Pino M, Felmer P: Semi-classical states for nonlinear Schrödinger equations. Annales Inst H Poincaré 1998, 15: 127-149.
9. Cingolani S, Lazzo M: Multiple positive solutions to nonlinear Schrödinger equation with competing potential functions. J Diff Equ 2000, 160: 118-138.
10. Ding YH, Lin FH: Solutions of perturbed Schrödinger equations with critical nonlinearity. Calc Var 2007, 30: 231-249.
11. Garcia Azoero J, Peral Alonso I: Existence and non-uniqueness for the p -Laplacian: Nonlinear eigenvalues. Commun Partial Diff Equ 1987, 12: 1389-1430.
12. Alves CO, Ding YH: Multiplicity of positive solutions to a p -Laplacian equation involving critical nonlinearity. J Math Anal Appl 2003, 279: 508-521.
13. Liu CG, Zheng YQ: Existence of nontrivial solutions for p -Laplacian equations in N . J Math Anal Appl 2011, 380: 669-679.
14. Mawhin J, Willem M: Critical Point Theory and Hamiltonian Systems. Springer-Verlag, New York; 1989.View Article
15. Li YY, Guo QQ, Niu PC: Global compactness results for quasilinear elliptic problems with combined critical Sobolev-Hardy terms. Non Anal 2011, 74: 1445-1464.
16. Ghoussoub N, Yuan C: Multiple solutions for quasi-linear PDES involving the critical Sobolev and Hardy exponents. Trans Am Math Soc 2000, 352: 5703-5743.
17. Brézis H, Lieb E: A relation between pointwise convergence of functions and convergence of functional. Proc Am Math Soc 1983, 88: 486-490.