On p-Laplace Equations with Singular Nonlinearities and Critical Sobolev Exponent
Abstract
In this paper, we deal with p-Laplace equations with singular nonlinearities and critical Sobolev exponent. By using the Nehari manifold, Mountain Pass theorem, and Maximum principle theorem, we prove the existence of at least four distinct nontrivial solutions.
1. Introduction
The term represented by the function f(x, u)≔|x|−αu|u|−β with 0 < β < 1 is the key to this famous work because we will allow us to combine the perturbation with the variational methods to overcome shortcomings in the form of singularity. He is well known in the scientific literature that the problems dealt with in applied mathematics have their origins in different fields we will cite as example: heterogeneous chemical catalysis, kinetic chemical catalysis, heat induction or electrical induction, non-Newtonian fluid theory, and viscous fluid theory (see, e.g., [22–26]).
We encounter Problem (1) in many nonlinear phenomena, for instance, in the theory of quasi-regular and quasi-conformal mapping, in the generalized reaction-diffusion theory, in the turbulent flow of a gas in a porous medium, and in the non-Newtonian fluid theory (see [27–30]).
Before giving our main results, we state here some definitions, notations, and known results.
for all , where u± = max{u±, 0}.
We know that Eθ is a C1−function on
Here .,. denotes the product in the duality , .
From [3], S is achieved.
The main results are concluded as the following theorems.
Theorem 1. Assume that N ≥ 3, 0 ≤ α < (N/(q + 1))(q + β), 0 < β < 1, and λ verifying 0 < λ < λ∗; then, the system (1) has at least one positive solution.
Theorem 2. In addition to the assumptions of the Theorem 1, there exists Λ∗ ∈ (0, λ∗∗) such that if λ satisfying 0 < λ < Λ∗, then (1) has at least two positive solutions.
Theorem 3. Under the assumptions of Theorem 2 then, there exists a positive real λ∗∗ such that if λ satisfies 0 < λ < λ∗∗, then (1) has at least four nontrivial solutions.
This paper is organized as follows. In Section 2, we give some preliminaries. Sections 3 and 4 are devoted to the proofs of Theorems 1 and 2. In the last section, we prove Theorem 3.
2. Preliminaries
Definition 4 (see [31].)Let c ∈ ℝM be a Banach space and E ∈ C1(M, ℝ).
- (i)
is a Palais-Smale sequence at level c (in short (PS)c) in M for E
- (ii)
We say that E satisfies the (PS)c condition if any (PS)c sequence in M for E has a convergent subsequence
2.1. Nehari Manifold [32, 33]
In our work, we research the critical points as the minimizers of the energy functional associated to the problem (1) on the constraint defined by the Nehari manifold.
In order to obtain the first positive solution, we give the following important lemmas.
Lemma 5. Eθ is coercive and bounded from below on .
Proof. Let R0 > 0 such that Ω ⊂ B(0, R0) = {x ∈ ℝN : |x| < R0}. If , then by (14) and the Hölder inequality, we obtain
where,
Therefore, we obtain that
Thus, Eθ is coercive and bounded from below on .
We have the following results.
Lemma 6. Suppose that u0 is a local minimizer for Eθ on .If , then u0 is a critical point of Eθ.
Proof. If u0 is a local minimizer for Eθ on , then u0 is a solution of the optimization problem:
Hence, there exists a Lagrange multipliers μ ∈ ℝ such that
Thus,
But ϕ′(u0), u0 ≠ 0, since . Hence, μ = 0. This completes the proof.
Lemma 7. There exists a positive number λ∗ such that for all λ verifying
Proof. Let us reason by contradiction.
Suppose that for all λ such that 0 < λ < λ∗. Then, by (20) and for , we have
Moreover, by the Hölder inequality and the Sobolev embedding theorem, we obtain
From (26) and (27), we obtain λ ≥ λ∗, which contradicts our hypothesis.
For the sequel, we need the following Lemma.
Lemma 8.
(i) For all λ such that 0 < λ < λ∗, one has c ≤ c+ < 0
(ii) For all λ such that 0 < λ < λ∗∗ there exists C0 > 0 such hat c− > −λp/(p − 1 + β)C0
Proof.
- (i)
Let . By (20), we have
- (ii)
Let . By(20), we get
By Sobolev embedding theorem, we obtain
This implies
By the proof of Lemma 5, we have
Thus, for all λ such that 0 < λ < λ∗∗ we have Eθ(u) ≥ −λp/(p − 1 + β)C0 with
As in [34] we have the following result.
Proposition 9.
(i) For all λ such that 0 < λ < λ∗, there exists a sequence in
(ii) For all λ such that 0 < λ < λ∗∗, there exists a sequence in and for each .
Define
Lemma 10. Suppose that 0 < λ < λ∗. For each , there exists unique t+ and t− such that 0 < t+ < tM < t−, , and
Proof. With minor modifications, we refer the reader to [34].
3. Proof of Theorem 1
Now, taking as a starting point the work of Tarantello [35], we establish the existence of a local minimum for Eθ on .
Proposition 11. For all λ such that 0 < λ < λ∗, the functional Eθ has a minimizer , and it satisfies
- (i)
- (ii)
is a nontrivial solution of (1)
Proof. If 0 < λ < λ∗, then by Proposition 9, (i) there exists a (un) sequence in ; , thus, it bounded by Lemma 5. Then, there exists and we can extract a subsequence which will denoted by (un) such that
Thus, by (39), is a weak nontrivial solution of (1). Now, we show that (un) converges to strongly in . Suppose otherwise. By the lower semi-continuity of the norm, if we have and we obtain
We get a contradiction. Therefore, (un) converge to strongly in . Moreover, we have . If not, then by Lemma 10, there are two numbers and , uniquely defined so that and . In particular, we have . Since
which contradicts the fact that . Since and , then by Lemma 6, we may assume that is a nontrivial nonnegative solution of (1). By the Harnack inequality, we conclude that (see, e.g., [29]).
4. Proof of Theorem 2
Next, we establish the existence of a local minimum for Eθ on . For this, we require the following Lemmas.
Lemma 12. Let (un) be (PS)c sequence for Eθ for some c ∈ ℝ with un⟶u in .
Then, and Eθ(u) ≥ −λp/(1 + β)C(q, β, Ψ, S), with C(q, β, Ψ, S) > 0.
Proof. Let (un) ⊂ Su be a minimizing sequence for Eθ with Su is the unit sphere. By Ekeland’ s variational principle [12], we may assume . So (un) is a (PS)c sequence and therefore un⟶u after passing to a subsequence. Hence Eθ(u) = c and , which implies that , and
Therefore,
From (15) and considering ‖u‖ small enough, we get
Set f(t) = Dtp − λEt1−β for all t > 0, with
Using (46), we obtain that
We have C(p, q, β, Ψ, S) > 0 since 0 < β < 1. Then, we conclude that
Lemma 13. Let λ ∈ (0, λ∗∗); then, the functional Eθ satisfies the (PS)c condition in with c < c∗, where
Proof. If 0 < λ < λ∗∗, then by Proposition 9, (ii) there exists a (un), (PS)c sequence in ; thus, it bounded by Lemma 5. Then, there exists and we can extract a subsequence which will denoted by (un) such that
Then, u is a weak solution of (1). Let vn = un − u; then, by Brézis-Lieb [36], we obtain
Since
Hence, we may assume that
Moreover, by Sobolev inequality, we have
Combining (60) and (59), we obtain
Either,
Then from (58), (59), Lemma 13 and Lemma 12, we obtain
Thus,
Lemma 14. There exists and Λ∗ > 0 such that for all λ ∈ (0, Λ∗), one has
In particular, c < c∗ for all λ ∈ (0, Λ∗).
Proof. Let φε(x) satisfies (4). Then, we have
We consider the two functions:
Then, for all for all λ ∈ (0, λ∗∗),
By the continuity of f, there exists t0 > 0 such that
On the other hand we have
Then, we obtain
Now, taking λ > 0 such that
Set
We deduce that c− < c∗ for all λ ∈ (0, Λ∗); then, there exists tn > 0 such that with wn satisfying (4) and for all λ ∈ (0, Λ∗),
Lemma 15. For all λ such that 0 < λ < Λ∗ = min{λ∗∗, Λ1}, the functional Eθ has a minimizer in and it satisfies
is a nontrivial solution of (1) in .
Proof. By Proposition 9 (ii), there exists a sequence (un) for E, in for all λ ∈ (0, λ∗∗). From Lemmas 13, 18, and 8(ii), for λ ∈ (0, Λ1), Eθ satisfies condition and c− > 0. Then, we get that (un) is bounded in . Therefore, there exist a subsequence of (un) still denoted by (un) and such that (un) converges to strongly in and for all λ ∈ (0, Λ∗).
Finally, by using the same arguments as in the proof of Proposition 11 for all λ ∈ (0, λ∗), we have that is a solution of (1).
Now, we complete the proof of Theorem 2. By Proposition 11 and Lemma 15, we obtain that (1) has two positive solutions and . Since , then, and are distinct.
5. Proof of Theorem 3
Firstly, we need the following Lemmas.
Lemma 16. Under the hypothesis of theorem 3, there exist Λ2 > 0 such that is nonempty for any λ ∈ (0, Λ2).
Proof. Fix and let
Clearly g(0) = 0 and g(t)⟶−∞ as t⟶+∞. Moreover, we have
Then, there exists t0 > 0 such that g(t0) = 0. Thus, and is nonempty for any λ ∈ (0, Λ2).
Lemma 17. There exist δ, λ∗ positive real numbers such that ϕ′(u), u?<−?<0, for and any λ verifying
Proof. Let then by (14), (20) and the Holder inequality, it allows us to write
Thus, if
Lemma 18. Suppose q > 2, β ∈ (0, 1) and 0 < λ < min(Λ2, Λ3, Λ4) when
Then, there exist ε and η positive constants such that
- (i)
We have
- (ii)
There exists when ‖v‖ > ε, with ε = ‖u‖, such that Eθ(v) ≤ 0
Proof. We can suppose that the minima of Eθ are realized by and . The geometric conditions of the mountain pass theorem are satisfied. Indeed, we have the following:
By exploiting the function ϕ(t) = atp − bt1−β which achieve its maximum at the point t1 = (1 − β/p)p/(β − 1 + p)(a/b)(p − 1)/(q − 1) such that if
- (ii)
Let t > 0, then we have for all
Letting v = tφ for t large enough, we obtain Eθ(v) ≤ 0. For t large enough, we can ensure ‖v‖ > ε.
Proof of Theorem 19. If
Thus, uc is the third solution of our system such that and . Since (1) is odd with respect u, we obtain that −uc is also a solution of (1).
Finally, for every θ ∈ (0, 1), problem (4) has solution such that Eθ(uθ) = 0. Thus, there exist {θn} ⊂ (0, 1) with θn⟶0 as n⟶∞. Then, we get .
6. Conclusion
In our work, we have searched the critical points as the minimizers of the energy functional associated to the problem on the constraint defined by the Nehari manifold , which are solutions of our problem. Under some sufficient conditions on coefficients of equation of (1) such that N ≥ 3, 0 ≤ α < ((N(q + β))/((q + 1))) and β ∈ (0, 1), we split in two disjoint subsets and ; thus, we consider the minimization problems on and , respectively. In Sections 3 and 4 we have proved the existence of at least two nontrivial solutions on for all 0 < λ < λ∗∗≔min(λ∗, Λ4) if N ≥ 3 and β ∈ (0, 1).
Conflicts of Interest
The author declares that there is no conflicts of interest.
Acknowledgments
The author gratefully acknowledge Qassim University, represented by the Deanship of Scientific Research, on the material support for this research under the number (1250) during the academic year 1443AH/2022 AD.
Open Research
Data Availability
The functional analysis data used to support the findings of this study are included within the article.