# arXiv:1107.0375v1 [math.AP] 2 Jul 2011 2018. 10. 31.¢ The problems of this type are...

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### Transcript of arXiv:1107.0375v1 [math.AP] 2 Jul 2011 2018. 10. 31.¢ The problems of this type are...

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EXISTENCE AND MULTIPLICITY OF SOLUTIONS TO EQUATIONS

OF N−LAPLACIAN TYPE WITH CRITICAL EXPONENTIAL GROWTH IN RN

NGUYEN LAM AND GUOZHEN LU

Abstract. In this paper, we deal with the existence of solutions to the nonuniformly elliptic equation of the form

(0.1) − div (a (x,∇u)) + V (x) |u|N−2 u = f(x, u)

|x|β + εh(x)

in RN where 0 ≤ β < N , V : RN → R is a continuous potential satisfying V (x) ≥ V0 > 0 in RN and V −1 ∈ L1(RN ) or |{x ∈ RN : V (x) ≤ M}| < ∞ for every M > 0, f :

RN×R → R behaves like exp ( α |u|N/(N−1)

) when |u| → ∞ and satisfies the Ambrosetti-

Rabinowitz condition, h ∈ ( W 1,N

( RN ))

∗

, h 6= 0 and ε is a positive parameter. In particular, in the case of N−Laplacian, i.e,

(0.2) −∆Nu+ V (x) |u| N−2

u = f(x, u)

|x| β

+ εh(x)

using the minimization and the Ekeland variational principle, we obtain multiplicity of weak solutions of (0.2).

Moreover, we prove that it is not necessary to have the small nonzero perturbation εh(x) to get the nontriviality of the solution to the N−Laplacian equation

(0.3) −∆Nu+ V (x) |u| N−2

u = f(x, u)

|x| β

Finally, we will prove the above results when our nonlinearity f doesn’t satisfy the well- known Ambrosetti-Rabinowitz condition and thus derive the existence and multiplicity of solutions for a wider class of nonlinear terms f .

1. Introduction

In this paper, we consider the existence and multiplicity of nontrivial weak solution u ∈ W 1,N(RN) (u ≥ 0) for the nonuniformly elliptic equations of N−Laplacian type of the form:

(1.1) − div (a (x,∇u)) + V (x) |u|N−2 u = f(x, u)

|x|β + εh(x) in RN

where, in addition to some more assumptions on a(x, τ) and f which will be specified later in Section 2, we have

|a (x, τ)| ≤ c0

( h0 (x) + h1 (x) |τ |

N−1 )

Key words and phrases. Ekeland variational principle, Mountain-pass Theorem, Variational methods, Critical growth, Moser-Trudinger inequality, N−Laplacian, Ambrosetti-Rabinowitz condition.

Corresponding Author: G. Lu at gzlu@math.wayne.edu. Research is partly supported by a US NSF grant DMS0901761.

1

http://arxiv.org/abs/1107.0375v1

2 NGUYEN LAM AND GUOZHEN LU

for any τ in RN and a.e. x in RN , h0 ∈ LN/(N−1) ( RN ) and h1 ∈ L

∞ loc

( RN ) and f satisfies

critical growth of exponential type such as f : RN×R → R behaves like exp ( α |u|N/(N−1)

)

when |u| → ∞ and when f either satisfies or does not satisfy the Ambrosetti-Rabinowitz condition.

A special case of our equation in the whole Euclidean space when a (x,∇u) = |∇u|N−2∇u has been studied extensively, both in the case N = 2 (the prototype equation is the Lapla- cian in R2) and in the case N > 3 in RN for the N−Laplacain, see for example [11], [2], [3], [29], [19], [15, 16, 17], [5], etc. We should mention that problems involving Laplacian in bounded domains in R2 with critical exponential growth have been studied in [4], [19], [7], [8], [12], [32], etc. and for N−Laplacian in bounded domains in RN (N > 2) by the authors of [2], [15], [29].

The problems of this type are important in many fields of sciences, notably the fields of electromagnetism, astronomy, and fluid dynamics, because they can be used to accu- rately describe the behavior of electric, gravitational, and fluid potentials. They have been extensively studied by many authors in many different cases: bounded domains and unbounded domains, different behaves of the nonlinearity, different types of boundary conditions, etc. In particular, many works focus on the subcritical and critical growth of the nonlinearity which allows to treat the problem variationally using general critical point theory.

In the case p < N , by the Sobolev embedding, the subcritical and critical growth for the p−Laplacian mean that the nonlinearity f cannot exceed the polynomial of degree p∗ = Np

N−p . The case p = N is special, since the corresponding Sobolev space W 1,N0 (Ω) is

a borderline case for Sobolev embeddings: one has W 1,N0 (Ω) ⊂ L q (Ω) for all q ≥ 1, but

W 1,N0 (Ω) * L ∞ (Ω). So, one is led to ask if there is another kind of maximal growth in

this situation. Indeed, this is the result of Pohozaev [30], Trudinger [34] and Moser [28], and is by now called the Moser-Trudinger inequality: it says that if Ω ⊂ RN is a bounded domain, then

sup u∈W 1,N0 (Ω), ‖∇u‖LN≤1

1

|Ω|

∫

Ω

eαN |u| N

N−1 dx < ∞

where αN = Nw 1

N−1

N−1 and wN−1 is the surface area of the unit sphere in R N . Moreover,

the constant αN is sharp in the sense that if we replace αN by some β > αN , the above supremum is infinite.

This well-known Moser-Trudinger inequality has been generalized in many ways. For instance, in the case of bounded domains, Adimurthi and Sandeep proved in [3] that the following inequality

sup u∈W 1,N0 (Ω), ‖∇u‖LN≤1

∫

Ω

eαN |u| N

N−1

|x|β dx < ∞

holds if and only if α αN

+ β N

≤ 1 where α > 0 and 0 ≤ β < N .

On the other hand, in the case of unbounded domains, B. Ruf when N = 2 in [31] and Y. X. Li and B. Ruf when N > 2 in [25] proved that if we replace the LN -norm of ∇u in the supremum by the standard Sobolev norm, then this supremum can still be finite

ELLIPTIC EQUATIONS WITH CRITICAL GROWTH IN RN 3

under a certain condition for α. More precisely, they have proved the following:

sup u∈W 1,N0 (R

N ), ‖u‖N LN

+‖∇u‖N LN

≤1

∫

RN

( exp

( α |u|N/(N−1)

) − SN−2 (α, u)

) dx

{ ≤ ∞ if α ≤ αN , = +∞ if α > αN

,

where

SN−2 (α, u) = N−2∑

k=0

αk |u|kN/(N−1)

k! .

We should mention that for α < αN when N = 2, the above inequality was first proved by D. Cao in [11], and proved for N > 2 by Panda [29] and J.M. do O [15, 16] and Adachi and Tanaka [1].

Recently, Adimurthi and Yang generalized the above result of Li and Ruf [25] to get the following version of the singular Trudinger-Moser inequality (see [5]):

Lemma 1.1. For all 0 ≤ β < N, 0 < α and u ∈ W 1,N ( RN ) , there holds

∫

RN

1

|x|β

{ exp

( α |u|N/(N−1)

) − SN−2 (α, u)

} < ∞

Furthermore, we have for all α ≤ ( 1− β

N

) αN and τ > 0,

sup ‖u‖1,τ≤1

∫

RN

1

|x|β

{ exp

( α |u|N/(N−1)

) − SN−2 (α, u)

} < ∞

where ‖u‖1,τ = (∫

RN

( |∇u|N + τ |u|N

) dx )1/N

. The inequality is sharp: for any α > ( 1− β

N

) αN , the supremum is infinity.

Motivated by this Trudinger-Moser inequality, do Ó [15, 16] and do Ó, Medeiros and Severo [17] studied the quasilinear elliptic equations when β = 0 and Adimurthi and Yang [5] studied the singular quasilinear elliptic equations for 0 ≤ β < N , both with

the maximal growth on the singular nonlinear term f(x,u) |x|β

which allows them to treat

the equations variationally in a subspace of W 1,N ( RN ) . More precisely, they can find a

nontrivial weak solution of mountain-pass type to the equation with the perturbation

− div ( |∇u|N−2∇u

) + V (x) |u|N−2 u =

f(x, u)

|x|β + εh(x)

Moreover, they proved that when the positive parameter ε is small enough, the above equation has a weak solution with negative energy. However, it was not proved in [5] if those solutions are different or not. We also should stress that they need a small nonzero perturbation εh(x) in their equation to get the nontriviality of the solutions.

In this paper, we will study further about the equation considered in the whole space [2, 15, 16, 17, 5]. More precisely, we consider the existence and multiplicity of nontrivial weak solution for the nonuniformly elliptic equations of N−Laplacian type of the form:

(1.2) − div (a (x,∇u)) + V (x) |u|N−2 u = f(x, u)

|x|β + εh(x)

where |a (x, τ)| ≤ c0

( h0 (x) + h1 (x) |τ |

N−1 )

4 NGUYEN LAM AND GUOZHEN LU

for any τ in RN and a.e. x in RN , h0 ∈ LN/(N−1) ( RN ) and h1 ∈ L

∞ loc

( RN ) . Note that the

equation in [5] is a special case of our equation when a (x,∇u) = |∇u|N−2∇u. In fact, the elliptic equations of nonuniform type is a natural generalization of the p−Laplacian equation and were studied by many authors, see [18, 20, 21, 22, 33]. As mentioned earlier, the main features of this class of equations are that they are defined in the whole RN

and with the critical growth of the singular nonlinear term f(x,u) |x|β

and the nonuniform

nonlinear operator of p-Laplacian type. In spite of a possible failure of the Palais-Smale compactness condition, in this paper, we still use the Mountain-pass approach for the critical growth as in [15, 5, 16, 17] to derive a weak solution and get the nontriviality of this s

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