On existence and concentration of positive bound states of p-Laplacian equations in RN involving critical growth

On existence and concentration of positive bound states of p-Laplacian equations in RN involving critical growth

Nonlinear Analysis 62 (2005) 777 – 801 www.elsevier.com/locate/na On existence and concentration of positive bound states of p-Laplacian equations in...

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Nonlinear Analysis 62 (2005) 777 – 801 www.elsevier.com/locate/na

On existence and concentration of positive bound states of p-Laplacian equations in RN involving critical growth João Marcos do Ó∗,1 Departamento de Matemática, Universidade Fededral da Paraíba 58059-900, João Pessoa, PB Brazil Received 21 November 2003; accepted 14 March 2005

Abstract This paper deals with the study of the quasilinear critical problem ∗ −p p u + V (z)up−1 = f (u) + up −1 1, N u ∈ Cloc (R ) ∩ W 1,p (RN ), u > 0

in RN , in RN ,

(P )

where  is a small positive parameter; f is a subcritical nonlinearity; p∗ = pN/(N − p), 1 < p < N, is the critical Sobolev exponent; and V : RN → R is a function which is bounded from below away from zero such that inf j V > inf  V for some open bounded subset  of RN . We study whether we can find solutions of (P ) which concentrate around a local minima of V , not necessarily nondegenerate. The proof of this result is variational based on the local mountain-pass theorem. 䉷 2005 Elsevier Ltd. All rights reserved. MSC: 35J60; 35B25; secondary 35Q55; 58E05 Keywords: Elliptic problems; p-Laplacian; Critical growth; Variational methods; Mountain pass theorem

∗ Tel.: +55 83 216 7434; fax: +55 83 216 7277.

E-mail address: [email protected]. 1 Partially supported by PADCT/CT-INFRA/CNPq/MCT Grant # 620120/2004-5, PRONEX-MCT/Brazil and

Millennium Institute for the Global Advancement of Brazilian Mathematics-IM-AGIMB. 0362-546X/$ - see front matter 䉷 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.na.2005.03.093

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

1. Introduction The main purpose of this paper is to study the existence and concentration behavior of bound state for the quasilinear critical problem of the form −p p u + V (z)up−1 = f (u) + up 1, (RN ) ∩ W 1,p (RN ), u > 0 u ∈ Cloc

∗ −1

in RN , in RN ,

(P )

where  > 0 is a small real parameter; p u : =div(|∇u|p−2 ∇u) is the p-Laplacian, p ∗ = pN /(N − p), 1 < p < N, is the critical Sobolev exponent, and V : RN → R is a C 1 function satisfying (V0 ) there is a positive constant  such that V (z)  ∀z ∈ RN ; (V1 ) there is an open bounded subset  of RN such that inf V > inf V =: V0 . j



We also assume that f : R+ → R is a C 1 function satisfying the following conditions (f1 ) f (s) = o(s p−1 ) as s → 0; (f2 ) there are q1 , q2 ∈ (p − 1, p ∗ − 1),  > 0 such that f (s) s q1 , for all s > 0 and lim

s→∞

f (s) = 0; s q2

(f3 ) for some  ∈ (p, q2 + 1) we have 

s

0 < F (s) ≡ 

f (t) dt  f (s)s

for all s > 0;

0

(f4 ) the function s 1−p f (s) is nondecreasing for s > 0. The main result of this paper is stated as follows: Theorem 1.1. Suppose that the potential V satisfies (V0 )–(V1 ) and f satisfies (f1 )–(f4 ). Then there is o > 0 such that problem (P ) possesses a positive bound state solution u , for all 0 <  < o , provided that one of the following conditions holds: (a) N  p 2 ; (b) p < N < p2 , p ∗ − (c) p < N < p2 , p ∗ −

p p+1 p p+1

− 1 < q1 < p∗ − 1; − 1  q1 and large .

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Moreover, when 1 < p  2, u possesses at most one local (hence global) maximum z in RN , which is inside , such that lim V (z ) = Vo = inf V

→0+



and there are C and  positive constants such that     x − z    for all x ∈ RN . u (x)  C exp −    The study of such a class of problems in the semilinear case, which corresponds to p = 2, has been motivated in part by the search for standing waves for the nonlinear Schrödinger equation i

j 2 =−  + V (z) − ||r−1 , jt 2m

in RN ,

(1.1)

namely, solutions of the form (z, t) = exp(−iEt/)v(z), where , m, , and p are positive constants, p > 1, E ∈ R and v is real. In fact, it is readily checked that  satisfies (1.1) if, and only if, the function v(z) solves the semilinear elliptic equation

2 u + (V (z) − E)v = |v|r−1 v in RN . (1.2) 2m Floer and Weinstein [12], using Lyapunov–Schmidt methods have proved the existence of standing wave solutions concentrating at each given nondegenerate critical point of the potential V, provided that V is bounded, N = 1 and r = 3. Their method was extended by Oh [20,21] to higher dimensions, in the case 2 < r < (N + 2)/(N − 2). Rabinowitz [22] among others results obtained existence results under the assumption that inf V < lim inf |z|→∞ V (z) and 1 < r < (N + 2)/(N − 2). He used variational methods based on variants of the mountain-pass theorem and considered the case of degenerated critical point of the potential V. For this class of problems, Wang [28] complemented the work of Rabinowitz obtaining the concentration behavior of the solutions. Recently, in [9], del Pino and Felmer have proved the existence and concentration behavior of bounded state solutions under the potential conditions (V0 )−(V1 ) for subcritical nonlinearities. This result was complemented in [2] to elliptic problems involving critical growth. In this paper we extend these results, since we are considering a more general class of operator. To prove the existence of solutions, we adapt some ideas from [2,9] and to prove the decay of the solutions, we make use of the local estimates of Serrin [23]. To obtain the concentration behavior of solutions we use a recent result contained in [24], about symmetry of ground states solutions of quasilinear equations. Several papers have appeared recently about the p-Laplacian problems involving critical growth. For the case of bounded domains, we mention the works of Azorero and Alonso [3], Egnell [11] and Guedda and Veron [15], and references therein. As to unbounded domains, we recall the results of Alves et al. [1], Ben-Naoum et al. [4], Gonçalves and Alves [14] and Jianfu and Xi Ping [16]. We referred to their references for other related results. The underlying idea for proving Theorem 1.1 has two basic steps. First, in Section 2, we modify the function f (u) outside the domain  such that the associated energy functional −

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

to the modified problem satisfies the Palais–Smale condition and to which we may apply the mountain-pass theorem. In the last section, with the aid of some local estimates, we prove that the solution of the modified problem is in fact a solution for the original problem and we study the concentration behavior of the solution. Notation. In this paper we make use of the following notation: Let U be a domain in RN . C k, (U ), with k being a nonnegative integer and 0  < 1, denotes Hölder spaces; the norm in C k, (U ) is denoted by uk,, ; Lp (U ), 1  p  ∞, denotes Lebesgue spaces; the norm in Lp is denoted by |u|p ; W 1,p (U ), denotes Sobolev spaces; the norm in W 1,p (U ) is denoted by uW 1,p ; C, C0 , C1 , C2 , . . . denote (possibly different) positive constants; u+ = max{u, 0} and u− = min{u, 0}; A denotes the characteristic function of subset A of RN ; We denote by S the best Sobolev constant of the Sobolev embedding, D 1,m (RN ) → ∗ m L (RN ), that is, p

p

S = inf{|∇u|Lp /|u|Lp∗ : u ∈ D 1,m (RN )\{0}}.

(1.3)

According to Lemma 2 in [25], S is attained by the functions w given by w (z) =

C(N, p)(N−p)/p

2

[ + |z|p/(p−1) ](N−p)/p

(N−p)/p2    N − p p−1 with C(N, p) = N (1.4) p−1

for any z ∈ RN and any  > 0. 2. The modified functional Since we seek positive solutions, it is convenient to define f (s) = 0, for s  0. Also, we modify the nonlinearity f into a more appropriate one to obtain a existence result as an application of the mountain-pass theorem. Namely, we consider the following Carathéodory function:  ∗  (z)(f (s) + s p −1 ) + D (z)f(s) if s  0, g(z, s) =  0 if s < 0, where D = RN \,

 ∗ f (s) + s p −1 f(s) = −1 p−1 k s 

if s  a, if s > a,

∗ (s) = k > ( − p)−1 > 1 and a > 0 is such that f (a) + a p −1 = k −1 a p−1 . We set F s  1 2∗  f (t) dt and G(z, s) = F (s).  (F (s) + s ) +   D o 2∗ Notice that, using (f1 )–(f4 ) it is easy to check that the nonlinearity g(x, u) satisfies the following properties: ∗

(g1 ) g(z, s) = f (s) + s p −1 = o(s p−1 ), near the origin, uniformly in z ∈ RN ; ∗ (g2 ) g(z, s)  f (s) + s p −1 for all s > 0, z ∈ RN ;

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(g3 ) 0 < G(z, s)  g(z, s)s for all z ∈ , s > 0 or z ∈ D and s  a and 0  pG(z, s)  g(z, s)s  k1 (z)s p for all z ∈ D, s > 0. (g4 ) The function g(z, s)/s p−1 is increasing in s > 0 for each z fixed. Now, we consider the functional   1 J (u) = (|∇u|p + V (z)|u|p ) dz − G(z, u) dz, p RN RN defined on the reflexive Banach space 

 E = u ∈ W 1,p (RN ) : V (z)|u|p dz < ∞ , RN

endowed with the norm u : ={ RN (|∇u|p + V (z)|u|p ) dz}1/p . It is well known that J is in C 1 (E, R) (see [7]) with Fréchet derivative given by   g(z, u)v dz. [|∇u|p−2 ∇u∇v + V (z)|u|p−2 uv] dz − J  (u)v = RN

RN

It is standard to prove that J verifies the mountain-pass geometrical conditions. We include a proof for completeness. Lemma 2.1 (mountain-pass geometry). The functional J satisfies the following conditions: (i) there exist , > 0, such that J (u)  if u = , (ii) for any u ∈ C0∞ (, [0, +∞)), we have J∞ (tu) → −∞ as t → +∞. Proof. As usual, from our assumptions we have F (u) 

1 p ∗ |s| + C|s|p . 2p

Thus, using (g2 ) and Sobolev inequality, we find J (u) 

1 ∗ up − Cup . 2p

Hence, there exist constants , > 0, such that J (u)  if |u| = . Let u be a nontrivial function in C0∞ (, [0, +∞)). Thus, using (g2 ), for all t > 0 ∗  tp tp ∗ up . J (tu)  up − ∗ N p p R Of course, J (t ) → −∞ as t → ∞. This completes the proof.



Proposition 2.2. There exists a bounded sequence (un ) ⊂ E such that J (un ) → c,

0
1 N/p , S N

and J  (un ) → 0,

as

provided that one of conditions (1), (2) or (3) in Theorem 1.1 holds.

n → ∞,

(2.1)

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Proof. In view of Lemma 2.1, we may apply a version of mountain-pass theorem without a Palais–Smale condition (cf. [7,18]), to obtain a Palais–Smale sequence associated to the functional J, more precisely, (un ) ⊂ E such that J (un ) → c > 0

and

J  (un ) → 0,

(2.2)

where c = inf max J ((t)) ∈ t∈[0,1]

and

= { ∈ C([0, 1], E) : (0) = 0 and J ((1)) < 0}. Next, as a consequence of assumptions on g we prove that the mountain-pass minimax level c can be characterized in a simpler way, as has been established in [9,10] and [22] to the semilinear case. Assertion 2.1. c = inf max J (tv). v∈E v+  =0

t 0

(2.3)

Proof. From our hypothesis and Lemma 2.1, it is easy to check that for each fixed u ∈ E, such that u+  = 0, the function t −→ J (tu) has at most one critical point tu ∈ (0, +∞) and it satisfies  1 up = p−1 g(z, tu u)u dz. RN tu Furthermore, max J (tu) = J (tu u). t 0

Thus, inf max J (tv)  inf J (v),

v∈E v+  =0

t 0

v∈M

where M = {v = tu u : u ∈ E − {0} and tu ∈ (0, +∞)}. It is obvious that c  inf v∈M J (v). In order to prove the other inequality, given  ∈ , it is enough to obtain t ∈ (0, 1) such that u = (t ) ∈ M. Let us assume the contrary, that is, there is no t ∈ (0, 1) such that  (t)p = g(z, (t))(t) dz. RN

Thus, since (0) = 0, from (g1 ) we must have  g(z, (t))(t) dz ∀t ∈ (0, 1). (t)p > RN

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This estimate together with condition (g3 ) implies   1 1 J ((t)) = (t)p − G(z, (t)) dz > [g(z, (t))(t)−pG(z, (t))] dz p RN p RN  −p  G(z, (t)) dz  0 p  for all t ∈ (0, 1). But this is contrary to  ∈ . Thus, Assertion 2.1 holds.



Assertion 2.2. Every sequence (un ) ⊂ E satisfying (2.2) is bounded in E. Proof. Using assumption (g3 ) we find    1 1 1 1 J (un ) − J  (un )un = un p + [un g(z, un ) − G(z, un )] dz −  RN  p     1 1 1 p un  +  [un g(z, un ) − G(z, un )] dz − p   RN −    1 (p − ) 1 p un  + G(z, un ) dz −  p   RN −    1 1 (p − ) un p + −  V (z)|un |p dz p  pk  RN −     1 −p [|∇un |p + 1 − V (z)|un |p ] dz, (2.4) = N p k R which together with (2.2) implies that (un ) is bounded in E.



Now we closely follow the approach from [3], to prove the next result. Assertion 2.3. There exists v ∈ E − {0} such that max J (tv) < t 0

S N/p . N

(2.5)

Proof. For each > 0, consider the functions

(z)

(z) = (z)w (z) and v (z) = |z|  2

p∗

dz

1/p∗ ,

where ∈ C0∞ (RN , [0, 1]), (z) = 1 if |z|  1 and (z) = 0 if |z|  2. By a similar argument to that used in [3], we show that the functions w , and v satisfy the following

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

estimates: (A) |z|  1 |∇ (z)|p dz = O( (N−p)/p ), p∗ (B) k1 < |z|  2 (z) dz < k2 for sufficiently small, p∗ (C) |z|  1 |z|w (z) dz = O( (N−p)/p ), (D) RN |∇v (z)|p dz  S + O( (N−p)/p ). In view of Lemma 2.1, for each > 0 small, there exists t > 0 such that J (t v ) = max{J (tv ) : t  0}. Notice that, at t = t , we have d/dtJ (tv ) = 0. Thus, using (g1 ) and (f2 ),    p−1 p∗ −1 t [|∇v |p +V (z)|v |p ] dz= g(z, t v )v dz  (t v )q1 dz+t . RN

RN

RN

From this, condition (f2 ) and estimates (A)–(D), it follows that there is 0 > 0 such that t > 0 > 0 for all 0 < < 0 , where 0 is a positive constant independent of . Furthermore, by straightforward calculations we find  S N/p p q +1 (N−p)/p J (t v )  + O( )+ [C1 V (z)v − C2 v 1 ] dz N |z|  2

  S N/p p q1 +1 (N−p)/p (p−N)/p C0 + [C1 V (z)v − C2 v ] dz , +  N |z|  2 where C0 , C1 and C2 are positive constants independent of . Assertion 2.4. There is > 0 sufficiently small such that  p q +1 (p−N)/p C0 + [C1 V (z)v − C2 v 1 ] dz < 0. |z|  2

From the above estimate we easily see that max J (tv ) = J (t v ) < t 0

S N/p , N

and taking u = t v we obtain (2.5) and the proof of Assertion 2.3 is complete.



Proof of Assertion 2.4. Now we proceed to prove Assertion 2.4. Using estimates (A)–(D), and the expression of v we have (p−N)/p



 |z|  2

p

q +1

[C1 V (z)v − C2 v 1

] dz ( ) + ( ),

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

where

( ) = (p−N)/p



p

|z|  1

q +1

[C3 V (z)v − C4 v 1

785

] dz

 C5 (p −N)/p K − C6  (q1 +1)[(N−p)/p −(N−p)/p]+(p−1)N/p+(p−N)/p  (1−p)/p s N−1 ds K = p/(p−1) )N−p 0 (1 + s p q +1 [C3 V (z)v − C4 v 1 ] dz ( ) = (p−N)/p 1  |z|  2   p (p−N)/p  C5 w  C6 |z|p(p−N)/(p−1) dz  C7 2

2

1  |z|  2

1  |z|  2

for some positive constants C3 –C7 independent of . Finally, using these estimates and studying separately the conditions (a), (b) or (c) in Theorem 1.1, we prove that there exists > 0 such that

( )  C7 − C0 . Thus, Assertion 2.4 holds.



Finally, to complete the proof of Proposition 2.2 it is enough to use Assertions 2.1 and 2.2  Lemma 2.3. Let (un ) ⊂ E be a sequence satisfying (2.1). Then there is a sequence (yn ) ⊂ RN , and , > 0 such that  |un |p dz  . lim sup n→+∞

B (yn )

Furthermore, the sequence (yn ) is bounded in RN . Proof. Suppose that the first part of the Lemma is not satisfied. Since (un ) is bounded in E, using Lemma 1.1 in [17], it follows that  |un |q+1 dz → 0 as n → +∞ RN

for all p < q + 1 < p∗ . Thus, from our assumption on f we find    F (un ) dz = un f (un ) dz = on (1). RN

RN

Now, the expression of g(z, u) and (g3 ) yield    1  p∗ G(z, un ) dz  ∗ (un )+ dz+ |un |p dz + on (1) p ∪{un  a} pk (RN −)∩{un >a} RN

(2.6)

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

and  RN

 un g(z, un ) dz =

p∗

∪{un  a}

(un )+ dz +

 k

 (RN −)∩{un >a}

|un |p dz + on (1).

From (2.7) and J  (un ).un = on (1), we conclude that    p∗ un p − |un |p dz + on (1) = (un )+ dz. k (RN −)∩{un >a} ∪{un  a}

(2.7)

(2.8)

Let .  0 be such that   p |un |p dz → .. un  − k (RN −)∩{un >a} Notice that . > 0, otherwise we have     p p p |un | dz → 0, un   C un  − k (RN −)∩{un >a} that is, un → 0 in E, which implies that c = 0 and we get a contradiction with c  > 0. Thus, from (2.8) we have  p∗ (un )+ dz → .. ∪{un  a}

From J (un ) = c + on (1) and (2.6) it follows that  1 G(z, un ) dz c + on (1) = un p − N p R     1  1 p∗  |un |p dz − ∗ (un )+ dz un p − p k (RN −)∩{un >a} p ∪{un  a} and letting n → ∞ we get .  Nc.

(2.9)

Now, using (1.3) we have

 un  − k p

 (RN −)∩{un >a}

p

|un | dz  S

 ∪{un  a}

p∗ un

p/p∗ dz

.

Thus, passing to the limit and using (2.9) we achieve c

1 N/p , S N

which is a contradiction with (2.1). It remains to prove that (yn ) is bounded in RN . For this end we consider as test function un  , where  ∈ C0∞ (RN , [0, 1]),  (z) = 0 if |z| ,  (z) = 1 if |z|  2 and |∇  (z)|  C −1 for all z ∈ RN .

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

787

Since, J  (un )( un ) = on (1), we obtain       1 |∇un |p + V (z) − |un |p  dz  1− |un |p  dz  N k k RN R = − un |∇un |p−2 ∇un ∇  dz N R     + g(z, un )un − |un |p  dz + on (1). k RN If  is large enough,  ⊂ B (0), and from (g3 ) we have   C 1 p  1− |un |p  dz  un W 1,p + on (1). N k  R From (2.10), we conclude that (yn ) is bounded in RN .

(2.10)



Now we are ready to state the following existence result: Theorem 2.4. For all  > 0, the functional   . 1 p p p [ |∇u| + V (z)|u| ] dz − G(z, u) dz J (u) = p RN RN possesses a positive critical point u ∈ E at the level c =

inf

max J (tv).

(2.11)

v∈E−{0} t  0

Proof. We know that there exists a bounded sequence (un ) ⊂ E such that 1 N/p S , and J (un ) → 0, as n → ∞. N Then, up to a subsequence, un / u weakly in E. Now, using the same kind of ideas contained in [1,3,16] we can prove that, for all ∈ E, we have   |∇un |p−2 ∇un ∇ dz → |∇u |p−2 ∇u ∇ dz, N N R R p−2 V (z)|un | un dz → V (z)|u |p−2 u dz, N R RN   g(z, un ) dz → g(z, u ) dz. J (un ) → c ,

0 < c <

RN

RN

From these facts, together with J (un ) → 0 and passing to the limit, we easily obtain   [|∇u |p−2 ∇u ∇ +V (z)|u |p−2 u ] dz= g(z, u ) dz ∀ ∈ E, (2.12) RN

that is, u is a critical point of J . Assertion 2.5. u > 0 on RN .

RN

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

Proof. First, using Lemma 2.3, we are going to prove that u is nontrivial. We know that B (yn ) ⊂ BR (0) for all n, with suitable R > 0. Thus, up to a subsequence, 0<

√ p

 |un |Lp (B (yn ))  |un |Lp (BR (0))  |u |Lp (BR (0)) + |un − u |Lp (BR (0)) ,

which together with the Sobolev’s compact embedding theorem implies that u is nontrivial. Let u = (u )+ + (u )− and take = (u )− as test the function in (2.12); then   {|∇(u )− |p + V (z)(u )− |p } dz = g(z, (u )− )(u )− dz = 0. RN

RN

Hence (u )− = 0 almost everywhere in RN . Therefore u  0 almost everywhere in RN . Now, we claim that u > 0. Indeed, by contradiction, suppose that there exists x0 ∈ RN such that u (x0 ) = 0. Notice that u is a weak supersolution of the problem  −p u + V (x)up−1 = g(x, u)), x ∈ Br (x0 ), u(x) = 0 x ∈ jBr (x0 ). Now, using a standard bootstrap argument we may show that u ∈ L∞ (RN ); see Proposition 3.6. Hence, by Harnack’s inequality, see Theorem 1.2 in [27], we have u ≡ 0 in Br (x0 ), which is a contradiction.  Finally, it only remains to prove that the critical point u is in the level given in (2.11). For that matter, we use assumption (g3 ) and Fatou’s lemma, to obtain 1 c  max J (tu ) = J (u ) = J (u ) − J (u )u t 0 p  1 = [u g(z, u ) − pG(z, u )] dz p RN  

1  lim inf [un g(z, un ) − pG(z, un )] dz n→∞ p RN 

1  = lim inf J (un ) − J (un )un = c . n→∞ p Thus, u is a solution with minimal energy J (u ) = c and the proof of Theorem 2.4 is complete. 

3. Proof of Theorem 1.1 3.1. Existence of solution Let I denote the energy functional   1 (|∇u|p + V (x)|u|p ) dx − G(x, u) dx I (u) = p RN RN

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

defined in E = {u ∈ W

1,p



N

(R ) :

RN

789

V (x)|u|p dx < ∞},

associated with the problem  −p u + V (x)up−1 = g(x, u) in RN , u>0 in RN . From Theorem 2.4, the family of positive functions v (x) = u (z) = u (x), z = x is such that each v is a critical point of I at the level b = I (v ) =

inf

max I (tv).

v∈E \{0} t  0

It is easy to check that b = −N c . Furthermore, using Assertion 2.3 we also conclude that b < N1 S N/p . In order to derive a useful estimate of the mountain-pass minimax level b we consider a test function related to the solution of the autonomous problem  ∗ −p u + V0 up−1 = f (u) + up −1 in RN , (3.1) u>0 in RN . It is known that under assumptions (f1 )–(f4 ), problem (3.1) possesses a ground state solution  at the level c0 = I0 () =

inf

max I0 (tv) <

v∈E−{0} t  0

1 N S2, N

(3.2)

where I0 is defined as 1 I0 (u) = p

 RN

p

p

(|∇u| + V0 |u| ) dx −



 RN

p∗

u F (u) + +∗ p

 dx

(cf. [8]). Furthermore, in the case 1 < p  2, we have that  must be radially symmetric about some origin O in RN and the corresponding function (r) obeys  (r) < 0 for all r > 0 (see details in [5,6,24]). Lemma 3.1. lim sup→0 b  c0 . Proof. Let  be a ground state solution of problem (3.1), which without loss of generality we may assume maximizes at zero. Now consider the test function  (x) = (x)(x), where ∈ C0∞ (RN , [0, 1]), (x) = 1 if |x|  1 and (x) = 0 if |x|  2. It is easy to check that  →  in W 1,p (RN ), I0 ( ) → I0 (), as  → 0, and the support of  is

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

contained in  = {x ∈ RN : x ∈ }. For each  > 0 consider t ∈ (0, +∞) such that maxt  0 I (t  ) = I (t  ), thus b =

max I (tv)  max I (t  ) = I (t  ) t 0   ∗  (t  )p p p F (t  ) + dx. [|∇  | + V (x)| | ] dx − p∗ RN RN

inf

v∈E \{0} t  0 p 

t p

=

Assertion 3.1. t → 1 as  → 0. Proof. Since I (t  )(t  ) = 0, using assumption (f2 ) we have   ∗ p t (|∇  |p + V (x)| |p ) dx = [f (t  )t  + (t  )p ] dx N N R R ∗  [(t  )q1 +1 + (t  )p ] dx. RN

(3.3)

Since ( ) is bounded, from this estimate we derive easily that (t ) is bounded from above and below. Thus, up to a subsequence, we have t → t1 > 0. Passing to the limit in the first expression of (3.3), we have   ∗ −p p p (|∇ | + V0 || ) dx = t1 [f (t1 )t1  + (t1 )p ] dx. (3.4) RN

RN

Now, subtracting (3.4) from   p p (|∇ | + V0 || ) dx = N

R

we achieve  0=

RN

f (t1 ) (t1 )p−1



R

N

[f () + p ] dx,

  f ( ) ∗ p∗ −p p − p−1  dx + (t1 − 1) p dx. N  R

Thus, from (f4 ), we have t1 = 1.



Finally, we notice that we also have p  t (V (x) − V0 )| |p ) dx. I (t  ) = I0 (t  ) + p RN Thus, taking the limit as  → 0, using the fact that V (x) in bounded on the support of and the Lebesgue dominated convergence theorem, we conclude the proof of Lemma 3.1.  Now we have I (v )  c0 + o (1), where o (1) goes to zero as  → 0. Since for u ∈ W 1,p (RN ), from (V0 ) and (g2 ),

   1 . 1 p p p∗ ¯ I (u)  I (u) = F (u) + ∗ (u+ ) dx, (|∇u| + |u| ) dx − p RN p RN

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

791

then each b is bounded from below by c¯ > 0, the mountain-pass minimax level of the functional I¯. Notice that  p g(x, v )v dx |v |E = RN

and for  suitable small,   p G(x, v ) dx + c0 + 1, |v |E  p RN which together with assumption (g3 ) implies that     p [G(x, v ) − g(x, v )v ] dx + c0 + 1 − 1 |v |E  N p R [G(x, v ) − g(x, v )v ] dx + c0 + 1  N R −  ( − p)G(x, v ) dx + c0 + 1 RN −  ( − p) (−p) p p V (x)v dx + c0 + 1  |v |E +c0 +1.  N kp kp R − Thus |v |E  C, where C is a positive constant independent of . Of course, we have that (v ){0<  0 } is bounded in W 1,p (RN ). Lemma 3.2. There are 0 > 0, a family (y ){0<  0 } ⊂ RN and positive constants R, such that  p v dx  for all 0 < 0 . BR (y )

Proof. Assume, for the sake of contradiction, that there is a sequence n  0 such that for all R > 0,  p lim sup vn dx = 0. n→∞

x∈RN

BR (x)

Using Lemma 1.1 in [17], it follows that   F (vn ) dx = vn f (vn ) dx = on (1). RN

RN

This implies the estimates    1  p∗ p G(z, vn ) dx  ∗ vn dx + vn dx + on (1) N p pk R n ∪{vn  a} Dn ∩{vn >a}

(3.5)

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

and 

 RN

vn g(z, vn ) dx =

p∗

vn dx +

n ∪{vn  a}

 k



p

Dn ∩{vn >a}

vn dx + on (1), (3.6)

where D = RN \ . From equality (3.6) and In (vn ).vn = 0 we have vn p −

 k





p

Dn ∩{vn >a}

vn dx + on (1) =

p∗

n ∪{vn  a}

vn dx.

(3.7)

Since c¯ > 0, we have   p p vn  − v dx → . > 0. k Dn ∩{vn >a} n

(3.8)

Thus, from (3.7) and (3.8), 

p∗

vn dx → ..

n ∪{vn  a}

Using estimate (3.5) and the fact that In (vn )  c0 + on (1), we conclude that .  N c0 .

(3.9)

Now, using (1.3) we have

 vn  − k p





p

(RN −)∩{vn >a}

|vn | dx  S

p∗

∪{vn  a}

p/p∗

vn dx

.

Thus, passing to the limit and using (3.9) we achieve c0 

1 N/p S , N

which is a contradiction for (3.2), and the proof of Lemma 3.2 is complete.



Lemma 3.3. The family (y ){0<  0 } is bounded in RN and moreover, dist(y , ) R. Proof. For each  > 0, we set K = {x ∈ RN : dist(x, ) } and  (x) = (x), where  ∈ C ∞ (RN , [0, 1]) is such that (x) = 1 if x ∈ / K , (x) = 0 if x ∈  and |∇ |  C −1 . −1 Notice that |∇  |  C  . Using assumption (V0 ), we see that 

1  1− k



p

RN

|v |  dx 

 RN



 p |∇v |p + V (x) − v  dx. k

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

793

On the other hand, using I (v )v  = 0, condition (g3 ) and the fact that the support of  does not intercept  , we obtain   p v ] dx [|∇v |p + V (x) − k RN     p p−2 − v |∇v | ∇v ∇  dx + g(z, v )v − v  dx N N k R R    p p−2 =− v |∇v | ∇v ∇  dx + f˜(v )v − v  dx N k RN R p−2 ∇v ∇  dx − v |∇v | RN  (p−1)/p  1/p −1 p p |∇v | dx |v | dx  C −1 |v |p .  C RN

RN

Thus, from these estimates, we have   1  1− |v |p  dx  C −1 |v |p . k RN Notice that, if there is a sequence n  0 such that BR (yn ) ∩ {x ∈ RN : n x ∈ K } = ∅, then



1  1− k

 BR (yn )

|vn |p n dx  C −1 n |vn |p .

But this is contrary to Lemma 3.2. Thus, for all  > 0 there is an x such that x ∈ K and |x − y |  R, which implies that dist(y , ) R + . From this we conclude the proof.  Remark 1. From Lemma 3.3, we can see that the family (y ){0<  0 } given in Lemma 3.2, can be taken such that y ∈  for all 0 <  < 0 . Indeed, since dist(y , ) R, if necessary, we can replace y by −1 x where x ∈  and |y − −1 x | < R. Thus,   0 <  |v |p dx  |v |p dx BR (y )

B2R (−1 x )

and if we replace R by 2R in the Lemma 3.2, we have our claim. Next, we are going to prove that there is 0 > 0 such that the set

E = {x ∈ RN : v (x)  a and x ∈ / } is empty, for all 0 <  < 0 . For that matter we have the following basic result: Lemma 3.4. The following limits hold: (i) lim→0 b = c0 ;

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

(ii) lim→0 V (y ) = V0 ; (iii) lim→0 |E | = 0, where |E | denotes the Lebesgue measure of E . Proof. (i) Let n  0 and yn = yn . Since n yn ∈ , up to a subsequence, we have n yn → x0 ∈ . Set vn (x) = vn (x), n (x) = vn (x + yn ), En = En and Fn = Fn , where

F = {x ∈ RN : v (x + y )  a and x + y ∈ / }.

(3.10)

It is clear that |E | = |F |, since F is a translation of E . From the definition of n , we have for all ∈ C0∞ (RN ),   p−1 p−2 {|∇ n | ∇ n ∇ + V (n x + n yn )n } dx = g(n x + n y, n ) dx RN

RN

(3.11) W 1,p (RN )

and n W 1,p = vn W 1,p is bounded. Thus, we may assume that there is 0 ∈ such that n / 0 in W 1,p (RN ) and n (x) → 0 (x) a.e. in RN . Using Lemma 3.2, and taking R0 > 0 such that BR (yn ) ⊂ BR0 (0) for all n, we have  p  |n |Lp (BR (yn ))  |n |Lp (BR (0))  |n − 0 |Lp (BR0 (y)) + |0 |Lp (BR0 (y)) . From this estimate, using the Sobolev’s compact embedding theorem, we conclude that 0 is nontrivial and so nonnegative. Now, taking the limit in (3.11) and proceeding as in the proof of Theorem 2.4, we achieve that 0 is a critical point of the energy functional   1 ˜ I˜() = G(x, (|∇ |p + V (x0 )||p ) dx − ) dx, p RN RN that is,   p−1 p−2 [|∇ 0 | ∇ 0 ∇ + V (x0 )0 ] dx = RN

RN

g(x, ˜ 0 ) dx

∀ ∈ C0∞ (RN ), (3.12)

˜ is the primitive of where G p∗ −1

 g (x, 0 ) = (x)[f (0 ) + 0

] + (1 − (x))f(0 )

and

(x) = lim  (n x + n yn ) a.e. in RN . n→∞

Notice that, if x0 ∈ , we have (x) = 1 for all x ∈ RN , and so 0 is a critical point of the energy functional     ∗ p 1 p p ˜ Ix0 () = F () + ∗ dx. (|∇ | + V (x0 )|| ) dx − p RN p RN

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

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On the other hand, if x0 ∈ j, without loss of generality we suppose that the outer normal vector  in x0 is (1, 0, . . . , 0). Let P = {x ∈ RN : x1 < 0}. Notice that  ≡ 1 on P, since for each x ∈ P , we have that n x + n yn ∈ , for n large, because n yn ∈ . Thus, in both cases ∗  g (x, s) = f (s) + s 2 −1 , for all x ∈ P . This implies that the mountain-pass minimax level c˜ associated to the functional I˜ is equal to the mountain-pass minimax level c˜x0 associated to the functional I˜x0 . Indeed, from (g2 ), we have I˜x0 (u)  I˜(u), for all u ∈ W 1,p (RN ) and then c˜  c˜x0 . On the other hand, I˜x0 (u) = I˜(u) for all u with support contained in P. From (3.2), using Fatou’s Lemma and Lemma 3.1, we get   0 )] dx pc0  p I(0 ) = g (x, 0 ) − pG(x, [0 N R × lim inf [n g(n x + n yn , n ) − pG(n x + n yn , n )] dx N n→∞  R [n g(n x + n yn , n ) − pG(n x + n yn , n )] dx  lim inf N n→∞ R \Fn  lim inf [vn g(n x, vn ) − pG(n x, vn )] dx n→∞

RN \En

= lim inf [pI n (vn ) − In (vn )vn ]  pc0 .

(3.13)

n→∞

Thus (i) holds. Notice that if (ii) does not hold (that is, V (x0 ) > V0 ) we have c0 < c  I(0 ) = c0 , which is a contradiction; then V (x0 ) = V0 . To show (iii), we observe that from (3.13), we have  1 lim [vn g(n x, vn ) − pG(n x, vn )] dx = c0 n→∞ p RN \E n and lim

1 p

lim

1 p

n→∞

Thus n→∞

(3.14)

 RN

[vn g(n x, vn ) − pG(n x, vn )] dx = c0 .

 En

[vn g(n x, vn ) − pG(n x, vn )] dx = 0.

(3.15)

Now, using the definition of g(z, s) and assumption (f3 ) we can prove that 

   p ∗ [vn g(n x, vn )−pG(n x, vn )] dx= 1− ∗ a p +af (a)−pF (a) |En |>0, p En which together with (3.15) implies that limn→∞ |En | = 0, and the proof is complete. ∗

Lemma 3.5. v (x + y )(RN \F ) (x) converges to 0 in Lp (RN ).



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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

Proof. Following the notation of Lemma 3.4, we set  (x) = v (x + y ). We have proved in last lemma that b → c0 and that n converges in the weak sense to 0 , a ground state solution of the autonomous problem (3.1). From the proof of Lemma 3.4 and the regularity result below, we also have that g(x + y ,  ) converges uniformly over compacts to p∗ f (0 ) + 0 . Moreover, it follows from the definition of g and (3.10), using the Hölder’s inequality, that   p ∗ −p   p p g(x + y ,  ) dx =   | |Lp∗ |F | p∗ = o (1), k F k F which together with assumption (g3 ) implies that  G(x + y ,  ) dx = o (1). F

Now from (3.14) and definition of g, we have  pc0 + on (1) = [n g(n x + n yn , n ) − pG(n x + n yn , n )] dx RN \Fn    p∗ p∗ n dx. [n f (n ) − pF (n )] dx + 1 − = N N p R \Fn R \Fn Thus

 N

R \Fn

p∗ n

 dx →

and the proof is complete.

p∗

N

R

0 dx



We use the classical interactions method due to Moser to prove the regularity of the weak solutions, more precisely, we shall prove the following result: Proposition 3.6. v belongs to Ls (RN ) for all s ∈ [p ∗ , +∞]. Moreover, |v |∞  C, for all 0 <  < 0 and the solutions v decay uniformly to zero as |x| → +∞. Proof. In order to use the same kind of argument in [23], we are going to prove by induction that v ∈ Ln (RN ) for all n =pn , where =N/(N −p). By Gagliardo–Nirenberg–Sobolev inequality we have that v ∈ L1 . Assume that v ∈ Ln (RN ); then, we shall prove that v ∈ Ln+1 (RN ). For this end we consider the test function = p v [Tk (v )]sn , where Tk (v ) = min{k, v }, sn = p(n − 1) and  ∈ C0∞ (RN , [0, 1]). Using the fact that v is a critical point of I and assumptions (g2 ), (f1 ) and (f2 ) we find     p−1 p−1 p∗ −1 p−2 [|∇v | ∇v ∇ + V (x)v ] dx 

dx, v + C()v RN RN 2 which implies that   |∇v |p−2 ∇v ∇ dx  C() N

R

p∗ −1

N

R

v

dx.

(3.16)

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

797

From (3.16), it is easy to see that  p [Tk (v )]sn |∇v |p dx + sn p v [Tk (v )]sn −1 |∇v |p−2 ∇v ∇[Tk (v )] dx N RN R   p∗  −p p−1 v [Tk (v )]sn |∇v |p−2 ∇v ∇  + v p [Tk (v )]sn dx.



RN

RN

(3.17)

By Young’s inequality it follows that    

RN

  p−1 v [Tk (v )]sn |∇v |p−2 ∇v ∇  dx 

p   (p − 1) p−1 1 p p sn p   [Tk (v )] |∇v | dx + p v [Tk (v )]sn |∇ |p dx. N N p p  R R (3.18)

Using Gagliardo–Nirenberg–Sobolev inequality, we obtain |v [Tk (v )]

sn p

p |Lp∗



p p



|∇ | v [Tk (v )]u dx + p [Tk (v )]sn |∇v |p dx RN  p 

sn p + p v [Tk (v )]sn −p |∇[Tk (v )]|p dx , p RN

C

sn

RN

where C = C(N, p, ). This estimate together with (3.17) and (3.18) implies  sn p p |∇ |p v [Tk (v )]sn dx |v [Tk (v )] p |Lp∗  C p(n−1) RN

 p∗ p sn + v  [Tk (v )] dx . RN

Now, in order to prove that u ∈ Ln+1 (|x| ) for some large  > 0, we consider the function  ∈ C0∞ (RN , [0, 1]) such that  ≡ 1 if |x|  > 4,  ≡ 0 if |x|  − 2 and |∇ |  1. Hence, by Holder’s inequality,  RN

sn

p∗

p∗ −p

p

v p [Tk (v )]sn dx  |v [Tk (v )] p |Lp∗ |v |Lp∗ (|x|  /2) .

Thus sn

sn

p

p

|v [Tk (v )] p |Lp∗  C p(n−1) {||∇ |v [Tk (v )] p |Lp sn

p

p∗ −p

+ |v [Tk (v )] p |Lp∗ |v |Lp∗ (|x|  /2) }.

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801

Since |v |Lp∗  C, for all  ∈ (0, 0 ), we can take  suitably large such that [2C p(n−1) ] p∗ −p |v |Lp∗ (|x|  /2)  1, for all  ∈ (0, 0 ). Thus, we get the estimate sn

sn

p

p

|v [Tk (v )] p |Lp∗ (|x|  )  |v [Tk (v )] p |Lp∗  p  C p(n−1) |∇ |p v [Tk (v )]sn dx N R p(n−1)  C vn dx |x|  /2

for all  ∈ (0, 0 ), where C = C(N, p, , ). Therefore, letting k → +∞, by the dominated convergence theorem, 1

|v |Ln+1 (|x|  )  C n 

n−1 n

|v |Ln (|x|  /2)

∀ ∈ (0, 0 ).

(3.19)

We can use the same argument taking  ∈ C0∞ (RN , [0, 1]) with  ≡ 1 if |x0 − x|  ,  ≡ 0 if |x0 − x|  2 and |∇ |  2/ , to prove that 1

|v |Ln+1 (|x|   )  C n 

n−1 n

|v |Ln (|x|  2 )

∀ ∈ (0, 0 ),

(3.20)

where  is a suitable small positive constant independent of x0 and C = C(N, p, ,  ). Therefore, from (3.19) and (3.20), by a standard covering argument we can show that 1

|v |Ln+1  C n 

n−1 n

|v |Ln

∀ ∈ (0, 0 ).

Interaction yields |v |Ln+1  C

 1

n 

 n−1

n

|v |L1

∀ ∈ (0, 0 ),

where C is independent of n, since both series are convergent. Finally, letting n → ∞, and observing that |u|∞  limn→∞ |u|Ln we deduce easily that v ∈ L∞ (RN ) and, besides, |v |∞  C

for all 0 <  < 0 .

Since v ∈ L1 (RN ) ∩ L∞ (RN ), using the interpolation inequality, we prove that v ∈ L (RN ) for all  ∈ [1 , ∞]. By a similar argument used to prove Theorem 1 in [23] (see also [13, Theorem 8.17]), for any open ball Br (x) of radius r centered at any x ∈ RN and some constant C(N, 2 ), the nonnegative function u ∈ W 1,p (RN ) such that −p u  h(x) in the weak sense, satisfies the estimate sup u(y)  C{|u|Lp (B2r (x)) + |h|L2 (B2r (x)) }.

Br (x)

Thus, for the family {v } we have p∗ −1

sup v  C{|v |Lp (B2r (x)) + |v

Br (x)

|L2 (B2r (x)) } ∀ ∈ (0, 0 ).

J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801 p∗ −1

799 p∗ −1

By the preceding results we know that v ∈ L2 (RN ) and, moreover, |v |L2 (RN )  C where C is independent of . Therefore, the uniform vanishing property of the family {v }0<<0 is implied.  The next regularity result is a direct consequence of the previous proposition and a result due to Tolksdorf (cf. [26]). 1, Corollary 3.7. The functions v belongs to Cloc (Br ), where  = (r) ∈ (0, 1).

Finally, since the solutions v decay uniformly to zero as |x| → +∞, we can take  > 0 such that  (x) = v (x + y )  a for all |x|  and for all  ∈ (0, 0 ). On the other hand, taking 0 to be suitably small we see that B (0) ⊂  . Therefore, in both cases we see that p∗ −1 g(x + y,  ) = f ( ) +  in RN for all  ∈ (0, 0 ). Therefore the existence of a positive bounded state solution of problem (P ) for all  ∈ (0, 0 ) is proved. When 1 < p  2, elliptic regularity theory implies that  belongs to class C 2 and  converges in C 2 to 0 . Using Lemma 3.6, we have that  possesses a global maximum point x and after translation we may assume that  (0) = max|x|  R  = maxRN  , for some R > 0. Now, using that 0 is radially symmetric and a similar result to the Lemma 4.2 in [19], we can prove that for  sufficiently small,  possesses no critical points other than the origin. Finally, we are going to prove the exponential decay. Lemma 3.8. The family { }0<<0 satisfies

 (x)  C exp(− |x|) ∀x ∈ RN , where C and are positive constants independents of . Proof. Using assumption (f1 ) and the fact that the solutions  decay uniformly to zero as |x| → +∞, we can take 0 > 0 such that 1−p

2(f ( (x))

+  (x)p

∗ −p

)  V0 = inf V (x) 

for all |x| 0 .

Consequently, −p  +

V0 p−1 V0 p−1 ∗   f ( (x)) +  (x)p −1 −   0 2 2

for all |x| 0 .

Let  and M be positive constants such that (p − 1)p < V0 /2 and  (x)  M exp(−0 ) for all |x| = 0 . Hence, the function (x) = M exp(−|x|) satisfies   V0 V0 p−1 − (p − 1)p p−1 > 0 for all x  = 0.   −p  + 2 2 Since p > 1, we have that the function : RN → R, (x) = |x|p is convex, thus (|x|p−2 x − |y|p−2 y)(x − y)  0

for all x, y ∈ RN .

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J. Marcos do Ó / Nonlinear Analysis 62 (2005) 777 – 801 1,p

We now take as a test function = max{ − , 0} ∈ W0 (|x| > 0 ). Hence, combining these estimates,

  V0 p−1 p−1 p−2 p−2 ( −  (|∇  | ∇  − |∇ | ∇ ) + ) dx 0 2 RN V0 p−1  ( − p−1 )( − ) dx  0 for all |x| 0 . 2 {x∈RN :  } Therefore, the set {x ∈ RN : |x| 0 and  (x) (x)} is empty. From this we can easily conclude the proof.  Acknowledgements Part of this work was done while the author was visiting the IMECC-UNICAMP/BRAZIL. The author thanks Professor Marcelo Santos for some suggestions to improve this paper and all the faculty and staff of IMECC-UNICAMP for their kind hospitality.

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