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