(School of Mathematical Sciences,Xiamen University,Xiamen 361005,China)
generalized complex Monge-Ampè;re type equation; gradient estimate; Hermitian manifold
DOI: 10.6043/j.issn.0438-0479.201711005
备注
利用Bernstein方法建立了Hermitian流形上带有梯度项的广义复Monge-Ampère型方程的梯度的先验估计.广义复Monge-Ampère型方程的结构在证明中发挥了重要作用.
We apply Bernstein method to derive the a priori gradient estimates for generalized complex Monge-Ampère-type equations involving gradient terms on compact Hermitian manifolds.Structural conditions of such generalized complex Monge-Ampère type equations play some crucial roles.
引言
令(M,ω)为一个复n维紧致的Hermitian流形,ω=(-1)1/2gi(-overj)dzi∧d(-overz)j为Kähler形式.本文中研究了带梯度项的广义复Monge-Ampère型方程的梯度估计
ψχnu=∑n-1k=0(n!)/(k!(n-k)!)ckχku∧ωn-k,(1)
其中,ck均为满足∑n-1k=0ck>0的非负常数,χ(z,ζ)为一个光滑的实(1,1)-形式,χu=χ(z,du)+(-1)1/2(-over)u,ψ 为正的光滑函数,且
χξ(-overη)(z,ζ):=χ(z,ζ)(ξ,(-overη)),ξ,η∈T1,0zM,
且(z,ζ)∈T*CM.(2)
若c0=1且其他的常数为零,则方程(1)就是著名的复Monge-Ampère型方程.带梯度项的复Monge-Ampère型方程的一个特殊且重要的例子是Sasakian度量空间的测地线方程[1].本研究的目的之一是将他们的估计推广到更一般的情形.当c0=c1=…=cn-3=0时,笔者得到了方程(1)的C2,α-估计[2].
对于标准的方程而言,即 χ 为流形 M 上一个光滑的实(1,1)-形式,这类形如式(1)的方程的研究可追溯到文献[3-6],这些工作研究了复 Monge-Ampère 方程.从那以后,这类方程引起了很多有趣且重要的研究,可
参考文献[7-14]及其引用的文献.
众所周知,Hessian型完全非线性椭圆方程Dirichlet问题的梯度估计是非常难的.就笔者所知,即使在Riemann情形下,已知的也只不过4种情形.列举如下:1)Γ=Γn; 2)如果λj<0,对于Γσ,当σ>supΓ f,那么存在δ>0使得fj≥δ∑fi; 3)((-overM),g)的截面曲率非负; 4)在集合{λ∈Γ:inf(-overM) ψ≤f(λ)≤sup(-overM) ψ}上有 ∑fi(λ)λi≥0,并且存在函数w∈C2((-overM))使得Δ2w≥χ.有兴趣的读者请
参考文献[15-18].与Riemann情形相比,复流形情形下的梯度估计更少.依据已知的结果,读者可
参考文献[10-11,19-21],在这些文献中,研究了复Monge-Ampère方程、反σk方程还有具非负全纯双截面曲率的紧致Kähler形上的复Hessian方程的梯度估计.
在陈述本文中主要结果之前,需要介绍一些符号.在局部坐标(z1,…,zn)下,记
i=/(zi),
^-i=/((-overz)i),
χi(-overj)=χ(z,du)(i,^-j),
χi(-overj)k:=Δk(χi(-overj))=χi(-overj),k+χi(-overj),ζαuαk+χi(-overj),(-overζ)αu(-overα)k,….(3)
同时需假设χ满足如下结构条件:
χi(-overj),ζαζβ=0,
χi(-overj),ζα(-overζ)β=0,
χi(-overj),(-overζ)α(-overζ)β=0.(4)
本文中的主要结果可如下表述:
定理1 如果条件(4)成立且存在一个函数u_-∈C2(M)使得 χu_->0,且
ψχn-1u_--∑n-1k=0((n-1)!)/(k!(n-k)!)kckχk-1u_-∧ωn-k>0,(5)
那么对于方程(1)满足χu>0的解 u∈C3(M),存在一个依赖|ψ|C0,1(M)及其他已知信息的常数C,使得
supM|Δu|≤C(1+supM|Δu|).(6)
注1 定理 1推广了Guan等[1]的梯度估计.条件(5)可看成一种锥条件[13],有兴趣的读者可
参考文献 [9-10,12,22].
1 预备知识
记 λ=λ(χu)为 χu关于Kähler形式ω的特征根.令 σk为一个初等对称函数,其定义为
σk(λ)=∑1≤i1<…<ik≤nλi1…λik,(7)
方程(1)可等价地写成
F(χu):=-∑kck(σk(λ(χu)))/(σn(λ(χu)))=-ψ.(8)
本文中主要结果的关键是下面的引理1.Fang等[9]首先对反σk方程证明这个引理1.Guan[15-16]和Székelyhidi[22]将它推广到更一般的Hessian方程.
引理1 假设条件(5)成立,那么存在两个正常数R0,ε>0,使得当|χu|≥R0时,有
Fi(-overj)((χu_-)i(-overj)-(χu)i(-overj))≥ε(1+Fi(-overj)gi(-overj)).(9)
本文中,使用陈联络Δ 进行计算.在局部坐标z=(z1,…,zn)下,使用如下符号:
vi=Δ/(zi)v,
vij=Δ/(zj)Δ/(zi)v,vi(-overj)=Δ/((-overz)j/sub>)<Δ/(zi)v,….(10)
给定一个 Hermitian矩阵A={ai(-overj)},记
Fi(-overj)(A)=(F)/(ai(-overj))(A),
Fi(-overj),k(-overl)(A)=(2F)/(ai(-overj)ak(-overl))(A).(11)
2 定理的证明
定理1的证明 考虑如下闸函数
=Aeη,
η=B[u_--u-inf(-overM)(u_--u)],
其中 A 和 B 为两个待定的正常数.
假设e|Δu|2 在流形M的内部点 p∈M 达到最大值,记 W=|Δu|2,并且选取一个全纯局部坐标 z=(z1,…,zn),使得在 p 点处满足
gi(-overj)=δij,
χi(-overj)+ui(-overj)=λiδij,
Fi(-overj)=fiδij.(12)
由假设可知,在 p 点处有
{(Wi)/W+i=0,
(W(-overi))/W+(-overi)=0,
(Wi(-overi))/W-(|Wi|2)/(W2)+i(-overi)≤0.(13)
约定下文中的计算均在 p 点处进行.通过计算可知
Wi=∑k(ukiu(-overk)+ukui(-overk)),
Wi(-overi)= ∑k|u(-overk)i|2+2∑kRe(ui(-overi)ku(-overk))+
∑k,lRi(-overi)k(-overl)ulu(-overk)+∑k|ui(-overk)-∑lTkilu(-overl)|2-
∑k|∑lTkilu(-overl)|2.(14)
由此
|Wi|2≤|Δu|2∑k|uki|2-
2|Δu|2Re(ukui(-overk)(-overi)).(15)
对方程(8)进行求导可得
Fi(-overi)(ui(-overi)k+χi(-overi),ζαuαk+χi(-overi),(-overζ)αu(-overα)k)=ψk-Fi(-overi)χi(-overi),k.(16)
现在,利用前文中的假设(4)得到
L(W)≥Fi(-overi)|uki|2-C|Δu|(1+∑Fi(-overi))-
C|Δu|2∑Fi(-overi),(17)
式中的L为方程(8)的线性化算子
Lv=Fi(-overj)vi(-overj)+Fi(-overj)χi(-overj),ζαvα+Fi(-overj)χi(-overj),(-overζ)αv(-overα),
v∈C2(M).(18)
简单计算可得
i=ηi,
i(-overi)=(|ηi|2+ηi(-overi)).(19)
使用 Cauchy-Schwarz 不等式和假设(4),得到
2-1Re(ukui(-overk)(-overi))≥2Re(λiuiη(-overi))-
1/2|Δu|2|ηi|2-C|Δu|2(20)
和
L=Lη+Fi(-overi)|ηi|2.(21)
再由式(13),(15)~(21),有
|Δu|2(1/2Fi(-overi)|ηi|2+Lη)-
C/|Δu|(1+∑Fi(-overi))-C|Δu|2
∑Fi(-overi)-(C|Δu|2)/∑Fi(-overi)≤
-2Re(fiλiuiη(-overi)).(22)
下面控制上式的右端项.不妨假设 |Δu|>|Δu_-|,注意到 ∑fiλi≤nψ,可知
-2∑Re(fiλiuiη(-overi))≤
4B|Δu|2∑fiλi≤
4nBψ|Δu|2.(23)
可以验证 ∑Fi(-overi) 有一个正的下界,即
∑Fi(-overi)≥κ>0.
下面,依据引理1来进行讨论.假设 |λ|≤R0,其中 R0,ε 均为引理 1中的常数,那么存在常数K1>0,使得
1/(K1)≤Fi(-overi)=fi≤K1
是平凡的.
若|λ|≥R0,则由式(4)和引理 1可知
L(u_--u)≥ε∑Fi(-overi)≥(εκ)/(1+κ)(1+∑Fii).
因此,
(Bεκ)/(1+κ)(1+∑Fi(-overi))-C/(|Δu|)(1+∑Fi(-overi))-
(C+C/)∑Fi(-overi)-4nBψ≤0.(24)
不失一般性,可假设 λ1≥…≥λn.如果 A,B1,并且
Fn(-overn)>K:=8n(1+κ)sup(-overM) ψ/(εκ),
那么
|Δu|≤C.
对于余下的情形,可假设对任意的1≤i≤n 有fi=Fi(-overi)≤K.需要证明
∑fiλ2i≤C.(25)
为证明式(25),仅需要验证存在某个正数δ>0,使得λn≥δ.
综上可知,如果λi≤λj,则
fjλj≤fiλi,
因而,
fnλn≥1/n∑fiλi≥ψ/n,
λn≥ψ/(nK).(26)
由Cauchy-Schwarz 不等式
-2Re(fiλiuiη(-overi))≤
1/4|Δu|2fi|η(-overi)|2+4fiλ2i.(27)
由式(22),(25),(27)和引理1可得到定理1梯度估计的证明.
- [1] GUAN P F,ZHANG X.Regularity of the geodesic equation in the space of Sasake metrics[J].Adv Math,2012,230:321-371.
- [2] YUAN R R.On a class of fully nonlinear elliptic equations containing gradient terms on compact Hermitian manifolds[EB/OL].[2017-03-12].https:∥cms.math.ca/10.4153/CJM-2017-015-9.
- [3] AUBIN T.Equations du type Monge-Ampère sur les varietes Kahleriennes compactes[J].Bull Sci Math,1978,102:63-95.
- [4] BEDFORD E,TAYLOR B.The Dirichlet problem for a complex Monge-Ampère equation[J].Invent Math,1976,37:1-44.
- [5] CAARELLI L A,KOHN J,NIRENBERG L,et al.The Dirichlet problem for nonlinear second-order elliptic equations,Ⅱ.Complex Monge-Ampère,and uniformaly elliptic,equations[J].Comm Pure Appl Math,1985,38:209-252.
- [6] YAU S T.On the Ricci curvature of a compact Kahler manifold and the complex Monge-Ampère equation Ⅰ[J].Comm Pure Appl Math,1978,31:339-411.
- [7] CHEN X X.A new parabolic ow in Kahler manifolds[J].Comm Anal Geom,2004,12:837-852.
- [8] DONALDSON S K.Moment maps and dieomorphisms[J].Asian J Math,1999,3:1-16.
- [9] FANG H,LAI M J,MA X N.On a class of fully nonlinear ow in Kahler geometry[J].J Reine Angew Math,2011,653:189-220.
- [10] GUAN B,LI Q.The Dirichlet problem for a complex Monge-Ampère type equation on Hermitian manifolds[J].Adv Math,2013,246:351-367.
- [11] GUAN B,SUN W.On a class of fully nonlinear elliptic equations on Hermitian manifolds[J].Calc Var Partial Dierential Equations,2015,54:901-916.
- [12] SUN W.On a class of fully nonlinear elliptic equations on closed Hermitian manifolds[J].J Geom Anal,2016,26:2459-2473.
- [13] SONG J,WEINKOVE B.On the convergence and singularities of the J-flow with applications to the Mabuchi energy[J].Comm Pure Appl Math,2008,61:210-229.
- [14] KOMZSIK L.Implicit computational solution of generalized quadratic eigenvalue problems[J].Elsevier Science Publishers B V,2001,37(10):799-810.
- [15] SMITH H A,SINGH R K,SORENSEN D C.Formulation and solution of the non-linear,damped eigenvalue problem for skeletal systems[J].International Journal for Numerical Methods in Engineering,1995,38(18):3071-3085.
- [16] GUAN B.The Dirichlet problem for fully nonlinear elliptic equations on Riemannian manifolds[EB/OL].[2017-03-12].https:∥arxiv.org/abs/1403.2133.
- [17] LI Y Y.Some existence results of fully nonlinear elliptic equations of Monge-Ampère type[J].Comm Pure Appl Math,1990,43:233-271.
- [18] URBAS J.Hessian equations on compact Riemannian manifolds[C]∥Nonlinear Problems in Math-ematical Physics and Related Topics Ⅱ.New York:Kluwer/Plenum,2002:367-377.
- [19] BLOCKIV.A gradient estimate in the Calabi-Yau theorem[J].Math Ann,2009,344:317-327.
- [20] HANANI A.Equations du type de Monge-Ampère sur les varietes hermitiennes compactes[J].J Funct Anal,1996,137:49-75.
- [21] HOU Z.Complex Hessian equation on Kahler manifold[J].Int Math Res Not,2009,16:3098-3111.
- [22] SZEKELYHIDI G.Fully non-linear elliptic equations on compact Hermitian manifolds[EB/OL].[2017-03-12].https:∥arxiv.org/abs/1501.02762.