ANOTE ON IMMERSED MANIFOLr)S
.IN’A−EUCLIDEAN SPACE
BY
SEIIcHI YAMAGUCHI
L馳lntro己uction. S. S. Chem, R. K. Lashof, T. Otsuki, I B. Y. Chell and o01ers.
have investigated the Lipschitz−Kming curvature k(P,e)of an oriented,◎ompaぱL
manifold Mn immersed桓an.(陀ト1V十d麺卯sionq1 Euclidean space E”’N and obtained
many beauU∩Ul results.
The purPose of t1亘s paper is fo『generalize B. Y. Chen・s theorem in[2]‘t6証hざ
case of higher codimension. . .... ..、『
2.Prdimina口es. Letルfs be an〃−d㎞CnsiOnal oriented, compact manifold*)and
x:Mn→E佛be an iMmersion of Mカ・馳ihto a EUclidean’space E堺 of d垣1ension−〃1.
1£tF(Mりand F(Eりbe the bundles of orthonormal frames of M”alld E楊, respeσ
tively. Letβthe set of elements b=(P,el,“°,β楊)such that(ρ,θ1,…, en)∈F(M”)
and(x(ク), e1,…,θ那)∈F(EづwhoSe’orientation“is』Coh6rellt with the o皿e ofk Ein,
identifying ei w紅h.dx(θ,)(i,±, k,…=1,2,…, n).’. Then ・: B→M籏may be.◎onside鵬d,・
as a pmbcipal b㎜(ile‘with五bre Oω×SO(m−n)∬and X:β→F(Eりis natUra皿y−・
defined by x(b)=(x(ρ), el, e2,… ,θ楊). Let By be the bundle of unit normal v㏄tor
of x(Mりso that a point ofβ“is『apair(ク,θ)where e、is a unit normal v㏄tor at
x(P).
The structure equations of E況are given by ‘ .
dx=ΣθAε且, deA=ΣθABeB,θ旭+θ斑=0, dθ.=Σθβ八θ以, dθ.B=Σθ.c∧θcβ.
五 β β .一 ’ .c
(∠1,B, … ==1,2, … ,〃1) ぺ L .’㌧t
whoseθA andθ佃are differential 1−fbrms oll F(Eあ). LetωA and toAB by−the map二−’
ph19 X. Then We have . 』『 “ = 1 ’ 一’
ω’=0,tO,i一ΣAri,妨,塩∫=んヵ (r,ぷ,’,…=n+1, n+2,…,〃2). 『
フ
Tbe symmetric matriX(んξ5)is called the’secOnd fundamental fbrm at(ρ, er).パ暁.
de丘ne the k−tl mean curvature Kk(ク,er)at(ρ,θア)∈βッby w
…(・i・+’旬一1+¥㈲KKp・…)t・’一 …”
The volume element of Mカcan be written as dV=ω1∧...∧ω泥.−The(〃21一π一1>
f・rm d・−q・・.−Gt・A・・述ω͡一・(・・tn b・・Tggard・・ap(m−〃−1)−f・・m・n.β・su・h・th・t it・
. 、’ .. 〆 .「. .’.こ
*)Manifolds, m砲pings, metrics,...,etc. are assumed to be.diiferentiable and of
class C−. ‘1学
[19]
20
S.YAMAGUCHI
restriction to a丘bre Spm−n−1, then the(m−1)−fbrm do八dV’can be regarded as the
volumew element of莇.
In[5], we㎞ow that
(1) T(・・)≡!。。1頂・・の14γ∧da≧鴫β鍋
where Kl〔ρ,θ)denotes the Lipschitz−Killi㎎㏄Tvature, Cm_1 the volume of the unit
(〃−1)dilnensional sphere andβ‘(ハのthe就h Betti number of M・. If the equality
sign of(1)holds, then the immersion x:バグ絡→E餌is caned a minhnal㎞be(1ding.
B.Y. Chen[3,4]has proved the fbllowings:
TH厚OR巳M A・ Let x:∼ぼカ→・E郁加q4元〃mprsion oゾα〃orピη絃Z(ごρmρααηκzπが0∼d
ハ4パ脚E拐,乃¢ηw加ツβ
T(・)≡1。“故…)〃M・=・ Cm−・⑭,
where X(∼の吻0’θぷthe Eular chqrac’eアistic・∫、」t4ne
THEOREM B. Under sa〃leα∬umptionρ∫Thθore〃2/1,’乃θLipぷc乃ノ’z肩KZ〃切g curva−
ture K(ρ,θ)ぷaガsfies’he j〃eq〃ality
(・) ∫。⑭〃∧da≧曝、,(吻 ・
蝋
’(3) 1。⑭醐吻≦−Cm.冒β、ト、(働
w擁4−{(ク,e)∈β〃;丞(ρ,・)≧o}卿4β一{(?,・)∈β・;K(〃,のくo}.職β卿晦
ぷξ8馨ρ〆(2)qnd(3)holdsぴρ〃40nり∼ぴ’カβカηmぴぷψ∼I X麺〃鉱掘∼斑『. ・ 揚
3・Theorem, Now, we put
8‘(P,θ)一疏(P,e)#li−K(ρ,θ),
where n/i is positive even integer. Then we.can prove the .
THEOREM. Let x:Mカ→E楊be an伽膨ζぷio〃〈)f anρrien’ed・co〃ψαc’微π〃bぼM江
in E”wれカθゾb〃bwingクroperty ; .
(P) {(ρ,の∈β〃:岳(P;θ)≧0}⊇{(ク,の∈β“:K(ク,θ)>0}.
Then we』wθ’he follo吻9 inequaliり・
(・) ∫譜(b,‘・脚M・≧Cm一藁β・・(吻
W乃ε’θ〃/i is poぷ肋θεγθπ’〃’eger. The eqtiatityぷなn holdsぴand・O吻ぴ’舵加㎝θr一
ぷ迦xξぷa〃吻’施1imbedding.
PROOF. We set
S+={(P,e)∈3・:岳(ρ,e)≧0} and &{(P,ε)∈3“:9;(ク, e)<旬.
Then the set Sr is empty. In血ct, if(ρ,の∈β夕belong to&, by de丘nition
’ Ki(ρ, e)”/L瓦(ρ,θ)<0.
A N.OTII ON IMMERSED MANIFOLDS IN A EUCLIDEAN SPACE
As Ki(P, e)nli≧0,
Henoe we get
(5)
21
it holds that K(p, e)>0. But this◎ontradrcts th6 property(P).
!。.9i(P・・eldV∧d・ 一!。.9i(P・・e)dV∧d・
一!.。臨卿八d・−1、.K(…e)・VA・・
≧0.
By v加ue of(2), we have
[旦2]
∼
私(ρ,のカ’idV∧吻≧Cm−1Σβ2輌(Mカ).
β〃 き=O
Now suppose that the equaHty sign of(4)holds, then by(5)it fb皿ows that
(・) 1。砲・͡一場燗.‘・..
On the other hand, making use of(2), we get
(・) !.K(P,・)一一一場ぷX
カ
and consequently,(6)一・and(7)meanτ(.4x)一(7,。_、Σβ,. The convetse of this is
‘=1
垣vial.
The author wishes to express his sincere thanks to Prof. B. Y. Chen who gave
advices.
[1]
[2]
−1=]
34
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[5]
[6]
[7]
REFERENCES
B.Y. Chen:Some integral fbrmulas of the Gurss−Kronecker curvrture, K6dai Math.
Sem. Repり20(1968),410−413. − .
B.Y. Chen:On an inequaUty of TJ. W∬1more, Proc. Amer. Math. S㏄.,26(197の,
473−479.
B.Y. Chen:On the Lip輌一㎜ng c田vat田e of㎞e□anifold,皿pub臨h劇.
B.Y. Chen:G−total curvature of㎞ersed manifolds,」. Di窟. Geometry,7(1972),
371−391.
S.S. Chem孤d R. K. Lashof:On the total c肛vature of immersed manifolds, Amer.
」.Math.,79(1957),306−318;H, Michigan Math. J.,5(1958),5−12.
T.Otsuki:On the tota1 curvature of surfaces in Euolidean spaces, Japanese J. Math.,
35(1966),6i−71.
S.Yamaguchi:Remarks on the scalar curvature of immefsed mqnifolds, to appear.
DEPARTMENT OF MATHEMATICS
SC】ENCE UNWERSITY OF TOKYO
TOKYO, JAPAN