25 Matching Annotations
  1. Jul 2018
    1. pontaneous collapse theories

      Penrose's interpretation (objective reduction is one of those).

  2. arxiv.org arxiv.org
    1. Forsimplicity, let us assume that the boundary of Ω has only one component.Letι: Σ :=∂Ω→Rnbe its isometric embedding. Letν:ι(Σ)→Sn−1be the outer unit normal. Sinceι(Σ) is assumed to be a strictly convexhypersurface inRnthere is a smooth family of embeddingsF: Σ×[0,∞]→RnwhereFt(σ) =F(σ, t) =ι(σ) +tν(ι(σ)).Note thatFt(Σ) are the ‘outer’ distance surfaces ofι(Σ). IfˆΩ denotes thebounded domain enclosed byι(Σ), then{Ft(Σ)}t≥0foliatesRn\ˆΩ and theEuclidean metric on this set can be written asG=dt2+gt,wheregtis the first fundamental form of the embeddingFt: Σ→Rn.
  3. May 2018
    1. we use the dilationinvariance of weighted H ̈older norms together with suitable curvature conditionsto obtain uniform bounds of solutions to the initial value problem (1) with initialconditionu−1(1 +ǫ,·) on [1 +ǫ,∞). By Arzela-Ascoli Theorem, there exists aweak solution to (1) withu−1(1,·) = 0 (Theorem 2). S
    2. We introduce the scaling transformation ̃u(t) =√tt+ 1u(t+ 1) wheret∈(0,∞).
  4. Apr 2018
    1. Theorem 2.1.The initial value problem (2.1) has a unique solutionuonΣ0×[0,∞)such that(a)u(z) = 1 +m0ρn−2+vwherem0is a constant andvsatisfies|v|=Oρ1−nand|∇0v|=O(ρ−n);(b)The metricds2=u2dr2+gris asymptotically flat in the sense of (2.23) with scalarcurvatureR≡0outsideΣ0;(c)The ADM massmADMofds2is given byc(n)mADM= (n−1)ωn−1m0= limr→∞ZΣrH0(1−u−1)dσr= limr→∞ZΣr(H0−H)dσr,for some positive constantc(n), whereH0andHare the mean curvatures ofσrwith respect to the Euclidean metric andds2respectively.

      A menos de uma normalização, o valor constante no item (c) pode ser escolhido como sendo $$c(n)= 2(n-1) \omega_{n-1}$$

    2. ∇0and∇20are the gradient and Hessianoperator of the Euclidean metric respectively. If we writeu2dr2+gr=∑i,jgijdzidzj.Then direct computations show (see the computations in (2.24), (2.27) below, for example):(2.23)|gij−δij|+ρ|∇0gij|+ρ2|∇20gij|≤Cρ2−n.By the result in [B1], the ADM mass of the metricds2=u2dr2+gris well defined, becausethe scalar curvature ofds2is zero outside a compact set.
    3. the scalar curvatureRofds2is given byR= (1−u−2)Rρ+u−2n−1∑i,jR0ijij+ 2n−1∑i=1Rnini= (1−u−2)Rρ+u−2R0−2u−1∆ρu+ 2u−3∂u∂ρH0whereR0is the scalar curvature ofNwith respect tods20andRρis the scalar curvatureof Σρwith the induced metric.
    4. he second fun-damental formhijof Σρwith respect tods2is given by(1.6)hij=u−1h0ij.
    5. he second fundamental formh0ij,1≤i,j≤n−1 of Σρwith respect to the normalen=∂∂ρis given by(1.3)ωni=n−1∑j=1h0ijωj.
  5. Sep 2017
    1. Theorem 1.1.LetMn1andMn2be hypersurfaces ofNn+1that are tan-gent atpand let0be a unitary vector that is normal toMn1atp. SupposethatMn1remains aboveMn2in a neighborhood ofpwith respect to0. De-note byH1r(x)andH2r(x)ther-mean curvature atx2WofMn1andMn2,respectively. Assume that, for somer,1rn, we haveH2r(x)H1r(x)in a neighborhood of zero; ifr2, assume also that2(0), the principal cur-vature vector ofM2at zero, belongs tor. ThenMn1andMn2coincide in aneighborhood ofp

      Princípio da tangência no interior, para as curvaturas médias de ordem superior.

    2. LetMn1andMn2be hypersurfaces ofNn+1that are tangentatp, i.e., which satisfyTpM1=TpM2. Fix a unitary vector0that is normaltoMn1atp. We say thatMn1remains aboveMn2in a neighborhood ofpwith respect to0if, when we parametrizeMn1andMn2by'1and'2asin (1.1), the corresponding functions1and2satisfy1(x)2(x) in aneighborhood of zero.

      O conceito de uma hipersuperfície está (localmente) acima ou abaixo de uma outra.

    1. Lemma 4.2.The functionm(r) =ZΣrH0(1−u−1)dσris nonincreasing inr, whereH0is the mean curvature ofΣrinRn.

      Essa fórmula de monoticidade de fato vale em um cenário mais amplo, vide essa anotação, por exemplo.

    2. we can solve (2.1)with initial valueu−10= 0. In fact, by Lemma 2.2,u0satisfies:1−exp−Zr0ψ(s)ds−12≤u0(x,r)≤1−exp−Zr0φ(s)ds−12.This means that Σ0is a minimal surface with respect to the asymptotically flat metricu2dr2+gr.

      Esse é um ingrediente fundamental na nossa abordagem para a desigualdade de Alexandrov-Frenchel via desigualdade de Penrose.

    3. solve (2.1) and show that the metricds2=u2dr2+gris asymptotically flatoutside Σ0. We will also compute the mass ofds2.

      Vide teorema 2.1, no final da sessão.

    4. Let Σ0be a compact strictly convex hypersurface inRn,Xbe the position vector ofa point on Σ0, and letNbe the unit outward normal of Σ0atX. Let Σrbe the convexhypersurface described byY=X+rN, withr≥0. The Euclidean space outside Σ0canbe represented by(Σ0×(0,∞),dr2+gr)wheregris the induced metric on Σr. Consider the following initial value problem(2.1)2H0∂u∂r= 2u2∆ru+ (u−u3)Rron Σ0×[0,∞)u(x,0) =u0(x)whereu0(x)>0 is a smooth function on Σ0,H0andRrare the mean curvature and scalarcurvature of Σrrespectively, and ∆ris the Laplacian operator on Σr.

      Note que de agora em diante o autor se detém a estudar esse caso particular, onde estão inteiramente determinadas as geometrias intrínseca e extrínseca das folhas do semi cilindro, obtido folheando-se pelas paralelas o exterior da hipersuperfície estritamente convexa dada a priori.

    5. u2dρ2+gρhas the scalar curvatureR, if and onlyifusatisfies(1.10)H0∂u∂ρ=u2∆ρu+12(u−u3)Rρ−12uR0+u32R.

      Observe que essa equação fica inteiramente determinada pela especificação da geometria intrínseca e extrínseca das folhas.

      Para uma ideia do que é essencial se saber sobre a geometria das folhas do semi cilindro, vide essa anotação.

    6. Given a functionRonN, we want to find the equation forusuch that(1.2)ds2=u2dρ2+gρhas scalar curvatureR.

      O papel da aplicação \( u: N \longrightarrow \mathbb{R} \) é distorcer as fibras do semi cilindro \( N \), por dilatações e torções, deixando a geometria intrínseca das folhas invariante, de tal forma que o resultado seja um semi cilindro com a curvatura escalar prescrita \( \mathcal{R} \).

    7. Let Σ be a smooth compact manifold without boundary with dimensionn−1 and letN= [a,∞)×Σ equipped with a Riemannian metric of the form(1.1)ds20=dρ2+gρfor a point (ρ,x)∈N. Heregρis the induced metric on Σρwhich is the level surfaceρ=constant

      Isso significa que a construção a seguir é feita a partir de um semi cilindro em que a geometria das folhas é dada a priori.

      Esse artigo não trata da construção desse semi cilindro inicial.

  6. arxiv.org arxiv.org
    1. By (4), we haveddtZΣ×{t}(Hη−Hu)dσt!=ZΣ×{t}(η−1−u−1)H21+K(η−u)−12(η−1−u−1)(H21+|h1|2)dσt.(9)By the Gauss equation and the assumption thatRic(gη) = 0, we have(10)2K=H2η−|hη|2=η−2(H21−|h1|2).Therefore, it follows from (9) and (10) that(11)ddtZΣ×{t}(Hη−Hu)dσt!=−ZΣ×{t}K(η−u)2u−1dσt≤0,where we also used the assumption thatK >0.
    2. Assumption:The scalar curvatureR(gt) =: 2Kofgtand the meancurvatureH1of the leaves Σ×{t}with respect tog1are everywhere positive.Proposition 2(cf. [2], [23], [22]).Under the above assumption, given anypositive functionu0onΣ×{0}, there is a smooth positive functionuonΣ×[0, t0]such that the scalar curvatureR(gu)ofguis identically zero andu|t=0=u0.

      A prova dessa proposição deixa mais claro o que é essencial saber sobre a geometria das folhas do semi cilindro reto, para que seja possível deformar suas fibras prescrevendo a curvatura escalar, conforme foi descrito (com mais generalidade) por Shi-Tam.

  7. Dec 2015
    1. Lemma 2.3.(2.1) has a unique solutionufor allrwhich satisfies the estimates in Lemma2.2.
    2. Let Σ0be a smooth compact strictly convex hypersurface inRn. Letrbe the distance function from Σ0. Then the metric on the exteriorNof Σ0is given bydr2+gr, wheregris the induced metric on Σr, which is the hypersurface with distancerfrom Σ0. The functionuwith prescribed scalar curvatureR= 0 is given by2H0∂u∂r= 2u2∆ru+ (u−u3)RrwhereH0is the mean curvature of Σr,Rris the scalar curvature of ΣrandR0is the scalarcurvature of Σrwith the induced metric fromRnand ∆ris the Laplacian on Σr.
  8. Mar 2015
    1. θ dμ ≥ p 16 π | Σ |

      Qual a relação dessa desigualdade com a dita desigualdade de Penrose Riemanniana provada por Huisken-Ilmanen e Bray?

    2. GIBBONS-PENROSE INEQUALITY

      Qual a relação dessa desigualdade com a dita desigualdade de Penrose Riemanniana provada por Huisken-Ilmanen e Bray?

    3. θ dμ ≥ p 16 π | Σ |

      Isso significa que a taxa expansão nula futura (para fora) \( \theta \) é no mínimo $$ \sqrt{16 \pi |\Sigma|} $$