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Riemannian Geometry is a subfield of Differential Geometry, which specifically studies "Riemannian Manifolds", manifolds with "Riemannian Metrics", which means that they are equipped with continuous inner products.

23 votes
1 answer
1k views

Eigenvalues of Laplace operator

Assume that $(M,g)$ is a Riemannian manifold. Is there any relation between the sequence of eigenvalues of Laplace operator acting on the space of smooth functions and the sequence of eigenvalues of …
Ali Taghavi's user avatar
18 votes
3 answers
2k views

Can the Laplace operator on $n-$ manifolds be represented as a sum of $n$ second order deriv...

EDIT: According to some comments on this post I revise the title to remove the misunderestanding. Assume that $M$ is a Riemannian manifold of dimension $n$. The natural Laplace operator associated t …
Ali Taghavi's user avatar
17 votes
2 answers
1k views

Are there some intrinsic invariants of surfaces other than Gaussian curvature?

The principal curvatures of a surface is denoted by $\kappa_{1}, \kappa_{2}$. Let $P(x,y)$ be a polynomial with real coefficients. Assume that $P(\kappa_{1}, \kappa_{2})$ is an intrinsically inv …
Ali Taghavi's user avatar
17 votes

Finding a 1-form adapted to a smooth flow

If the vector field is geodesible then such $1$ - form exists. A geodesible flow on a manifold $M$ is a one dimensional foliation associated with a non vanishing vector field such that …
Ali Taghavi's user avatar
13 votes
5 answers
3k views

A geometric proof of the Gauss-Lucas theorem

Motivated by a geometric proof of the Fundamental Theorem of Algebra we ask: Is there a geometric proof for the Gauss-Lucas theorem? Since we are working on a half plane, can one imagine a possible p …
Ali Taghavi's user avatar
12 votes
3 answers
2k views

Limit cycles as closed geodesics (in negatively or positively curved space)

Updated 1/25/2023 I just added a related post below: Jacobi fields, Conjugate points and limit cycle theory EDIT: Here is a related post which concern quadratic vector fields rather than Van de …
Ali Taghavi's user avatar
10 votes
3 answers
713 views

Number of disjoint simple closed geodesics

According to Jairo comment on the first version of this question I revise the question as follows; Let $g$ be a real analytic Riemannan metric on $S^{2}$. Is it true to say that: There are at most a …
Ali Taghavi's user avatar
10 votes
1 answer
308 views

A characterization of round sphere

Let $(M,g)$ be a $k$ dimensional compact Riemannan manifold which is isometrically embeded in $\mathbb{R}^{k+1}$. The distance arising from the Riemannian metric is denoted by $d_g$.The Euclidian dist …
Ali Taghavi's user avatar
9 votes
1 answer
676 views

Does every manifold admit a Lagrangian Riemannian metric?

Let $(M,g)$ be a Riemannian manifold. The $LC$ connection associated to the metric gives an $n$ dimensional distribution $D$ for $TM$. Let $\omega$ be the symplectic structure of $TM$ which is obtain …
Ali Taghavi's user avatar
8 votes
3 answers
411 views

Extension of a vector field to an orthonormal frame for a flat metric

Assume that $U$ is an open set in the plane and $X$ is a non vanishing vector field on $U$. Is there a non vanishing vector field $Y$ on $U$ such that the pair $\{X,Y \}$ plays the role of an orthono …
Ali Taghavi's user avatar
8 votes
1 answer
364 views

Can a harmonic vector field possess a limit cycle?

Can a harmonic vector field $X$ on a Riemannian surface $(M,g)$ possess a limit cycle(An isolated periodic orbit)? Note that the Laplacian of a vector field is defined via natural correspondence bet …
Ali Taghavi's user avatar
7 votes
2 answers
357 views

Is every Lie subgroup of a Lie group isometric to all its conjugates?

Let $G$ be a Lie group with a left invariant metric. Assume that $N$ is a Lie subgroup of $G$. For a given $g\in G$, are $N$ and $g^{-1} N g$ necessarily isometric Riemannian manifold when they inher …
Ali Taghavi's user avatar
7 votes
1 answer
335 views

A characterization of flat metrics via global vector fields

Let $(M,g)$ be a Riemannian manifold with $LC$ conncection $\nabla$. Assume that for every three global vector fields $X,Y,Z \in \chi^{\infty}(M)$ with $[X,Y]=0$ we have $\nabla_{X} \nabla_{ …
Ali Taghavi's user avatar
7 votes
0 answers
519 views

Limit cycles as closed geodesics(2)

Hilbert 16th problem asks for a uniform upper bound $H(n)$ for the number of limit cycles of a polynomial vector field of degree $n$ on the plane. Here is an updated proof of the fi …
Ali Taghavi's user avatar
7 votes
1 answer
835 views

Hilbert 16th problem via hyperbolic geometry

More than 16 years ago, I heard from someone that he thinks that there is a possible relation between Hilbert's 16th problem(for $n=2$) and Hyperbolic geometry. He says that a po …
Ali Taghavi's user avatar

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