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G. Santhanam

Publications and source records attributed to G. Santhanam.

6 recordsLinked to original sources
arXiv2019

Some sharp bounds for Steklov eigenvalues

This work is an extension of a result given by Kuttler and Sigillito (SIAM Rev $10$:$368-370$, $1968$) on a star-shaped bounded domain in $\mathbb{R}^2$. Let $Ω$ be a star-shaped bounded domain in a hypersurface of revolution, having smooth boundary. In this article, we obtain a sharp lower bound for all Steklov eigenvalues on $Ω$ in terms of the Steklov eigenvalues of the largest geodesic ball contained in $Ω$ with the same center as $Ω$. We also obtain similar bounds for all Steklov eigenvalues on star-shaped bounded domain in paraboloid, $P = \left\lbrace (x, y, z) \in \mathbb{R}^{3} : z = x^2 + y^2\right\rbrace$.

math.DG↗
arXiv2013

Sharp upper bound for the first eigenvalue

Let $M$ be a closed hypersurface in a noncompact rank-1 symmetric space $(\bar{\mathbb{M}}, ds^2)$ with $-4 \leq K_{\bar{\mathbb{M}}} \leq -1,$ or in a complete, simply connected Riemannian manifold $\mathbb{M}$ such that $0 \leq K_{\mathbb{M}} \leq δ^2$ or $K_{\mathbb{M}} \leq k$ where $k = -δ^2$ or 0. In this paper we give sharp upperbounds for the first eigenvalue of laplacian of $M$.

math.DG↗
arXiv2012

Sharp upper bound and a comparison theorem for the first nonzero Steklov eigenvalue

In this paper we prove that given a volume, among all domains with smooth boundary in rank-1 symmetric spaces of noncompact type, geodesic balls maximizes the first nonzero Steklov eigenvalue. We also prove a comparison result for the first nonzero Steklov eigenvalue for domains in simply connected Riemannian manifolds with certain curvature bounds.

math.DG↗
arXiv1995

The First Eigenvalue of $P$-manifolds

Antonio Ros gave a lower bound for the first eigenvalue $λ_1$ of $Δ$ of a $P$-manifold $(M, g)$ in terms of the lower bound on the Ricci curvature $Ric_M$ and asked what happened when this lower bound was achieved. In this paper we look in to this question and show that there are strong implications on the geometry and topology of the underlying manifold. In particular we show that in case of spheres or real projective spaces we have isometry with the standard metric. In other cases, with some additional hypothesis, we again show isometry with standard models.

dg-ga↗
arXiv1995

A Generalisation of Obata's theorem

In a complete Riemannian manifold $(M, g)$ if the hessian of a real valued function satisfies some suitable conditions then it restricts the geometry of $(M, g)$. In this paper we characterize all compact rank-1 symmetric spaces, as those Riemannian manifolds $(M, g)$ admitting a real valued function $u$ such that the hessian of $u$ has atmost two eigenvalues $-u$ and $-{{u+1}\over 2}$, under some mild hypothesis on $(M, g)$. This generalises a well known result of Obata which characterizes all round spheres.

dg-ga↗