$f:Mrightarrow M$ is an isometry and $ker(Id - d_{gamma(t)}f) = mathbb{R} dot{gamma}(t)$, show that $gamma$...












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Let M be a Riemannian manifold, $gamma: I rightarrow M$ be a curve which is parameterized with constant speed and $f:Mrightarrow M$ be an isometry with $f circ gamma = gamma$. Furthermore $ker(Id - d_{gamma(t)}f) = mathbb{R} dot{gamma}(t), forall t$. Show that $gamma$ is a geodesic then.



I need some help with this. I don't know how f plays into this. We know that $d_{gamma(t)}f(adot{gamma}(t)) = adot{gamma}(t)$ for any $a in mathbb{R}$ , then for $ mathbb{R} ni c = langle dot{gamma(t)}, dot{gamma(t)} rangle = langle d_{gamma(t)}f(dot{gamma}(t)), d_{gamma(t)}f(dot{gamma}(t)) rangle$.



I don't see how any of this is supposed to be related to $nabla_{dot{gamma}}dot{gamma}$.



Why is it important that f is an isometry?










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    $begingroup$


    Let M be a Riemannian manifold, $gamma: I rightarrow M$ be a curve which is parameterized with constant speed and $f:Mrightarrow M$ be an isometry with $f circ gamma = gamma$. Furthermore $ker(Id - d_{gamma(t)}f) = mathbb{R} dot{gamma}(t), forall t$. Show that $gamma$ is a geodesic then.



    I need some help with this. I don't know how f plays into this. We know that $d_{gamma(t)}f(adot{gamma}(t)) = adot{gamma}(t)$ for any $a in mathbb{R}$ , then for $ mathbb{R} ni c = langle dot{gamma(t)}, dot{gamma(t)} rangle = langle d_{gamma(t)}f(dot{gamma}(t)), d_{gamma(t)}f(dot{gamma}(t)) rangle$.



    I don't see how any of this is supposed to be related to $nabla_{dot{gamma}}dot{gamma}$.



    Why is it important that f is an isometry?










    share|cite|improve this question









    $endgroup$















      1












      1








      1





      $begingroup$


      Let M be a Riemannian manifold, $gamma: I rightarrow M$ be a curve which is parameterized with constant speed and $f:Mrightarrow M$ be an isometry with $f circ gamma = gamma$. Furthermore $ker(Id - d_{gamma(t)}f) = mathbb{R} dot{gamma}(t), forall t$. Show that $gamma$ is a geodesic then.



      I need some help with this. I don't know how f plays into this. We know that $d_{gamma(t)}f(adot{gamma}(t)) = adot{gamma}(t)$ for any $a in mathbb{R}$ , then for $ mathbb{R} ni c = langle dot{gamma(t)}, dot{gamma(t)} rangle = langle d_{gamma(t)}f(dot{gamma}(t)), d_{gamma(t)}f(dot{gamma}(t)) rangle$.



      I don't see how any of this is supposed to be related to $nabla_{dot{gamma}}dot{gamma}$.



      Why is it important that f is an isometry?










      share|cite|improve this question









      $endgroup$




      Let M be a Riemannian manifold, $gamma: I rightarrow M$ be a curve which is parameterized with constant speed and $f:Mrightarrow M$ be an isometry with $f circ gamma = gamma$. Furthermore $ker(Id - d_{gamma(t)}f) = mathbb{R} dot{gamma}(t), forall t$. Show that $gamma$ is a geodesic then.



      I need some help with this. I don't know how f plays into this. We know that $d_{gamma(t)}f(adot{gamma}(t)) = adot{gamma}(t)$ for any $a in mathbb{R}$ , then for $ mathbb{R} ni c = langle dot{gamma(t)}, dot{gamma(t)} rangle = langle d_{gamma(t)}f(dot{gamma}(t)), d_{gamma(t)}f(dot{gamma}(t)) rangle$.



      I don't see how any of this is supposed to be related to $nabla_{dot{gamma}}dot{gamma}$.



      Why is it important that f is an isometry?







      differential-geometry






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      asked Jan 7 at 13:26









      eager2learneager2learn

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          This is a consequence of the fact that, under your given assumptions, $gamma$ constitutes a local parameterization of an immersed submanifold of $M$ which is fixed by an isometry. But such immersed submanifolds are totally-geodesic. In this instance, the immersed submanifold is of dimension 1 and an immersed, totally-geodesic submanifold of dimension 1 is just a geodesic.






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            $begingroup$

            This is a consequence of the fact that, under your given assumptions, $gamma$ constitutes a local parameterization of an immersed submanifold of $M$ which is fixed by an isometry. But such immersed submanifolds are totally-geodesic. In this instance, the immersed submanifold is of dimension 1 and an immersed, totally-geodesic submanifold of dimension 1 is just a geodesic.






            share|cite|improve this answer









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              $begingroup$

              This is a consequence of the fact that, under your given assumptions, $gamma$ constitutes a local parameterization of an immersed submanifold of $M$ which is fixed by an isometry. But such immersed submanifolds are totally-geodesic. In this instance, the immersed submanifold is of dimension 1 and an immersed, totally-geodesic submanifold of dimension 1 is just a geodesic.






              share|cite|improve this answer









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                $begingroup$

                This is a consequence of the fact that, under your given assumptions, $gamma$ constitutes a local parameterization of an immersed submanifold of $M$ which is fixed by an isometry. But such immersed submanifolds are totally-geodesic. In this instance, the immersed submanifold is of dimension 1 and an immersed, totally-geodesic submanifold of dimension 1 is just a geodesic.






                share|cite|improve this answer









                $endgroup$



                This is a consequence of the fact that, under your given assumptions, $gamma$ constitutes a local parameterization of an immersed submanifold of $M$ which is fixed by an isometry. But such immersed submanifolds are totally-geodesic. In this instance, the immersed submanifold is of dimension 1 and an immersed, totally-geodesic submanifold of dimension 1 is just a geodesic.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 2 days ago









                Or EisenbergOr Eisenberg

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