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Robert Bryant
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Yes, one can always do this. Start with a $p$-centered local coordinate system $(x^\sigma,y^\rho)$ on an open $p$-neighborhood $U\subset M$ such that $S\cap U$ is given by $y^\rho=0$ $(1\le\rho\le r)$. Then there will exist functions $F^\sigma_\rho(x)$ such that $V$ along $S\cap U$ is given by the equations $$ \mathrm{d}x^\sigma + F^\sigma_\rho(x)\,\mathrm{d}y^\rho = 0 $$ (summation convention assumed). This is the same as $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) - y^\rho\,\mathrm{d}(F^\sigma_\rho(x)) = 0. $$ Since $y^\rho=0$ along $S$, this says that $V$ along $S$ is defined by $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) = 0, $$ so take $\bar x^\sigma = x^\sigma+F^\sigma_\rho(x)y^\rho$, and let $(\bar x^\sigma,y^\rho)$ be your new coordinate system. (One can easily check that these are local coordinates in an open neighborhood of $S\cap U\subset U$.)

Added Remark: Just a comment on your terminology: Literally, what you are defining is not a splitting of the normal bundle of $S$, but rather a choice of a normal bundle along $S$, and you are asking whether there are any local invariants that distinguish such choices. As the above shows, the answer is 'no'. In fact, there is even a global version: For two normal bundles $V_1$ and $V_2$ along a closed submanifold $S$, there is a diffeomorphism of $M$ that fixes $S$ and carries $V_1$ to $V_2$.

Note also that, in the holomorphic category (in contrast to the smooth case), normal bundles need not be unique in this sense, and may not even exist.

Yes, one can always do this. Start with a $p$-centered local coordinate system $(x^\sigma,y^\rho)$ on an open $p$-neighborhood $U\subset M$ such that $S\cap U$ is given by $y^\rho=0$ $(1\le\rho\le r)$. Then there will exist functions $F^\sigma_\rho(x)$ such that $V$ along $S\cap U$ is given by the equations $$ \mathrm{d}x^\sigma + F^\sigma_\rho(x)\,\mathrm{d}y^\rho = 0 $$ (summation convention assumed). This is the same as $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) - y^\rho\,\mathrm{d}(F^\sigma_\rho(x)) = 0. $$ Since $y^\rho=0$ along $S$, this says that $V$ along $S$ is defined by $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) = 0, $$ so take $\bar x^\sigma = x^\sigma+F^\sigma_\rho(x)y^\rho$, and let $(\bar x^\sigma,y^\rho)$ be your new coordinate system. (One can easily check that these are local coordinates in an open neighborhood of $S\cap U\subset U$.)

Yes, one can always do this. Start with a $p$-centered local coordinate system $(x^\sigma,y^\rho)$ on an open $p$-neighborhood $U\subset M$ such that $S\cap U$ is given by $y^\rho=0$ $(1\le\rho\le r)$. Then there will exist functions $F^\sigma_\rho(x)$ such that $V$ along $S\cap U$ is given by the equations $$ \mathrm{d}x^\sigma + F^\sigma_\rho(x)\,\mathrm{d}y^\rho = 0 $$ (summation convention assumed). This is the same as $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) - y^\rho\,\mathrm{d}(F^\sigma_\rho(x)) = 0. $$ Since $y^\rho=0$ along $S$, this says that $V$ along $S$ is defined by $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) = 0, $$ so take $\bar x^\sigma = x^\sigma+F^\sigma_\rho(x)y^\rho$, and let $(\bar x^\sigma,y^\rho)$ be your new coordinate system. (One can easily check that these are local coordinates in an open neighborhood of $S\cap U\subset U$.)

Added Remark: Just a comment on your terminology: Literally, what you are defining is not a splitting of the normal bundle of $S$, but rather a choice of a normal bundle along $S$, and you are asking whether there are any local invariants that distinguish such choices. As the above shows, the answer is 'no'. In fact, there is even a global version: For two normal bundles $V_1$ and $V_2$ along a closed submanifold $S$, there is a diffeomorphism of $M$ that fixes $S$ and carries $V_1$ to $V_2$.

Note also that, in the holomorphic category (in contrast to the smooth case), normal bundles need not be unique in this sense, and may not even exist.

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Robert Bryant
  • 108.4k
  • 8
  • 341
  • 453

Yes, one can always do this. Start with a $p$-centered local coordinate system $(x^\sigma,y^\rho)$ on an open $p$-neighborhood $U\subset M$ such that $S\cap U$ is given by $y^\rho=0$ $(1\le\rho\le r)$. Then there will exist functions $F^\sigma_\rho(x)$ such that $V$ along $S\cap U$ is given by the equations $$ \mathrm{d}x^\sigma + F^\sigma_\rho(x)\,\mathrm{d}y^\rho = 0 $$ (summation convention assumed). This is the same as $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) - y^\rho\,\mathrm{d}(F^\sigma_\rho(x)) = 0. $$ Since $y^\rho=0$ along $S$, this says that $V$ along $S$ is defined by $$ \mathrm{d}(x^\sigma+F^\sigma_\rho(x)y^\rho) = 0, $$ so take $\bar x^\sigma = x^\sigma+F^\sigma_\rho(x)y^\rho$, and let $(\bar x^\sigma,y^\rho)$ be your new coordinate system. (One can easily check that these are local coordinates in an open neighborhood of $S\cap U\subset U$.)