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Paul Cusson
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This question is cross-posted (with modifications) from MSE. The original question is probably unfit for MathOverflow (although a professor I asked said that this is very nontrivial), but I'm hoping my follow-up questions and related discussion are of interest. To give an idea of my weak background, I am currently still going through Griffiths and Harris.

To rehash, let $X = \mathbb{C}^n / \Lambda$ be a complex torus of complex dimension $n$, with the lattice $\Lambda$ satisfying the Riemann conditions. Knowing that this condition guarantees that $X$ embeds in $\mathbb{CP}^N$ for some $N$, there exists a family of homogeneous polynomials whose zero locus is the embedded torus.

My original question was to ask for explicit examples of such embedded tori (for $n > 1$, as the case of elliptic curves is well known) and their corresponding polynomials. After reviewing the recommended literature I still could not figure out even a simple example, though I'm sure some must be known and there should be a method to directly compute these polynomials given $\Lambda$. I did learn in Birkenhake-Lange's textbook that nothing more than cubics are enough.

But it was pointed out to me that there are some subtleties that would make this a difficult task, which lead to my updated questions:

Given $X$, what is the smallest integer $N$ such that $X$ embeds in $\mathbb{CP}^N$? And is this number $N$ independent of the choice of lattice $\Lambda$? I.e. does it only depend on the dimension $n$ of the torus?

Mention of complete intersection (which I don't know about yet) was brought up, and if I remember correctly, it can be used to argue that any complex dimension $2$ torus cannot embed in $\mathbb{CP}^4$. and if I remember correctly, it can be used to argue that any complex dimension $2$ torus cannot embed in $\mathbb{CP}^4$.

At the very least, I would be happy with a reference for a polynomial description of the simplest non-trivial case, $n=2$, for some "easy" $\Lambda$, just to get me started.

This question is cross-posted (with modifications) from MSE. The original question is probably unfit for MathOverflow (although a professor I asked said that this is very nontrivial), but I'm hoping my follow-up questions and related discussion are of interest. To give an idea of my weak background, I am currently still going through Griffiths and Harris.

To rehash, let $X = \mathbb{C}^n / \Lambda$ be a complex torus of complex dimension $n$, with the lattice $\Lambda$ satisfying the Riemann conditions. Knowing that this condition guarantees that $X$ embeds in $\mathbb{CP}^N$ for some $N$, there exists a family of homogeneous polynomials whose zero locus is the embedded torus.

My original question was to ask for explicit examples of such embedded tori (for $n > 1$, as the case of elliptic curves is well known) and their corresponding polynomials. After reviewing the recommended literature I still could not figure out even a simple example, though I'm sure some must be known and there should be a method to directly compute these polynomials given $\Lambda$. I did learn in Birkenhake-Lange's textbook that nothing more than cubics are enough.

But it was pointed out to me that there are some subtleties that would make this a difficult task, which lead to my updated questions:

Given $X$, what is the smallest integer $N$ such that $X$ embeds in $\mathbb{CP}^N$? And is this number $N$ independent of the choice of lattice $\Lambda$? I.e. does it only depend on the dimension $n$ of the torus?

Mention of complete intersection (which I don't know about yet) was brought up, and if I remember correctly, it can be used to argue that any complex dimension $2$ torus cannot embed in $\mathbb{CP}^4$.

At the very least, I would be happy with a reference for a polynomial description of the simplest non-trivial case, $n=2$, for some "easy" $\Lambda$, just to get me started.

This question is cross-posted (with modifications) from MSE. The original question is probably unfit for MathOverflow (although a professor I asked said that this is very nontrivial), but I'm hoping my follow-up questions and related discussion are of interest. To give an idea of my weak background, I am currently still going through Griffiths and Harris.

To rehash, let $X = \mathbb{C}^n / \Lambda$ be a complex torus of complex dimension $n$, with the lattice $\Lambda$ satisfying the Riemann conditions. Knowing that this condition guarantees that $X$ embeds in $\mathbb{CP}^N$ for some $N$, there exists a family of homogeneous polynomials whose zero locus is the embedded torus.

My original question was to ask for explicit examples of such embedded tori (for $n > 1$, as the case of elliptic curves is well known) and their corresponding polynomials. After reviewing the recommended literature I still could not figure out even a simple example, though I'm sure some must be known and there should be a method to directly compute these polynomials given $\Lambda$. I did learn in Birkenhake-Lange's textbook that nothing more than cubics are enough.

But it was pointed out to me that there are some subtleties that would make this a difficult task, which lead to my updated questions:

Given $X$, what is the smallest integer $N$ such that $X$ embeds in $\mathbb{CP}^N$? And is this number $N$ independent of the choice of lattice $\Lambda$? I.e. does it only depend on the dimension $n$ of the torus?

Mention of complete intersection (which I don't know about yet) was brought up, and if I remember correctly, it can be used to argue that any complex dimension $2$ torus cannot embed in $\mathbb{CP}^4$.

At the very least, I would be happy with a reference for a polynomial description of the simplest non-trivial case, $n=2$, for some "easy" $\Lambda$, just to get me started.

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Paul Cusson
  • 1.8k
  • 9
  • 15

Explicit family of polynomials describing embedded torus in complex projective space

This question is cross-posted (with modifications) from MSE. The original question is probably unfit for MathOverflow (although a professor I asked said that this is very nontrivial), but I'm hoping my follow-up questions and related discussion are of interest. To give an idea of my weak background, I am currently still going through Griffiths and Harris.

To rehash, let $X = \mathbb{C}^n / \Lambda$ be a complex torus of complex dimension $n$, with the lattice $\Lambda$ satisfying the Riemann conditions. Knowing that this condition guarantees that $X$ embeds in $\mathbb{CP}^N$ for some $N$, there exists a family of homogeneous polynomials whose zero locus is the embedded torus.

My original question was to ask for explicit examples of such embedded tori (for $n > 1$, as the case of elliptic curves is well known) and their corresponding polynomials. After reviewing the recommended literature I still could not figure out even a simple example, though I'm sure some must be known and there should be a method to directly compute these polynomials given $\Lambda$. I did learn in Birkenhake-Lange's textbook that nothing more than cubics are enough.

But it was pointed out to me that there are some subtleties that would make this a difficult task, which lead to my updated questions:

Given $X$, what is the smallest integer $N$ such that $X$ embeds in $\mathbb{CP}^N$? And is this number $N$ independent of the choice of lattice $\Lambda$? I.e. does it only depend on the dimension $n$ of the torus?

Mention of complete intersection (which I don't know about yet) was brought up, and if I remember correctly, it can be used to argue that any complex dimension $2$ torus cannot embed in $\mathbb{CP}^4$.

At the very least, I would be happy with a reference for a polynomial description of the simplest non-trivial case, $n=2$, for some "easy" $\Lambda$, just to get me started.