Involution action on $H^3(S^1times S^2)$
$begingroup$
I am studying about involution action $I^*$ on de Rham cohomology group $H^3(S^1times S^2)$ induced from an action $Icdot (z,x)=(overline{z},-x) $ where $S^1times S^2subset mathbb{C}times mathbb{R}^3$. Note that, by Kunneth formula, $$H^3(S^1times S^2)=mathbb{R}.$$
I figured out the action of $I^*$ on $H^2(S^1times S^2)$ in a similar way with my previous question
Involution action on $H^1(S^1times S^2)$.
However, I am stuck at identifying the action on $H^3(S^1times S^2)$.
I was trying to pick $dtheta in Omega^1(S^1)$ and $dsin Omega^2(S^2)$ where $theta(overline{z})=-theta(z)$ and $s(-x)=-s(x)$. And it seems leading me to create $omega=dthetawedge ds$ as a generator of $H^3(S^1times S^2)$. But I am not sure if I am going in right direction since the $omega$ seems not the one for some anticlimatic reason.
Any help would be appreciated! Thank you in advance!
group-actions de-rham-cohomology involutions
$endgroup$
add a comment |
$begingroup$
I am studying about involution action $I^*$ on de Rham cohomology group $H^3(S^1times S^2)$ induced from an action $Icdot (z,x)=(overline{z},-x) $ where $S^1times S^2subset mathbb{C}times mathbb{R}^3$. Note that, by Kunneth formula, $$H^3(S^1times S^2)=mathbb{R}.$$
I figured out the action of $I^*$ on $H^2(S^1times S^2)$ in a similar way with my previous question
Involution action on $H^1(S^1times S^2)$.
However, I am stuck at identifying the action on $H^3(S^1times S^2)$.
I was trying to pick $dtheta in Omega^1(S^1)$ and $dsin Omega^2(S^2)$ where $theta(overline{z})=-theta(z)$ and $s(-x)=-s(x)$. And it seems leading me to create $omega=dthetawedge ds$ as a generator of $H^3(S^1times S^2)$. But I am not sure if I am going in right direction since the $omega$ seems not the one for some anticlimatic reason.
Any help would be appreciated! Thank you in advance!
group-actions de-rham-cohomology involutions
$endgroup$
add a comment |
$begingroup$
I am studying about involution action $I^*$ on de Rham cohomology group $H^3(S^1times S^2)$ induced from an action $Icdot (z,x)=(overline{z},-x) $ where $S^1times S^2subset mathbb{C}times mathbb{R}^3$. Note that, by Kunneth formula, $$H^3(S^1times S^2)=mathbb{R}.$$
I figured out the action of $I^*$ on $H^2(S^1times S^2)$ in a similar way with my previous question
Involution action on $H^1(S^1times S^2)$.
However, I am stuck at identifying the action on $H^3(S^1times S^2)$.
I was trying to pick $dtheta in Omega^1(S^1)$ and $dsin Omega^2(S^2)$ where $theta(overline{z})=-theta(z)$ and $s(-x)=-s(x)$. And it seems leading me to create $omega=dthetawedge ds$ as a generator of $H^3(S^1times S^2)$. But I am not sure if I am going in right direction since the $omega$ seems not the one for some anticlimatic reason.
Any help would be appreciated! Thank you in advance!
group-actions de-rham-cohomology involutions
$endgroup$
I am studying about involution action $I^*$ on de Rham cohomology group $H^3(S^1times S^2)$ induced from an action $Icdot (z,x)=(overline{z},-x) $ where $S^1times S^2subset mathbb{C}times mathbb{R}^3$. Note that, by Kunneth formula, $$H^3(S^1times S^2)=mathbb{R}.$$
I figured out the action of $I^*$ on $H^2(S^1times S^2)$ in a similar way with my previous question
Involution action on $H^1(S^1times S^2)$.
However, I am stuck at identifying the action on $H^3(S^1times S^2)$.
I was trying to pick $dtheta in Omega^1(S^1)$ and $dsin Omega^2(S^2)$ where $theta(overline{z})=-theta(z)$ and $s(-x)=-s(x)$. And it seems leading me to create $omega=dthetawedge ds$ as a generator of $H^3(S^1times S^2)$. But I am not sure if I am going in right direction since the $omega$ seems not the one for some anticlimatic reason.
Any help would be appreciated! Thank you in advance!
group-actions de-rham-cohomology involutions
group-actions de-rham-cohomology involutions
asked Dec 24 '18 at 6:11
Lev BanLev Ban
1,0721317
1,0721317
add a comment |
add a comment |
1 Answer
1
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oldest
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$begingroup$
As you have defined it, $omega$ doesn't make sense because you can't take the wedge product of a form on $S^1$ with a form on $S^2$. Instead, let $pi_i : S^1times S^2 to S^i$ be the natural projections. Then $pi_1^*dtheta$ and $pi_2^*ds$ are both forms on $S^1times S^2$, so their wedge product $omega = (pi_1^*dtheta)wedge(pi_2^*ds)$ is defined.
Let $I_1 : S^1to S^1$ be given by $I_1(z) = bar{z}$ and $I_2 : S^2to S^2$ be given by $I_2(x) = -x$, then $I(z, x) = (I_1(z), I_2(x))$. Said another way, $pi_1circ I = I_1circpi_1$ and $pi_2circ I = I_2circ pi_2$. Therefore,
$$I^*pi_1^*dtheta = (pi_1circ I)^*dtheta = (I_1circ pi_1)^*dtheta = pi_1^*(I_1^*dtheta) = pi_1^*(-dtheta) = -pi_1^*dtheta$$
and
$$I^*pi_2^*ds = (pi_2circ I)^*ds = (I_2circ pi_2)^*ds = pi_2^*(I_2^*ds) = pi_2^*(-ds) = -pi_2^*ds.$$
Therefore $I^*omega = (I^*pi_1^*dtheta)wedge(I^*pi_2^*ds) = (-dtheta)wedge(-ds) = dthetawedge ds = omega$.
$endgroup$
1
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
1
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
|
show 1 more comment
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$begingroup$
As you have defined it, $omega$ doesn't make sense because you can't take the wedge product of a form on $S^1$ with a form on $S^2$. Instead, let $pi_i : S^1times S^2 to S^i$ be the natural projections. Then $pi_1^*dtheta$ and $pi_2^*ds$ are both forms on $S^1times S^2$, so their wedge product $omega = (pi_1^*dtheta)wedge(pi_2^*ds)$ is defined.
Let $I_1 : S^1to S^1$ be given by $I_1(z) = bar{z}$ and $I_2 : S^2to S^2$ be given by $I_2(x) = -x$, then $I(z, x) = (I_1(z), I_2(x))$. Said another way, $pi_1circ I = I_1circpi_1$ and $pi_2circ I = I_2circ pi_2$. Therefore,
$$I^*pi_1^*dtheta = (pi_1circ I)^*dtheta = (I_1circ pi_1)^*dtheta = pi_1^*(I_1^*dtheta) = pi_1^*(-dtheta) = -pi_1^*dtheta$$
and
$$I^*pi_2^*ds = (pi_2circ I)^*ds = (I_2circ pi_2)^*ds = pi_2^*(I_2^*ds) = pi_2^*(-ds) = -pi_2^*ds.$$
Therefore $I^*omega = (I^*pi_1^*dtheta)wedge(I^*pi_2^*ds) = (-dtheta)wedge(-ds) = dthetawedge ds = omega$.
$endgroup$
1
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
1
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
|
show 1 more comment
$begingroup$
As you have defined it, $omega$ doesn't make sense because you can't take the wedge product of a form on $S^1$ with a form on $S^2$. Instead, let $pi_i : S^1times S^2 to S^i$ be the natural projections. Then $pi_1^*dtheta$ and $pi_2^*ds$ are both forms on $S^1times S^2$, so their wedge product $omega = (pi_1^*dtheta)wedge(pi_2^*ds)$ is defined.
Let $I_1 : S^1to S^1$ be given by $I_1(z) = bar{z}$ and $I_2 : S^2to S^2$ be given by $I_2(x) = -x$, then $I(z, x) = (I_1(z), I_2(x))$. Said another way, $pi_1circ I = I_1circpi_1$ and $pi_2circ I = I_2circ pi_2$. Therefore,
$$I^*pi_1^*dtheta = (pi_1circ I)^*dtheta = (I_1circ pi_1)^*dtheta = pi_1^*(I_1^*dtheta) = pi_1^*(-dtheta) = -pi_1^*dtheta$$
and
$$I^*pi_2^*ds = (pi_2circ I)^*ds = (I_2circ pi_2)^*ds = pi_2^*(I_2^*ds) = pi_2^*(-ds) = -pi_2^*ds.$$
Therefore $I^*omega = (I^*pi_1^*dtheta)wedge(I^*pi_2^*ds) = (-dtheta)wedge(-ds) = dthetawedge ds = omega$.
$endgroup$
1
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
1
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
|
show 1 more comment
$begingroup$
As you have defined it, $omega$ doesn't make sense because you can't take the wedge product of a form on $S^1$ with a form on $S^2$. Instead, let $pi_i : S^1times S^2 to S^i$ be the natural projections. Then $pi_1^*dtheta$ and $pi_2^*ds$ are both forms on $S^1times S^2$, so their wedge product $omega = (pi_1^*dtheta)wedge(pi_2^*ds)$ is defined.
Let $I_1 : S^1to S^1$ be given by $I_1(z) = bar{z}$ and $I_2 : S^2to S^2$ be given by $I_2(x) = -x$, then $I(z, x) = (I_1(z), I_2(x))$. Said another way, $pi_1circ I = I_1circpi_1$ and $pi_2circ I = I_2circ pi_2$. Therefore,
$$I^*pi_1^*dtheta = (pi_1circ I)^*dtheta = (I_1circ pi_1)^*dtheta = pi_1^*(I_1^*dtheta) = pi_1^*(-dtheta) = -pi_1^*dtheta$$
and
$$I^*pi_2^*ds = (pi_2circ I)^*ds = (I_2circ pi_2)^*ds = pi_2^*(I_2^*ds) = pi_2^*(-ds) = -pi_2^*ds.$$
Therefore $I^*omega = (I^*pi_1^*dtheta)wedge(I^*pi_2^*ds) = (-dtheta)wedge(-ds) = dthetawedge ds = omega$.
$endgroup$
As you have defined it, $omega$ doesn't make sense because you can't take the wedge product of a form on $S^1$ with a form on $S^2$. Instead, let $pi_i : S^1times S^2 to S^i$ be the natural projections. Then $pi_1^*dtheta$ and $pi_2^*ds$ are both forms on $S^1times S^2$, so their wedge product $omega = (pi_1^*dtheta)wedge(pi_2^*ds)$ is defined.
Let $I_1 : S^1to S^1$ be given by $I_1(z) = bar{z}$ and $I_2 : S^2to S^2$ be given by $I_2(x) = -x$, then $I(z, x) = (I_1(z), I_2(x))$. Said another way, $pi_1circ I = I_1circpi_1$ and $pi_2circ I = I_2circ pi_2$. Therefore,
$$I^*pi_1^*dtheta = (pi_1circ I)^*dtheta = (I_1circ pi_1)^*dtheta = pi_1^*(I_1^*dtheta) = pi_1^*(-dtheta) = -pi_1^*dtheta$$
and
$$I^*pi_2^*ds = (pi_2circ I)^*ds = (I_2circ pi_2)^*ds = pi_2^*(I_2^*ds) = pi_2^*(-ds) = -pi_2^*ds.$$
Therefore $I^*omega = (I^*pi_1^*dtheta)wedge(I^*pi_2^*ds) = (-dtheta)wedge(-ds) = dthetawedge ds = omega$.
answered Dec 24 '18 at 22:02
Michael AlbaneseMichael Albanese
63.8k1599309
63.8k1599309
1
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
1
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
|
show 1 more comment
1
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
1
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
1
1
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
More generally, there's a Kunneth theorem for deRham cohomology: $H^*(X)otimes H^*(Y)longrightarrow H^*(Xtimes Y)$ given by the formula of this post is an isomorphism of algebras.
$endgroup$
– Pedro Tamaroff♦
Dec 24 '18 at 22:18
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@Michael Albanese Come to think of it, $ds$ seems not $2$ -form. Is it still vaild argument?
$endgroup$
– Lev Ban
Dec 26 '18 at 19:48
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@LeB: What do you mean by $ds$? I thought you meant a two-form on $S^2$ (not the exterior derivative of a function, which is not a two-form).
$endgroup$
– Michael Albanese
Dec 26 '18 at 21:29
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
$begingroup$
@MichaelAlbanese I am sorry! I got a bit confused. If it is not too much, could you let me know which kind of 2 form I can use of for this problem?
$endgroup$
– Lev Ban
Dec 26 '18 at 23:38
1
1
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
$begingroup$
The two form $omega = x,dywedge dz - y,dxwedge dz + z,dxwedge dy$ on $mathbb{R}^3$ restricts to a closed form on $S^2$ which generates $H^2_{text{dR}}(S^2)$, and satisfies $I_2^*omega = -omega$.
$endgroup$
– Michael Albanese
Dec 27 '18 at 1:19
|
show 1 more comment
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