π Topological realization: Sm C Man X(C) X βcomplex e.g. P 1 P 1 (C)=CP 1 β S 2 manifold of solutions in Cβ motivic induced map spectrum π E a,b (X) E a (X(C)) mot top βalgebraicβ βtopologicalβ
π Topological realization: Sm C Man X(C) X βcomplex e.g. P 1 P 1 (C)=CP 1 β S 2 manifold of solutions in Cβ motivic induced map spectrum π E a,b (X) E a (X(C)) mot top βalgebraicβ βtopologicalβ Question: How to detect whether classes in E* (X(C)) are algebraic, i.e., top are in the image of π ?
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum E 2 * , *(X) mot π H 2 * , *(X;Z) mot
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum E 2 *(X) E 2 * , *(X) top mot π π H 2 * , *(X;Z) H 2 *(X;Z) mot singular cohomology
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E E 2 *(X) E 2 * , *(X) top mot βΊ π π π H H 2 * , *(X;Z) H 2 *(X;Z) mot singular cohomology
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E E 2 *(X) E 2 * , *(X) top mot βΊ π π =cl H π H H 2 * , *(X;Z) H 2 *(X;Z) mot singular cohomology
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E E 2 *(X) E 2 * , *(X) top mot βΊ π π =cl H π H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H singular cohomology
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E Alg 2 *(X) β E 2 *(X) E 2 * , *(X) top mot E βΊ π π =cl H π H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H singular cohomology
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E Alg 2 *(X) β E 2 *(X) E 2 * , *(X) top mot E must βΊ π π factor through =cl H π H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H singular cohomology
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E Alg 2 *(X) β E 2 *(X) E 2 * , *(X) top mot E must βΊ π π factor through =cl H π H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H singular cohomology Easier task:
π motivic Obstruction: Given E HZ. Eilenberg-MacLane Thom map spectrum π E Alg 2 *(X) β E 2 *(X) E 2 * , *(X) top mot E must βΊ π π factor through =cl H π H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H singular cohomology Easier task: describe using E 2 *(X(C))\Alg 2 *(X) H 2 *(X;Z)\Alg 2 *(X) top E H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) MGL 2 * , *(X) β L* Z MU 2 *(X) β L* Z π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) MGL 2 * , *(X) β L* Z MU 2 *(X) β L* Z Totaro β³ π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) MGL 2 * , *(X) β L* Z MU 2 *(X) β L* Z Levine + Totaro Levine-Morel β β³ π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) MGL 2 * , *(X) β L* Z MU 2 *(X) β L* Z Levine + β in general Totaro Levine-Morel β β³ π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) MGL 2 * , *(X) β L* Z MU 2 *(X) β L* Z Levine + β in general Totaro Levine-Morel β β³ π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H β’ Atiyah-Hirzebruch: cl H is not surjective onto integral Hodge classes.
Atiyah-Hirzebruch, Totaro, Levine-Morel: π MGL MGL 2 * , *(X) MU 2 *(X) MGL 2 * , *(X) β L* Z MU 2 *(X) β L* Z Levine + β in general Totaro Levine-Morel β β³ π H =cl H H 2 * , *(X;Z) Alg 2 *(X) β H 2 *(X;Z) mot H β’ Atiyah-Hirzebruch: cl H is not surjective onto integral Hodge classes. β’ Totaro: new classes in kernel of cl H .
A different perspective: Fix a prime p.
A different perspective: Brown-Peterson, Fix a prime p. Quillen |v i |=2(p i -1) MU (p) splits as a wedge of suspensions of spectra BP with BP = Z (p) [v 1 ,v 2 ,β¦]. *
A different perspective: Brown-Peterson, Fix a prime p. Quillen |v i |=2(p i -1) MU (p) splits as a wedge of suspensions of spectra BP with BP = Z (p) [v 1 ,v 2 ,β¦]. * quotient map BP BP/(v n+1 ,β¦) =: BP β¨ n β© For every n: with BP β¨ n β© = Z (p) [v 1 ,β¦,v n ] *
A different perspective: Brown-Peterson, Fix a prime p. Quillen |v i |=2(p i -1) MU (p) splits as a wedge of suspensions of spectra BP with BP = Z (p) [v 1 ,v 2 ,β¦]. * quotient map BP BP/(v n+1 ,β¦) =: BP β¨ n β© For every n: with BP β¨ n β© = Z (p) [v 1 ,β¦,v n ] * The Brown-Peterson tower (Wilson): β¦ β¦ BP BP β¨ n β© BP β¨ 1 β© BP β¨ 0 β© BP β¨ -1 β© p=2: 2-local HZ (p) HF p connective K-theory
Milnor operations:
Milnor operations: For every n: stable cofibre sequence v n |v n | |v n |+1 β BP β¨ n β© BP β¨ n β© BP β¨ n β© BP β¨ n-1 β© β
Milnor operations: For every n: stable cofibre sequence v n |v n | |v n |+1 β BP β¨ n β© BP β¨ n β© BP β¨ n β© BP β¨ n-1 β© β with an induced exact sequence (for any space X) +|v n | BP β¨ n β© * (X) BP β¨ n β© *(X) q n BP β¨ n β© * +|v n |+1 (X) BP β¨ n-1 β© *(X)
Milnor operations: For every n: stable cofibre sequence v n |v n | |v n |+1 β BP β¨ n β© BP β¨ n β© BP β¨ n β© BP β¨ n-1 β© β with an induced exact sequence (for any space X) +|v n | BP β¨ n β© * (X) BP β¨ n β© *(X) q n BP β¨ n β© * +|v n |+1 (X) BP β¨ n-1 β© *(X) BP β¨ n-1 β© Thom map +|v n |+1 (X;F p ) HF p H*(X;F p ) H* Q n
Milnor operations: For every n: stable cofibre sequence v n |v n | |v n |+1 β BP β¨ n β© BP β¨ n β© BP β¨ n β© BP β¨ n-1 β© β with an induced exact sequence (for any space X) +|v n | BP β¨ n β© * (X) BP β¨ n β© *(X) q n BP β¨ n β© * +|v n |+1 (X) BP β¨ n-1 β© *(X) BP β¨ n-1 β© nth Milnor Thom operation: map Q 0 =Bockstein p n-1 p n-1 +|v n |+1 (X;F p ) Q n =P Q n-1 -Q n-1 P HF p H*(X;F p ) H* Q n
The LMT obstruction in action: BP 2 *(X) β² q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Q n
The LMT obstruction in action: BP 2 *(X) β² q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Q n π±
The LMT obstruction in action: BP 2 *(X) β² q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) β² q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT β² q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT β² π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT β² π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT β² q n π± n-1 π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT if β² = 0 q n π± n-1 π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT then if β² = 0 q n π± n-1 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT then if β² = 0 q n π± n-1 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n Q n π± π± Question: Is π± algebraic?
The LMT obstruction in action: BP 2 *(X) LMT then if β² = 0 q n π± n-1 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n Q n π± π±
The LMT obstruction in action: BP 2 *(X) LMT then if β² = 0 q n π± n-1 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n Q n π± π± Levine-Morel-Totaro obstruction:
The LMT obstruction in action: BP 2 *(X) LMT then if β² = 0 q n π± n-1 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n β 0 Q n π± π± if Levine-Morel-Totaro obstruction: If Q n π± β 0,
The LMT obstruction in action: BP 2 *(X) LMT then β² q n π± n-1 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n β 0 Q n π± π± if Levine-Morel-Totaro obstruction: If Q n π± β 0,
The LMT obstruction in action: BP 2 *(X) LMT then β² q n π± n-1 β 0 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n β 0 Q n π± π± if Levine-Morel-Totaro obstruction: If Q n π± β 0,
The LMT obstruction in action: BP 2 *(X) LMT then β² β q n π± n-1 β 0 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n β 0 Q n π± π± if Levine-Morel-Totaro obstruction: If Q n π± β 0,
The LMT obstruction in action: BP 2 *(X) LMT then β² β β q n π± n-1 β 0 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n β 0 Q n π± π± if Levine-Morel-Totaro obstruction: If Q n π± β 0,
The LMT obstruction in action: BP 2 *(X) LMT then β² β β q n π± n-1 β 0 π± n π± n-1 q n BP β¨ n β© 2 * +|v n |+1 (X) BP β¨ n β© 2 *(X) BP β¨ n-1 β© 2 *(X) βΊ +|v n |+1 (X;F p ) H 2 *(X;F p ) H 2 * Z*(X) Q n β 0 Q n π± π± if Levine-Morel-Totaro obstruction: If Q n π± β 0, then π± is not algebraic.
Voevodskyβ s motivic Milnor operations:
Voevodskyβ s motivic Milnor operations: There are motivic operations mod p-motivic Q n β π 2p n -1,p n -1 mot Steenrod algebra
Voevodskyβ s motivic Milnor operations: There are motivic operations mod p-motivic Q n β π 2p n -1,p n -1 mot Steenrod algebra For a smooth complex variety X: mot Q n i+2p n -1,j+p n -1 (X;F p ) i,j H (X;F p ) H mot mot mod p-motivic cohomology
Voevodskyβ s motivic Milnor operations: There are motivic operations mod p-motivic Q n β π 2p n -1,p n -1 mot Steenrod algebra For a smooth complex variety X: mot Q n i+2p n -1,j+p n -1 (X;F p ) i,j H (X;F p ) H mot mot mod p-motivic cohomology 2i,i Recall: = CH i (X;Z/p) H (X;F p ) and mot i,j H (X;F p ) = 0 if i>2j. mot
Obstructions revisited: X smooth complex variety mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H mot mot βΊ topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n
Obstructions revisited: X smooth complex variety mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n
Obstructions revisited: X smooth complex variety mot Q n mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n
Obstructions revisited: X smooth complex variety mot Q n mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n π±
Obstructions revisited: X smooth complex variety mot Q n mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n Q n π± β 0 π± if
Obstructions revisited: X smooth complex variety mot Q n mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ β topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n Q n π± β 0 π± if
Obstructions revisited: X smooth complex variety mot Q n mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ β topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n Q n π± β 0 π± if Observation: The LMT-obstruction is particular to smooth varieties and bidegrees (2i,i).
Obstructions revisited: X smooth complex variety mot Q n mot Q n 2i,i 2i+2p n -1,i+p n -1 (X;F p ) H (X;F p ) H = 0 mot mot βΊ β topological realization 2i+2p n -1 H 2i (X;F p ) H (X;F p ) Q n Q n π± β 0 π± if Observation: The LMT-obstruction is particular to smooth varieties and bidegrees (2i,i). Example: Q n π β 0 for π the fundamental class of a suitable Eilenberg-MacLane space, though π is algebraic.
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