ising model and total positivity
play

Ising model and total positivity Pavel Galashin MIT - PowerPoint PPT Presentation

Ising model and total positivity Pavel Galashin MIT galashin@mit.edu University of Toronto Colloquium, January 7, 2019 Joint work with Pavlo Pylyavskyy arXiv:1807.03282 Pavel Galashin (MIT) Ising model and total positivity U of Toronto,


  1. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): not a good model for ferromagnetism Q: how does | � F | depend on T ◦ ? | � F | T ◦ � F | � F | T ◦ Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 6 / 29

  2. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): not a good model for ferromagnetism Q: how does | � F | depend on T ◦ ? | � F | T ◦ � F | � F | T ◦ Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 6 / 29

  3. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): not a good model for ferromagnetism Q: how does | � F | depend on T ◦ ? | � F | T ◦ � F | � F | T ◦ Curie point (P. Curie, 1895) Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 6 / 29

  4. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): not a good model for ferromagnetism Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 7 / 29

  5. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 ⇒ not a good model for Ising (1925): no phase transition in 1D = ferromagnetism Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 7 / 29

  6. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 ⇒ not a good model for Ising (1925): no phase transition in 1D = ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 7 / 29

  7. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 ⇒ not a good model for Ising (1925): no phase transition in 1D = ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Peierls (1937): phase transition in Z d for d ≥ 2 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 7 / 29

  8. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 ⇒ not a good model for Ising (1925): no phase transition in 1D = ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Peierls (1937): phase transition in Z d for d ≥ 2 � √ T c = 1 1 � for Z 2 Kramers–Wannier (1941): critical temperature 2 log 2 + 1 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 7 / 29

  9. Ising model: phase transition Let G ⊂ Z d be a (2 N + 1) × (2 N + 1) square and J e = 1 T for some fixed T ∈ R > 0 . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 8 / 29

  10. Ising model: phase transition Let G ⊂ Z d be a (2 N + 1) × (2 N + 1) square and J e = 1 T for some fixed T ∈ R > 0 . Suppose that σ u = +1 for all u ∈ ∂ G . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 8 / 29

  11. Ising model: phase transition Let G ⊂ Z d be a (2 N + 1) × (2 N + 1) square and J e = 1 T for some fixed T ∈ R > 0 . Suppose that σ u = +1 for all u ∈ ∂ G . v Let v be the vertex in the middle of the square. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 8 / 29

  12. Ising model: phase transition Let G ⊂ Z d be a (2 N + 1) × (2 N + 1) square and J e = 1 T for some fixed T ∈ R > 0 . Suppose that σ u = +1 for all u ∈ ∂ G . v Let v be the vertex in the middle of the square. Define the spontaneous magnetization N →∞ (Prob( σ v = +1) − Prob( σ v = − 1)) M ( T ) := lim Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 8 / 29

  13. Ising model: phase transition Let G ⊂ Z d be a (2 N + 1) × (2 N + 1) square and J e = 1 T for some fixed T ∈ R > 0 . Suppose that σ u = +1 for all u ∈ ∂ G . v Let v be the vertex in the middle of the square. Define the spontaneous magnetization N →∞ (Prob( σ v = +1) − Prob( σ v = − 1)) M ( T ) := lim Theorem (Onsager (1944),Onsager–Kaufman (1949), Yang (1952)) M ( T ) T c T Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 8 / 29

  14. Ising model: phase transition Let G ⊂ Z d be a (2 N + 1) × (2 N + 1) square and J e = 1 T for some fixed T ∈ R > 0 . Suppose that σ u = +1 for all u ∈ ∂ G . v Let v be the vertex in the middle of the square. Define the spontaneous magnetization N →∞ (Prob( σ v = +1) − Prob( σ v = − 1)) M ( T ) := lim Theorem (Onsager (1944),Onsager–Kaufman (1949), Yang (1952)) 1 M ( T ) ≍ ( T c − T ) 8 T c T Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 8 / 29

  15. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): no phase transition in 1D = ⇒ not a good model for ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Peierls (1937): phase transition in Z d for d ≥ 2 � √ T c = 1 1 for Z 2 � Kramers–Wannier (1941): critical temperature 2 log 2 + 1 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 9 / 29

  16. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): no phase transition in 1D = ⇒ not a good model for ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Peierls (1937): phase transition in Z d for d ≥ 2 � √ T c = 1 1 for Z 2 � Kramers–Wannier (1941): critical temperature 2 log 2 + 1 Onsager, Kaufman, Yang (1944–1952): exact expressions for the free energy and spontaneous magnetization Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 9 / 29

  17. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): no phase transition in 1D = ⇒ not a good model for ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Peierls (1937): phase transition in Z d for d ≥ 2 � √ T c = 1 1 for Z 2 � Kramers–Wannier (1941): critical temperature 2 log 2 + 1 Onsager, Kaufman, Yang (1944–1952): exact expressions for the free energy and spontaneous magnetization Belavin–Polyakov–Zamolodchikov (1984): conjectured conformal invariance of the scaling limit at T = T c for Z 2 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 9 / 29

  18. Ising model: history Suggested by by W. Lenz to his student E. Ising in 1920 Ising (1925): no phase transition in 1D = ⇒ not a good model for ferromagnetism Historically, we let G := Z d ∩ Ω for some Ω ⊂ R d and set all J e := 1 T for some temperature T ∈ R > 0 . Peierls (1937): phase transition in Z d for d ≥ 2 � √ T c = 1 1 for Z 2 � Kramers–Wannier (1941): critical temperature 2 log 2 + 1 Onsager, Kaufman, Yang (1944–1952): exact expressions for the free energy and spontaneous magnetization Belavin–Polyakov–Zamolodchikov (1984): conjectured conformal invariance of the scaling limit at T = T c for Z 2 Smirnov, Chelkak, Hongler, Izyurov, ... (2010–2015): proved conformal invariance and universality of the scaling limit at T = T c for Z 2 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 9 / 29

  19. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. b 3 b 2 b 4 b 1 b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  20. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). b 3 b 2 b 4 b 1 b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  21. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 b 4 b 1 b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  22. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 M ( G , J ) is a symmetric matrix b 4 b 1 b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  23. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 M ( G , J ) is a symmetric matrix with 1’s on the diagonal b 4 b 1 b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  24. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 M ( G , J ) is a symmetric matrix with 1’s on the diagonal and nonnegative entries b 4 b 1 b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  25. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 M ( G , J ) is a symmetric matrix with 1’s on the diagonal and nonnegative entries b 4 b 1 Lives inside R ( n 2 ) b 5 b 6 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  26. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 M ( G , J ) is a symmetric matrix with 1’s on the diagonal and nonnegative entries b 4 b 1 Lives inside R ( n 2 ) b 5 b 6 X n := { M ( G , J ) | ( G , J ) is a planar Ising network with n boundary vertices } Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  27. Ising model: boundary correlations Recall: G is embedded in a disk. Let b 1 , . . . , b n be the boundary vertices. Correlation: � σ u σ v � := Prob( σ u = σ v ) − Prob( σ u � = σ v ). Definition Boundary correlation matrix: M ( G , J ) = ( m ij ) n i , j =1 , where m ij := � σ b i σ b j � . b 3 b 2 M ( G , J ) is a symmetric matrix with 1’s on the diagonal and nonnegative entries b 4 b 1 Lives inside R ( n 2 ) b 5 b 6 X n := { M ( G , J ) | ( G , J ) is a planar Ising network with n boundary vertices } X n := closure of X n inside the space of n × n matrices. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 10 / 29

  28. Boundary correlations: an example for n = 2 J e b 2 b 1 b 2 b 1 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  29. Boundary correlations: an example for n = 2 J e b 2 b 1 b 2 b 1 � 1 � m 12 M ( G , J ) = m 12 1 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  30. Boundary correlations: an example for n = 2 J e b 2 b 1 b 2 b 1 � 1 � m 12 = � σ 1 σ 2 � = 2 exp( J e ) − 2 exp( − J e ) m 12 M ( G , J ) = , m 12 1 2 exp( J e ) + 2 exp( − J e ) Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  31. Boundary correlations: an example for n = 2 J e b 2 b 1 b 2 b 1 � 1 � m 12 = � σ 1 σ 2 � = 2 exp( J e ) − 2 exp( − J e ) m 12 M ( G , J ) = , m 12 1 2 exp( J e ) + 2 exp( − J e ) J e = 0 J e ∈ (0 , ∞ ) J e = ∞ m 12 = 0 m 12 ∈ (0 , 1) m 12 = 1 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  32. Boundary correlations: an example for n = 2 J e b 2 b 1 b 2 b 1 � 1 � m 12 = � σ 1 σ 2 � = 2 exp( J e ) − 2 exp( − J e ) m 12 M ( G , J ) = , m 12 1 2 exp( J e ) + 2 exp( − J e ) J e = 0 J e ∈ (0 , ∞ ) J e = ∞ m 12 = 0 m 12 ∈ (0 , 1) m 12 = 1 We have X 2 ∼ = [0 , 1) and X 2 ∼ = [0 , 1]. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  33. Boundary correlations: an example for n = 2 J e b 2 b 1 b 2 b 1 � 1 � m 12 = � σ 1 σ 2 � = 2 exp( J e ) − 2 exp( − J e ) m 12 M ( G , J ) = , m 12 1 2 exp( J e ) + 2 exp( − J e ) J e = 0 J e ∈ (0 , ∞ ) J e = ∞ m 12 = 0 m 12 ∈ (0 , 1) m 12 = 1 We have X 2 ∼ = [0 , 1) and X 2 ∼ = [0 , 1]. X n is neither open nor closed inside R ( n 2 ). Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  34. Boundary correlations: an example for n = 2 J e ∞ b 2 b 1 b 2 b 1 b 2 b 1 � 1 � m 12 = � σ 1 σ 2 � = 2 exp( J e ) − 2 exp( − J e ) m 12 M ( G , J ) = , m 12 1 2 exp( J e ) + 2 exp( − J e ) J e = 0 J e ∈ (0 , ∞ ) J e = ∞ m 12 = 0 m 12 ∈ (0 , 1) m 12 = 1 We have X 2 ∼ = [0 , 1) and X 2 ∼ = [0 , 1]. X n is neither open nor closed inside R ( n 2 ). X n is obtained from X n by allowing J e = ∞ (i.e., contracting edges). Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 11 / 29

  35. Part 2: Total positivity

  36. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  37. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  38. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 RowSpan ∈ Gr(2 , 4) 0 2 1 1 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  39. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 RowSpan ∈ Gr(2 , 4) 0 2 1 1 ucker coordinates: for I ⊂ [ n ] := { 1 , 2 , . . . , n } of size k , Pl¨ Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  40. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 RowSpan ∈ Gr(2 , 4) 0 2 1 1 ucker coordinates: for I ⊂ [ n ] := { 1 , 2 , . . . , n } of size k , Pl¨ ∆ I := k × k minor with column set I . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  41. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 ∆ 13 = 1 ∆ 12 = 2 ∆ 14 = 1 RowSpan ∈ Gr(2 , 4) 0 2 1 1 ∆ 24 = 3 ∆ 34 = 1 ∆ 23 = 1 . ucker coordinates: for I ⊂ [ n ] := { 1 , 2 , . . . , n } of size k , Pl¨ ∆ I := k × k minor with column set I . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  42. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 ∆ 13 = 1 ∆ 12 = 2 ∆ 14 = 1 RowSpan ∈ Gr(2 , 4) 0 2 1 1 ∆ 24 = 3 ∆ 34 = 1 ∆ 23 = 1 . ucker coordinates: for I ⊂ [ n ] := { 1 , 2 , . . . , n } of size k , Pl¨ ∆ I := k × k minor with column set I . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  43. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 ∆ 13 = 1 ∆ 12 = 2 ∆ 14 = 1 RowSpan ∈ Gr(2 , 4) 0 2 1 1 ∆ 24 = 3 ∆ 34 = 1 ∆ 23 = 1 . ucker coordinates: for I ⊂ [ n ] := { 1 , 2 , . . . , n } of size k , Pl¨ ∆ I := k × k minor with column set I . Definition (Postnikov (2006)) The totally nonnegative Grassmannian is Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  44. The totally nonnegative (TNN) Grassmannian Gr( k , n ) := { W ⊂ R n | dim( W ) = k } . Gr( k , n ) := { k × n matrices of rank k } /(row operations) . Example: � 1 − 1 � 1 0 ∆ 13 = 1 ∆ 12 = 2 ∆ 14 = 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 ∆ 24 = 3 ∆ 34 = 1 ∆ 23 = 1 . ucker coordinates: for I ⊂ [ n ] := { 1 , 2 , . . . , n } of size k , Pl¨ ∆ I := k × k minor with column set I . Definition (Postnikov (2006)) The totally nonnegative Grassmannian is Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 13 / 29

  45. Example: Gr ≥ 0 (2 , 4) � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  46. Example: Gr ≥ 0 (2 , 4) � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  47. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  48. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  49. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  50. Example: Gr ≥ 0 (2 , 4) u 2 u 1 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  51. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  52. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  53. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  54. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0, ∆ 34 = 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  55. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0, ∆ 34 = 0 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  56. Example: Gr ≥ 0 (2 , 4) u 2 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 4 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0, ∆ 34 = 0, ∆ 14 = 0. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  57. Example: Gr ≥ 0 (2 , 4) u 2 u 4 u 3 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 1 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0, ∆ 34 = 0, ∆ 14 = 0. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  58. Example: Gr ≥ 0 (2 , 4) u 2 u 3 u 1 � 1 � 1 0 − 1 RowSpan ∈ Gr ≥ 0 (2 , 4) 0 2 1 1 u 1 u 2 u 3 u 4 u 4 ∆ 13 = 1 , ∆ 24 = 3 , ∆ 12 = 2 , ∆ 34 = 1 , ∆ 14 = 1 , ∆ 23 = 1 . In Gr(2 , 4), we have a Pl¨ ucker relation: ∆ 13 ∆ 24 = ∆ 12 ∆ 34 + ∆ 14 ∆ 23 . Top cell: ∆ 13 , ∆ 24 , ∆ 12 , ∆ 34 , ∆ 14 , ∆ 23 > 0 Codimension 1 cells: ∆ 12 = 0, ∆ 23 = 0, ∆ 34 = 0, ∆ 14 = 0. Codimension 2 cell: ∆ 12 = ∆ 14 = ∆ 24 = 0. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 14 / 29

  59. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  60. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  61. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Williams (2007), Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  62. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Williams (2007), Postnikov–Speyer–Williams (2009), Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  63. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Williams (2007), Postnikov–Speyer–Williams (2009), Rietsch–Williams (2010). Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  64. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Williams (2007), Postnikov–Speyer–Williams (2009), Rietsch–Williams (2010). Theorem (G.–Karp–Lam (2017)) Gr ≥ 0 ( k , n ) is homeomorphic to a k ( n − k ) -dimensional closed ball. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  65. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Williams (2007), Postnikov–Speyer–Williams (2009), Rietsch–Williams (2010). Theorem (G.–Karp–Lam (2017)) Gr ≥ 0 ( k , n ) is homeomorphic to a k ( n − k ) -dimensional closed ball. Theorem (G.–Karp–Lam (2019+)) The closure of each boundary cell is homeomorphic to a closed ball. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  66. The topology of Gr ≥ 0 ( k , n ) Theorem (Postnikov (2006)) Each boundary cell (some ∆ I > 0 and the rest ∆ J = 0 ) is an open ball. Conjecture (Postnikov (2006)) The closure of each boundary cell is homeomorphic to a closed ball. Williams (2007), Postnikov–Speyer–Williams (2009), Rietsch–Williams (2010). Theorem (G.–Karp–Lam (2017)) Gr ≥ 0 ( k , n ) is homeomorphic to a k ( n − k ) -dimensional closed ball. Theorem (G.–Karp–Lam (2019+)) The closure of each boundary cell is homeomorphic to a closed ball. Theorem (Smale (1960), Freedman (1982), Perelman (2003)) Let C be a compact contractible topological manifold whose boundary is homeomorphic to a sphere. Then C is homeomorphic to a closed ball. Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 15 / 29

  67. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

  68. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory N = 6 supersymmetric ? OG ≥ 0 ( n , 2 n ) ← → ← → Chern-Simons matter theory Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

  69. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory N = 6 supersymmetric ? OG ≥ 0 ( n , 2 n ) ← → ← → Chern-Simons matter theory Recall: Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

  70. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory N = 6 supersymmetric ? OG ≥ 0 ( n , 2 n ) ← → ← → Chern-Simons matter theory Recall: Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . The orthogonal Grassmannian: OG( n , 2 n ) := { W ∈ Gr( n , 2 n ) | ∆ I ( W ) = ∆ [2 n ] \ I ( W ) for all I } . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

  71. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory N = 6 supersymmetric ? OG ≥ 0 ( n , 2 n ) ← → ← → Chern-Simons matter theory Recall: Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . The orthogonal Grassmannian: OG( n , 2 n ) := { W ∈ Gr( n , 2 n ) | ∆ I ( W ) = ∆ [2 n ] \ I ( W ) for all I } . Definition (Huang–Wen (2013)) The totally nonnegative orthogonal Grassmannian: OG ≥ 0 ( n , 2 n ) := OG( n , 2 n ) ∩ Gr ≥ 0 ( n , 2 n ) Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

  72. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory N = 6 supersymmetric ? OG ≥ 0 ( n , 2 n ) ← → ← → Chern-Simons matter theory Recall: Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . The orthogonal Grassmannian: OG( n , 2 n ) := { W ∈ Gr( n , 2 n ) | ∆ I ( W ) = ∆ [2 n ] \ I ( W ) for all I } . Definition (Huang–Wen (2013)) The totally nonnegative orthogonal Grassmannian: OG ≥ 0 ( n , 2 n ) := OG( n , 2 n ) ∩ Gr ≥ 0 ( n , 2 n ), i.e., OG ≥ 0 ( n , 2 n ) := { W ∈ Gr( n , 2 n ) | ∆ I ( W ) = ∆ [2 n ] \ I ( W ) ≥ 0 for all I } . Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

  73. The totally nonnegative orthogonal Grassmannian N = 4 supersymmetric Gr ≥ 0 ( k , n ) ← → amplituhedron ← → Yang–Mills theory N = 6 supersymmetric ? OG ≥ 0 ( n , 2 n ) ← → ← → Chern-Simons matter theory Recall: Gr ≥ 0 ( k , n ) := { W ∈ Gr( k , n ) | ∆ I ( W ) ≥ 0 for all I } . The orthogonal Grassmannian: OG( n , 2 n ) := { W ∈ Gr( n , 2 n ) | ∆ I ( W ) = ∆ [2 n ] \ I ( W ) for all I } . Definition (Huang–Wen (2013)) The totally nonnegative orthogonal Grassmannian: OG ≥ 0 ( n , 2 n ) := OG( n , 2 n ) ∩ Gr ≥ 0 ( n , 2 n ), i.e., OG ≥ 0 ( n , 2 n ) := { W ∈ Gr( n , 2 n ) | ∆ I ( W ) = ∆ [2 n ] \ I ( W ) ≥ 0 for all I } . dim(Gr ≥ 0 ( n , 2 n )) = n 2 Pavel Galashin (MIT) Ising model and total positivity U of Toronto, 01/07/2019 16 / 29

Download Presentation
Download Policy: The content available on the website is offered to you 'AS IS' for your personal information and use only. It cannot be commercialized, licensed, or distributed on other websites without prior consent from the author. To download a presentation, simply click this link. If you encounter any difficulties during the download process, it's possible that the publisher has removed the file from their server.

Recommend


More recommend