Classical and quantum aspects ofultradiscrete solitons

Atsuo Kuniba (Univ. Tokyo)

2 April 2009, Glasgow

Tau function of KP hierarchy

τi(x) = 〈i|eH(x) exp( N∑

j=1

cjψ(pj)ψ∗(qj)

)|i〉

(eH(x) = time evolution op. involving β1, β2, . . .)

τi(x) = det(1 + F )

= 1 +∑

1≤j≤NFjj +

∑

1≤j1

Ultradiscrete (tropical) limit

lim²→+0

² log τi(x)

with an elaborate ²-tuning of the parameters

cj, pj, qj, βm

leads to a tropical tau function associated withcombinatorial data called Rigged Configuration in Bethe ansatz.

Solitons in tau function ↔ Strings in Bethe ansatzcjψ(pj)ψ

∗(qj)

Example from sln=4

λ

02

3

µ(1)

10

µ(2)

0

µ(3)Rigged configuration

(µ, r) = (λ, (µ(1), r(1)), . . . , (µ(n−1), r(n−1)))

µ(a): configuration (Young diagram)

r(a): rigging (integers attached to µ(a))

(+ selection rule)

Charge of rigged configuration

c(µ, r) :=1

2

n−1∑

a,b=1

Cab min(µ(a), µ(b)) − min(λ, µ(1)) +

n−1∑a=1

|r(a)|

min(λ, µ) =∑

ij min(λi, µj), |r| =∑

i ri

(Cab) = Cartan matrix of sln)

Regard rigged conf. = {strings}, string = row attached with rigging.

Tropical tau function

τi(λ) = − min(ν,s)

{c(ν, s) + |ν(i)|} (1≤ i≤n)

min(ν,s)

extends over the power set of (µ, r). e.g.,

µ(1)

02

3

µ(2)

10

µ(3)

0

Proposition ([K-Sakamoto-Yamada 2007] “Tropical Hirota eq”. )

τ̄k,i−1 + τk−1,i = max(τ̄k,i + τk−1,i−1, τ̄k−1,i−1 + τk,i − λk),

where

τk,i = τi(λ1, . . . , λk), τ̄k,i = τk,i|r(a)→r(a)+δa1µ(1)

Rigged configuration originates in string hypothesis in Bethe ansatz

Example from sl2 (Heisenberg chain)

H =L∑

k=1

(σxkσxk+1 + σ

ykσ

yk+1 + σ

zkσ

zk+1)

Bethe equation for length L = 6 chain with 3 down spins.

(u1 + i

u1 − i

)6=

(u1 − u2 + 2i)(u1 − u3 + 2i)(u1 − u2 − 2i)(u1 − u3 − 2i)

,

(u2 + i

u2 − i

)6=

(u2 − u1 + 2i)(u2 − u3 + 2i)(u2 − u1 − 2i)(u2 − u3 − 2i)

,

(u3 + i

u3 − i

)6=

(u3 − u1 + 2i)(u3 − u2 + 2i)(u3 − u1 − 2i)(u3 − u2 − 2i)

.

• 0.859•• −0.859

000

•2.02i

••−2.02i

0

•−0.472 − i

•−0.472 + i

• −0.944

00

•−i

• •i

01

•0.472 − i

•0.472 + i

• 0.944

02

Kerov-Kirillov-Reshetikhin (1986) gave a canonical bijection

“Bethe root” “Bethe vector”

{rigged configurations} KKR←→ {highest paths}000

121212 (1 =↑, 2 =↓)

0 111222

00

121122

01

112212

02

112122

which may viewed as a combinatorial analogue of Bethe ansatz.

Higher rank example (sl4)

{rigged configurations} 1:1←→ {highest paths}

λ

02

3

µ(1)

10

µ(2)

0

µ(3)

←→ 111 122 22 13 23 4 3

“Bethe roots” “Bethe vectors”

highest path = b1 b2 . . . bL

bi = row shape (λi) semistandard tableau.

(+ highest condition)

Example of KKR algorithm from sl3

00

1

0 021

0 01

0

01

0 11

0 1 ∅

∅ ∅ ∅ ∅ ∅ ∅∅

-2 -3

-1 -2 -3

-2 -1 -1

Top left rigged configurationKKR7−→ 11232132

Theorem.([KSY])

Image of the KKR map

(λ, (µ(1), r(1)), . . . , (µ(n−1), r(n−1)))KKR7−→ b1 . . . bL

bk = (

xk,1︷ ︸︸ ︷1 . . . 1, . . . ,

xk,n︷ ︸︸ ︷n . . . n)︸ ︷︷ ︸

λk

(semistandard tableau),

is given by

xk,i = τk,i − τk−1,i − τk,i−1 + τk−1,i−1

We will see that this is an analogue of

u = −2∂2 log τ

∂x2

for KdV eq.

Crystals for Uq(ŝln)

Bl = { i1, . . . , il | semistandard}

equipped with crystal structures.

ul := 11. . . 1 ∈ Bl is the (classically) highest element.

An element of Bλ1 ⊗ Bλ2 ⊗ · · · is called a path.

Combinatorial R

R : Bl ⊗ Bm ∼→ Bm ⊗ Bl, x ⊗ y 7→ ỹ ⊗ x̃

x̃i − xi = yi − ỹi = Qi(x ⊗ y) − Qi−1(x ⊗ y) (i mod n),

xi = ] of letter i in tableau x (yi : similar),

Qi(x ⊗ y) = min1≤k≤n

{k−1∑

j=1

xi+j +n∑

j=k+1

yi+j} · · · i th local energy.

Example : 1233 ⊗ 124 ' 133 ⊗ 1224

will be denoted by

1233

124

133

1224 or simply 1233

124

133

1224

Energy Ei of path b1 ⊗ · · · ⊗ bk (i mod n)

Ei(b1 ⊗ · · · ⊗ bk) := Sum of Qi(x ⊗ y) attached to all vertices in

bkb2b1u∞

Theorem.([KSY] “Tropical fermionic formula”)

Suppose b1 ⊗ · · · ⊗ bL KKR←→ (µ, r) −→ {τk,i}. Then,

Ei(b1 ⊗ · · · ⊗ bk) = τk,i (1 ≤ k ≤ L)

Uq(ŝln) vertex model at q = 0

Tl : B1 ⊗ B1 ⊗ B1 ⊗ · · · −→ B1 ⊗ B1 ⊗ B1 ⊗ · · ·b1 ⊗ b2 ⊗ b3 ⊗ · · · 7−→ b′1 ⊗ b′2 ⊗ b′3 ⊗ · · ·

· · ·Bl 3 ulb1 b2 b3 b4

b′1 b′2 b

′3 b

′4

T1, T2, . . . : commuting family of time evolutions(deterministic transfer matrices)

Example of time evolution T2 :

11 11 11 11 11 11 11 11 1114 24 12 11 131 4 2 1 1 3 1 1 1 1 1 1 1

1 1 1 4 2 1 3 1 1 1 1 1 111 11 11 11 11 11 11 11 11 1114 24 12 13

1 1 1 1 1 4 2 3 1 1 1 1 111 11 11 11 11 11 11 11 11 1114 24 34 13

1 1 1 1 1 1 1 2 4 3 1 1 111 11 11 11 11 11 11 11 11 1112 14 34 13

1 1 1 1 1 1 1 1 2 1 4 3 1

The dynamics on vertical edges reproduces Box-ball systemwith carrier (Takahashi, Satsuma, Matsukidaira).

· · · 1421131111111 · · ·· · · 1114213111111 · · ·· · · 1111142311111 · · ·· · · 1111111243111 · · ·· · · 1111111121431 · · ·

1= empty box, 2, 3, 4 = colored balls.

Theorem.([KSY])

(1) Tropical tau function

= Energy of crystal (math) · · · previous theorem= Baxter’s corner transfer matrix for box-ball system (phys)

Let b1 b2 · · · bL KKR←→ (µ, r) −→ {τk,i}. Then,

b1 b2 · · · bk

τk,i = ] of “balls” in

?

time evolution T∞

(2) Tropical Hirota equation = eq. of motion of box-ball system.

Bethe ansatz Corner transfer matrix

main combinatorial object rigged configurationenergy (charge)

in crystal

role in box-ball system action-angle variable tau function

dynamics linear bilinear

Dynamics of box-ball system in terms of rigged configuration

t = 0: 111122221111133211431111111111111111111111111111

t = 1: 111111112222111133214311111111111111111111111111

t = 2: 111111111111222211133243111111111111111111111111

t = 3: 111111111111111122221132433111111111111111111111

t = 4: 111111111111111111112221322433111111111111111111

t = 5: 111111111111111111111112211322433211111111111111

t = 6: 111111111111111111111111122111322143321111111111

t = 7: 111111111111111111111111111221111322114332111111

(148)

λ

4t6 + 3t

11 + 2t

µ(1) µ(2)

10

µ(3)

0

configuration · · · conserved quantity (action variable)rigging · · · linear flow (angle variable)

KKR bijection · · · direct/inverse scattering map (separation of variables)

Summary so far

KP tau

Tropical tau

Charge

classical

quantum

Ultradiscretization (top down)

Comb. Bethe ansatz (bottom up)

(energy of crystal)

• KKR theory = inverse scattering scheme of box-ball systemon ∞ lattice [K-Okado-S-Takagi-Y 2006]

• Initial value problem solved and General N -soliton solutionconstructed for ŝln symmetric tensor reps. [KSY 2007]

(ŝl2 2-dim. rep. case also by [Mada-Idzumi-Tokihiro 2008])

Periodic generalization (sl2 case)

Tl : B1 ⊗ B1 ⊗ · · · ⊗ B1 −→ B1 ⊗ B1 ⊗ · · · ⊗ B1b1 ⊗ b2 ⊗ · · · ⊗ bL 7−→ b′1 ⊗ b′2 ⊗ · · · ⊗ b′L

· · ·Bl 3 ub1 b2 b3 b4

b′1 b′2 b

′3 b

′4

bL

b′L

u′ ∈ Bl

Choice s.t. u=u′: periodic box-ball system (Yura-Tokihiro 2002)

Example of T3 : ( B1 = { 1 , 2 } )

1 1 2 2 2 1 1 1 1 2 2

2 2 1 1 1 2 2 2 1 1 1

122 112 111 112 122 222 122 112 111 111 112 122

Action-angle variables

any path highest path rigged conf.

cyclic shift KKR

b1......bL 7−→ bd+1...bLb1...bd 7−→ (µ, I) (not unique)

Iµg

Iµg−1

Iµ1¾ µ1

-

···¾ µg−1 -

¾ µg-

µ = (µ1, . . . , µg)

I = (Iµ1, . . . , Iµg)

pi := L − 2∑

j∈µ min(i, j)

Lemma. (For simplicity assume µ1 > · · · > µg)

• µ is unique and invariant under {Tl} (action variable)

• (I + d h1)/AZg is unique (angle variable), where

hl = (min(l, i))i∈µ ∈ Zg, A =(δijpi + 2 min(i, j)

)i,j∈µ

P(µ) := {paths whose action variable = µ} iso-level set

J (µ) := Zg/AZg set of angle variables

Φ : P(µ) −→ J (µ) by Φ(b1 . . . bL) := (I + d h1)/AZg

Theorem. ([KT-Takenouchi 2006] “Tropical Abel-Jacobi” map)

Φ is a bijection and

P(µ) Φ−→ J (µ)Tl

yyTl

P(µ) Φ−→ J (µ)is commutative.

where Tl(J) = J + hl on J (µ).

Nonlinear dynamics becomes straight motion in

J (µ) = Zg/AZg,which is an tropical analogue of Jacobi variety.

Solution of initial value problem (inverse method)

22121111222111direct scattering Φ

- 36

2

?

linear flow T 10003

30032006

1002

mod AZ3

54

10

inverse scattering Φ−1¾

?

12211122111122(answer)

T 10003

Tropical Riemann theta (z ∈ Rg):Θ(z) := − min

n∈Zg{tnAn/2 + tnz}

Theorem. ([K-Sakamoto 2006] “Tropical Jacobi inversion”)

J (µ) → P(µ)(µ, I) 7→ b1 b2 . . . bL (∈ {1, 2}L)

is given by

bk = 1 + Θ(J − kh1

) − Θ(J − (k−1)h1)

− Θ(J − kh1 + h∞)+ Θ

(J − (k−1)h1 + h∞

),

with Ji = Ii − 12pµi.

• Also obtained in [Mada-Idzumi-Tokihiro 2008].

• Higher spin generalization, Θ-formula for Carrier [KS2008].

• Tropical period matrix A originates in Bethe ansatz at q = 0.(KKR is q = 1.)

Uq(ŝl2) Bethe equation at q = 0 under string hypothesis:

Ax ≡ constant vector mod AZg · · · linear!x ∈ (R/Z)g : Bethe root

Bethe root x1:1←→ J ∈ J (µ) = Zg/AZg via Ax = J.

• Generic dynamical period is the minimum N s.t.

N ×(velocity vector) ∈ AZg → N = LCM(1,

⋃

j

det A

det A[j]

).

A is known for ∀affine g [K-Nakanishi 2002].∃Conjectures for generic dyamical period, etc.

A(1)2 path = 121121213322111133211 ∈ B⊗211

l LCM of = period under Tl1 1, 21, 21, 21, 21 212 1, 822

29, 822

95, 411

46, 411

37822

3 1, 95922

, 959176

, 959169

, 959127

9594 1, 2877

50, 2877

400, 2877

820, 2877

4632877

A(1)3 path = 134·34·1·134·23·1·13 ∈ B3⊗B2⊗B1⊗B3⊗B2⊗B1⊗B2

(r, l) LCM of = period under T(r)l

(1,1) 1, 38039

, 956, 95

6, 380

31, 380

27, 380

29380

(1,2) 1, 19039

, 9512

, 9512

, 19031

, 19027

, 19029

190(2,1) 1, 190

13, 95

4, 95

4, 190

137, 190

9, 190

73190

(2,2) 1, 765, 38

3, 38

3, 76

41, 76

21, 76

3176

(2,3) 1, 956, 95

11, 95

11, 95

34, 95

48, 95

4195

(3,1) 1, 38013

, 952, 95

2, 380

137, 380

9, 380

263380

“I haven’t a slightest idea of what people did with it.”

· · · H. Bethe