Quantum critical transport, duality, and M-theory

hep-th/0701036

Christopher Herzog (Washington) Pavel Kovtun (UCSB)

Subir Sachdev (Harvard) Dam Thanh Son (Washington)

Talk online at http://sachdev.physics.harvard.edu

D. B. Haviland, Y. Liu, and A. M. Goldman, Phys. Rev. Lett. 62, 2180 (1989)

Superconductor

Insulator

2

Quantum critical point

0

Conductivity

0 0

40

T

T

eT

h

Trap for ultracold 87Rb atoms

M. Greiner, O. Mandel, T. Esslinger, T. W. Hänsch, and I. Bloch, Nature 415, 39 (2002).

Velocity distribution of 87Rb atoms

Superfliud

M. Greiner, O. Mandel, T. Esslinger, T. W. Hänsch, and I. Bloch, Nature 415, 39 (2002).

Velocity distribution of 87Rb atoms

Insulator

Outline

1. Boson Hubbard model – conformal field theory (CFT)

2. Hydrodynamics of CFTs

3. Duality

4. SYM3 with N=8 supersymmetry

Outline

1. Boson Hubbard model – conformal field theory (CFT)

2. Hydrodynamics of CFTs

3. Duality

4. SYM3 with N=8 supersymmetry

†

†

Degrees of freedom: Bosons, , hopping between the

sites, , of a lattice, with short-range repulsive interactions.

- ( 1)2

j

i j jj j

ji j

j

b

b b n n

j

UnH t

† j j jn b b

Boson Hubbard model

M.PA. Fisher, P.B. Weichmann, G. Grinstein, and D.S. Fisher

Phys. Rev. B 40, 546 (1989).

For small , superfluid

For large , insulator

Ut

Ut

The insulator:

Excitations of the insulator:

†Particles ~

Holes ~

Excitations of the insulator:

†Particles ~

Holes ~

scs

Insulator

0

0

Superfluid

0

scs

Insulator

0

0

Superfluid

0

Wil

Con

son

formal

-Fishe

field theor

r fixed p

y:

oint

Outline

1. Boson Hubbard model – conformal field theory (CFT)

2. Hydrodynamics of CFTs

3. Duality

4. SYM3 with N=8 supersymmetry

CFT correlator of U 1 current J

22

= p p

J p J p K pp

K: a universal number analogous to the level number of the Kac-Moody algebra in 1+1 dimensions

2

Application of Kubo formula shows that

4 2

eK

h

M. P. A. Fisher, Phys. Rev. Lett. 65, 923 (1990)

However: computation is at 0, with 0,

while experimental measurements are for

B

T

k T

However: computation is at 0, with 0,

while experimental measurements are for

B

T

k T

Does this matter ?

However: computation is at 0, with 0,

while experimental measurements are for

B

T

k T

2

2 2ret

For

Cha

CFTs in 1

rge densi

+1 dimensions, NO.

ty correlation at

Charge density correlation at 0 :

0 : conformally map plane to a

cyl

inder of

1circumf

erence , and

,

t

,t t

T

T

kJ k J

k

T

k K

2

2 2ret

hen analytically continue to real frequencies:

, ,t t

kJ k J k K

k

No diffusion of charge, and no hydrodynamics

Does this matter ?

However: computation is at 0, with 0,

while experimental measurements are for

B

T

k T

(almost always)

: Hydrodynamic, collision-dom

For CFTs in 2+1 dimensions, YES .

is a characteristic or time

: Collisionless physics

inaB

B

B

coll

k

decoherence isiok T

T

n

T

k

ted transport

K. Damle and S. Sachdev, Phys. Rev. B 56, 8714 (1997).

Does this matter ?

However: computation is at 0, with 0,

while experimental measurements are for

B

T

k T

Does this matter ?

(almost always)For CFTs in 2+1 dimensions, YES .

K. Damle and S. Sachdev, Phys. Rev. B 56, 8714 (1997).

CFT correlator of U 1 current J

22

= p p

J p J p K pp

K: a universal number analogous to the level number of the Kac-Moody algebra in 1+1 dimensions

2

Application of Kubo formula shows that

4 2

eK

h

CFT correlator of U 1 current at 0J T

22

= p p

J p J p K pp

K: a universal number analogous to the level number of the Kac-Moody algebra in 1+1 dimensions

2

Application of Kubo formula shows that

4 2

eKT h

CFT correlator of U 1 current at 0J T

2 2

,

2 2

The projectors are defined by

while , are universal functions o

and ; ( ,

f and

)

, , = , ,

i jT L Tij ij

L T

T T L L

k k p pP P P p

kK k T T

kk p

J k J k k P K k P K k

2 2

Application of Kubo formula shows that

4 4 2 0, 2 0,T Le e

K KT h h

Outline

1. Boson Hubbard model – conformal field theory (CFT)

2. Hydrodynamics of CFTs

3. Duality

4. SYM3 with N=8 supersymmetry

Excitations of the insulator:

†Particles ~

Holes ~

Approaching the transition from the superfluid Excitations of the superfluid: (A) Spin waves

Approaching the transition from the superfluid Excitations of the superfluid: (B) Vortices

vortex

Approaching the transition from the superfluid Excitations of the superfluid: (B) Vortices

vortex

E

Approaching the transition from the superfluid Excitations of the superfluid: Spin wave and vortices

scs

Insulator

0

0

Superfluid

0

Wil

Con

son

formal

-Fishe

field theor

r fixed p

y:

oint

C. Dasgupta and B.I. Halperin, Phys. Rev. Lett. 47, 1556 (1981)

s, ccs s

Insulator

0

0

0

Superfluid

0

0

Wil

Con

son

formal

-Fishe

field theor

r fixed p

y:

oint

s

C. Dasgupta and B.I. Halperin, Phys. Rev. Lett. 47, 1556 (1981)

Consequences of duality on CFT correlators of U 1 currents

2 2, , = , ,T T L LJ k J k k P K k P K k

2 2

Application of Kubo formula shows that

4 4 2 0, 2 0,T Le e

K KT h h

C. Herzog, P. Kovtun, S. Sachdev, and D.T. Son, hep-th/0701036

Outline

1. Boson Hubbard model – conformal field theory (CFT)

2. Hydrodynamics of CFTs

3. Duality

4. SYM3 with N=8 supersymmetry

ab 2 2, , = , ,a b T T L LJ k J k k P K k P K k

The self-duality of the 4D SO(8) gauge fields leads to

2 2

Application of Kubo formula shows that

4 4 2 0, 2 0,T Le e

K KT h h

C. Herzog, P. Kovtun, S. Sachdev, and D.T. Son, hep-th/0701036

ab 2 2, , = , ,a b T T L LJ k J k k P K k P K k

The self-duality of the 4D SO(8) gauge fields leads to

2 2

Application of Kubo formula shows that

4 4 2 0, 2 0,T Le e

K KT h h

C. Herzog, P. Kovtun, S. Sachdev, and D.T. Son, hep-th/0701036

Holographic self-duality

Open questions

1. Does KLKT = constant (i.e. holographic self-duality) hold for SYM3 SCFT at finite N ?

2. Is there any CFT3 with an Abelian U(1) current whose conductivity can be determined by self-duality ? (unlikely, because global and topological U(1) currents are interchanged under duality).

3. Is there any CFT3 solvable by AdS/CFT which is not (holographically) self-dual ?

4. Is there an AdS4 description of the hydrodynamics of the O(N) Wilson-Fisher CFT3 ? (can use 1/N expansion to control strongly-coupled gravity theory).