Non-Equilibrium Thermodynamics and Conformal Field Theory Roberto Longo Colloquium Local Quantum Physics and beyond - in memoriam Rudolf Haag Hamburg, September 2016 Based on a joint work with S. Hollands and previous works with Bischoff, Kawahigashi, Rehren and Camassa, Tanimoto, Weiner
General frame Non-equilibrium thermodynamics : study physical systems not in thermodynamic equilibrium but basically described by thermal equilibrium variables. Systems, in a sense, near equilibrium. Non-equilibrium thermodynamics has been effectively studied for decades with important achievements, yet the general theory still missing. The framework is even more incomplete in the quantum case, non-equilibrium quantum statistical mechanics . We aim provide a general, model independent scheme for the above situation in the context of quantum, two dimensional Conformal Quantum Field Theory . As we shall see, we provide the general picture for the evolution towards a non-equilibrium steady state .
A typical frame described by Non-Equilibrium Thermodynamics: probe R 1 R 2 . . . . . . β 1 β 2 Two infinite reservoirs R 1 , R 2 in equilibrium at their own temperatures T 1 = β − 1 1 , T 2 = β − 1 2 , and possibly chemical potentials µ 1 , µ 2 , are set in contact, possibly inserting a probe. As time evolves, the system should reach a non-equilibrium steady state. This is the situation we want to analyse. As we shall see the Operator Algebraic approach to CFT provides a model independent description, in particular of the asymptotic steady state, and exact computation of the expectation values of the main physical quantities.
Thermal equilibrium states Gibbs states Finite system, A matrix algebra with Hamiltonian H and evolution τ t = Ad e itH . Equilibrium state ϕ at inverse temperature β given by ϕ ( X ) = Tr ( e − β H X ) Tr ( e − β H ) KMS states (Haag, Hugenholtz, Winnink) Infinite volume, A a C ∗ -algebra, τ a one-par. automorphism group of A , B a dense ∗ -subalgebra. A state ϕ of A is KMS at inverse temperature β > 0 if for X , Y ∈ B ∃ F XY ∈ A ( S β ) s.t. � � ( a ) F XY ( t ) = ϕ X τ t ( Y ) � � ( b ) F XY ( t + i β ) = ϕ τ t ( Y ) X where A ( S β ) is the algebra of functions analytic in the strip S β = { 0 < ℑ z < β } , bounded and continuous on the closure ¯ S β .
Non-equilibrium steady states Non-equilibrium statistical mechanics : A non-equilibrium steady state NESS ϕ of A satisfies property ( a ) in the KMS condition, for all X , Y in a dense ∗ -subalgebra of B , but not necessarily property ( b ). For any X , Y in B the function � � F XY ( t ) = ϕ X τ t ( Y ) is the boundary value of a function holomorphic in S β . (Ruelle) Example: the tensor product of two KMS states at temperatures β 1 , β 2 is a NESS with β = min ( β 1 , β 2 ). Problem: describe the NESS state ϕ and show that the initial state ψ evolves towards ϕ t →∞ ψ · τ t = ϕ lim
obius covariant nets (Haag-Kastler nets on S 1 ) M¨ obius covariant net A on S 1 is a map A local M¨ I ∈ I → A ( I ) ⊂ B ( H ) I ≡ family of proper intervals of S 1 , that satisfies: ◮ A. Isotony . I 1 ⊂ I 2 = ⇒ A ( I 1 ) ⊂ A ( I 2 ) ◮ B. Locality . I 1 ∩ I 2 = ∅ = ⇒ [ A ( I 1 ) , A ( I 2 )] = { 0 } ◮ C. M¨ obius covariance . ∃ unitary rep. U of the M¨ obius group M¨ ob on H such that U ( g ) A ( I ) U ( g ) ∗ = A ( gI ) , g ∈ M¨ ob , I ∈ I . ◮ D. Positivity of the energy . Generator L 0 of rotation subgroup of U (conformal Hamiltonian) is positive. ◮ E. Existence of the vacuum . ∃ ! U -invariant vector Ω ∈ H (vacuum vector), and Ω is cyclic for � I ∈I A ( I ).
Consequences ◮ Irreducibility : � I ∈I A ( I ) = B ( H ). ◮ Reeh-Schlieder theorem : Ω is cyclic and separating for each A ( I ). ◮ Bisognano-Wichmann property : Tomita-Takesaki modular operator ∆ I and conjugation J I of ( A ( I ) , Ω), are U ( δ I (2 π t )) = ∆ it I , t ∈ R , dilations U ( r I ) = J I reflection (Fr¨ ohlich-Gabbiani, Guido-L.) ◮ Haag duality : A ( I ) ′ = A ( I ′ ) ◮ Factoriality : A ( I ) is III 1 -factor (in Connes classification) ◮ Additivity : I ⊂ ∪ i I i = ⇒ A ( I ) ⊂ ∨ i A ( I i ) (Fredenhagen, Jorss).
Local conformal nets Diff ( S 1 ) ≡ group of orientation-preserving smooth diffeomorphisms of S 1 Diff I ( S 1 ) ≡ { g ∈ Diff ( S 1 ) : g ( t ) = t ∀ t ∈ I ′ } . A local conformal net A is a M¨ obius covariant net s.t. F. Conformal covariance . ∃ a projective unitary representation U of Diff ( S 1 ) on H extending the unitary representation of M¨ ob s.t. U ( g ) A ( I ) U ( g ) ∗ = A ( gI ) , g ∈ Diff ( S 1 ) , U ( g ) xU ( g ) ∗ = x , x ∈ A ( I ) , g ∈ Diff I ′ ( S 1 ) , − → unitary representation of the Virasoro algebra [ L m , L n ] = ( m − n ) L m + n + c 12( m 3 − m ) δ m , − n [ L n , c ] = 0, L ∗ n = L − n .
Representations A (DHR) representation ρ of local conformal net A on a Hilbert space H is a map I ∈ I �→ ρ I , with ρ I a normal rep. of A ( I ) on B ( H ) s.t. I ⊂ ˜ I , ˜ ρ ˜ I ↾ A ( I ) = ρ I , I , I ⊂ I . ρ is diffeomorphism covariant : ∃ a projective unitary representation U ρ of Diff ( S 1 ) on H such that ρ gI ( U ( g ) xU ( g ) ∗ ) = U ρ ( g ) ρ I ( x ) U ρ ( g ) ∗ for all I ∈ I , x ∈ A ( I ) and g ∈ Diff ( S 1 ). Index-statistics relation (L.): � �� 1 ρ I ′ � � ′ : ρ I � A ( I ′ ) 2 d ( ρ ) = A ( I ) √ DHR dimension = Jones index
Complete rationality �� �� � ′ : � µ A ≡ A ( I 1 ) ∨ A ( I 3 ) A ( I 2 ) ∨ A ( I 4 ) < ∞ = ⇒ � d ( ρ i ) 2 µ A = i A is modular (Kawahigashi, M¨ uger, L.)
Circle and real line picture ∞ P' P -1 z �→ i z − 1 z + 1 We shall frequently switch between the two pictures.
KMS and Jones index Kac-Wakimoto formula (conjecture) Let A be a conformal net, ρ representations of A , then Tr( e − tL 0 ,ρ ) lim Tr( e − tL 0 ) = d ( ρ ) t → 0 + Analog of the Kac-Wakimoto formula (theorem) ρ a representation of A : ( ξ, e − 2 π K ρ ξ ) = d ( ρ ) where K ρ is the generator of the dilations δ I and ξ is any vector cyclic for ρ ( A ( I ′ )) such that ( ξ, ρ ( · ) ξ ) is the vacuum state on A ( I ′ ).
U (1)-current net Let A be the local conformal net on S 1 associated with the U (1)-current algebra. In the real line picture A is given by A ( I ) ≡ { W ( f ) : f ∈ C ∞ R ( R ) , supp f ⊂ I } ′′ where W is the representation of the Weyl commutation relations � W ( f ) W ( g ) = e − i fg ′ W ( f + g ) associated with the vacuum state ω � ∞ || f || 2 ≡ ω ( W ( f )) ≡ e −|| f || 2 , p | ˜ f ( p ) | 2 d p 0 where ˜ f is the Fourier transform of f .
� � � W ( f ) = exp − i f ( x ) j ( x ) dx � � � fg ′ dx j ( f ) , j ( g ) = i There is a one parameter family { γ q , q ∈ R } of irreducible sectors and all have index 1 (Buchholz, Mack, Todorov) � 1 Ff W ( f ) , � γ q ( W ( f )) ≡ e i F ∈ C ∞ , F = q . 2 π q is the called the charge of the sector.
A classification of KMS states (Camassa, Tanimoto, Weiner, L.) How many KMS states do there exist? Completely rational case A completely rational: only one KMS state (geometrically constructed) β = 2 π exp: net on R A → restriction of A to R + exp ↾ A ( I ) = Ad U ( η ) η diffeomorphism, η ↾ I = exponential geometric KMS state on A ( R ) = vacuum state on A ( R + ) ◦ exp ϕ geo = ω ◦ exp Note: Scaling with dilation, we get the geometric KMS state at any give β > 0.
Comments About the proof: Essential use of the thermal completion and Jones index . A net on R , ϕ KMS state: In the GNS representation we apply Wiesbrock theorem A ( R + ) ⊂ A ( R ) hsm modular inclusion → new net A ϕ Want to prove duality for A ϕ in the KMS state, but A ϕ satisfies duality up to finite Jones index. Iteration of the procedure... Conjecture: A ⊂ B finite-index inclusion of conformal nets, ε : B → A conditional expectation. If ϕ is a translation KMS on A then ϕ ◦ ε is a translation KMS on B .
Non-rational case: U (1)-current model The primary (locally normal) KMS states of the U (1)-current net are in one-to-one correspondence with real numbers q ∈ R ; each state ϕ q is uniquely determined by − 1 4 � f � 2 ϕ q ( W ( f )) = e iq f dx · e � S β where � f � 2 S β = ( f , S β f ) and � S β f ( p ):=coth β p 2 � f ( p ). In other words: Geometric KMS state: ϕ geo = ϕ 0 Any primary KMS state: ϕ q = ϕ geo ◦ γ q . where γ q is a BMT sector.
Virasoro net: c = 1 (With c < 1 there is only one KMS state: the net is completely rational) Primary KMS states of the Vir 1 net are in one-to-one correspondence with positive real numbers | q | ∈ R + ; each state ϕ | q | is uniquely determined by its value on the stress-energy tensor T : � � � 12 β 2 + q 2 π ϕ | q | ( T ( f )) = f dx . 2 The geometric KMS state corresponds to q = 0, and the 12 β 2 + q 2 π corresponding value of the ‘energy density’ 2 is the lowest one in the set of the KMS states. (We construct these KMS states by composing the geometric state with automorphisms on the larger U (1)-current net.)
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