数理解析研究所講究録
Lectures on the eight-vertex model and bosonization(Solvable Lattice Models 2004 : Recent Progress on Solvable Lattice Models )
Michael Lashkevich
Abstract
These are introductory lectures on application of the free field representation (bosonization) techniques to the solid-on-\S olid (SOS) and eight-vertex models.We start from the very beginnings, including the physical badcground of lattice models and some basic information on quantum integrability.After definitions of the eight-vertex and SOS models, we describe their relation known as the vertex-face correspondence.Then, skipping the Bethe ansatz solution, wc turn to the problem of calculation of correlation functions by mcaiis of the fit.cficld rcprcscntation.We explain, how the vertex-face correspondence works on the level of vertex operators and bosonization, making it possible to express the correlation functions of the eight-vertex model in terms of the free field representation aimed to describe the SOS model.1 Eight-vertex model arid commuting traxisfer Ilatl $\cdot$ ice.\'Since we shall speak about some models of physical importance.let us formulate first the general physical framework.Consider a classical system of interacting particles.Let $C$ be a state of this system, which can run some (generally infinite) set of admissible states.Let $E(C)$ be the energy of the state C. defined by usual IIamiltonian mechanics.Suppose that the system weakly interacts with a thermal bath of the temperature $T$ .The most fundamental postulate of statistical mechanics, the Gibbs law, says that the probability of the state $C$ is given by $w(C)= \frac{1}{Z}e^{-B(C)/T}$ .(1.1) lt is easy to understand, what is the proportionality coefficient $1/Z$ .As the total probability for thc system to be in any state is unity.we have for the partition functions of the system $Z= \sum_{c}e^{-F_{}(C)/\mathit{7}}$ .(1.2) Since the space of configurations can be continu$ \mathit{0}\prime 18,$ $\dagger,11\mathrm{e}_{\backslash }\mathrm{s}\mathrm{u}\mathrm{m}$ may turn out to be an $\mathrm{i}\mathrm{t}\iota \mathrm{t}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{a}\downarrow\downarrow \mathrm{i}o\mathrm{n}$ , but we shall not consider this general case in these lectures.The partition function encodes the most fundamental observable thermodynamic function of the model, the free eneryy:$F=E-TS=-T\log$ Z.(1.3)Here $E$ is the total energy of the system, $E= \sum E(C)w(c,)=\frac{T^{\sim}d}{Z(T)dT},Z(T)=-T^{2}\frac{dF}{dTT}=F-T\frac{dF}{dT}$ , while $S=-\sum w(c,)\log w(C)=-\frac{d\Gamma'}{dT}$is the entropy.The first equality in (1.3) is the thermodynamic definition of the free energy, which, in principle, was established before Gibbs, while the second equality provides its statistical interpretation.Let $f_{i}\langle C$ ) be some functions of the state of the system.The correlation functions are generic expectation values $\langle f_{1}\ldots f_{r}')=\sum_{c}|\iota)(C)f\iota(C)\ldots f_{n}(C)$ .