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arXiv 1906.07565cond-mat.stat-mechhep-thmath-phmath.MP
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反铁磁Potts模型和$SL(2,\mathbb{R})/U(1)$西格玛模型中的共形不变边界条件

Conformally invariant boundary conditions in the antiferromagnetic Potts model and the $SL(2,\mathbb{R})/U(1)$ sigma model

Niall F. Robertson, Jesper Lykke Jacobsen, Hubert Saleur

摘要:

我们开始研究的正方形晶格$Q$状态Potts反铁磁体的边界版本,与$Q \in [0,4]$实,动机的事实,即相应的体模型的连续极限是一个非紧的CFT,密切相关的$SL(2,\mathbb{R})_k/U(1)$欧几里德黑洞陪集模型。虽然各种类型的共形边界条件(离散和连续膜)已正式确定的$SL(2,\mathbb{R})_k/U(1)$陪集CFT,我们只能在这项工作中,以确定共形边界条件(CBC)导致离散边界谱。共形边界条件(CBC),我们发现有两种类型。第一种是自由边界Potts自旋,我们证实了一个古老的猜想的共形能级的生成函数,并显示它们与字符的非线性变形的$W_\infty$代数。第二种CBC是新的,它对应于将波茨自旋的值限制为$Q_1$大小的子集,或其大小的互补值$Q-Q_1$,在沿边界的交替位置上。它只在反铁磁情况下是共形的。利用代数和数值技巧,我们证明了相应的谱母函数产生陪集CFT的离散表示的所有特征。在陪集CFT的相关的离散状态的归一化边界被发现有一个简单的解释在晶格模型中的边界相变。对于$\sqrt{Q} = 2 \cos \fracπ{k}$,与$k \ge 3$整数,我们还展示了如何我们的边界条件可以重新制定的RSOS高度模型。然后,谱生成函数与紧凑的$SU(2)_{k-2} / U(1)$ parafermion理论的弦函数(具有对称性$Z_{k-2}$)。需要新的alt条件来覆盖所有字符串函数。

英文摘要:

We initiate a study of the boundary version of the square-lattice $Q$-state Potts antiferromagnet, with $Q \in [0,4]$ real, motivated by the fact that the continuum limit of the corresponding bulk model is a non-compact CFT, closely related with the $SL(2,\mathbb{R})_k/U(1)$ Euclidian black-hole coset model. While various types of conformal boundary conditions (discrete and continuous branes) have been formally identified for the the $SL(2,\mathbb{R})_k/U(1)$ coset CFT, we are only able in this work to identify conformal boundary conditions (CBC) leading to a discrete boundary spectrum. The conformal boundary conditions (CBC) we find are of two types. The first is free boundary Potts spins, for which we confirm an old conjecture for the generating functions of conformal levels, and show them to be related to characters in a non-linear deformation of the $W_\infty$ algebra. The second type of CBC - which corresponds to restricting the values of the Potts spins to a subset of size $Q_1$, or its complement of size $Q-Q_1$, at alternating sites along the boundary - is new, and turns out to be conformal in the antiferromagnetic case only. Using algebraic and numerical techniques, we show that the corresponding spectrum generating functions produce all the characters of discrete representations for the coset CFT. The normalizability bounds of the associated discrete states in the coset CFT are found to have a simple interpretation in terms of boundary phase transitions in the lattice model. For $\sqrt{Q} = 2 \cos \fracπ{k}$, with $k \ge 3$ integer, we show also how our boundary conditions can be reformulated in terms of a RSOS height model. The spectrum generating functions are then identified with string functions of the compact $SU(2)_{k-2} / U(1)$ parafermion theory (with symmetry $Z_{k-2}$). The new alt conditions are needed to cover all the string functions.

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