Abstract
We extend the approach to \(\tau \)-functions as Widom constants developed by Cafasso, Gavrylenko and Lisovyy to orthogonal loop group Drinfeld–Sokolov reductions and isomonodromic deformations systems. The combinatorial expansion of the \(\tau \)-function as a sum of correlators, each expressed as products of finite determinants, follows from using multicomponent fermionic vacuum expectation values of certain dressing operators encoding the initial conditions and dependence on the time parameters. When reduced to the orthogonal case, these correlators become finite Pfaffians and the determinantal \(\tau \)-functions, both in the Drinfeld–Sokolov and isomonodromic case, become squares of \(\tau \)-functions of Pfaffian type. The results are illustrated by several examples, consisting of polynomial \(\tau \)-functions of orthogonal Drinfeld–Sokolov type and isomonodromic ones with four regular singular points.
Similar content being viewed by others
Notes
More generally, one could set \(h_i:= H_i+\delta _{i,0}c\), where c is the central extension element. But since the central extension will play no part, we omit it, and just deal with the loop algebra \(L\mathfrak {g}\).
In general, the \(D_\ell ^{(1)}\) case admits two sets of abelian flows, labeled by times \(t_{2k+1}\) and \(t'_{2k+1}\), as in [7]. For the sake of clarity of exposition, we restrict ourselves to the first only, and set \(t'_{2k+1}=0\).
See [17], Appendix E, or [3, 18, 19] for the definition of Cartan coordinates in the context of the BKP hierarchy. In our context, by “Cartan coordinate”, we simply mean the Pfaffian expression \(\mathrm {Pf}(\mathsf{{d}}_{\vec {\lambda }})\), specifying the initial condition in the isotropic Grassmannian.
Note that in the previous sections we dealt with Riemann–Hilbert problems on the unit circle, while here the circle has radius R. Everything is easily generalized to this case by reinserting the radius R in the expressions where needed. All our quantities depend only on the splitting of the space \(L^2(S^1)\) into the subspace \({\mathcal {H}}^N_+\) of functions admitting analytic continuation inside the circle and those \({\mathcal {H}}^N_-\) admitting analytic continuation outside.
References
Bershtein, M., Gavrylenko, P., Marshakov, A.: Twist-field representations of \(W\)-algebras, exact conformal blocks and character identities. JHEP 08, 108 (2018)
Bonelli, G., Globlek, F., Tanzini, A.: Counting Yang–Mills instantons by surface operator renormalization group flow. Phys. Rev. Lett. 126(23), 231602 (2021)
Balogh, F., Harnad, J., Hurtubise, J.: Isotropic Grassmannians, Plücker and Cartan maps. J. Math. Phys. 62(2), 021701 (2021)
Cafasso, M., Gavrylenko, P., Lisovyy, O.: Tau functions as Widom constants. Commun. Math. Phys. 365(2), 741–772 (2019)
Cafasso, M., du CrestdeVilleneuve, A., Yang, D.: Drinfeld–Sokolov hierarchies, tau functions, and generalized schur polynomials. SIGMA 14, 104 (2018)
Cafasso, M., Chao-Zhong, W.: Tau functions and the limit of block Toeplitz determinants. Int. Math. Res. Not. 2015(20), 10339–10366 (2015)
Cafasso, M., Chao-Zhong, W.: Borodin–Okounkov formula, string equation and topological solutions of Drinfeld–Sokolov hierarchies. Lett. Math. Phys. 109(12), 2681–2722 (2019)
Del Monte, F., Desiraju, H., Gavrylenko, P.: Isomonodromic tau functions on a torus as fredholm determinants, and charged partitions. arXiv preprint arXiv:2011.06292 (2020)
Drinfeld, V.G., Sokolov, V.V.: Lie algebras and equations of Korteweg-de Vries type. J. Math. Sci. 30, 1975–2036 (1985)
Dubrovin, B.: Geometry of 2-D topological field theories. Lect. Notes Math. 1620, 120–348 (1996)
Fan, H., Francis, A., Jarvis, T., Merrell, E., Ruan, Y.: Witten’s \(D_4\) integrable hierarchies conjecture. Chin. Ann. Math. Ser. B 37(2), 175–192 (2016)
Feigin, E., van de Leur, J., Shadrin, S.: Givental symmetries of Frobenius manifolds and multi-component KP tau-functions. Adv. Math. 224(3), 1031–1056 (2010)
Gavrylenko, P., Iorgov, N., Lisovyy, O.: Higher rank isomonodromic deformations and \(W\)-algebras. Lett. Math. Phys. 110(2), 327–364 (2019)
Gavrylenko, P., Lisovyy, O.: Fredholm determinant and Nekrasov sum representations of isomonodromic tau functions. Commun. Math. Phys. 363, 1–58 (2018)
Gavrylenko, P., Lisovyy, O.: Pure \(SU(2)\) gauge theory partition function and generalized Bessel kernel. Proc. Symp. Pure Math. 18, 181–208 (2018)
Gavrylenko, P.G., Marshakov, A.V.: Free fermions, \(W\)-algebras and isomonodromic deformations. Theor. Math. Phys. 187(2), 649–677 (2016)
Harnad, J., Balogh, F.: Tau Functions and Their Applications. Cambridge University Press (2021)
Harnad, J., Orlov, A.Y.: Bilinear expansions of lattices of KP \(\tau \)-functions in BKP \(\tau \)-functions: a fermionic approach. J. Math. Phys. 62(1), 013508 (2021)
Harnad, J., Orlov, A.Y.: Polynomial KP and BKP \(\tau \)-functions and correlators. Annales Henri Poincaré (2021)
Jaffe, A., Lesniewski, A., Weitsman, J.: Pfaffians on Hilbert space. J. Fun. Anal. 83(2), 348–363 (1989)
Jimbo, M., Miwa, T.: Solitons and infinite dimensional Lie algebras. Publ. RIMS Kyoto Univ. 19(2), 943–1001 (1983)
Kac, V.G.: Infinite Dimensional Lie Algebras. Cambridge University Press (1990)
Kac, V.G., Rozhkovskaya, N., van de Leur, J.: Polynomial tau-functions of the KP, BKP, and the s-component KP hierarchies. J. Math. Phys. 62(2), 021702 (2021)
Kac, V.G., van de Leur, J.W.: Equivalence of formulations of the MKP hierarchy and its polynomial tau-functions. Jpn. J. Math. 13(2), 235–271 (2018)
Kac, V., van de Leur, J.: Polynomial tau-functions of bkp and dkp hierarchies. J. Math. Phys. 60(7), 071702 (2019)
Liu, S.-Q., Ruan, Y., Zhang, Y.: BCFG Drinfeld–Sokolov hierarchies and FJRW-theory. Invent. Math. 201(2), 711–772 (2015)
Macdonald, I.G.: Symmetric Functions and Hall Polynomials. Oxford University Press (1998)
Miwa, T., Jimbo, M., Date, E.: Solitons: Differential Equations, Symmetries and Infinite-Dimensional Algebras, Volume 135 of Cambridge Tracts in Mathematics. Cambridge University Press, Cambridge (2000)
Rains, E.M.: Correlation functions for symmetrized increasing subsequences. arXiv preprint math/0006097 (2000)
Sato, M.: Soliton equations as dynamical systems on infinite dimensional Grassmann manifold. Publ. RIMS Kyoto Univ. 2, 30–46 (1981)
Sato, M., Jimbo, M., Miwa, K.: Studies on holonomic quantum fields I–V. Proc. Japan Acad. 53A, 219–224 (1977)
Sato, M., Jimbo, M., Miwa, K.: Studies on holonomic quantum fields VI–VII. Proc. Japan Acad. 54A(1–5), 136–141 (1978)
van de Leur J.: BKP tau-functions as square roots of KP tau-functions. arXiv:2103.16290 (2021)
You, Y.: Polynomial solutions of the BKP hierarchy and projective representations of symmetric groups. Infinite-dimensional Lie algebras and groups (Luminy-Marseille, 1988). Adv. Ser. Math. Phys. 7, 449–464 (1989)
Acknowledgements
The authors would like to thank M. Caffasso, P. Gavrylenko, O. Lisovyy and D. Yang for helpful discussions that contributed much to clarifying the results presented here. This work was partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Data sharing
Data sharing is not applicable to this article since no new data were created or analyzed in this study.
Additional information
Communicated by Nikolai Kitanine.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Appendices
A Appendix. A Polynomial \(\tau \)-Function of \(B^{(1)}_2\) Type
Recall equation (4.28) in the main text, representing the map between decreasing sequences of positive half-integers \(\{p_{\alpha ,i}\}_{i=1}^{n_\alpha }\) and strict partitions
In the tables below we group the coefficients in the Pfaffian minor expansions by the total weight of the N-tuple of (positive) strict partitions obtained by adding 1 to each part:
counting the overall power of z (resp. \(z^{-1}\)) in the Fourier expansion of \(\mathsf{{a}}\) (respectively \(\mathsf{{d}}\)) that contribute to the Pfaffian minor. For example
has weight \(|\vec {\lambda }|=2\), since it contains two Fourier coefficients of \(\mathsf{{a}}\) of weight 0 that multiply \(z^0w^0\), while
has weight \(|\vec {\lambda }|=4\), since it contains two Fourier coefficients of \(\mathsf{{a}}\) of weight 2, that multiply zw.
1.1 A.1 The Pfaffian \(\mathsf{{d}}\) Coefficients
1.2 A.2 The Pfaffian \(\mathsf{{a}}\) Coefficients
B Appendix. Matrix Representation of Orthogonal Affine Lie Algebras
In the following, \(e_{ij}\) is the elementary matrix \((e_{ij})_{\alpha \beta }:=\delta _{\alpha i}\delta _{\beta j}\).
1.1 B.1 Matrix Realization of \(B_\ell ^{(1)}\)
-
Weyl generators:
$$\begin{aligned}&E_0=\frac{1}{2}(e_{1,2\ell }+e_{2,2\ell +1}), \quad F_0=2\left( e_{2\ell ,1}+e_{2\ell +1,2} \right) , \nonumber \\&H_0 =e_{1,1}+e_{2,2}-e_{2l,2l}-e_{2l+1,2l+1}, \nonumber \\&E_i=e_{i+1,i}+e_{2l+2-i,2l+1-i}, \quad F_i=e_{i,i+1}+e_{2\ell +1-i,2\ell +2-i} \nonumber \\&H_i=-e_{i,i}+e_{i+1,i+1}-e_{2\ell +1-i,2\ell +1-i}+e_{2\ell +2-i,2\ell +2-i}, \quad i=1,\dots ,\ell -1, \nonumber \\&E_\ell =e_{\ell +1,\ell }+e_{\ell +2,\ell +1}, \quad F_{\ell }=e_{\ell ,\ell +1}+e_{\ell +1,\ell +2}, \quad H_\ell =-e_{\ell ,\ell }+e_{\ell +2,\ell +2}. \nonumber \\ \end{aligned}$$(B.1) -
Cartan matrix:
$$\begin{aligned} A=\left( \begin{array}{cccccc} 2 &{}\quad 0 &{}\quad -1 &{}\quad 0 &{}\quad \cdots &{}\quad 0 \\ 0 &{}\quad 2 &{}\quad -1 &{}\quad &{}\quad &{}\quad \vdots \\ -1 &{}\quad -1 &{}\quad 2 &{}\quad \ddots &{}\quad &{}\quad 0 \\ 0 &{}\quad &{}\quad \ddots &{}\quad \ddots &{}\quad -1 &{}\quad 0 \\ \vdots &{}\quad &{}\quad &{}\quad -1 &{}\quad 2 &{}\quad -1 \\ 0 &{}\quad \cdots &{}\quad 0 &{}\quad 0 &{}\quad -2 &{}\quad 2 \end{array} \right) _{(\ell +1)\times (\ell +1)}, \end{aligned}$$(B.2) -
Chevalley involution:
$$\begin{aligned} S= & {} \mathrm {antidiag}\left( 1,-1,1,\dots ,-1,1 \right) _{2\ell +1\times 2\ell +1} \nonumber \\= & {} \left( \begin{array}{cccccc} 0 &{}\quad 0 &{}\quad \cdots &{}\quad &{}\quad &{}\quad 1 \\ 0 &{}\quad 0 &{}\quad \cdots &{}\quad &{}\quad -1 &{}\quad 0 \\ 0 &{}\quad 0 &{}\quad \cdots &{}\quad 1 &{}\quad 0 &{}\quad 0 \\ 0 &{}\quad 0 &{}\quad \ddots &{}\quad 0 &{}\quad 0 &{}\quad 0 \\ 0 &{}\quad -1 &{}\quad 0 &{}\quad &{}\quad \cdots &{}\quad 0 \\ 1 &{}\quad 0 &{}\quad 0 &{}\quad &{}\quad \cdots &{}\quad 0 \end{array} \right) _{2\ell +1\times 2\ell +1}. \end{aligned}$$(B.3)
1.2 B.2 Matrix Realization of \(D_\ell ^{(1)}\)
-
Weyl generators:
$$\begin{aligned}&E_0=\frac{1}{2}(e_{1,2\ell -1}+e_{2,2\ell }), \quad F_0=2\left( e_{2\ell -1,1}+e_{2\ell ,2}\right) , \nonumber \\&H_0 =e_{1,1}+e_{2,2}-e_{2l-1,2l-1}-e_{2l,2l}, \nonumber \\&E_i=e_{i+1,i}+e_{2l+1-i,2l-i}, \quad F_i=e_{i,i+1}+e_{2\ell -i,2\ell +1-i} \nonumber \\&H_i=-e_{i,i}+e_{i+1,i+1}-e_{2\ell -i,2\ell -i}+e_{2\ell +1-i,2\ell +1-i}, \quad i=1,\dots ,\ell -1, \nonumber \\&E_\ell =\frac{1}{2}\left( e_{\ell +1,\ell -1}+e_{\ell +2,\ell }\right) , \quad F_{\ell }=2\left( e_{\ell -1,\ell +1}+e_{\ell ,\ell +2}\right) , \nonumber \\&H_\ell =-e_{\ell -1,\ell -1}-e_{\ell ,\ell }+e_{\ell +1,\ell +1} +e_{\ell +2,\ell +2}. \end{aligned}$$(B.4) -
Cartan matrix:
$$\begin{aligned} A=\left( \begin{array}{cccccc} 2 &{}\quad 0 &{}\quad -1 &{}\quad 0 &{}\quad \cdots &{}\quad 0 \\ 0 &{}\quad 2 &{}\quad -1 &{}\quad &{}\quad &{}\quad \vdots \\ -1 &{}\quad -1 &{}\quad 2 &{}\quad \ddots &{}\quad &{}\quad 0 \\ 0 &{}\quad &{}\quad \ddots &{}\quad \ddots &{}\quad -1 &{}\quad -1 \\ \vdots &{}\quad &{}\quad &{}\quad -1 &{}\quad 2 &{}\quad 0 \\ 0 &{}\quad \cdots &{}\quad 0 &{}\quad -1 &{}\quad 0 &{}\quad 2 \end{array} \right) _{(\ell +1)\times (\ell +1)}. \end{aligned}$$(B.5) -
Chevalley involution:
$$\begin{aligned} S=\mathrm {antidiag}\left( 1,-1,1,\dots ,(-1)^{\ell },(-1)^{\ell },(-1)^{\ell +1},\dots ,-1,1\right) _{2\ell \times 2\ell }. \end{aligned}$$(B.6)
Rights and permissions
About this article
Cite this article
Bertola, M., Del Monte, F. & Harnad, J. Fredholm Pfaffian \(\tau \)-Functions for Orthogonal Isospectral and Isomonodromic Systems. Ann. Henri Poincaré 23, 4521–4554 (2022). https://doi.org/10.1007/s00023-022-01204-x
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00023-022-01204-x