1. J. I. Abdullaev and S. N. Lakaev, “On the spectral properties of the matrix-valued Friedrichs model,” in Many-Particle Hamiltonians: Spectra and Scattering, vol. 5 of Adv. Soviet Math. (Amer. Math. Soc., Providence, RI, 1991), pp. 1–37.
2. R. D. Amado and J. V. Noble, “Efimov’s effect: a new pathology of three-particle systems. I,” Phys. Lett. B 35(1), 25–27 (1971).
3. R. D. Amado and J. V. Noble, “Efimov’s effect: a new pathology of three-particle systems. II,” Phys. Rev. D 5(8), 1992–2002 (1972).
4. F. A. Berezin and M. A. Shubin, The Schrödinger Equation (Moskov. Gos. Univ., Moscow, 1983) [Kluwer Academic Publ., Dordrecht, 1991].
5. V. N. Efimov, “Weakly-bound states of three resonantly-interacting particles,” Yadernaya Fiz. 12(5), 1080–1091 (1970) [Sov. J. Nucl. Phys. 12 (5), 589–595 (1971)].