Spectrum of three-body bound States in a finite volume.

The spectrum of a bound state of three identical particles with a mass m in a finite cubic box is studied. It is shown that in the unitary limit, the energy shift of a shallow bound state is given by ΔE=c(κ^{2}/m)(κL)^{-3/2}|A|^{2}exp(-2κL/sqrt[3]), where κ is the bound-state momentum, L is the box size, |A|^{2} denotes the three-body analog of the asymptotic normalization coefficient of the bound state wave function, and c is a numerical constant. The formula is valid for κL≫1.