I have a simple question. What is the equation for the elementary-excitation spectrum of superfluid helium over whole momentum space, not just near the origin (i.e., phonon excitations $\epsilon=cp$) or near the minimum around $p_0$ (i.e., roton excitations $\epsilon=\Delta+(p-p_0)^2/2\mu$)? I am basically asking how I can generate (or plot) the following spectrum? Thanks. 
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Farokh
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