Vacuons and Quasi-phonons: The Hidden Side of Bogoliubov Collective Excitations

Abstract

Loris Ferrari

In a series of papers [1, 2, 3], the author exactly diagonalized the truncated Hamiltonian Hc , proposed by Bogoliubov [4, 5], as a low energy approximation for the weakly interacting boson gas. In addition to the well know collective excitations (CEs) resulting from the Bogoliubov Canonic Approximation (BCA) [6, 7], and denoted as quasi-phonons (QPs), the exact eigenstates of Hc exhibit a new kind of CEs (the `hidden side' which the title alludes to), that we denote as vacuons. Those CEs are created/annihilated by adsorp-tion/emission of a quantum of energy twice as large as the activation energy of a QP. Being momentless, they are reminiscent of Cooper pairs of bosons, with opposite moments. The e_ects of the vacuons on the dynamics of the gas are discussed, with their possible exper-imental evidence.

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