- Fedichev and Fischer [195, 194] have investigated WKB estimates of the cosmological particle production rate and (1+1) dimensional cosmologies, both in expanding BECs.
- Lidsey [403], and Fedichev and Fischer [196] have focussed on the behaviour of cigar-like condensates in grossly-asymmetric traps.
- Barceló et al. [46, 47] have focussed on BECs and tried to mimic FLRW behaviour as closely as possible, both via free expansion, and via external control of the scattering length using a Feshbach resonance.
- Fischer and Schützhold [206] propose the use of two-component BECs to simulate cosmic inflation.
- Weinfurtner [674, 675] has concentrated on the approximate simulation of de Sitter spacetimes.
- Weinfurtner, Jain, et al. have undertaken both numerical [328] and general theoretical [677, 683] analyses of cosmological particle production in a BEC-based FLRW universe.

In all of these models the general expectations of the relativity community have been borne out – the theory definitely predicts particle production, and the very interesting question is the extent to which the formal predictions are going to be modified when working with real systems experimentally [47]. We expect that these analogue models provide us with new insights as to how their inherent modified-dispersion relations affect cosmological processes such as the generation of a primordial spectrum of perturbations (see, for example, [85, 84, 86, 87, 88, 89, 90, 122, 179, 269, 296, 297, 343, 380, 381, 406, 426, 423, 424, 425, 458, 459, 460, 487, 566, 587, 588, 589, 600] where analogue-like ideas are applied to cosmological inflation).

An interesting side-effect of the original investigation, is that birefringence can now be used to model “variable speed of light” (VSL) geometries [58, 181]. Since analogue models quite often lead to two or more “excitation cones”, rather than one, it is quite easy to obtain a bimetric or multi-metric model. If one of these metrics is interpreted as the “gravitational” metric and the other as the “photon” metric, then VSL cosmologies can be given a mathematically well-defined and precise meaning [58, 181].

Living Rev. Relativity 14, (2011), 3
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