https://doi.org/10.1140/epjc/s10052-021-09546-2
Regular Article - Theoretical Physics
A varying dark energy effective speed of sound parameter in the phantom Universe
1
Departamento de Física, Universidade da Beira Interior, Rua Marquês D’Ávila e Bolama, 6200-001, Covilhã, Portugal
2
Centro de Matemática e Aplicações da Universidade da Beira Interior, Rua Marquês D’Ávila e Bolama, 6200-001, Covilhã, Portugal
3
Department of Physics, University of the Basque Country UPV/EHU, P.O. Box 644, 48080, Bilbao, Spain
4
IKERBASQUE, Basque Foundation for Science, 48011, Bilbao, Spain
Received:
2
February
2021
Accepted:
10
August
2021
Published online:
9
September
2021
We analyse the phenomenological effects of a varying Dark Energy (DE) effective speed of sound parameter, 
, on the cosmological perturbations of three phantom DE models. Each of these models induce a particular abrupt future event known as Big Rip (BR), Little Rip (LR), and Little Sibling of the Big Rip (LSBR). In this class of abrupt events, all the bound structures in the Universe would be ripped apart at a finite cosmic time. We compute the evolution of the perturbations, 
growth rate and forecast the current matter power spectrum. We vary the parameter in the interval [0, 1] and compute the relative deviation with respect 
. In addition, we analyse the effect of gravitational potential sign flip that occurs at very large scale factors as compared with the current one.
© The Author(s) 2021
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Funded by SCOAP3
