We explore the cosmological constraints on the parameter w _ { dm } of the dark matter barotropic equation of state ( EoS ) to investigate the “ warmness ” of the dark matter fluid .
The model is composed by the dark matter and dark energy fluids in addition to the radiation and baryon components .
We constrain the values of w _ { dm } using the latest cosmological observations that measure the expansion history of the Universe .
When w _ { dm } is estimated together with the parameter w _ { de } of the barotropic EoS of dark energy we found that the cosmological data favor a value of w _ { dm } = 0.006 \pm 0.001 , suggesting a warm dark matter , and w _ { de } = -1.11 \pm 0.03 that corresponds to a phantom dark energy , instead of favoring a cold dark matter and a cosmological constant ( w _ { dm } = 0 ,w _ { de } = -1 ) .
When w _ { dm } is estimated alone but assuming w _ { de } = -1 , -1.1 , -0.9 , we found w _ { dm } = 0.009 \pm 0.002 , 0.006 \pm 0.002 , 0.012 \pm 0.002 respectively , where the errors are at 3 \sigma ( 99.73 % ) , i.e. , w _ { dm } > 0 with at least 99.73 % of confidence level .
When ( w _ { dm } , \Omega _ { dm 0 } ) are constrained together , the best fit to data corresponds to ( w _ { dm } = 0.005 \pm 0.001 , \Omega _ { dm 0 } = 0.223 \pm 0.008 ) and with the assumption of w _ { de } = -1.1 instead of a cosmological constant ( i.e. , w _ { de } = -1 ) .
With these results we found evidence of w _ { dm } > 0 suggesting a warm dark matter , independent of the assumed value for w _ { de } , but where values w _ { de } < -1 are preferred by the observations instead of the cosmological constant .
These constraints on w _ { dm } are consistent with perturbative analyses done in previous works .