The extension of the standard model by a real gauge singlet scalar is the simplest but the most studied model with sometimes controversial ideas on the ability of the model to address the dark matter (DM) and the electroweak phase transition (EWPT) issues simultaneously. For this model, we obtain analytically slightly different conditions for strongly first-order EWPT and apply that in computation of the DM relic density where the real scalar plays the role of the DM particle. We show that the scalar in this model before imposing the invisible Higgs decay constraint, can be responsible for all or part of the DM abundance, while at the same time gives rise to a strongly first- order EWPT required for the baryogenesis. When the constraints from the direct detection experiments such as XENON100 or LUX/XENON1t are considered, the model is excluded completely.

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