  We show that a phase transition may take place in the early Universe at a
temperature $T_*$ via a Standard Model singlet scalar field which happens to
couple to right handed neutrinos (RHN) resulting a temperature dependent mass
for them that finally relaxes to a constant value after electroweak phase
transition (EWPT). As a result, a requisite amount of lepton asymmetry can be
produced at a temperature close to $T_*$ satisfying the observed baryon
asymmetry of the Universe via sphaleron process even when the zero temperature
masses of the RHNs fall in sub GeV regime providing a testable scenario for
leptogenesis. Interestingly, the framework is also capable of predicting a
primordial lepton asymmetry (generated at a temperature below the EWPT), as
hinted by helium abundance measuring experiments, bearing a correlation with
early phase of leptogenesis.
