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The influence of severe plastic deformation on the rejuvenation behavior and the boson heat capacity peak of a Pd₄₀Ni₄₀P₂₀ metallic glass is investigated for as-cast and pre-annealed states. Deformation by high-pressure torsion leads to a two-stage rejuvenation behavior, quantified by the structural enthalpy and fictive temperature, in coincidence with a strongly enhanced excess heat capacity at low temperatures, quantified by the boson peak height. Correlations between structural enthalpy, fictive temperature and the boson peak height were analyzed. The results show that the boson peak is not only related to the structural enthalpy but associated with the so-called “overshoot” of the glass transition. A universal link is established between the fictive temperature and the boson peak height, even under the joint influence of deformation and heat treatment. The significance of this link is that it sheds light on the structural connection between high-temperature relaxation and low-temperature excess vibrational density of states.