The relativistic energy-momentum relationship is expressed as:
\[
E^2 = p^2 c^2 + m^2 c^4,
\]
with:
- \( E \) representing the particle's total energy,
- \( p \) denoting the particle's momentum,
- \( c \) signifying the speed of light in a vacuum,
- \( m \) indicating the particle's rest mass.
This equation originates from special relativity and establishes a connection between a particle's energy, its momentum, and its rest mass.
Final Answer: \( E^2 = p^2 c^2 + m^2 c^4 \).