Mass in special relativity what causes these particles to be termed "massless." However, even massless particles have a relativistic mass, which varies with their observed energy in various frames of reference, The invariant mass is the ratio of four-momentum (the four-dimensional generalization of classical momentum) to four-velocity: and is also the ratio of four-acceleration to four-force when the rest mass is constant. The four-dimensional form of Newton's second law is: The relativistic expressions for "E" and "p" obey the relativistic energy–momentum relation: where the m is the rest mass, or the invariant mass for systems, and "E" is the total energy. The equation is
Smith–Minkowski–Siegel mass formula all the "p"-masses have their standard value, then the total mass is the standard mass where The values of the Riemann zeta function for an even integers "s" are given in terms of Bernoulli numbers by So the mass of "ƒ" is given as a finite product of rational numbers as If the form "f" has a p-adic Jordan decomposition where "q" runs through powers of "p" and "f" has determinant prime to "p" and dimension "n"("q"), then the "p"-mass is given by Here "n"(II) is the sum of the dimensions of all Jordan components of type 2 and "p"