Double concerto for violin, cello, and piano, Beethoven's Triple Concerto for Violin, Cello, Piano and Orchestra being perhaps the most notable, but there have been many; see the list of triple concertos for violin, cello, and piano. A notable quadruple concerto is Olivier Messiaen's incomplete "Concert à quatre". Double concerto A double concerto (Italian: "Doppio concerto"; German: "Doppelkonzert") refers to two distinct variations on the concerto. Most often, it refers to a concerto featuring two performers, as opposed to the usual single performer, in the solo role. These two performers' instruments may be of the same type, as in Bach's, Concerto for
Double beta decay or double beta decay are predicted to be very long; hence, quadruple beta decay is unlikely to be realized. The eight candidate nuclei for quadruple beta decay include Zr, Xe, and Nd capable of quadruple beta-minus decay, and Xe, Ba, Gd, and Dy capable of quadruple beta-plus decay or electron capture. In theory, quadruple beta decay may be experimentally observable in three of these nuclei, with the most promising candidate being Nd. Double beta decay In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa,