This article is about the hypothetical decay of nucleons (protons or neutrons) into other subatomic particles. For the type of radioactive decay in which a nucleus ejects a proton, see Proton emission. For the radioactive decay where a proton within a nucleus converts to a neutron, see positron emission.
"Nucleon decay" redirects here. For decay of neutrons, see neutron decay.
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron.[1] The proton decay hypothesis was first formulated by Andrei Sakharov in 1967. Despite significant experimental effort, proton decay has never been observed. If it does decay via a positron, the proton's half-life is constrained to be at least 1.67×1034 years.[2]
According to the Standard Model, the proton, a type of baryon, is stable because baryon number (quark number) is conserved (under normal circumstances; see Chiral anomaly for an exception). Therefore, protons will not decay into other particles on their own, because they are the lightest (and therefore least energetic) baryon. Positron emission and electron capture—forms of radioactive decay in which a proton becomes a neutron—are not proton decay, since the proton interacts with other particles within the atom.
Some beyond-the-Standard-Model grand unified theories (GUTs) explicitly break the baryon number symmetry, allowing protons to decay via the Higgs particle, magnetic monopoles, or new X bosons with a half-life of 1031 to 1036 years. For comparison, the universe is roughly 1.38×1010 years old.[3] To date, all attempts to observe new phenomena predicted by GUTs (like proton decay or the existence of magnetic monopoles) have failed.
Quantum tunnelling may be one of the mechanisms of proton decay.[4][5][6]
Quantum gravity[7] (via virtual black holes and Hawking radiation) may also provide a venue of proton decay at magnitudes or lifetimes well beyond the GUT scale decay range above, as well as extra dimensions in supersymmetry.[8][9][10][11]
There are theoretical methods of baryon violation other than proton decay including interactions with changes of baryon and/or lepton number other than 1 (as required in proton decay). These included B and/or L violations of 2, 3, or other numbers, or B − L violation. Such examples include neutron oscillations and the electroweak sphaleron anomaly at high energies and temperatures that can result between the collision of protons into antileptons[12] or vice versa (a key factor in leptogenesis and non-GUT baryogenesis).
^Ishfaq Ahmad (1969), "Radioactive decays by Protons. Myth or reality?", The Nucleus, pp. 69–70
^Francis, Matthew R. (22 September 2015). "Do protons decay?". symmetry magazine. Retrieved 2020-11-12.
^Talou, P.; Carjan, N.; Strottman, D. (1998). "Time-dependent properties of proton decay from crossing single-particle metastable states in deformed nuclei". Physical Review C. 58 (6): 3280–3285. arXiv:nucl-th/9809006. Bibcode:1998PhRvC..58.3280T. doi:10.1103/PhysRevC.58.3280. S2CID 119075457.
^"adsabs.harvard.edu".
^Trixler, F. (2013). "Quantum Tunnelling to the Origin and Evolution of Life". Current Organic Chemistry. 17 (16): 1758–1770. doi:10.2174/13852728113179990083. PMC 3768233. PMID 24039543.
^Bambi, Cosimo; Freese, Katherine (2008). "Dangerous implications of a minimum length in quantum gravity". Classical and Quantum Gravity. 25 (19): 195013. arXiv:0803.0749. Bibcode:2008CQGra..25s5013B. doi:10.1088/0264-9381/25/19/195013. hdl:2027.42/64158. S2CID 2040645.
^Adams, Fred C.; Kane, Gordon L.; Mbonye, Manasse; Perry, Malcolm J. (2001). "Proton Decay, Black Holes, and Large Extra Dimensions - NASA/ADS". International Journal of Modern Physics A. 16 (13): 2399–2410. arXiv:hep-ph/0009154. Bibcode:2001IJMPA..16.2399A. doi:10.1142/S0217751X0100369X. S2CID 14989175.
^Al-Modlej, Abeer; Alsaleh, Salwa; Alshal, Hassan; Ali, Ahmed Farag (2019). "Proton decay and the quantum structure of space–time". Canadian Journal of Physics. 97 (12): 1317–1322. arXiv:1903.02940. Bibcode:2019CaJPh..97.1317A. doi:10.1139/cjp-2018-0423. hdl:1807/96892. S2CID 119507878.
^Giddings, Steven B. (1995). "The black hole information paradox". arXiv:hep-th/9508151.
^Alsaleh, Salwa; Al-Modlej, Abeer; Farag Ali, Ahmed (2017). "Virtual black holes from the generalized uncertainty principle and proton decay". Europhysics Letters. 118 (5): 50008. arXiv:1703.10038. Bibcode:2017EL....11850008A. doi:10.1209/0295-5075/118/50008. S2CID 119369813.
^Tye, S.-H. Henry; Wong, Sam S. C. (2015). "Bloch wave function for the periodic sphaleron potential and unsuppressed baryon and lepton number violating processes". Physical Review D. 92 (4): 045005. arXiv:1505.03690. Bibcode:2015PhRvD..92d5005T. doi:10.1103/PhysRevD.92.045005. S2CID 73528684.
In particle physics, protondecay is a hypothetical form of particle decay in which the protondecays into lighter subatomic particles, such as a neutral...
example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted...
Protons have a positive charge distribution, which decays approximately exponentially, with a root mean square charge radius of about 0.8 fm. Protons...
slowly and inexorably grow darker. According to theories that predict protondecay, the stellar remnants left behind will disappear, leaving behind only...
Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is...
Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can...
isotope consists of only a single proton, it is given the formal name protium. The proton has never been observed to decay, and hydrogen-1 is therefore considered...
hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay to the other particle, which has opposite...
neutrons or protonsdecay by beta decay (including positron decay), electron capture or more exotic means, such as spontaneous fission and cluster decay. The...
and in neutron scattering experiments. A free neutron spontaneously decays to a proton, an electron, and an antineutrino, with a mean lifetime of about 15...
Hence neutron decay conserves baryon number B and lepton number L separately, so also the difference B − L is conserved. Protondecay is a prediction...
free neutron has a greater mass than a free proton. However, see protondecay. Understanding of the beta decay process developed over several years, with...
unification might be detected through indirect observations of the following: protondecay, electric dipole moments of elementary particles, or the properties of...
which consists of two protons and two neutrons. It has a charge of +2 e and a mass of 4 Da. For example, uranium-238 decays to form thorium-234. While...
radioactive, with extremely long half-lives (discounting the possibility of protondecay, which would make all nuclides ultimately unstable). Some stable nuclides...
(both protons and neutrons) exhibit a lower energy state when their number is even, rather than odd. This stability tends to prevent beta decay (in two...
95% confidence. Decay to smaller vacuum expectation value, resulting in decrease of Casimir effect and destabilization of proton. Decay to vacuum with...
protons at a target to produce positron-emitting radionuclides, e.g. fluorine-18. Radionuclide generators contain a parent radionuclide that decays to...
: §IIIE If protons are not stable, white dwarfs will also be kept warm by energy released from protondecay. For a hypothetical proton lifetime of 1037...
types of nuclear decay. Unstable nuclides with a nonoptimal number of neutrons or protonsdecay by beta decay (including positron decay), electron capture...
type) are around 1 TeV/c2 (i.e., about 1000 times the proton mass). By definition, leptoquarks decay directly into a quark and a lepton or an antilepton...
not enough decay energy is available to allow it, and thus electron capture is the sole decay mode. For example, rubidium-83 (37 protons, 46 neutrons)...