In General > s.a. experiments in quantum mechanics; hadrons [structure]; protons.
* History: 1932, Discovered by James Chadwick; 1934, Chadwick and Goldhaber measured the mass accurately enough to determine that a neutron was not an electron-proton bound state (as Rutherford had predicted); 2002, Evidence for neutrinoless double-β decay reported, and quantum states in gravitational field.
* Mass: Its value is mn = 1.6749 × 10−27 kg.
* Lifetime: An isolated neutron survives just 15 minutes before it decays into a proton, electron, and an antineutrino; Astrophysicists rely on a precise value of the free neutron lifetime to calculate the rate of nucleosynthesis during the big bang, and particle physicists use it to constrain fundamental parameters of the standard model; Yet measured lifetimes vary by about a percent, about 8 seconds (or 2.6 σ), and the discrepancy is still unresolved (2018); 2015, Cosmological data give 905.7 ± 7.8 s, while the "bottle method" with ultracold neutrons gives 905.7 ± 7.8 s, and the "beam method" 888.0 ± 2.1 s; 2018, the discrepancy is now 3.8 σ; One possibility is that the neutron can decay into a dark matter particle; 2018, The "bottle method" gives 877.7 s; 2020, Proposed space-based measurement.
* Electric dipole moment: In the standard model, the strong interaction should violate T-reversal symmetry, and thus CP symmetry; But such a symmetry violation would result in a neutron electric dipole moment 10 orders of magnitude larger than the current bound; In 1977, Roberto Peccei and Helen Quinn discovered a simple dynamical mechanism to enforce strong CP symmetry which, as Steven Weinberg and Frank Wilczek independently realized, implies the existence of the axion; 2006, The best current upper bound is 2.9 × 10−26 e·cm (90% c.l.), but soon other experiments will do better; 2020, New experimental value of (0.0 ± 1.1stat ± 0.2sys) × 10−26 e·cm; > s.a. CPT theorem.
* n-p mass difference: The measured difference is only 0.14% of the average of the two masses (a slightly smaller or larger value would have led to a dramatically different universe), and results from a competition between electromagnetic effects and the mass difference between the up and down quarks.
@ General references: Dubbers & Schmidt RMP(11), Paul a1205-proc [particle physics, astrophysics and cosmology with neutrons].
@ History: De Gregorio HSPBS(05)phy [early 1930s], phy/06; Recami HJ-a1712 [Majorana]; Ecker a2007 [Chadwick].
@ Structure: van den Brand & Huberts PW(96)feb [charge distribution]; Smith AS(10)#6; Arrington et al PRL(12) [structure function, from inclusive deuteron and proton deep-inelastic scattering].
@ Electric dipole moment: Fortson et al PT(03)jun; Baker et al PRL(06) [upper bound]; Domínguez et al PRD(09)-a0907 [and QED vacuum fluctuations]; Abel et al PRL(20) [upper bound]; > s.a. Wikipedia page.
@ n-p mass difference: Feynman & Speisman PR(54); Dashen & Frautschi PR(64) [proved wrong, see Kim phy/04]; Borsanyi et al Sci(15)mar [ab initio calculation]; > s.a. Kim's page.
@ Lifetime: Wietfeldt & Greene RMP(11); Yue et al PRL(13); Salvati et al JCAP(16)-a1507 [cosmological constraints]; Fornal & Grinstein PRL(18)-a1801 + news pw(18)jan [decay into dark matter particle]; Czarnecki et al PRL(18) + news pt(18)may, sn(18)may, is(18)may [update on dark matter and discrepancy]; Giacosa a1909-proc [discrepancy, and the Zeno effect]; news Phys(20)jun [space-based measurement].
@ Other topics: Altschul qp/99 [gravity and acceleration]; news riken(13)jan [magnetic refocusing of a neutron beam].

Neutron Interferometry > s.a. experiments in quantum mechanics; geometric phase; quantum equivalence principle.
* And gravity: Gravity-induced phases have already been detected, and they show that gravity at the quantum level is not a purely geometric effect, since the mass of the employed particles appears explicitly in the interference expression.
@ General references: Greenberger RMP(83) [and quantum mechanics, rev]; Rauch HPA(88); Unnerstall PLA(90) [comment]; Rauch & Vigier PLA(90); Rauch FP(93); Benatti & Floreanini PLB(99)qp [semigroups and dissipative evolution]; Felber et al FP(99) [in space and time]; Rauch & Werner 00 [r PT(02)jun]; Wu et al IJTP(10)-a0910 [quantum theory approach]; Klein FP(12) [history]; Klepp et al PTEP-a1407 [and fundamental quantum phenomena].
@ Geometric and quantum phases: Werner CQG(94); Littrell et al PRA(97); Allman et al PRA(97); Bhandari qp/01/PRL; Rauch et al Nat(02)jun [confinement-induced]; Sponar et al JPA(10)-a1002; Werner FP(12) [observation of geometric phase].
@ And gravity: Wolf FP(90) [and quantum gravity]; Werner CQG(94); Camacho PLA(99)qp, PLA(99)qp; Varjú & Ryder AJP(00)may [general relativistic treatment]; Nandi & Zhang PRD(02)gq [and equivalence principle]; Camacho & Macías PLB(05) [and torsion]; Abele & Leeb NJP(12); Galiautdinov & Ryder GRG(17)-a1701 [derivation in the weak-field approximation].
@ Related topics: Gähler & Zeilinger AJP(91)apr [wave phenomena, interference and diffraction]; > s.a. Goos-Hänchen Effect; gravitomagnetism.

Other Phenomenology > s.a. Beta Decay; CPT tests; neutron stars.
@ General references: Snow PT(13)mar [slow neutrons and fundamental physics]; Tureanu PRD(18)-a1804 [neutron-antineutron oscillations]; Sponar et al a2012 [tests of fundamental concepts of quantum mechanics].
@ Quantum states in gravitational field: Nesvizhevsky et al NIM(00), Nat(02)jan; Schwarzschild PT(02)mar; Olevik et al qp/02; Westphal gq/02 [theory]; Nesvizhevsky PRD(03), comment Hansson et al PRD(03)qp, reply PRD(03); Jenke et al PRL(14) [and constraints on dark energy and dark matter]; > s.a. tests of newtonian gravity.
@ Scattering and interactions: news pw(06)dec [and paper dating]; Alexandrov G&C(08) [and higher-dimensional gravity]; Furrer et al 09 [in condensed-matter physics]; Chen & Kotlarchyk 07 [interaction with matter].
@ Neutrinoless double-β decay: Klapdor-Kleingrothaus in(02)hp, et al FP(02); Klapdor-Kleingrothaus FP(03); Dell'Oro et al AHEP(16)-a1601 [rev].
> Related topics: see brane world [neutron disappearance]; optical technology [neutron holography].

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