K L → 2μ DECAY

We study the time evolution of the distribution functions for hot and or degenerate gases of two flavors of Dirac neutrinos as a result of flavor mixing and dephasing. This is achieved by obtaining the time evolution of the flavor density matrix directly from quantum field theory at finite temperature and density. The time evolution features a rich hierarchy of scales which are widely separated in the nearly degenerate or relativistic cases and originate in interference phenomena between particle and antiparticle states. In the degenerate case the flavor asymmetry ∆N (t) relaxes to the asymptotic limit ∆N (∞) = ∆N (0) cos 2 (2θ) via dephasing resulting from the oscillations between flavor modes that are not Pauli blocked, with a power law 1/t for t > ts ≈ 2kF /∆M 2 . kF is the largest of the Fermi momenta. The distribution function for flavor neutrinos and antineutrinos as well as off-diagonal densities are obtained. Flavor particle-antiparticle pairs are produced by mixing and oscillations with typical momentum k ∼M the average mass of the neutrinos. An effective field theory description emerges on long time scales in which the Heisenberg operators obey a Bloch-type equation of motion valid in the relativistic and nearly degenerate cases. We find the non-equilibrium propagators and correlation functions in this effective theory and discuss its regime of validity as well as the potential corrections.

Section: A Equilibrated Gas Of Mass Eigenstatesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Oscillations and evolution of a hot and dense gas of flavor neutrinos: A quantum field theory study

Boyanovsky

2004

“…The neutrino oscillations are described by the density matrix formalism, see for instance [17]. However, we will mainly be interested in the resonance condition, which for ν a ↔ ν s oscillations is given by [18] δm 2 cos 2θ…”

Section: Maximal Asymmetry At Given Temperaturementioning

confidence: 99%

Maximum lepton asymmetry from active-sterile neutrino oscillations in the early Universe

Buras¹,

Semikoz²

2001

A large lepton asymmetry could be generated in the Early Universe by oscillations of active to sterile neutrinos with a small mixing angle sin 2θ < 10 −2 . The final order of magnitude of the lepton asymmetry η is mainly determined by its growth in the last stage of evolution when the MSW resonance dominates the kinetic equations. In this paper we present a simple way of calculating the maximum possible lepton asymmetry which can be created. Our results are in good agreement to previous calculations. Furthermore, we find that the growth of asymmetry does not obey any particular power law. We find that the maximum possible asymmetry at the freeze-out of the n/p ratio at T ∼ 1 MeV strongly depends on the mass-squared difference δm 2 : the asymmetry is negligible for |δm 2 | ≪ 1 eV 2 and reaches asymptotically large values for |δm 2 | ∼ > 50 eV 2

“…The existence of a sizable linear γ polarization and the possibility of its detection by internal pair conversion [50,51], as well as the presence of a T noninvariant term have been pointed out in [46].…”

Section: Time Reversal Invariance In the Decay To ππEmentioning

confidence: 99%

“…The decay of neutral kaons into π + π − γ has been studied in view of gaining information on symmetry violations which could not be obtained from the decay into π + π − , especially on CP violation of a different origin than the kaon's time evolution [46][47][48][49].…”

Section: Time Reversal Invariance In the Decay To ππEmentioning

confidence: 99%

Plate with a hole obeys the averaged null energy condition

Graham

Olum

2005

During the recent years experiments with neutral kaons have yielded remarkably sensitive results which are pertinent to such fundamental phenomena as CPT invariance (protecting causality), timereversal invariance violation, coherence of wave functions, and entanglement of kaons in pair states. We describe the phenomenological developments and the theoretical conclusions drawn from the experimental material. An outlook to future experimentation is indicated.