Decays τ → (η, η')K–ντ in the extended Nambu–Jona-Lasinio model

Abstract

The decays τ → (η, η )K − ντ are described in the framework of the extended Nambu-Jona-Lasinio model. Both full and differential widths of these decays are calculated. The vector and scalar channels are considered. In the vector channels, the subprocesses with intermediate K * (892) and K * (1410) mesons play the main role. In the scalar channels, the subprocesses with intermediate K * 0 (800) and K * 0 (1430) mesons are taken into account. Scalar channels play a less important role in calculation of the full width of the decay τ → (η, η )K − ντ . The obtained results are in satisfactory agreement with the experimental data.

Excitonic condensation in systems of strongly correlated electrons

“…In the 1970s Volkov and collaborators showed in a series of articles [12][13][14] that excitonic condensation in slightly offstoichiometric systems leads to formation of a uniform ferromagnetic state, although the normal state does not exhibit a magnetic instability. The idea of an excitonic ferromagnet was revived at the beginning of 2000s in the context of hexaborides (section 5.1).…”

“…The classification elsewhere [11] includes only the non-magnetic polar EC states. In the mid-1970s Volkov and collaborators showed that in doped material with an unequal number of electrons and holes the ferromagnetic EC state develops characterised by simultaneous presence of finite singlet and triplet components [12][13][14].…”

“…Doping. The weak-coupling theory of doped excitonic insulator was developed by Volkov and collaborators [12][13][14] for systems without Hund's coupling. They showed that such systems tend to develop ferromagnetic order due to simultaneous appearance of the spin-singlet and spin-triplet order.…”

“…In 1999 Young et al [114] reported observations of 600 K ferromagnetism in La 0.005 Ca 0.995 B 6 . Ferromagnetism in a slightly doped semiconductor lead several groups to generalise the weak-coupling theory of excitonic ferromagnetism pioneered by Volkov and collaborators [12][13][14] to the case of multiple Fermi surface sheets [76,77,[115][116][117]. Nevertheless, subsequent investigations showed that the band gap in parent compound CaB 6 is ≈1 eV [118] and thus inconsistent with the EC scenario.…”