τ lepton decays

We discuss recent results on τ lepton physics obtained at the BABAR,Belle and KEDR detectors.They include tests of lepton universality using new measurements of τ lepton mass and some branching fractious.Also described are selected results on τ lepton hadronic decays coming from BABAR and Belle.     

Processes with heavy ion collisions

Some Coulomb effects in heavy ion collisions are considered. Among them the process of muon and lepton pair creation, Coulomb and unitary corrections, statistics of multiple pair production. Effects of multiple photon exchange in process of lepton pair production by linearly polarized photon on nuclei are considered. This process is used for measuring the polarization of initial photon. Relativistic muon energy loss due to the light lepton pair production in the Coulomb field are calculated. Also we consider the effects of multiple photon exchange in elastic lepton scattering on unscreened atomic field and discuss the possible experimental testing.     

Large transverse momentum lepton pair production at the Large Hadron Collider

We study the large transverse momentum distribution of lepton pairs produced in heavy-ion collisions, making use of the perturbative QCD. Referring to the calculation of the parton-parton production process into lepton pairs at the Relativistic Heavy Ion Collider (RHIC), the production of lepton pairs at large transverse momentum is extended to the Large Hadron Collider (LHC). The contribution of the parton-parton production process into lepton pairs in Pb-Pb collisions at the LHC is calculated, including the complete processes at large transverse momentum. Lepton pair production with the direct single photon process and the resolved single photon process are considered and confirmed to be significant at the LHC.     

See-saw neutrino masses induced by a triplet of leptons

Neutrinos can acquire mass through the see-saw mechanism by extending the lepton sector of the Standard Model. The most generalSU(2) _L assignments allowed for the exotic leptons are the singlet and triplet representations. A model is constructed involving a triplet of exotic leptons. In this model lepton number is broken. Therefore lepton number violating processes, in particular those involving the lepton triplet, could provide distinctive experimental signatures.     

Baryogenesis from mixing of lepton doublets

It is shown that the mixing of lepton doublets of the Standard Model can yield sizable contributions to the lepton asymmetry, that is generated through the decays of right-handed neutrinos at finite temperature in the early Universe. When calculating the flavour-mixing correlations, we account for the effects of Yukawa as well as of gauge interactions. We compare the freeze-out asymmetry from lepton-doublet mixing to the standard contributions from the mixing and direct decays of right-handed neutrinos. The asymmetry from lepton mixing is considerably large when the mass ratio between the right-handed neutrinos is of order of a few, while it becomes Maxwell-suppressed for larger hierarchies. For an intermediate range between the case of degenerate right-handed neutrinos (resonant leptogenesis) and the hierarchical case, lepton mixing can yield the main contribution to the lepton asymmetry.     

Photon-neutrino interactions

We discuss the interaction of photons with neutrinos including two lepton loops. The parity violation in the γ ν → γν channel due to two lepton loops is substantially enhanced relative to the one lepton loop contribution. However, there is no corresponding enhancement in the parity conserving amplitude in either the direct or the cross channel \(\gamma \gamma \to v\bar v\).     

Leptogenesis: The other cuts

For standard leptogenesis from the decay of singlet right-handed neutrinos, we derive source terms for the lepton asymmetry that are present in a finite density background but absent in the vacuum. These arise from cuts through the vertex correction to the decay asymmetry, where in the loop either the Higgs boson and the right-handed neutrino or the left-handed lepton and the right-handed neutrino are simultaneously on-shell. We evaluate the source terms numerically and use them to calculate the lepton asymmetry for illustrative points in parameter space, where we consider only two right-handed neutrinos for simplicity. Compared to calculations where only the standard cut through the propagators of left-handed lepton and Higgs boson is included, sizable corrections arise when the masses of the right-handed neutrinos are of the same order, but the new sources are found to be most relevant when the decaying right-handed neutrino is heavier than the one in the loop. In that situation, they can yield the dominant contribution to the lepton asymmetry.     

A TROUBLE FOR COMPOSITE QUARK AND LEPTON MODELS

In composite quark and lepton models a factor which depends on the quark or lepton mass ratio appears in the effective weak coupling constant of quarks and leptons. It comes from the Lorentz (contraction of the composite quark and lepton wave functions and may cause a trouble for their weak coupling constant universality.     

论反常作用、轻子结构和μ-e质量差

本文提出了反常作用的μ荷观点,μ荷不仅是一种反映μ-e禁戒性的量子数,而且是反常作用的承担者。在此观点下,讨论了轻子结构和μ-e质量差,得到了关于轻子结构的一些普遍定理。例如,证明了电子的反常作用和电磁作用形状因子相同等。在讨论轻子结构的基础上,得到了将μ-e质量差和轻子的电磁结构相联系的公式,证明了主要由于电磁作用干涉产生的μ荷-μ矩作用是反常作用自能的主要部分,它是负值,故是电子参与反常作用。利用电子的电磁结构数据能合理地解释μ-e质量差,而后者也提供了有关电子电磁结构的进一步知识。     

Neutrino masses from SUSY: Different contributions and their implications

We discuss the various sources of neutrino masses in supersymmetric standard models with explicit lepton number violation. We show that the bilinear lepton number violating soft terms in models with either bilinear or trilinear lepton number violating couplings in the superpotential, play an important role in determining the neutrino mass spectrum. A comparative study of the neutrino mass spectrum and its implications for the present neutrino anomalies in these models is presented.     

Equation of State of Protoneutron Star Matter

We have calculated the equation of state of protoneutron star matter by using the lowest order constrained variational method. In our calculations, the modern Argonne potential (AV₁₈) together with its older model potential (AV₁₄) are used. It is found that the equation of state for high lepton fraction is stiffer than for low lepton fraction. It is seen that the increasing effect of pressure due to high lepton fraction and due to entropy are comparable. It is shown that the temperature and adiabatic index depend on the values of both entropy and lepton fraction.     

Lepton number conserving and non-conserving weak interactions

A gauge theory of weak and electromagnetic interactions based on a group containing the SU(4) group of unitary unimodular transformations on the lepton and quark quartets, is shown to be possible only if lepton and/or baryon number are not exactly conserved, or if there exist particles that cannot be built of quarks and leptons. The spontaneous breakdown of lepton number conservation in terms of tadpole-producing spinless leptons is considered.     

Incident contamination lepton doses measured using radiochromic film in radiotherapy

Measurement of lepton contamination is achieved across a radiotherapy photon beam and peripheral doses using radiochromic film. An extrapolation technique is used where several layers are suspended in air to measure incident contamination without the effects of phantom scatter. Surface dose was measured as 11% of D_max for 6 MV beams at central axis and 9% for 10 MV photons for a 10×10 cm field size. Peripheral lepton doses were found to decrease compared to central, however, were still measurable. Peripheral lepton dose was found to increase with field size and was 12% and 15%, 2 cm outside the geometric field edge of a 30×30 cm field size at 6 and 10 MV respectively. Radiochromic film is a suitable dosimeter for measurement of lepton contamination absorbed dose to surface layers of skin.     

τ lepton decays

We discuss recent results on τ lepton physics obtained at the BABAR, Belle and KEDR detectors They include tests of lepton universality using new measurements of T lepton mass and some branching fractions Also described are selected results on τ lepton hadronic decays coming from BABAR and Belle.     

Search for lepton flavor violating decays tau(+/-) --> l(+/-)pi0, l(+/-)eta, l(+/-)eta'

A search for lepton flavor violating decays of the tau lepton to a lighter mass lepton and a pseudoscalar meson has been performed using 339 fb;{-1} of e;{+}e;{-} annihilation data collected at a center-of-mass energy near 10.58 GeV by the BABAR detector at the SLAC PEP-II storage ring. No evidence of a signal has been found, and upper limits on the branching fractions are set at the 10;{-7} level.     

Search for flavor lepton number violation in slepton decays at LHC

We show that in supersymmetric models with explicit flavor lepton number violation due to soft supersymmetry breaking mass terms there could be detectable flavor lepton number violation in slepton decays. We estimate the potential for discovery of lepton flavor number violation in slepton decays at LHC. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 139–144 (25 January 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Coherent active-sterile neutrino flavor transformation in the early universe

We solve the problem of coherent Mikheyev-Smirnov-Wolfenstein resonant active-to-sterile neutrino flavor conversion driven by an initial lepton number in the early Universe. We find incomplete destruction of the lepton number in this process and a sterile neutrino energy distribution with a distinctive cusp and high energy tail. These features imply alteration of the nonzero lepton number primordial nucleosynthesis paradigm when there exist sterile neutrinos with rest masses m(s) approximately 1 eV. This could result in better light element probes of (constraints on) these particles.     

Possible identification of the outgoing lepton in neutral current reactions

It may be possible to determine whether the outgoing lepton in muonless neutrino and antineutrino reactions is identical with the incident particle, even if the outgoing lepton is massless and has the same helicity. The possibility depends upon the presence of anti-hermitean currents, which can cause characteristic differences between neutrino and antineutrino reactions.