Modern Physics Letters A

Recent high-sensitivity observation of the nearby radio galaxy M87 has provided important insights into the central engine that drives the large-scale outflows seen in radio, optical and X-rays. This review summarizes the observational status achieved in the high energy (HE < 100 GeV) and very high energy (VHE > 100 GeV) gamma-ray domains, and discusses the theoretical progress in understanding the physical origin of this emission and its relation to the activity of the central black hole.

In the simplest little Higgs model the new flavor-changing interactions between heavy neutrinos and the Standard Model leptons can generate contributions to some lepton flavor violating decays of Z-boson at one-loop level, such as Z→τ^±μ^∓, Z→τ^±e^∓ and Z→μ^±e^∓. We examine the decay modes and find that the branching ratios can reach 10^-7 for the three decays, which should be accessible at the GigaZ option of the ILC.

We suggest a simple model, based on the type-I seesaw mechanism, for the lepton mass matrices. The model hinges on an Abelian symmetry which leads to mass matrices with some vanishing matrix elements. The model predicts one massless neutrino and M_eμ = 0 (M is the effective light-neutrino Majorana mass matrix). We show that these predictions agree with the present experimental data if the neutrino mass spectrum is inverted, i.e. if m₃ = 0, provided the Dirac phase δ is very close to maximal (±π/ 2). In the case of a normal neutrino mass spectrum, i.e. when m₁ = 0, the agreement of our model with the data is imperfect — the reactor mixing angle θ₁₃ is too small in our model. Minimal leptogenesis is not an option in our model due to the vanishing elements in the Yukawa-coupling matrices.

Quantum fields written on noncommutative spacetime (Groenewold–Moyal plane) obey twisted commutation relations. In this paper we show that these twisted commutation relations result in Hanbury–Brown Twiss (HBT) correlations that are distinct from that for ordinary bosonic or fermionic fields, and hence can provide useful information about underlying noncommutative nature of spacetime. The deviation from usual bosonic/fermionic statistics becomes pronounced at high energies, suggesting that a natural place is to look at Ultra High Energy Cosmic Rays (UHECRs). Since the HBT correlations are sensitive only to the statistics of the particles, observations done with UHECRs are capable of providing unambiguous signatures of noncommutativity, without any detailed knowledge of the mechanism and source of origin of UHECRs.

The single production of fourth family sneutrino via R-parity violating interactions in electron–positron collisions has been investigated. We study the decays of into different flavor dilepton e^±μ^∓ via R-parity violation. It is shown that R-parity violating couplings (λ₄₁₁, λ₄₁₂) down to 0.001 will be reachable at future linear colliders which would provide better accuracy comparing to the indirect measurements as complementary to the LHC results.

Constrained Hartree–Fock–Bogoliubov theory with SLy4 and SLy5 Skyrme forces is used to investigate the shape transition between spherical and γ-unstable nuclei in ^38–66Ti. By examining potential energy curves and neutron single-particle levels of even–even Ti isotopes, ^46,52,60Ti are suggested as possible candidates of the nuclei with E(5) symmetry.

We study the thermodynamics of soft wall model in AdS/QCD framework. The low temperature phase of QCD is described by thermal AdS and high temperature phase by AdS black hole solution of five-dimensional gravity with negative cosmological constant. The chemical potential is introduced via the solution of U(1) vector field in the bulk. The difference of action densities in two phases is studied and the results are compared with hard wall model. The quark number susceptibility is also calculated in both models.