Modern Physics Letters A

D6-branes intersecting at angles allow for phenomenologically appealing constructions of four-dimensional string theory vacua. While it is straightforward to obtain non-supersymmetric realizations of the standard model, supersymmetric and stable models with three generations and no exotic chiral matter require more involved orbifold constructions. The T⁶/(ℤ₄×ℤ₂×Ωℛ) case is discussed in detail. Other orbifolds including fractional D6-branes are treated briefly.

Striking events with isolated charged leptons, large missing transverse momentum and large transverse momentum of the hadronic final state were observed at the electron proton collider HERA in a data sample corresponding to an integrated luminosity of about 130 pb^-1. The H1 collaboration observed 11 events with isolated electrons or muons and with . Only 3.4±0.6 events were expected from Standard Model (SM) processes. Six of these events have , while 1.3±0.3 events were expected. The ZEUS collaboration observed good agreement with the SM. However, ZEUS found two events with a similar event topology, but tau leptons instead of electrons or muons in the final state. Only 0.2±0.05 events were expected from SM processes. For various hypotheses, the compatibility of the experimental results was investigated with respect to the SM and with respect to possible explanations beyond the SM. Prospects for the high-luminosity HERA-II data taking period are given.

We study the direct CP violation effect in the decay mode B⁺→ϕK⁺. This decay mode is dominated by the loop induced penguin diagram with a tiny contribution from the annihilation diagram. Therefore, the standard model expectation of direct CP violation is negligibly small. Using QCD factorization approach we find the CP asymmetry in the standard model to be at percent level. We consider then two scenarios beyond the standard model, the model with an extra vector-like down quark (VLDQ) and the R-parity violating supersymmetric model (RPV) and show that the direct CP violating asymmetry in B⁺→ϕK⁺ could be as large as ~ 85% (70%) in VLDQ (RPV) model.

A model of a hydrogenic content of atmosphere of the isolated neutron star 1E1207.4-5209 is proposed. It is based on the assumption that the main component in the atmosphere is the exotic molecular ion and that there exists a magnetic field in the range of (4±2)×10¹⁴G. Photoionization and photodissociation correspond to two absorption features at 0.7 keV and 1.4 keV, respectively, discovered by Chandra observatory¹ and confirmed by XMM–Newton.¹¹ The model predicts one more absorption feature at 80–150 eV corresponding to photodissociation .

In this work we propose two Lagrange multipliers with distinct coefficients for the light-front gauge that leads to the complete (non-reduced) propagator. This is accomplished via (n·A)²+(∂·A)² terms in the Lagrangian density. These lead to a well-defined and exact though Lorentz non invariant light-front propagator.

The recent observations of type Ia supernovae strongly support that the universe is accelerating now and decelerated in the recent past. This may be the evidence of the breakdown of the standard Friedmann equation. Instead of a linear function of the matter density, we consider a general function of the matter density to modify the Freidmann equation. We propose a new model which explains the recent acceleration and the past deceleration. Furthermore, the new model also gives a decelerated universe in the future. The new model gives Ω_m0=0.46 and z_T=0.44.

A superstring action is quantised with Neveu–Schwarz (NS) and Ramond (R) boundary conditions. The zero mass states of the NS sector are classified as the vector gluons, W-mesons, B_μ-mesons and scalars containing Higgs. 15 zero mass fermions are obtained from the Ramond sector. A spacetime supersymmetric Hamiltonian of the Standard Model is presented without any conventional SUSY particles.