Modern Physics Letters A

We review recent work toward constructing, via five-dimensional holographic duals, four-dimensional theories in which spin-2 states (gravitons) are emergent. The basic idea is to extend to gravity model-building the applications of holographic duality to phenomenology construction.

We investigate velocity frame dragging with the boosted Schwarzschild black string solution and the boosted Kaluza–Klein bubble solution, in which a translational symmetry along the boosted z-coordinate is implemented. The velocity frame dragging effect can be nullified by the motion of an observer using the boost symmetry along the z-coordinate if it is not compact. However, in spacetime with the compact z-coordinate, we show that the effect cannot be removed since the compactification breaks the global Lorentz boost symmetry. As a result, the comoving velocity depends on r and the momentum parameter along the z-coordinate becomes an observer independent characteristic quantity of the black string and bubble solutions. The dragging induces a spherical ergo-region around the black string.

A recent article from the Pierre Auger Collaboration links the direction of charged cosmic rays to possible extragalactic sites of emission. The correlation of the direction of such particles with the direction of the emitter allows constraining the value of large-scale magnetic fields B. Assuming for B a coherence length λ in the range between 1 Mpc and 10 Mpc, we find values of B between 0.3 and 0.9 nG.

A framework is proposed for field theory with a new energy scale. The proposal is based on the idea, appearing for example in Deformed Special Relativity (DSR), of building phenomenological models for quantum gravity by taking momentum space to be curved rather than flat. In this work, this idea is implemented by introducing a fifth dimension and by imposing an extra constraint on physical field configurations in addition to the mass shell constraint. Advantages of this approach are that Lorentz symmetry is explicitly preserved and that an interacting scalar field model constructed in this way can be shown to be unitary. Implications for electrodynamics are discussed but the interpretation of the extra dimension needs to be clarified before making predictions for experiments.

The paper presents a fit to rapidity distributions of various hadrons measured in heavy-ion experiments at different beam energies. As examples distributions of various identified hadron species measured at GSI SIS and at BNL RHIC are presented and very good agreement between the fit and the data is found. The basis of the fits is a simple Feynman gas model, namely the two-cylinder gas model, for secondary particle production. The model assumption is that there are projectile and target cylinders that are the sources of emitted particles. The conjecture is that at low and intermediate energies the cylinders overlap totally, at high energy the cylinders overlap partly, while at very high energy a gap appears between the two cylinders.

We study the exclusive flavor changing neutral current process in the leptophobic Z′ model, where charged leptons do not couple to the extra Z′ boson. The branching ratio, as well as, the longitudinal, transversal and normal polarizations are calculated. It has been shown that all these physical observables are very sensitive to the existence of new physics beyond the standard model and their experimental measurements can give valuable information about it.

Using the technique of spectral decomposition, we investigated the late-time tails of massless and massive coupled scalar fields in the background of a black hole with a global monopole. We found that due to the existence of the coupling between the scalar and gravitational fields, the massless scalar field decay faster at timelike infinity i₊, and so does the massive one in the intermediate late time. But the asymptotically late-time tail for the massive scalar field is not affected and its decay rate is still t^-5/6.