Modern Physics Letters A

Understanding properties of QCD matter created in ultra-relativistic heavy-ion collisions is a major goal of RHIC and LHC experiments. Suppression of light and heavy flavor observables is a powerful tool to understand these properties and the suppressions of underlying partons appear to suggest a clear hierarchy in the suppression of these observables. However, the measurements show significant qualitative differences between the observed and intuitively expected patterns, in particular for neutral pions and single electrons at RHIC and for charged hadrons and D mesons at LHC, which are denoted as heavy flavor puzzles at RHIC and LHC. In this review, we discuss these puzzles and also summarize evidence that they can be consistently explained within the same theoretical framework.

We investigate the possible large extra dimensions (LED) effects induced by the Kaluza–Klein (KK) gravitons up to the QCD next-to-leading order (NLO) on ZZW production at the large hadron collider (LHC). The integrated cross-sections and some kinematic distributions are presented in both the Standard Model (SM) and the LED model. The numerical results demonstrate that the NLO QCD corrections are sizeable and remarkably reduce the leading order (LO) LED effect depending strongly on the phase space. The NLO LED relative discrepancies of the total cross-section could become sizable for the ZZW production, if we apply proper event selection criteria. We find that the LO result overestimates the LED effect and is insufficient to provide a believable theoretical prediction.

In this paper, we will analyze a system of multiple M2-branes in between two M5-branes. This will be analyzed by studying Bagger–Lambert–Gustavsson (BLG) theory on a manifold with two boundaries. The original BLG theory will be modified to make it gauge and supersymmetric invariant in presence of the boundaries. However, this modified theory will only preserve half the supersymmetry of the original theory. We will also analyze the deformation of this theory caused by noncommutativity between Grassman coordinates and spacetime coordinates. Finally, we will analyze the Higgsing of this theory to deformed D2-branes with boundaries.

The energy–momentum tensor is used to introduce the Casimir force of the massive scalar field acting on a nonpenetrating surface. This expression can be used to evaluate the vacuum force by employing the appropriate field operators. To simplify our formalism, we also relate the vacuum force expression to the imaginary part of the Green function via the fluctuation–dissipation theorem and Kubo's formula. This allows one to evaluate the vacuum force without resorting to the process of field quantization. These two approaches are used to calculate the attractive force between two nonpenetrating plates. Special attention is paid to the generalization of the formalism to D+1 spacetime dimensions.

We work out simple tree level relations in a top condensate model with dynamical electroweak symmetry breaking. We find that in this picture the mass of the composite Higgs boson at tree level is given by where m_t is the mass of the top quark.

It is usually assumed that any consistent interaction either deforms or retains the gauge symmetries of the corresponding free theory. We propose a simple model where an obvious irreducible gauge symmetry does not survive an interaction, while the interaction is consistent as it preserves the number of physical degrees of freedom. The model turns out admitting a less obvious reducible set of gauge generators which is compatible with the interaction and smooth in coupling constant. Possible application to gravity models is discussed.

The cosmological constant Λ of general relativity is a natural consequence of embedding Einstein's theory in a five-dimensional (5D) theory of the type needed for unification. The exact 5D solution for Λ<0 shows waves in ordinary three-dimensional (3D) space with properties similar to those of de Broglie or matter waves. Here the dispersion relation is derived for matter waves in a toy two-phase model, where regions with Λ<0 and Λ>0 average on the large scale to Λ≃0, thus providing in principle a resolution of the cosmological-constant problem. A striking result of the analysis is that the dispersion relation is bimodal, with a well-defined window of high-frequency transmission which effectively defines the speed of light.