Modern Physics Letters A

The creation of QCD is one of greatest achievements in the history of science. It has radically changed our conception of the fundamental ontology of the physical world and its underlying dynamics. What it has discovered are more than new particles and a new force, but rather a deeper level of physical reality, a new kind of entities. Dynamically, the strong nuclear forces are no longer taken to be fundamental, but are relegated to the status of the un-cancelled residue of far stronger long range force mediated by gluon. From a long term perspective, perhaps more important than these discoveries is that it breaks a new path to explore many novel features of an unknown layer of the physical world, such as instanton, the theta vacuum and effective energy. The notion of effective energy allows us to conceptualize the mysterious quantum number flow and hadronization. Although the metaphysical status of effective energy is not quite clear at this moment, but a window is open for conceptualizing the physical world that is in complex processes of transmutations in a unified way.

We review the theoretical interpretation of deep-inelastic electron–proton scattering at low values of the Bjorken variable x ≃Q²/W² ≲ 0.1. The process proceeds via the interaction of quark–antiquark color-dipole fluctuations of the (virtual) photon with the proton. In terms of the forward Compton scattering amplitude, two reaction channels contribute to the interaction of the color dipole with the gluon field in the proton. Dependent on the kinematics, there is either color transparency, corresponding to a cancellation of the amplitudes for the two reaction channels, or saturation, occurring when the process is dominated by a single interaction channel. The connection between the color-dipole picture and the pQCD improved parton model is elaborated upon.

Holographic screens are the generalization of the event horizon of a black hole in entropic force scheme, which are defined by setting Newton potential ϕ constant, i.e. e^2ϕ = c = const. We demonstrate that the integrated first law of thermodynamics is equivalent to the (r-r) component of Einstein equations, so that we strengthen the correspondence between thermodynamics and gravity. We show that there are not only the first law of thermodynamics, but also kinds of phase transitions of holographic screens. These phase transitions are characterized by the discontinuity of their heat capacities. In (n+1)-dimensional Reissner–Nordström–anti-de Sitter (RN-AdS) spacetime, we analyze three kinds of phase transitions, which are of the holographic screens with Q = 0 (charge), constant Φ (electrostatic potential) and nonzero constant Q. In the Q = 0 case, only the holographic screens with 0≤c<1 can undergo phase transition. In the constant Φ case, the constraints become as , where is a dimensional-dependent parameter. By verifying the Ehrenfest equations, we show that the phase transitions in this case are all second order phase transitions. In the constant Q case, there might be two, or one, or no phase transitions of holographic screens, depending on the values of Q and c.

Chevallier–Polarski–Linder (CPL) parametrization for the equation of state (EoS) of dark energy in terms of cosmic redshift or scale factor have been frequently studied in the literature. In this study, we consider cosmic time-based CPL parametrization for the EoS parameter of the effective cosmic fluid that fills the fabric of spatially flat and homogeneous Robertson–Walker (RW) spacetime in General Relativity. The model exhibits two worthy features: (i) It fits the observational data from the latest H(z) and Union 2.1 SN Ia compilations matching the success of ΛCDM model. (ii) It describes the evolution of the Universe from the matter-dominated phase to the recent accelerating phase similar to the ΛCDM model but leads to Big Rip end of the Universe contrary to the everlasting de Sitter expansion in the ΛCDM model. We investigate the matter and dark energy sources in the model, in particular, behavior of the dynamical dark energy responsible for the Big Rip end of Universe.

Representations of SO(4, 2) are constructed using 4×4 and 2×2 matrices with elements in ℍ' ⊗ ℂ and the known isomorphism between the conformal group and SO(4, 2) is written explicitly in terms of the 4×4 representation. The Clifford algebra structure of SO(4, 2) is briefly discussed in this language, as is its relationship to other groups of physical interest.

We demonstrate that the fermions in Reissner–Nordström–anti-de Sitter black hole background in the chiral limit m = 0, are related to an N = 4 extended one-dimensional supersymmetry with nontrivial topological charges. We also show that the N = 4 extended supersymmetry is unbroken and we extend the two N = 2 one-dimensional supersymmetries that the system also possesses, to have a trivial central charge. The implications of the trivial central charge on the Witten index are also discussed.

A cosmological model with an inhomogeneous viscous dark fluid coupled with dark matter in a flat Friedmann–Robertson–Walker (FRW) universe is investigated. The influence of dark matter on the behavior of an inhomogeneous viscous fluid of this kind, responsible for cosmic acceleration and for the appearance of different types of singularities, is analyzed in detail. In particular, the critical points corresponding to the solutions of the background equations in a useful approximation are obtained explicitly.