Modern Physics Letters A

Centrality definition in A + A collisions at colliders such as RHIC and LHC suffers from a correlated systematic uncertainty caused by the efficiency of detecting a p + p collision ($50\pm 5\%$ for PHENIX at RHIC). In A + A collisions where centrality is measured by the number of nucleon collisions, $N_{\mathrm{\text{coll}}}$, or the number of nucleon participants, $N_{\mathrm{\text{part}}}$, or the number of constituent quark participants, $N_{\mathrm{\text{qp}}}$, the error in the efficiency of the primary interaction trigger (Beam–Beam Counters) for a p + p collision leads to a correlated systematic uncertainty in $N_{\mathrm{\text{part}}}$, $N_{\mathrm{\text{coll}}}$ or $N_{\mathrm{\text{qp}}}$ which reduces binomially as the A + A collisions become more central. If this is not correctly accounted for in projections of A + A to p + p collisions, then mistaken conclusions can result. A recent example is presented in whether the mid-rapidity charged multiplicity per constituent quark participant $(d{N}_{\mathrm{\text{ch}}}/d\eta )/N_{\mathrm{\text{qp}}}$ in Au + Au at RHIC was the same as the value in p + p collisions.

Muon pair production in exclusive radiative decays ${\chi }_{cJ}\to J/\psi \mu \mu$, ${\chi }_{bJ}\to \mathrm{{\rm Y}}\mu \mu$ is considered. We present numerical values of the branching fractions and distributions over various kinematical variables.

In recent years, many studies have been conducted to reconstruct the physical properties of scalar fields by establishing a connection between some energy densities and a scalar field of dark energies. In this paper, using the extended five-dimensional (5D) Kaluza–Klein model, we establish a correspondence among modified holographic dark energy and the tachyon, K-essence and dilaton scalar-field models. We also graphically illustrate the evolution of the equation-of-state parameter versus time.

Cosmological models with time-dependent $\mathrm{\Lambda }$ (read as $\mathrm{\Lambda }(t)$) have been investigated widely in the literature. Models that solve background dynamics analytically are of special interest. Additionally, the allowance of past or future singularities at finite cosmic time in a specific model signals for a generic test on its viabilities with the current observations. Following these, in this work we consider a variety of $\mathrm{\Lambda }(t)$ models focusing on their evolutions and singular behavior. We found that a series of models in this class can be exactly solved when the background universe is described by a spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) line element. The solutions in terms of the scale factor of the FLRW universe offer different universe models, such as power-law expansion, oscillating, and the singularity free universe. However, we also noticed that a large number of the models in this series permit past or future cosmological singularities at finite cosmic time. At last we close the work with a note that the avoidance of future singularities is possible for certain models under some specific restrictions.

We consider the piecewise flat spacetime and a simplicial analog of the Palatini form of the general relativity (GR) action where the discrete Christoffel symbols are given on the tetrahedra as variables that are independent of the metric. Excluding these variables with the help of the equations of motion gives exactly the Regge action.

This paper continues our previous work. Now, we include the parity violation term and the analog of the Barbero–Immirzi parameter introduced in the orthogonal connection form of GR. We consider the path integral and the functional integration over the connection. The result of the latter (for certain limiting cases of some parameters) is compared with the earlier found result of the functional integration over the connection for the analogous orthogonal connection representation of Regge action.

These results, mainly as some measures on the lengths/areas, are discussed for the possibility of the diagram technique where the perturbative diagrams for the Regge action calculated using the measure obtained are finite. This finiteness is due to these measures providing elementary lengths being mostly bounded and separated from zero, just as the finiteness of a theory on a lattice with an analogous probability distribution of spacings.

In a recent paper, He, Gao and Cai [Phys. Rev. D 89, 083510 (2014)], found a rigorous proof, based on analytical solutions of the Wheeler–DeWitt (WDWE) equation, of the spontaneous creation of the universe from nothing. The solutions were obtained from a classical potential $V=k{a}^2$, where $a$ is the scale factor. In this paper, we present a complementary (to that of He, Gao and Cai) solution to the WDWE equation with $V=k{a}^n$. I have found an exponential expansion of the true vacuum bubble for all scenarios. In all scenarios, we found a power law behavior of the scale factor result which is in agreement with another studies.

The electron–photon interaction (the spinor–vector field interaction) in the de Sitter ambient space formalism is investigated in the first (leading order) approximation. The interaction Lagrangian and the scattering matrix are presented. In this approximation, the scattering matrix can be written as a expansion of the interaction Lagrangian. The tree-diagram of electron–photon scattering amplitude is calculated. Finally, the Minkowski limit is considered.