International Journal of Modern Physics A

In this paper, we present a review of forward physics measurements performed with LHC Runs 1 and 2 data. In particular, measurements based on proton–proton collisions with different center-of-mass energies (0.9–13 TeV) are reviewed. We focus on measurements exploring the forward phase space using the available instrumentation at the different LHC experiments, and report on forward jet and forward energy flow measurements.

We study a class of extensions of the $k$-contracted Poincaré algebra under the hypothesis of generalizing the Bargmann algebra and its central charge. As we will see this type of contractions will lead in a natural way to consider the codajoint Poincaré algebra and some of their contractions. Among them there is one such that considering the quotient of it by a suitable ideal, the (stringy) $p$-brane Galilei algebra is recovered.

Propagator for spinning particle described in the Feshbach–Villars formalism is set up using the bosonic coherent state path integral. The boson model for the charge-spin symmetry is presented following the Schwinger recipe. The calculations are explicitly evaluated in the case of the step potential. The perturbation technique is used and the series are exactly summed.

We examine the possibility of using single-Higgs production at an $e^{+}{e}^{-}$ collider with polarized beams to measure, or constrain, indirectly a possible anomalous triple-Higgs coupling, which can contribute to the process via one-loop diagrams. In the dominant process $e^{+}{e}^{-}\to ZH$, longitudinally polarized beams can lead to an improvement in the cross-section by 50% for $e^{-}$ and $e^{+}$ polarizations of $-0.8$ and $+0.3$, respectively. This corresponds to an improvement in the sensitivity to the triple-Higgs coupling of about 18% for a center-of-mass energy of 250 GeV and an integrated luminosity of 2 ab${}^{-1}$, making a strong case of beam polarization. This also implies that with polarized beams, the luminosity needed to get a particular sensitivity is less by about 33% as compared to that needed with unpolarized beams. Even when only the $e^{-}$ beam is polarized $-0.8$, the improvement in the sensitivity is about 8%. We also study the effect of longitudinal beam polarization on the sensitivity to the triple-Higgs coupling of Higgs production through the subdominant process $e^{+}{e}^{-}\to H\nu \bar{\nu }$ occurring through $WW$ fusion.

In this work, we consider the generalized quantum electrodynamics proposed by Podolsky in Heisenberg picture via Källén methodology. We investigate the effects of higher-order derivatives to understand the qualitative and quantitative aspects of vacuum polarization. In addition, the most general structure of induced current and polarization tensor that emerge naturally by a perturbative scheme “à la” Källén is also obtained. Afterward, we discuss the physical implication of charge renormalization in the perspective of unitary and stable Podolsky theory.

We consider $R^2$ corrected model, i.e. $f(R)=R+\alpha R^2+\beta R^{2}ln(\beta R)$, where $R$ is the Ricci scalar and $\alpha$, $\beta$ are arbitrary constant values, to investigate some of the interior configurations of static anisotropic spherical charged stellar structures. The existence of electric charge and a strong electric field confirms due to the higher values of pressure distribution and energy density of the matter inside the stars. Furthermore, for compact star configurations, we also consider the simplified MIT bag model equation of state (EoS) given by $p_r=\frac{1}{3}(\rho -4B)$, where $p_r$ is radial pressure, $\rho$ is energy density and $B$ is bag constant. This approach allows to find electric charge from the Einstein–Maxwell field equations. We have extensively discussed the behavior of the electric charge and anisotropic fluid distribution factor for five different values of $\beta$. Interestingly, it is noticed during this study, for smaller values of $\beta$ we get intensity in electric charge. The Tolman–Oppenheimer–Volkoff equation (TOV), is modified in order to carry electric charge. In particular, we model the compact star candidates SAXJ 1808.4–3658 and Vela X-1 and give graphical representation of some important properties such as equilibrium condition, mass-radius ratio and surface redshift. In the end, our calculated solutions provide strong evidences for more realistic and viable charged stellar model.

We study the problem of pair creation of scalar particles by an electric field in curved Snyder space. We find exact solutions for the Klein–Gordon equation with a constant electric field in terms of hypergeometric functions. Then we calculate the pair creation probability and the number of created pairs of particles through Bogoliubov transformation technique.

An approach to the quantization of gravity in the presence of matter is examined which starts from the classical Einstein–Hilbert action and matter approximated by “point” particles minimally coupled to the metric. Upon quantization, the Hamilton constraint assumes the form of the Schrödinger equation: it contains the usual Wheeler–DeWitt term and the term with the time derivative of the wave function. In addition, the wave function also satisfies the Klein–Gordon equation, which arises as the quantum counterpart of the constraint among particles’ momenta. Comparison of the novel approach with the usual one in which matter is represented by scalar fields is performed, and shown that those approaches do not exclude, but complement each other. In final discussion it is pointed out that the classical matter could consist of superparticles or spinning particles, described by the commuting and anticommuting Grassmann coordinates, in which case spinor fields would occur after quantization.

Deriving the gravitational effective action directly from exact renormalization group is very complicated, if not impossible. Hence, to study the effects of running gravitational coupling which tends to a non-Gaussian UV fixed point (as it is supposed by the asymptotic safety conjecture), two steps are usually adopted. Cutoff identification and improvement of the gravitational coupling to the running one. As suggested in Ref. 1, a function of all independent curvature invariants seems to be the best choice for cutoff identification of gravitational quantum fluctuations in curved space–time and makes the action improvement, which saves the general covariance of theory, possible. Here, we choose Ricci tensor square for this purpose and then the equation of motion of improved gravitational action and its spherically symmetric vacuum solution are obtained. Indeed, its effect on the massive particles’ trajectory and the black hole thermodynamics is studied.

We propose a stellar model under the $f(𝕋,{𝒯})$ gravity following Mazur–Mottola’s conjecture${}^{1,2}$ known as gravastar which is generally believed as a viable alternative to black hole. The gravastar consists of three regions, viz., (I) interior region, (II) intermediate shell region, and (III) exterior region. The pressure within the interior core region is assumed to be equal to the constant negative matter-energy density which provides a constant repulsive force over the thin shell region. The shell is assumed to be made up of fluid of ultrarelativistic plasma and following the Zel’dovich’s conjecture of stiff fluid³ it is also assumed that the pressure which is directly proportional to the matter-energy density according to Zel’dovich’s conjecture, does cancel the repulsive force exerted by the interior region. The exterior region is completely vacuum and it can be described by the Schwarzschild solution. Under all these specifications, we find out a set of exact and singularity-free solutions of the gravastar presenting several physically valid features within the framework of alternative gravity, namely $f(𝕋,{𝒯})$ gravity,⁴ where the part of the gravitational Lagrangian in the corresponding action is taken as an arbitrary function of torsion scalar $𝕋$ and the trace of the energy–momentum tensor ${𝒯}$.