International Journal of Modern Physics A

While the LHCb detector was specifically designed for measuring heavy-flavor physics, it has also proven itself as a forward general purpose detector with flexible data acquisition, excellent lifetime resolution and charged particle identification. This makes LHCb an ideal laboratory for exploring phenomena related to quantum chromodynamics (QCD), particularly with heavy-flavor content. This review explores some of the novel QCD measurements from LHCb, with an emphasis placed on comparisons to predictions from the Pythia 8 Monte Carlo event generator.

Quantum chromodynamics (QCD), the theory of the strong interactions, involves quarks interacting with non-Abelian gluon fields. This theory has many features that are difficult to impossible to see in conventional diagrammatic perturbation theory. This includes quark confinement, mass generation and chiral symmetry breaking. This paper is a colloquium level overview of the framework for understanding how these effects come about.

We study $S_4$ flavor symmetric inverse seesaw model which has the possibility of simultaneously addressing neutrino phenomenology, dark matter (DM) and baryon asymmetry of the universe (BAU) through leptogenesis. The model is the extension of the standard model by the addition of two (RH) neutrinos and three sterile fermions leading to a keV scale sterile neutrino DM and two pairs of quasi-Dirac states. The CP violating decay of the lightest quasi-Dirac pair present in the model generates lepton asymmetry which then converts to BAU. Thus, this model can provide a simultaneous solution for nonzero neutrino mass, DM content of the universes and the observed baryon asymmetry. The $S_4$ flavor symmetry in this model is augmented by additional $Z_4\times Z_3$ symmetry to constrain the Yukawa Lagrangian. A detailed numerical analysis has been carried out to obtain DM mass, DM-active mixing as well as BAU both for normal hierarchy as well as inverted hierarchy. We try to correlate the two cosmological observables and found a common parameter space satisfying the DM phenomenology and BAU. The parameter space of the model is further constrained from the latest cosmological bounds on the observables.

In this paper, we investigate anisotropic fluid cosmology in a situation where the space–time metric back-reacts in a local, time-dependent way to the presence of inhomogeneities. We derive exact solutions to the Einstein field equations describing Friedmann–Lemaítre–Robertson–Walker (FLRW) large-scale cosmological evolution in the presence of local inhomogeneities and time-dependent backreaction. We use our derivation to tackle the cosmological constant problem. A cosmological constant emerges by averaging the backreaction term on spatial scales of the order of 100 Mpc, at which our universe begins to appear homogeneous and isotropic. We find that the order of magnitude of the “emerged” cosmological constant agrees with astrophysical observations and is related in a natural way to baryonic matter density. Thus, there is no coincidence problem in our framework.

In this paper, we have considered the generalized cosmic Chaplygin gas (GCCG) in the background of Brans–Dicke (BD) theory and also assumed that the Universe is filled in GCCG, dark matter and radiation. To investigate the data fitting of model parameters, we have constrained the model using recent observations. Using ${\chi }^2$ minimum test, the best-fit values of the model parameters are determined by OHD+CMB+BAO+SNIa joint data analysis. We have drawn the contour figures for different confidence levels $1\sigma$, $2\sigma$ and $3\sigma$. To examine the viability of the GCCG model in BD theory, we have also determined △AIC and △BIC using the information criteria (AIC and BIC). Graphically, we have analyzed the natures of the equation of state parameter and deceleration parameter for our best-fit values of model parameters. Also, we have studied the square speed of sound $v_s^2$ which lies in the interval $(0,1)$ for expansion of the Universe. So, our considered model is classically stable by considering the best-fit values of the model parameters due to the data analysis.

A modified Hayward metric of magnetically charged black hole space–time based on rational nonlinear electrodynamics with the Lagrangian ${ℒ}=-{ℱ}/(1+2\beta {ℱ})$ is considered. We introduce the fundamental length, characterizing quantum gravity effects. If the fundamental length vanishes the general relativity coupling to rational nonlinear electrodynamics is recovered. We obtain corrections to the Reissner–Nordström solution as the radius approaches infinity. The metric possesses a de Sitter core without singularities as $r\to 0$. The Hawking temperature and the heat capacity are calculated. It was shown that phase transitions occur and black holes are thermodynamically stable at some event horizon radii. We demonstrate that curvature invariants are bounded and the limiting curvature conjecture takes place.

We present the published data of ALICE at mid-rapidity region ($\left|y\right|<0.5$) to study the $p_T$ spectra of light-flavor hadrons in different charged-particle multiplicities ($\frac{d{N}_{\mathrm{\text{ch}}}}{d\eta }$) for $p+p$ collisions at $\sqrt{s}=7$ TeV. We parametrize the $p_T$ spectra of different hadrons such as pion (${\pi }^{+}+{\pi }^{-}$), kaon ($K^{+}+K^{-}$), $K_S^0$, $K^{\ast 0}$ ($K^{\ast 0}+\overline{K^{\ast 0}}$), $\varphi$, proton ($p+\bar{p}$), lambda ($\mathrm{\Lambda }+\bar{\mathrm{\Lambda }}$), cascade (${\mathrm{\Xi }}^{-}+{\bar{\mathrm{\Xi }}}^{+}$) and omega (${\mathrm{\Omega }}^{-}+{\bar{\mathrm{\Omega }}}^{+}$) using Tsallis distribution. We perform this analysis by considering both differential and single freeze-out scenarios. In the differential freeze-out scenario, both the Tsallis parameters $n$ and $T$ increase with charged multiplicities for most of the particles. This implies that the multipartonic interactions increase the multiplicities in $p+p$ collisions and it brings the system towards thermal equilibrium. Here we observe that both $n$ and $T$ have different trends with different masses of particles. The parameters $n$ and $T$ are higher for massive particles (except for multistrange baryons) in comparison to lighter ones, which supports the differential freeze-out scenario and suggests that massive particles freeze-out earlier from the system. In the case of single freeze-out scenario, the value of parameter $n$ has a little variation with multiplicity and the parameter $T$ increases with multiplicity. This implies that the degree of thermalization remains similar for the events of different multiplicity classes.

In this paper, inflation in the framework of Einstein–Cartan theory is revisited. Einstein–Cartan theory is a natural extension of the General Relativity with nonvanishing torsion. The connection on Riemann–Cartan space–time is only compatible with the cosmological principal for a particular form of torsion. We also show this form to be compatible with gauge invariance principle for non-Abelian and Abelian gauge fields under a certain deviced coupling procedure. We adopt an Abelian gauge field in the form of “cosmic triad”. The dynamical field equations are obtained and shown to sustain cosmic inflation with a large number of e-folds. We emphasize that at the end of inflation, torsion vanishes and the theory of Einstein–Cartan reduces to the General Relativity with the usual FRW geometry.

The model of exponential electromagnetic field is coupled to Lovelock gravitational field in $d$-dimensional spacetime geometry. In this context, new class of magnetically charged nonsingular or regular Lovelock black holes has been introduced. The asymptotic behavior of resulting metric function in the vicinity of $r=0$ is studied. The obtained asymptotic expressions in both even and odd critical dimensions show the finiteness and regularity of the solution at $r=0$. The thermodynamic quantities such as Hawking temperature and specific heat capacity at constant magnetic charge corresponding to the nonsingular black hole are computed. The tunneling probability associated with Hawking radiations from these black holes is calculated as well.