International Journal of Modern Physics A

Simulations of the Dirac equation have allowed to mimic measurably the predicted unusual characteristics of the electron motion, e.g. Zitterbewegung and Klein paradox that are beyond current technical capabilities. In this paper, it is shown that a Bose–Einstein condensate experiment carried out corroborates these results, but in addition exhibits a particular feature of an observable represented by a Dirac self-adjoint time operator introduced in relativistic quantum mechanics.

In this study, the effects of the generalized uncertainty principle on the theory of gravity are analyzed. Inspired by Verlinde’s entropic gravity approach and using the modified Unruh temperature, the generalized Einstein field equations with cosmological constant are obtained and corresponding conservation law is investigated. The resulting conservation law of energy–momentum tensor dictates that the generalized Einstein field equations are valid in a very limited range of accelerations. Moreover, the modified Newton’s law of gravity and the modified Poisson equation are derived. In a certain limit, these modified equations reduce to their standard forms.

We study the loop-induced decays $h^0\to \gamma \gamma$ and $h^0\to gg$ in the Minimal Supersymmetric Standard Model (MSSM) with quark flavor violation (QFV), identifying $h^0$ with the Higgs boson with a mass of 125 GeV, where $\gamma$ and $g$ are photon and gluon, respectively. We perform a MSSM parameter scan and a detailed analysis around a fixed reference point respecting theoretical constraints from vacuum stability conditions and experimental constraints, such as those from $B$-meson data and electroweak precision data, as well as recent limits on Supersymmetric (SUSY) particle masses from LHC experiments. We find that (i) the relative deviation of the decay width $\mathrm{\Gamma }(h^0\to gg)$ from the Standard Model value, $\mathrm{\text{DEV}}(g)$, can be large and negative, $\lesssim -15\%$, (ii) the analogous deviation of $\mathrm{\Gamma }(h^0\to \gamma \gamma )$ is strongly correlated, $\mathrm{\text{DEV}}(\gamma )\simeq -1/4\mathrm{\text{DEV}}(g)$ for $\mathrm{\text{DEV}}(g)\lesssim -4\%$, (iii) the relative deviation of the width ratio $\mathrm{\Gamma }(h^0\to \gamma \gamma )/\mathrm{\Gamma }(h^0\to gg)$ from the SM value, $\mathrm{\text{DEV}}(\gamma /g)$, can be large (up to $\sim$20%), (iv) the deviations can be large due to the up-type squark loop contributions, (v) the SUSY QFV parameters can have a significant effect on these deviations. Such large deviations can be observed at a future $e^{+}{e}^{-}$ collider like ILC. Observation of the deviation patterns as shown in this study would favor the MSSM with flavor-violating squark mixings and encourage to perform further studies in this model.

The possibility of physics beyond the Standard Model is studied. The requirement of finiteness of the zero-point energy density and pressure or the requirement of the Lorentz invariance of the zero-point stress-energy tensor in Minkowski space–time, implies regularization sum rules on the number of degrees of freedom and mass of fundamental particles spectrum. The consequences of these sum rules on the existence of particles beyond the Standard Model are studied. If these sum rules are to be satisfied, it is shown that some simple and minimal extensions of the Standard Model such as the two-Higgs-doublet model, right-handed neutrinos, mirror symmetry cannot be complete extensions in their current forms. The only exception is unbroken supersymmetry and may be broken supersymmetry. A comparison between different regularization schemes is also done. It is shown that while all considered regularization schemes give a Lorentz invariant expression for the zero-point stress-energy tensor in Minkowski space, their physical interpretations are quite different.

In this paper, we investigate the geodesic structure of Clifton–Barrow black hole space–time. Through the numerical analysis of the effective potential and the motion equation, the orbital types of test particles and photons and the corresponding orbital motion diagrams of each orbital types under certain conditions are obtained. We find that angular momentum $b$ and $\delta$ determine the existence of bound orbits and circular orbits. And we also find that the radius of unstable circular orbit decreases with increases in $b$ while the radius of stable circular orbit increases. Furthermore, as $\delta$ increases, the radius of unstable circular orbit increases, while the radius of stable circular orbit decreases. For null geodesic, parameters $b$ and $\delta$ do not affect the types of null orbits. The radius of the unstable circular orbits increases with the increase of $\delta$. However, the radius of the unstable circular orbits remains unchanged as $b$ increases. Also, we show that the precession direction of the bound orbits of the test particles is counterclockwise for $b=2.15$, but clockwise with $b=3.6$. Moreover, different energy values have an effect on the curvature of escape and absorb orbits curve.

We perform a numerical study to recognize the difference between various massive potentials in the massive gravity on the holographic thermalization in the AdS and AdS–Gauss–Bonnet gravities in 4+1 dimensions. In this space–time, three different massive potentials contribute to the graviton mass. We analyze the effects of these terms on the time evolution of entanglement entropy and the corresponding thermalization time. We also trace the effect of Gauss–Bonnet coupling on the thermalization process. The behavior of the holographic mutual information and size of the kinks, appearing in a large interval, are also studied.

We study the production of a light top-squark pair in association with the lightest Higgs boson $({\tilde{t}}_1{\tilde{t}}_1^{\ast }{h}_1)$, as predicted by the Next-to-Minimal Supersymmetric Standard Model (NMSSM) in proton–proton collisions at center-of-mass energies of 13 TeV and 33 TeV. We scan randomly about 10 million points of the NMSSM parameter space, allowing all possible decays of the lightest top-squark and lightest Higgs boson, with no further assumptions, except for known physical constraints such as perturbative bounds, dark matter relic density consistent with recent Planck experiment measurements, Higgs mass bounds on the next to lightest Higgs boson, $h_2$, assuming it is consistent with LHC measurements for the Standard Model Higgs boson, LEP bounds for the chargino mass and $Z$ invisible width, experimental bounds on $B$ meson rare decays and some LHC experimental bounds on SUSY particle spectra different to the particles involved in our analysis. We find that for low mass top-squark, the dominating decay mode is ${\tilde{t}}_1\to b{\tilde{\chi }}_1^{\pm }$ with ${\tilde{\chi }}_1^{\pm }\to W^{\pm }{\tilde{\chi }}_1^0$. We use three benchmark points with the highest cross-sections, which naturally fall within the compressed spectra of the top-squark, and make a phenomenological analysis to determine the optimal event selection that maximizes the signal significance over backgrounds. We focus on the leptonic decays of both $W$’s and the decay of the lightest Higgs boson into $b$-quarks $(h_1\to b\bar{b})$. Our results show that the high luminosity LHC will have limitations to observe the studied SUSY scenario and only a proton collider with a collision energy above 33 TeV will be able to observe this signal with more than three standard deviations over background, albeit for stop masses below 300 GeV.