International Journal of Modern Physics A

We review the recent theoretical progress in the construction and solution of the evolution equations which govern the scale dependence for the twist-3 structure and fragmentation functions of the nucleon.

The fractal characteristics of multiparticle final state are first studied in the $e^{+}{e}^{-}$ collision of $\sqrt{s}=250\mathrm{\text{GeV}}$, with the MC simulation generator Jetset7.4 and Herwig5.9. The results show that this multiparticle final state has a double-Hurst-exponent fractals characteristics, which means that the resulting NFM obeys the scaling law well using both the two sets of Hurst exponents to partition the three-dimensional phase space isotropically and anisotropically. Their fractal indices and the effective fluctuation strength are also predicted.

We study the gravitational baryogenesis mechanism for generating baryon asymmetry in the context of running vacuum models. Regardless of whether these models can produce a viable cosmological evolution, we demonstrate that they produce a nonzero baryon-to-entropy ratio even if the universe is filled with conformal matter. This is a sound difference between the running vacuum gravitational baryogenesis and the Einstein–Hilbert one, since in the latter case, the predicted baryon-to-entropy ratio is zero. We consider two well known and most used running vacuum models and show that the resulting baryon-to-entropy ratio is compatible with the observational data. Moreover, we also show that the mechanism of gravitational baryogenesis may constrain the running vacuum models.

The behavior of levels near the threshold of the lower continuum in superheavy H-like atoms with $Z\alpha >1$, caused by the interaction $\mathrm{\Delta }{U}_{\mathrm{\text{AMM}}}$ of the electron’s magnetic anomaly (AMM) dynamically screened at small distances $\ll 1/m$, with the Coulomb field of atomic nucleus is considered by taking into account the complete dependence of electron’s wave function (WF) on $Z\alpha$. It is shown that the calculation of the contribution caused by $\mathrm{\Delta }{U}_{\mathrm{\text{AMM}}}$ via both the quark structure and the whole nucleus, considered as a uniformly charged extended Coulomb source, leads to results, which coincide within the accepted precision of calculations. It is also shown that there appears some difference in results between perturbative and nonperturbative methods of accounting for the contribution from $\mathrm{\Delta }{U}_{\mathrm{\text{AMM}}}$ within the corresponding Dirac equation (DE) in favor of the latter. Moreover, the growth rate of the contribution from $\mathrm{\Delta }{U}_{\mathrm{\text{AMM}}}$ reaches its maximum at $Z\sim 140\text{–}150$, while by further increase of $Z$ into the supercritical region $Z\gg Z_{\mathrm{\text{cr}},1}$, the shift of levels caused by $\mathrm{\Delta }{U}_{\mathrm{\text{AMM}}}$ near the lower continuum decreases monotonically to zero. The last result is generalized to the whole self-energy contribution to the shift of levels and so to the possible behavior of radiative QED-effects with virtual photon exchange near the lower continuum.

The ATLAS report in August 2016 provided an upper limit for the pp$\to$diboson and $t\bar{t}$ cross-sections. We consider a pseudoscalar-mediated fermionic dark matter together with gluon and photon effective operators interacting with the pseudoscalar. Choosing the resonance mass being $m_{\rho }=200$, 750 GeV and 2 TeV, beside the relic density and the invisible Higgs decay constraints we constrain more the space of parameters with the diboson and $t\bar{t}$ cross-section upper bounds. We finally provide some benchmarks consistent with all the constraints. Having exploited a pseudoscalar mediator, the DM-nucleon cross-section is velocity suppressed so that the model evades easily the bounds put by the future direct detection experiments such as XENON1T.

In early 1970, it was postulated that there exists a zero spin quantum field, called Higgs field, that is present in all universe. The potential energy of the Higgs field is transferred to particles. Hence they acquire mass. These ideas were essential in fulfilling the basic need for a particle, called Higgs, with mass. These particles are called Higgs particles with spin zero with its mass to be $\sim$125 GeV. This raises the question as to its physical effects. If these particles are present, will they exhibit a Casimir effect and also obey the Stefan–Boltzmann Law? Assuming the dynamics of this field, will these effects change with temperature. The present calculation uses thermo field dynamics formalism to calculate temperature effects.

Motivated by the physics of strings and branes, we develop a class of Markov chain Monte Carlo (MCMC) algorithms involving extended objects. Starting from a collection of parallel Metropolis–Hastings (MH) samplers, we place them on an auxiliary grid, and couple them together via nearest neighbor interactions. This leads to a class of “suburban samplers” (i.e. spread out Metropolis). Coupling the samplers in this way modifies the mixing rate and speed of convergence for the Markov chain, and can in many cases allow a sampler to more easily overcome free energy barriers in a target distribution. We test these general theoretical considerations by performing several numerical experiments. For suburban samplers with a fluctuating grid topology, performance is strongly correlated with the average number of neighbors. Increasing the average number of neighbors above zero initially leads to an increase in performance, though there is a critical connectivity with effective dimension $d_{\mathrm{\text{eff}}}\sim 1$, above which “groupthink” takes over, and the performance of the sampler declines.

It is well known that the jet production data at LHC provide important constraints on the medium and large-$x$ gluon parton distribution function (PDF), as well as on the large-$x$ sea quarks. In this work, we study the impact of recent CMS measurements for the inclusive jet production at center-of-mass energy of $\sqrt{s}$=13 TeV on the PDFs and their uncertainties. To this aim, with use of the FastNLO and xFitter framework, we apply the parton distribution re-weighting procedure to study the impact of CMS data on two NLO modern CT14 and MMHT PDF sets. As a result, we found that the fit quality obtained using both of these PDF sets is very good. Moreover, the CMS data can impact both the central values and uncertainties of some PDFs especially at low and large $x$ regions. Overall, it is indicated that the CT14 PDFs compared with the MMHT ones are more affected. We emphasis that the inclusion of these data in a new global analysis of PDFs can improve the determination of the gluon and quark PDFs at both low and large $x$ regions.

In the Standard Model, flavor violating decays of the top quark and of the Higgs boson are highly suppressed. Further, the flavor violating decays of the top and of the Higgs are also small in MSSM and not observable in current or in near future experiment. In this work, we show that much larger branching ratios for these decays can be achieved in an extended MSSM model with an additional vector-like quark generation. Specifically, we show that in the extended model, one can achieve branching ratios for $t\to h^{0}c$ and $t\to h^{0}u$ as large as the current experimental upper limits given by the ATLAS and the CMS Collaborations. We also analyze the flavor violating quark decay of the Higgs boson, i.e. $h^0\to s\bar{b}+\bar{b}s$ and $h^0\to b\bar{d}+\bar{b}d$. Here again, one finds that the branching ratio for these decays can be as large as $O(1)\%$. The analysis is done with inclusion of the CP phases in the Higgs sector, and the effect of CP phases on the branching ratios is investigated. Specifically, the Higgs sector spectrum and mixings are computed involving quarks and mirror quarks, squarks and mirror squarks in the loops consistent with the Higgs boson mass constraint. The resulting effective Lagrangian with inclusion of the vector-like quark generation induce flavor violating decays at the tree level. In the analysis, we also include the experimental constraints from the flavor changing quark decays of the $Z$ boson. The test of the branching ratios predicted could come with further data from LHC13 and such branching ratios could also be accessible at future colliders such as the Higgs factories where the Higgs couplings to fermions will be determined with greater precision.

Within the framework of Becchi–Rouet–Stora–Tyutin (BRST) formalism, we discuss some novel features of a two (1+1)-dimensional (2D) non-Abelian 1-form gauge theory (without any interaction with matter fields). Besides the usual off-shell nilpotent and absolutely anticommutating (anti-)BRST symmetry transformations, we discuss the off-shell nilpotent and absolutely anticommutating (anti-)co-BRST symmetry transformations. Particularly, we lay emphasis on the existence of the coupled (but equivalent) Lagrangian densities of the 2D non-Abelian theory in view of the presence of (anti-)co-BRST symmetry transformations where we pin-point some novel features associated with the Curci–Ferrari (CF-)type restrictions. We demonstrate that these CF-type restrictions can be incorporated into the (anti-)co-BRST invariant Lagrangian densities through the fermionic Lagrange multipliers which carry specific ghost numbers. The modified versions of the Lagrangian densities (where we get rid of the new CF-type restrictions) respect some precise symmetries as well as a couple of symmetries with CF-type constraints. These observations are completely novel as far as the BRST formalism, with proper (anti-)co-BRST symmetries, is concerned.