Modern Physics Letters A

In this work, we study the temperature and chemical potential dependence of the masses of sigma and pion mesons as well as the quark condensate by using a SU(2) flavor version of the Nambu–Jona–Lassino model, introducing a prescription that mimics confinement. We have found that as the temperature increases, the mass of sigma shifts down, while the pion mass remains almost constant. On the other hand, the quark condensate decreases as the temperature and chemical potential increases. We have also analyzed the temperature and chemical potential dependence of the spectral function of the sigma meson, from which we observe at low values of T and $\mu$ an absence of a peak. Furthermore, as the Mott temperature is reached, its value increases abruptly and a distinct peak emerges, which is related with the dissociation of the sigma. For the case of $\mu =0$, the Mott dissociation is exhibited about the temperature of 189 MeV. We have also obtained the chiral phase diagram and the meson dissociation for different values of $\mu$. From these results, we can state a relation between chiral symmetry restoration and Mott dissociation.

The pseudorapidity $(\eta )$ dependence of charged-particles ratios in three transverse momentum $(p_T)$ regions, obtained by hadron production models, in proton–proton collisions at 7 TeV are compared with the measurements of LHCb detector. Compared to the experimental data, the ${\pi }^{-}/{\pi }^{+}$ ratios are independent of $p_T$ and $\eta$ and are very well predicted by all models (DPMJETIII, EPOS1.99, EPOS-LHC, HIJING1.383, QGSJETII-04 and Sibyll2.3c). All models predict the $K^{-}/K^{+}$ ratio at low $p_T$ for $\eta <3.4$, but underestimate afterward while reproducing the experimental data at medium and high $p_T$ very well. The $\bar{p}/p$ ratio is described by the models very well at high $\eta$ in the low and medium $p_T$ region. At high $p_T$, models predict the experimental data well, except Sibyll2.3c that slightly overestimates. The $K/\pi$ ratio is predicted by EPOS1.99, HIJING and Sibyll at low $\eta$ and EPOS-LHC, EPOS1.99 and Sibyll predicted at high $\eta$ for low $p_T$. For medium $p_T$, EPOS1.99 and Sibyll predict very well for $\eta >3$ while EPOS-LHC and HIJING models reproduce the data for $\eta <3$. All models underpredict the $K/\pi$ ratio for $p_T>1.2\mathrm{\text{GeV}}/c$. For the $p/\pi$ and $p/K$ ratios, only Sibyll and EPOS1.99 models could reproduce some regions of $p_T$ and $\eta$. None of the models satisfactorily predict all the ratios. the same particle ratios are well described by most of the models while the discrepancies occur mostly in predicting the different particles ratios.

Recently, a 4-index generalization of the Einstein theory has been proposed by Moulin [F. Moulin, Eur. Phys. J. C 77, 878 (2017)]. Using this method, we find the most general 2-index field equations derivable from the Einstein–Hilbert action. The application of Newtonian limit, the role of gravitational coupling constant and the effects of the properties of ordinary energy–momentum tensor in obtaining a 4-index gravity theory have been studied. We also address the results of building Weyl free 4-index gravity theory. Our study displays that both the Einstein and Rastall theories can be obtained as the subclasses of a 4-index gravity theory which shows the power of 4-index method in unifying various gravitational theories. It is also obtained that the violation of the energy–momentum conservation law may be allowed in 4-index gravity theory, and moreover, the contraction of 4-index theory generally admits a non-minimal coupling between geometry and matter field in the Rastall way. This study also shows that, unlike the Einstein case, the gravitational coupling constant of 4-index Rastall theory generally differs from that of the ordinary 2-index Rastall theory.

In this paper, we will consider a cosmological model with two topological transitions of the space. The smooth 4-dimensional spacetime of the model admits topological transitions of its 3-dimensional slices. The whole approach is inspired by a class of exotic smoothness structures on $S^3\times ℝ$. In particular, this class of smoothness structures induces two topological transitions. Then, we are able to calculate the energy scales as associated to these topological transitions. For the first transition we will get the value of the GUT scale and the energy of the second transition is at the electroweak scale. The topology of the exotic $S^3\times ℝ$ determines both, the energy of the scales by certain topological invariants, and the existence of the right-handed sterile neutrino. It is the input for the seesaw mechanism. Secondly, based on this model, we are able to calculate the neutrino masses which are in a very good agreement with experiments. Finally, we will speculate, again based on topology, why there are three generations of neutrinos and an asymmetry between neutrinos and anti-neutrinos.

In this paper, we have researched tachyon field, k-essence and quintessence dark energy (DE) models for Friedmann–Robertson–Walker (FRW) universe with varying G and $\mathrm{\Lambda }$ in f(R, T) gravitation theory. The theory of f(R, T) is proposed by Harko et al. [Phys. Rev. D 84, 024020, 2011]. In this theory, R is the Ricci scalar and T is the trace of energy–momentum tensor. For the solutions of field equations, we have used linearly varying deceleration parameter (LVDP), the equation of state (EoS) and the ratio between $\mathrm{\Lambda }$ and Hubble parameter. Also, we have discussed some physical behavior of the models with various graphics.

Differential yields of light flavored charged hadrons in $pp$ collision at 0.9 TeV in the transverse momentum $(p_T)$ ranging from 0.1–2.5 GeV/c with pseudorapidity $\left|\eta \right|<0.5$ are presented here. The spectra obtained by Monte Carlo simulations with event generators — EPOS 1.99, EPOS-LHC, QGSJETII-04 and Sibyll2.3c — are compared with the ALICE measurements. For ${\pi }^{\pm }$ mesons, EPOS1.99, EPOS-LHC and QGSJETII-04 described the ALICE measurement very well almost in the entire $p_T$ range except QGSJETII-04 which underpredicts with $p_T$ below 0.4 GeV/c. The Sibyll2.3c model slightly overpredicts for $p_T<1$ GeV/c and underpredicts afterwards. For $K^{\pm }$ mesons, all models describe the experimental data qualitatively, except at high $p_T$, where the models slightly underpredict. The EPOS-LHC and QGSJETII-04 models, at low $p_T$, describe the distribution of the experimental measurements very well in both cases of protons and anti-protons, whereas the former underpredicts and the latter overpredicts at higher $p_T$. The EPOS1.99 overpredicts at low $p_T$ below 1 GeV/c, whereas it reproduces the results well above it. Sibyll2.3c overpredicts the distribution over the entire range of $p_T$. Models described the average transverse momentum $〈p_T〉$ of these hadron species as a function of their mass, showing small rise in the average $p_T$ with the mass of the particles. The same has been observed by the STAR collaboration with measurements in $pp$ reactions at $\sqrt{s}$ = 200 GeV and also in $pp$ collisions at $\sqrt{s}$ = 900 GeV.

A useful method, known as statefinder diagnostic, which may differentiate one dark energy (DE) model from others is applied in this work to a holographic dark energy (HDE) model from Tsallis entropy, called the Tsallis holographic dark energy (THDE) model. The evolutionary trajectories of this model are plotted in the statefinder parameter — planes and $\omega -{\omega }^{\prime }$ plane, and it is observed that the parameter $\delta$ of this model plays a magnificent role from the statefinder and $\omega -{\omega }^{\prime }$ plane viewpoints. Eventually, the evolutionary trajectories are plotted considering two different values of THDE energy density (${\mathrm{\Omega }}_T^0$), ${\mathrm{\Omega }}_T^0=0.69$, in the light of Planck 2018 results VI base-LCDM cosmology and ${\mathrm{\Omega }}_T^0=0.73$, in the light of SNe + BAO + OHD + CMB observation data.

We examine the possibilities of nontrivial phenomena of time-invariant entanglement and freezing dynamics of entanglement for qutrit-qutrit quantum systems. We find no evidence for time-invariant entanglement, however, we do observe that certain quantum states freeze their entanglement after decaying for some time. It is interesting that quantum states are changing whereas their entanglement remains constant. We find that the combined action of decoherence free subspaces and subspaces where quantum states decay, facilitate this phenomenon. This study is an extension of similar phenomena observed for qubit-qubit systems, qubit-qutrit, and multipartite quantum systems. We examine nonlocality of a specific family of states and find the certain instances where the states still remain entangled, however, they can either loose their nonlocality at a finite time or remain nonlocal for all times.

In this paper, we simulated an appropriate model for an advanced breeding blanket of future TOKAMAK fusion reactors with solid breeder (Li₄SiO₄) building material in the form of pebble beds, ODS ferritic steel as structural material and Beryllium as neutron multiplier. With the MCNPX code, the efficiency of this proposed model for the production and self-sufficiency of tritium was investigated. Total tritium breeding ratio of 1.15 is achieved. The helium-cooled pebble bed system and parameters of temperature and pressure are investigated by COMSOL multiphysics simulating software. The temperature of helium as cooling gas never exceeded 530${}^{\circ }$C and the tolerable temperature of beryllium was obtained at 650${}^{\circ }$C. In the proposed design, it is adequate to enrich the ⁶Li to 40%.