Modern Physics Letters A

Latest observations by Riess and coworkers in 2017 have reconfirmed their earlier observation that the universe is accelerating some 8% faster than the currently accepted cosmological model described. In this paper, we argue that this discrepancy can be eliminated by considering a universe consisting only of matter and dark energy. Interestingly, recently Mark Swissbank, R. Genzel et al. have concluded that nearly en billion years ago dark matter concentration was negligible.

We consider a novel model of gravity with a scalar field described by the Lagrangian with higher-order derivative terms in a cosmological context. The model has the same solution for the homogeneous and isotropic universe as in the model with the Einstein gravity, notwithstanding the additional higher-order terms. Finally, a possible modification scenario is briefly discussed.

In this paper, we have searched the existence of bulk viscous Bianchi-I embedded cosmological model in $f(R,T)=f_1(R)+f_2(R)f_3(T)$ gravity by taking into account the simplest coupling between matter and geometry such that $f_1(R)=f_2(R)=R$ and $f_3(T)=\zeta T$ with $\zeta$ a constant. To obtain the deterministic solution, we assume the scale factor in hybrid form — product of power law and exponential type of function that describes a model of transitioning universe and explain the physical behavior of early universe as well as present universe. It has been found that in the presence of bulk viscosity, the solution is stable and in favor of realization of the energy conditions (ECs) which turn into imply the derived model agrees with the cosmological viability. Some physical aspects of the model have been also discussed.

This work deals with dynamical system analysis of Holographic Dark Energy (HDE) cosmological model with different infra-red (IR)-cutoff. By suitable transformation of variables, the Einstein field equations are converted to an autonomous system. The critical points are determined and the stability of the equilibrium points are examined by Center Manifold Theory and Lyapunov function method. Possible bifurcation scenarios have also been explained.

The transverse momentum spectra of ${\pi }^{\pm }$ mesons, protons and antiprotons produced in proton–proton collisions at 200 GeV with hadron production models are reported. Two tunes of EPOS (EPOS1.99 and EPOS-LHC), three tunes of QGSJET (QGSJETI, QGSJETII-03, QGSJETII-04), DPMJET and HIJING models are used to obtain the spectra. The results are compared with the measurements of STAR collaboration obtained at mid-rapidity of $\left|y\right|<0.5$ in $p_T$ range of $0.3<p_T<10\mathrm{\text{GeV}}/c$. All models reproduce the ratios ${\pi }^{-}/{\pi }^{+}$ and $\overline{p}/p$ at low $p_T$ but could not predict well at high $p_T$. In addition, EPOS tunes and QGSJET tunes predict well the spectra of ${\pi }^{\pm }$ meson and the ratios $p/{\pi }^{+}$ and $\overline{p}/{\pi }^{+}$ at low $p_T$. The HIJING and the QGSJET (tune I only) could reproduce all the spectra and all the ratios at a satisfactory level of precision and were found good among the models considered in the current study at RHIC energy.

We examine the possible unparticle effects on $R(D^{(\ast )})$ associated with $B\to D^{(\ast )}\tau \nu$ decays by minimum-${\chi }^2$ fitting. Recent measurements from Belle and LHCb are included in this analysis. While it is true that the new experimental results of $R(D^{(\ast )})$ get closer to the Standard Model (SM) predictions, there is still room for new physics and unparticles are also one possibility. Our best-fit values are $R(D)=0.456$ and $R(D^{\ast })=0.270$, which are still far from the SM values by more than $(R(D))$ or almost $(R(D^{\ast }))$ $2\sigma$. We also find that the unparticle effects are quite safe to render the branching ratio $\mathrm{\text{Br}}(B_c\to \tau \nu )$ less than 10%.

The transverse momentum distribution of the differential production cross-sections of heavy flavored charm hadrons $({\mathrm{\Lambda }}_c^{+},D^0,D^{+},D^{\ast }{(2010)}^{+}$, $D_s^{+})$ in pp collisions at 7 TeV are simulated. Predictions of DPMJETIII.17-1, HIJING1.383 and Sibyll2.3c are compared to the differential cross-section measurements of the LHCb experimental data presented in the region of $0<p_T<8\mathrm{\text{GeV}}/c$ and $2.0<y<4.5$, where the pp center of mass frame is used to measure the transverse momentum and rapidity. The models reproduce only some regions of $p_T$ and/or bins of $y$ but none of them predict completely all the $y$ bins over the entire $p_T$ range.

This paper concerns the construction of k-uniform maximally mixed multipartite states by using the formalism of phase states for finite dimensional systems (qudits). The k-uniform states are a special kind of entangled (n)-qudits states, such that after tracing out arbitrary (n$-$k) subsystems, the remaining (k) subsystems are maximally mixed. We recall some basic elements about unitary phase operators of a multi-qudit system and we give the corresponding separable density matrices. Evolved density matrices arise when qudits of the multipartite system are allowed to interact via an Hamiltonian of Heisenberg type. The expressions of maximally mixed states are explicitly derived from multipartite evolved phase states and their properties are discussed.