International Journal of Modern Physics A

We review the equation of state of QCD matter at finite densities. We discuss the construction of the equation of state with net baryon number, electric charge, and strangeness using the results of lattice QCD simulations and hadron resonance gas models. Its application to the hydrodynamic analyses of relativistic nuclear collisions suggests that the interplay of multiple conserved charges is important in the quantitative understanding of the dense nuclear matter created at lower beam energies. Several different models of the QCD equation of state are discussed for comparison.

In this paper, we study the essence of $f(R,T)$ gravitation theory in five-dimensional Universe and see the role of dark energy in the form of wet dark fluid in a Kaluza–Klein Universe. It is found that the dark energy is not exaggerated in contributing to the accelerating expansion of the Universe though the expansion is inherent as a result of the theory itself and due to the geometric contribution of matter. It is interesting to see that in some model it is found that there was some era before the beginning of the present era. Some of the models are seen to go to $\mathrm{\Lambda }$CDM models in late future as in Einstein gravitation theory, starting the evolution with a big bang. Most of the models undergo early inflation as well as late-time accelerating expansion thus defining as good models for real astrophysical situations, with dark energy playing fundamental role in these Universe. Most interesting observation from this investigation is that we can developed new isotropic and anisotropic models of Kaluza–Klein Universe.

The main purpose of this paper is to lay the foundations of generalizing the AdS/CFT (holography) idea beyond the conformal setting. The main tool is to find suitable realizations of the bulk and boundary via group theory. We use all ten families of classical real semisimple Lie groups $G$ and Lie algebras ${𝒢}$. For this are used several group and algebra decompositions: the global Iwasawa decomposition and the local Bruhat and Sekiguchi-like decompositions. The same analysis is applied to the exceptional real semisimple Lie algebras.

We discuss the specificity of the interactions of the electroweak gauge boson excitations in models with warped extra dimensions and the Standard Model fields living in the bulk. In particular, we show that the couplings of the gauge boson excitations $W^{\prime }$, $Z^{\prime }$, and ${\gamma }^{\prime }$ to the SM gauge bosons treated as the zero modes of the 5D gauge fields are either exactly equal to zero or very much suppressed. In the former case, the three-particle and four-particle interaction Lagrangians of the SM gauge bosons and their lowest excitations are found explicitly. Meanwhile, the couplings of $W^{\prime }$, $Z^{\prime }$, and ${\gamma }^{\prime }$ to the SM fermions are nonzero allowing for their production and decays. These are the characteristic features of the gauge boson excitations in models with warped extra dimensions, which distinguish them from the gauge boson excitations in other models beyond the SM.

We follow an old suggestion made by Stueckelberg that there exists an intimate connection between weak interaction and gravity, symbolized by the relationship between the Fermi and Newton’s constants. We analyze the hypothesis that the effect of matter upon the metric that represents gravitational interaction in general relativity is an effective one. This leads us to consider gravitation to be the result of the interaction of two neutral spinorial fields ($g$-neutrinos) ${\mathrm{\Psi }}_g$ and ${\mathrm{\Omega }}_g$ with all kinds of matter and energy. We present three examples with only one $g$-neutrino: two static and spherically symmetric configurations and a cosmological framework for an isotropic dynamical universe. Without self-interaction, the associated effective geometry is precisely the Schwarzschild metric. On the other hand, a self-interacting $g$-neutrino generates a new gravitational black hole.

In this paper, we explore the behavior and anisotropic structure of quark stellar models in the framework of massive Brans–Dicke gravity. The system of field equations, representing a static sphere, is formulated by incorporating the MIT bag model. We use the Karmarkar condition for embedding class-one to formulate a relativistic model corresponding to a well-behaved radial metric function. The values of unknown parameters are determined through the matching of internal and external space–times at the hypersurface. The observed masses and radii of the strange star candidates (RXJ 1856-37, Her X-1 and PSR J1614-2230) specify the solution. Further, we evaluate the impact of the massive scalar field on state parameters and investigate the viability as well as stability of the self-gravitating objects. It is found that the obtained values of the bag constant (corresponding to each star) lie within the accepted range. Moreover, the anisotropic structure meets the necessary viability and stability criteria.

We discuss supergravity inflation in braneworld cosmology for the class of potentials $V(\varphi )=\alpha {\varphi }^{n}exp(-{\beta }^m{\varphi }^m)$ with $m=1,2$. These minimal SUGRA models evade the $\eta$ problem due to a broken shift symmetry and can easily accommodate the observational constraints. In the high energy regime $V/\lambda \gg 1$, the numerical predictions and approximate analytic formulas are given for the scalar spectral index $n_s$ and tensor-to-scalar ratio $r$. The models with smaller $n$ are preferred while the models with larger $n$ are out of the $2\sigma$ region. Remarkably, the ${\rho }^2/\lambda$ correction to the energy density in Friedmann equation results in sub-Planckian inflaton excursions $\mathrm{\Delta }\varphi <1$.

We present a systematic study of transverse momentum $(p_T)$ spectra of charged particles in $p+p$ and Xe$+$Xe collisions at $\sqrt{s_{NN}}=5.44$ TeV. The published data of invariant yields of charged particles as a function of $p_T$ is taken from ALICE at LHC in the mid-pseudorapidity region $\left|\eta \right|<0.8$. The modified form of Tsallis distribution is used here to analyze the $p_T$ spectra of charged particles. The power law of Tsallis/Hagedorn form gives very good description of the charged particle spectra in $p+p$ collisions within a $p_T$ range of 0.15 GeV/$c$ to 50 GeV/$c$. When we go from $p+p$ collisions to heavy-ion (Xe$+$Xe) collisions, the original form of Tsallis/Hagedorn distribution is not able to describe the $p_T$ spectra of charged particles properly. This may be occurred due to the medium effects or the final state effects. Here we discuss two types of medium effects of charged particles in Xe$+$Xe collisions, one is the transverse flow in the low to intermediate $p_T$ region ($p_T\le 7$ GeV/$c$) and the other is the energy loss in the high $p_T$ region ($p_T>7$ GeV/$c$), using the modified Tsallis distribution.