Modern Physics Letters A

The formulation of covariant brackets on the space of solutions to a variational problem is analyzed in the framework of contact geometry. It is argued that the Poisson algebra on the space of functionals on fields should be read as a Poisson subalgebra within an algebra of functions equipped with a Jacobi bracket on a suitable contact manifold.

The analysis of the covariant brackets on the space of functions on the solutions to a variational problem in the framework of contact geometry initiated in the companion letter${}^{19}$ is extended to the case of the multisymplectic formulation of the free Klein–Gordon theory and of the free Schrödinger equation.

A novel reduction procedure for covariant classical field theories, reflecting the generalized symplectic reduction theory of Hamiltonian systems, is presented. The departure point of this reduction procedure consists in the choice of a submanifold of the manifold of solutions of the equations describing a field theory. Then, the covariance of the geometrical objects involved, will allow to define equations of motion on a reduced space. The computation of the canonical geometrical structure is performed neatly by using the geometrical framework provided by the multisymplectic description of covariant field theories. The procedure is illustrated by reducing the D’Alembert theory on a five-dimensional Minkowski space-time to a massive Klein–Gordon theory in four dimensions and, more interestingly, to the Schrödinger equation in 3 + 1 dimensions.

We consider thermodynamic properties of a quark–gluon plasma related to quasiparticles having the internal structure. For this purpose, we employ a possible analogy between quantum chromodynamics and non-Abelian Proca-Dirac-Higgs theory. The influence of characteristic sizes of the quasiparticles on such thermodynamic properties of the quark–gluon plasma like the internal energy and pressure is studied. Sizes of the quasiparticles are taken into account in the spirit of the van der Waals equation but we take into consideration that the quasiparticles have different sizes, and the average value of these sizes depends on temperature. It is shown that this results in a change in the internal energy and pressure of the quark–gluon plasma. Also, we show that, when the temperature increases, the average value of characteristic sizes of the quasiparticles increases as well. This leads to the occurrence of a phase transition at the temperature at which the volume occupied by the quasiparticles is compared with the volume occupied by the plasma.

We simulate proton–proton interactions to study densities and multiplicities of charged particles at center-of-mass energy, $\sqrt{s}=7$ TeV in the forward region and compare predictions with experimental findings of LHCb detector. We use different event generators: Sibyll2.3c, EPOS (1.99 and LHC tunes), and DPMJETIII for the simulations. The kinematic region for momentum $p>2\mathrm{\text{GeV}}/c$, transverse momentum $p_T>0.2\mathrm{\text{GeV}}/c$ and $2.0<\eta <4.8$ in pseudorapidity is kept same as in the LHCb experiment for forward region. Predictions of different models and experimental data are presented and compared as a function of transverse momentum and pseudorapidity.

In this paper, we use the complexity equals action proposal and investigate holographic complexity for hyperscaling violating theories on different subregions of space-time enclosed by the null boundaries. We are interested in computing the onshell action for certain subregions of the intersection between the Wheeler DeWitt patch and the past, as well as, the future interior of a two-sided black brane. More precisely, we extend the results of Ref. 1 in parts, to hyperscaling violating geometries and to find the finite onshell action, we define the proper counter terms. We show that in computing the rate of complexification the dynamical exponent plays a crucial rule, but, at the late time, rate of the complexity growth is independent of the hyperscaling parameters.

In our recently proposed quantum theory of gravity, the universe is made of ‘atoms‘” of space-time-matter (STM). Planck scale foam is composed of STM atoms with Planck length as their associated Compton wave-length. The quantum dispersion and accompanying spontaneous localization of these STM atoms amounts to a cancellation of the enormous curvature on the Planck length scale. However, an effective dark energy term arises in Einstein equations, of the order required by current observations on cosmological scales. This happens if we propose an extremely light particle having a mass of about $10^{-33}{\mathrm{\text{eV/c}}}^2$, forty-two orders of magnitude lighter than the proton. The holographic principle suggests there are about $10^{122}$ such particles in the observed universe. Their net effect on space-time geometry is equivalent to dark energy, this being a low energy quantum gravitational phenomenon. In this sense, the observed dark energy constitutes evidence for quantum gravity. We then invoke Dirac’s large number hypothesis to also propose a dark matter candidate having a mass halfway (on the logarithmic scale) between the proton and the dark energy particle, i.e. about $10^{-12}{\mathrm{\text{eV/c}}}^2$.

In this paper, we study the quasinormal modes of the massless Dirac field for charged black holes in Rastall gravity. The spherically symmetric black hole solutions in question are characterized by the presence of a power-Maxwell field, surrounded by the quintessence fluid. The calculations are carried out by employing the WKB approximations up to the 13th-order, as well as the matrix method. The temporal evolution of the quasinormal modes is investigated by using the finite difference method. Through numerical simulations, the properties of the quasinormal frequencies are analyzed, including those for the extremal black holes. Among others, we explore the case of a second type of extremal black holes regarding the Nariai solution, where the cosmical and event horizon coincide. The results obtained by the WKB approaches are found to be mostly consistent with those by the matrix method. It is observed that the magnitudes of both real and imaginary parts of the quasinormal frequencies increase with increasing $\kappa$, the spin–orbit quantum number. Also, the roles of the parameters $Q$ and $w$, associated with the electric charge and the equation of state of the quintessence field, respectively, are investigated regarding their effects on the quasinormal frequencies. The magnitude of the electric charge is found to sensitively affect the time scale of the first stage of quasinormal oscillations, after which the temporal oscillations become stabilized. It is demonstrated that the black hole solutions for Rastall gravity in asymptotically flat spacetimes are equivalent to those in Einstein gravity, featured by different asymptotical spacetime properties. As one of its possible consequences, we also investigate the behavior of the late-time tails of quasinormal models in the present model. It is found that the asymptotical behavior of the late-time tails of quasinormal modes in Rastall theory is governed by the asymptotical properties of the spacetimes of their counterparts in Einstein gravity.

We have studied the deformation systematics of $E(2_1^{+})$ and $R_{42}(=E(4_1^{+})/E(2_1^{+}))$ values, yrast spectra, band structure and backbending phenomena in the neutron-deficient even–even ${}^{100\text{–}110}$Cd isotopes within the projected shell model (PSM) framework. The observations of the systematics of $E(2_1^{+})$ and $R_{42}$ values for ${}^{100\text{–}110}$Cd isotopes are well reproduced in present calculations. Our observations show that, as we move from ${}^{100}$Cd to ${}^{108}$Cd, the deformation increases and then it reduces up to ${}^{110}$Cd. This gives us a confirmation that ${}^{108}$Cd is the most deformed nucleus in this set of isotopic mass chain. The backbending phenomena is also observed in these isotopes, which can be related to the crossing of ground band (g-band) by 2-quasiparticle (qp) bands or s-bands. The pseudomagic character of ${}^{100}$Cd has also been observed.