Full Energy-momentum Tensor Research Articles

Estimating nucleon substructure properties in a unified model of p-Pb and Pb-Pb collisions

We apply a well tested hybrid transport model, which couples viscous hydrodynamics to a hadronic afterburner, to describe bulk observables in proton-lead and lead-lead collisions at sNN=5.02TeV. The quark-gluon plasma (QGP) initial conditions are modeled using the parametric TRENTo model with additional nucleon substructure parameters to vary the number and size of hot spots inside each nucleon, followed by a pre-equilibrium free streaming stage to match the full energy-momentum tensor of the initial state onto viscous hydrodynamics. Initial condition and QGP medium parameters, such as the temperature dependence of the QGP shear and bulk viscosities, are then calibrated using Bayesian parameter estimation to describe charged particle yields, mean pT and anisotropic flow harmonics of both collision systems in a single self-consistent framework. We find that the hybrid model provides a compelling, simultaneous description of both collision systems using appropriately chosen model parameters, and present new posterior estimates for the size and shape of the nucleon and temperature dependence of QGP shear and bulk viscosities.

Pointlike Electric Charge in Gravitational Field Theory

The existence of charged elementary ’point particles’ still is a basically unsolved puzzle in theoretical physics.The present work takes a fresh look at the problem by including gravity—without resorting to string theory. Using Einstein’s equations for the gravitational fields in a general static isotropic metric with the full energymomentum tensor (for the charged material mass and the electromagnetic fields) as the source term, a novel exact solution with a well-defined characteristic radius emerges where mass and charge accumulate:—with being the ’classical’ radius associated with the total charge and where is the Schwarzschild radius belonging to the observable mass (for the electron one has m and m). The resulting ’Einstein-Maxwell’ gravitational electron radius can also be written as , where m is the fundamental Planck length and the fine-structure constant, which yields m

Effects of initial-state dynamics on collective flow within a coupled transport and viscous hydrodynamic approach

We evaluate the effects of preequilibrium dynamics on observables in ultrarelativistic heavy-ion collisions. We simulate the initial nonequilibrium phase within A MultiPhase Transport (AMPT) model, while the subsequent near-equilibrium evolution is modeled using (2+1)-dimensional relativistic viscous hydrodynamics. We match the two stages of evolution carefully by calculating the full energy-momentum tensor from AMPT and using it as input for the hydrodynamic evolution. We find that when the preequilibrium evolution is taken into account, final-state observables are insensitive to the switching time from AMPT to hydrodynamics. Unlike some earlier treatments of preequilibrium dynamics, we do not find the initial shear viscous tensor to be large. With a shear viscosity to entropy density ratio of $0.12$, our model describes quantitatively a large set of experimental data on Pb+Pb collisions at the Large Hadron Collider(LHC) over a wide range of centrality: differential anisotropic flow $v_n(p_T) ~(n=2-6)$, event-plane correlations, correlation between $v_2$ and $v_3$, and cumulant ratio $v_2\{4\}/v_2\{2\}$.

The effect of backreaction on inflationary Brans–Dicke cosmology

In this paper, we study the effect of the quantum backreaction on Brans–Dicke cosmology in inflation era. We consider an inflaton field in the [Formula: see text]-dimensional spacetime in the framework of Brans–Dicke model. We use a new notation for the Brans–Dicke field in terms of the dilaton field. Then we obtain the vacuum expectation value of the full energy–momentum tensor using WKB approximation of the mode functions which satisfy the equations of motion. The obtained vacuum expectation values of energy–momentum tensor are divergent. In order to renormalize it, we introduce a constant cut-off [Formula: see text]. The vacuum expectation value of energy–momentum tensor is separated to the UV and IR parts by using [Formula: see text] cut-off. Then, we use the dimensional regularization method to eliminate divergences by introducing a counterterm action. Also, we calculate the IR contribution of the vacuum expectation value of energy–momentum tensor. Thus, we obtain a physically finite result for the quantum energy–momentum tensor. Finally, we find the effect of backreaction on scale factor.

The effect of backreaction of non-minimally coupled massless quintom fields in FLRW universe

In this paper the quantum backreaction of non-minimally coupled massless quintom fields in FLRW universe has been discussed. quintom model contains two massless scalar fields where one of scalar fields has positive kinetic energy and another one has negative kinetic energy term. In this model, we obtain the vacuum expectation value of the full energy–momentum tensor in different cosmological eras including inflation, radiation and matter dominated eras on FRLW universe with constant \(\epsilon \). This quantity is divergent in different cases. In order to renormalize it, we separate the vacuum expectation values of the full energy–momentum tensor to the UV and IR parts by using \(\mu \) cutoff. Then we eliminate the UV divergences by introducing a counterterm action and adding it to the action of the model. Also we calculate the IR part of the energy–momentum tensor during inflation and different transitions. For this purpose, we assume that the transition from one period to the next happens fast. Therefore we use a sudden transition approximation at matching time. In order to study behavior of the backreaction, we obtain the ratio of the dominant contribution of quantum energy density to the corresponding background quantity in different cosmological eras. Moreover, we show that the one-loop fluctuations of quintom model on de Sitter space give a contribution to the cosmological constant. Finally we obtain the effect of the quantum backreaction on the background geometry leading to new scale factor for cosmological eras.

Construction of topological field theories using the Batalin-Vilkovisky quantisation scheme

We discuss in detail the construction of topological field theories using the Batalin-Vilkovisky (BV) quantisation scheme. By carefully examining the dependence of the antibracket on an external metric, we show that differentiating with respect to the metric and the BRST charge do not commute in general. We introduce the energy-momentum tensor in this scheme and show that it is BRST invariant, both for the classical and quantum BRST operators. It is antifield dependent, guaranteeing gauge independence. For topological field theories, this energy-momentum has to be quantum BRST exact. This leads to conditions at each order in ħ. As an example of this procedure, we consider topological Yang-Mills thoery. We show how the reducible set of symmetries used in topological Yang-Mills can be recovered by means of trivial systems and canonical transformations. Self duality of the antighosts is properly treated by introducing an infinite tower of auxiliary fields. Finally, it is shown that the full energy-momentum tensor is classically BRST exact in the antibracket sense.

Local conservation laws for the Maxwell-Vlasov and collisionless kinetic guiding-center theories.

expressions for the and flux densities were determined. Here the full energy-momentum tensor and the angular momentum tensor are obtained via Noether's theorem. The appropriate symmetries of these tensors are shown and the local conservation laws are proven. These results are of importance for applications; e.g., knowledge of the total angular momentum combined with the can lead to an energy principle for linear stability analysis. The tensors are obtained in the usual way by first deter­ mining the general expression for an arbitrary variation of the total· Lagrangian density in normal position space x. We note, however, that there is a slight complication be­ cause the particle part of the Lagrangian is primarily defined on an extended space Y=(YY2) where y, is iden­ tical to x and Y2 is an additional coordinate that is needed in order to describe guiding centers. By means of transla­ tional invariance in x space and time, and rotational in­ variance in x space· the canonical tensors are obtained. These tensors are not gauge invariant, but each can be split into a divergence-free gauge-invariant part and a divergence-free non-gauge-invariant part. The gauge­ invariant energy-momentum tensor turns out to be sym­ metric in its spatial components. This is shown to follow from its relationship to the gauge-iI,lVariant part of the an­ gular momentum tensor. All of these expressions are also applicable to relativistic theories. Two applications are considered: first we treat the Maxwell-Vlasov equations and show that the gauge­ invariant parts of our tensors reduce to the usual well­ known expressions. Following this we treat the Maxwell­ kinetic guiding-center theory based on Littlejohn's guiding-center equations of motion.4