International Journal of Modern Physics A

This paper explores the effects of cloud of strings and quintessence on the thermodynamic features of the 4D Einstein–Gauss–Bonnet (EGB) Black Hole (BH). For this purpose, we have evaluated temperature, entropy, Gibb’s free energy and heat capacity of the 4D EGB BH in the presence of cloud of strings and quintessence. We have also shown the graphical behavior of all these physical quantities for various values of Gauss–Bonnet term $\alpha$, quintessence $q$, equation of state parameter $w$ and cloud of string $a=0,1,2,3$.

In this paper, we investigate properties of the conserved charge in general relativity, recently proposed by one of the present authors with his collaborators, in the inflation era, the matter dominated era and the radiation dominated era of the expanding Universe. We show that the conserved charge in the inflation era becomes the Bekenstein–Hawking entropy for de Sitter space, and it becomes the matter entropy and the radiation entropy in the matter and radiation dominated eras, respectively, while the charge itself is always conserved. These properties are qualitatively confirmed by a numerical analysis of a model with a scalar field and radiations. Results in this paper provide more evidences on the interpretation that the conserved charge in general relativity corresponds to entropy.

In this work, the mass spectrum of the first radial excitation axial vector meson nonet is considered in the framework of the nonrelativistic constituent quark model and Regge phenomenology. After that, we investigate the strong decay characteristics of these states within the ${}^3{P}_0$ model. The results are compared to values from other phenomenological models, and they may be beneficial in the prospective search for $2^3{P}_1$ meson nonets.

Cosmological Collider Physics gives us the opportunity to probe high-energy physics from observing the space–time fluctuations generated during inflation imprinted on the cosmic microwave background. In other words, it is a method to investigate physics on energy scales that cannot be reached by terrestrial accelerators by means of precise observations of the universe. In this paper, we focus on the case where the GUT scale is close to the energy scale of inflation, and calculate three-point function of inflaton by exchanging the Higgs boson in GUT at tree level. The results are found to be consistent with the current observed restrictions on non-Gaussianity without a drastic fine-tuning of parameters, and it might be possible to detect the signature of the Higgs boson in GUT by 21 cm spectrum, future LSS and future CMB depending on our model parameters.

We consider a scalar–tensor action model, both simple and peculiar at the same time, with a boundary term added that it is form-invariant both under the conformal transformation of the metric as well as under the reparametrization of the scalar field. Under this assumption, the boundary term proposed matches (except factors) with the Gibbons–Hawking–York term proposed in such a way it cancels the term(s) involving $\delta ({\partial }_{\lambda }{g}_{\mu \nu })$. A matter term is added to the action also. In the Jordan frame, the pure gravitational action becomes the Einstein–Hilbert action with a cosmological constant when the scalar field takes the constant value of their vev, ${\varphi }_0=〈0|\varphi |0〉$, which is no otherwise but the only stable minimum of the classical potential chosen which is logarithmic type. This potential presents a large plateau in which it is almost fully flat and the decay of the field from its initial value (assumed to be close to $M_P$) to vacuum draws a Low Field (or New Inflation) scenario. The model fits very well with the current paradigm of the universe and, under some assumptions, gives a good account of the value of the Higgs mass, the current value of the cosmological constant, e-folding, the Hubble parameter, the spectral index of scalar perturbations, etc. The model is not studied in Einstein’s frame. In this, only the expressions of the field and the potential, for a simple case, are achieved. As a result, we get that the nature of the decay of the initial value to its ground state for the scalar field, in this frame, should be by quantum tunneling and not by slow rolling.

Newton’s force law $\frac{dP}{dt}=F$ is derived from the Schrödinger equation for isolated macroscopic bodies, composite states of e.g. $N\sim 10^{25},10^{51},\dots$ atoms and molecules, at finite body temperatures. We first review three aspects of quantum mechanics (QM) in this context: (i) Heisenberg’s uncertainty relations for their center of mass (CM), (ii) the diffusion of the CM wave packet, and (iii) a finite body temperature which implies a metastable (mixed-) state of the body: photon emissions and self-decoherence. They explain the origin of the classical trajectory for a macroscopic body. The ratio between the range $R_q$ over which the quantum fluctuations of its CM are effective, and the body’s (linear) size $L_0$, $R_q∕L_0\lesssim 1$ or $R_q∕L_0\gg 1$, tells whether the body’s CM behaves classically or quantum mechanically, respectively. In the first case, Newton’s force law for its CM follows from the Ehrenfest theorem. We illustrate this for weak gravitational forces, a harmonic-oscillator potential, and for constant external electromagnetic fields slowly varying in space. The derivation of the canonical Hamilton equations for many-body systems is also discussed. Effects due to the body’s finite size such as the gravitational tidal forces appear in perturbation theory. Our work is consistent with the well-known idea that the emergence of classical physics in QM is due to the environment-induced decoherence, but complements and completes it, by clarifying the conditions under which Newton’s equations follow from QM, and by deriving them explicitly.