Narrow Results

We discuss the possibility of quintessence in the dilatonic domain walls including the Randall–Sundrum brane world. We obtain the zero mode effective action for gravitating objects in the dilatonic domain wall. First we consider the four-dimensional (4D) gravity and the Brans–Dicke graviscalar with a potential. This can be further rewritten as a minimally coupled scalar with the Liouville-type potential in the Einstein frame. However this model fails to induce the quintessence on the dilatonic domain wall because the potential is negative. Second we consider the 4D gravity with the dilaton. In this case we also find a negative potential. Any negative potential gives us negative energy density and positive pressure, which does not lead to an accelerating universe. Consequently it turns out that the zero mode approach of the dilatonic domain wall cannot accommodate the quintessence in cosmology.

It has been shown that Brans–Dicke (BD) theory in anisotropic cosmological model can solve the quintessence problem and we have accelerated expanding universe without any quintessence matter. Also the flatness problem has been discussed in this context.

We consider a model of interacting cosmological constant/quintessence, where dark matter and dark energy behave as, respectively, two coexisting phases of a fluid, a thermally excited Bose component and a condensate, respectively. In a simple phenomenological model for the dark components interaction we find that their energy density evolution is strongly coupled during the universe evolution. This feature provides a possible way out for the coincidence problem affecting many quintessence models.

Based on recently proposed unified models for dark matter and energy which are constructed by introducing a generalized Chaplygin vacuum fluid, we suggest in this paper a new scenario for quintessential inflation which does not rely on the existence of a specific potential for the vacuum field, but on a generalization of the definition of the Hilbert–Einstein action for a massless scalar field conformally-coupled to gravity that contains an extra Lagrangian term for the generalized vacuum Chaplygin fluid and the corresponding new surface term.

We study the time variation of the fine structure constant driven by quintessential dark energy which is coupled to electromagnetism. By employing phenomenological quintessential models which provide the scalar field with maximal dynamics and satisfy the constraints from SNIa observations and the WMAP, we show that the fifth force experiments restrict the variation of the value of α at the decoupling epoch with respect to the present-day value from being less than about 0.1%.

Recent astrophysical observations of quasar absorption systems indicate that the fine structure constant α and the proton-electron mass ratio μ may have evolved through the history of the universe. Motivated by these observations, we consider the cosmological evolution of a quintessence-like scalar field ϕ coupled to gauge fields and matter which leads to effective modifications of the coupling constants and particle masses over time. We show that a class of models where the scalar field potential V(ϕ) and the couplings to matter B(ϕ) admit common extremum in ϕ naturally explains constraints on variations of both the fine structure constant and the proton-electron mass ratio.

Pseudo-Nambu–Goldstone bosons (pNGBs) are simple and elegant candidates for radiatively stable models of quintessence and inflation. In this brief review, we first examine the observational status of pNGB-driven quintessence and inflation. We then discuss the construction of theoretically as well as observationally viable models of cosmological pNGBs. Special emphasis will be given to the constructions of models compatible with the requirements from String Theory.

Recently we proposed a new approach to test dark energy models based on the observational data. In that work we focused particularly on quintessence models for demonstration and invoked a widely used parametrization of the dark energy equation of state. In this paper we take the more recent SN Ia, CMB and BAO data, invoke the same parametrization, and apply this method of consistency test to five dark energy models, including the ΛCDM model, the generalized Chaplygin gas, and three quintessence models: exponential, power-law and inverse-exponential potentials. We find that the exponential potential of quintessence is ruled out at the 95.4% confidence level, while the other four models are consistent with data. This consistency test can be efficiently performed since for all models it requires the constraint of only a single parameter space that by choice can be easily accessed.

The thermodynamic and spectroscopic behavior of Schwarzschild black hole surrounded by quintessence are studied. We have derived the thermodynamic quantities and studied their behavior for different values of quintessence parameter. We put the background spacetime into the Kruskal-like coordinate to find the period with respect to Euclidean time. Also assuming that the adiabatic invariant obeys Bohr–Sommerfeld quantization rule, detailed study of area spectrum and entropy spectrum have been done for special cases of the quintessence state parameter. We find that the spectra are equally spaced.

Power-law cosmology with scale factor as power of cosmic time, a ∝t^α, is investigated. We review and discuss value of α obtained from various types of observation. Considering dark energy dominant era in late universe from z < 0.5, we use observational derived results from Cosmic Microwave Background (CMB) (WMAP7), Baryon Acoustic Oscillations (BAOs) and observational Hubble data to find power exponent α and other cosmological variables. α is found to be 0.99 ±0.02 (WMAP7+BAO+H₀) and 0.99 ±0.04 (WMAP7). These values do not exclude possibility of acceleration at 1σ hence giving viability to power-law cosmology in general. When considering scenario of canonical scalar field dark energy with power-law cosmology, we derive scalar field potential, exact scalar field solution and equation of state parameter. We found that the scenario of power-law cosmology containing dynamical canonical scalar field predicts present equation of state parameter w_{ϕ, 0} = -0.449±0.030 while the wCDM with WMAP7 data (model independent, w constant) allows a maximum (+1σ) value of w_{ϕ, 0} at -0.70 which is off the prediction range. However, in case of varying w_ϕ, the w_{ϕ, 0} value predicted from quintessential power-law cosmology is allowed within 1σ uncertainty.

In this paper we study the properties of Schwarzschild black hole surrounded by quintessence matter. The main objective of the paper is to show the existence of Nariai type black hole for special values of the parameters in the theory. The Nariai black hole with the quintessence has the topology dS₂ ×S₂ with dS₂ with a different curvature than what would be expected for the Schwarzschild–de Sitter degenerate black hole. Temperature and the entropy for the Schwarzschild–de Sitter black hole and the Schwarzschild-quintessence black hole are compared. The temperature and the curvature are computed for general values of the state parameter ω.

Black hole thermodynamic stability can be determined by studying the nature of heat capacity of the system. For Schwarzschild black hole the heat capacity is negative, but in the quintessence field, this system shows a second-order phase transition, implying the existence of a stable phase. We further discuss the equation of state of the present system. While analyzing the quasinormal modes (QNM), we find that the massive scalar QNM frequencies in the complex ω plane shows a dramatic change when we plot it as a progressive function of quintessence state parameter. We also find the Hawking temperature of the system via the method of tunneling.

The late-time evolution of Dirac field around spherically symmetric black hole surrounded by quintessece is studied numerically. Our results show that for lower values of the quintessence state parameter ϵ, Dirac field decays as power-law tail but with a slower decay rate than the corresponding Schwarzschild case. But for ϵ<-1/3, all the ℓ-poles of the Dirac field give up the power-law decay form and relax to a constant residual field at asymptotically late-times. The value of this residual field for which the field settles down varies on different surfaces. It has the lowest value on the black hole event horizon, increases as the radial distance increases and maximizes on the cosmological horizon.

We propose a dynamical (quintessence) model of dark energy in the current Universe with a renormalizable (Higgs-like) scalar potential. We prove the viability of our model (after fine-tuning) for the certain range of the average scalar curvature values, and study the cosmological signatures distinguishing our model from the standard description of dark energy in terms of a cosmological constant.

In this paper, by using the effective potential for the photons, we analyze the null geodesics and all kinds of orbits corresponding to the energy levels for the Reissner–Nordström black hole surrounded by quintessence with and compare our results with those obtained for the Schwarzschild black hole surrounded by quintessence matter. We also investigate the circular orbits and calculate the angle of deflection of the photons.

In the present work, a hidden scenario which cast a long-lived superheavy particle $A^0$ and simultaneously an extremely light particle $a$ with mass $m_a\sim 10^{-32}\text{–}10^{-33}$ eV is presented. The potential energy $V(a)$ of the particle $a$ models the vacuum energy density of the universe ${\rho }_c\simeq 10^{-47}{\mathrm{\text{GeV}}}^4$. On the other hand, the $A^0$ particle may act as superheavy dark matter at present times and the products of its decay may be observed in high energy cosmic ray events. The hidden sector proposed here include light fermions with masses near the neutrino mass $m_{\nu }\sim 10^{-2}$ eV and superheavy ones with masses of the order of the GUT scale, interacting through a hidden SU(2)_L interaction which also affects the ordinary sector. The construction of such combined scenario is nontrivial since the presence of light particles may spoil the stability of the heavy particle $A^0$. However, double Higgs mechanisms may be helpful for overcoming this problem. In this context, the stability of the superheavy particle $A^0$ is ensured due to chiral symmetry arguments elaborated in the text.

We calculate the Casimir energy of a massless scalar field in a cavity formed by nearby parallel plates orbiting a rotating spherical body surrounded by quintessence, investigating the influence of the gravitational field on that energy, at zero temperature. This influence includes the effects due to the spacetime dragging caused by the source rotation as well as those ones due to the quintessence. We show that the energy depends on all the involved parameters, as source mass, angular momentum and quintessence state parameter, for any radial coordinate and polar angle. We show that at the north pole the Casimir energy is not influenced by the quintessential matter. At the equatorial plane, when the quintessence is canceled, the result obtained in the literature is recovered. Finally, constraints in the quintessence parameters are obtained from the uncertainty in the current measurements of Casimir effect.

This comment is devoted to the recalculation of the Casimir energy of a massless scalar field in the Kerr black hole surrounded by quintessence derived in [B. Toshmatov, Z. Stuchlík and B. Ahmedov, Eur. Phys. J. Plus132, 98 (2017)] and its comparison with the results recently obtained in [V. B. Bezerra, M. S. Cunha, L. F. F. Freitas and C. R. Muniz, Mod. Phys. Lett. A32, 1750005 (2017)] in the spacetime [S. G. Ghosh, Eur. Phys. J. C76, 222 (2016)]. We have shown that in the more realistic spacetime which does not have the failures illustrated here, the Casimir energy is significantly bigger than that derived in [V. B. Bezerra, M. S. Cunha, L. F. F. Freitas and C. R. Muniz, Mod. Phys. Lett. A32, 1750005 (2017)], and the difference becomes crucial especially in the regions of near horizons of the spacetime.

In this paper, we study the thermodynamic stability of quintessence in the background of homogeneous and isotropic universe model. For the evolutionary picture, we consider two different forms of potentials and investigate the behavior of different physical parameters. We conclude that the quintessence model expands adiabatically and this expansion is thermodynamically stable for both potentials with suitable model parameters.

We present an investigation on thermodynamics of two different types of black holes viz. Kiselev black hole (asymptotically flat) and Taub–NUT (non-asymptotically flat) black hole. We compute the thermodynamic variables like black hole’s Hawking temperature and entropy at the black hole’s event horizon. Further, we derive the heat capacity and examine it to study the thermal stability of the black holes. We also calculate the rate of emission, assuming the black holes radiate energy in terms of photons by tunneling. We graphically represent all the parameters including the rate of emission of the black holes and interpret them physically. We depict a comparative study of thermodynamics between the aforesaid types of black holes. We find the existence of a transition of phase. Finally, we obtain the quantum corrected thermodynamics on the basis of general uncertainty principle and it is seen from the quantum-corrected entropy that it contains the logarithmic term. We offer comparative studies on joint effect of generalized uncertainty principle parameter $\alpha$ along with the concerned black holes’ parameters on the thermodynamics.