International Journal of Modern Physics D

We review our recent theoretical results about inequivalence between passive and active gravitational masses and energy in the semiclassical variant of general relativity, where the gravitational field is not quantized but matter is quantized. To this end, we consider the simplest quantum body with internal degrees of freedom — a hydrogen atom. We concentrate our attention on the following physical effects, related to electron mass. The first one is the inequivalence between passive gravitational mass and energy at the microscopic level. Indeed, the quantum measurement of gravitational mass can give a result which is different from the expected one, $m\ne m_e+\frac{E_1}{c^2}$, where the electron is initially in its ground state; $m_e$ is the bare electron mass. The second effect is that the expectation values of both the passive and active gravitational masses of stationary quantum states are equivalent to the expectation value of the energy. The most spectacular effects are the inequivalence of the passive and active gravitational masses and the energy at the macroscopic level for an ensemble of coherent superpositions of stationary quantum states. We show that, for such superpositions, the expectation values of passive and active gravitational masses are not related to the expectation value of energy by Einstein’s famous equation, $m\ne \frac{E}{c^2}$. In this paper, we also improve several drawbacks of the original pioneering works.

Cosmological and astrophysical surveys from radio to far-infrared, in both temperature and polarization, offer a unique view of the universe properties and of the formation and evolution of its structures. The last release, close to be finalized, of the Planck mission results sets the scene for cosmological models and parameters, while the comparison with other types of data sets raises the issue of possible tensions about some parameters, first of all the Hubble constant. At the same time, on the extragalactic side, Planck carried out the deepest systematic all-sky survey of SZ galaxy clusters and detected thousands of dusty galaxies and many hundreds of extragalactic radio sources, also allowing us to investigate many specific topics, including molecular hydrogen clouds in galactic halos. The exploitation of future generation of CMB missions and the next radio facilities will allow us to deeply investigate several topics in cosmology and astrophysics, from the existence of primordial gravitational waves to the energy releases in the primeval plasma, from the dawn ages and the epoch of reionization to the formation and evolution of early galaxies and clusters, while a wide set of open astrophysical problems can be studied with future IR missions.

DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna. The most important objective of DECIGO, among various sciences to be aimed at, is to detect gravitational waves coming from the inflation of the universe. DECIGO consists of four clusters of spacecraft, and each cluster consists of three spacecraft with three Fabry–Perot Michelson interferometers. As a pathfinder mission of DECIGO, B-DECIGO will be launched, hopefully in the 2020s, to demonstrate technologies necessary for DECIGO as well as to lead to fruitful multimessenger astronomy. B-DECIGO is a small-scale or simpler version of DECIGO with the sensitivity slightly worse than that of DECIGO, yet good enough to provide frequent detection of gravitational waves.

The LISA space mission requires laser frequency pre-stabilization of the 1064nm laser sources. While cavity-based systems are the current baseline, laser frequencies stabilized to a hyperfine transition in molecular iodine near 532nm are a possible alternative. Several setups with respect to space applications were developed, putting special emphasis on compactness and mechanical and thermal stability of the optical setup. Vibration testing and thermal cycling were performed. These setups show frequency noise below 20Hz/$\sqrt{\mathrm{\text{Hz}}}$ for frequencies between 4mHz and 1Hz with an absolute frequency reproducibility better than 1kHz. They fulfil the LISA requirements and offer an absolute laser frequency simplifying the initial spacecraft acquisition procedure. We present the current status of iodine-based frequency references and their applicability in space missions, especially within the LISA mission.

When photons from distant galaxies and stars pass through our neighboring environment, the wavelengths of the photons would be shifted by our local gravitational potential. This local gravitational redshift effect can potentially have an impact on the measurement of cosmological distance–redshift relation. Using available supernovae data, Wojtak, Davis and Wiis [J. Cosmol. Astropart. Phys. 2015 (2015) 025] found seemingly large biases of cosmological parameters for some extended models (nonflat $\mathrm{\Lambda }$CDM, $w$CDM, etc.). Huang [Phys. Rev. D 91 (2015) 121301] pointed out that, however, the biases can be reduced to a negligible level if cosmic microwave background (CMB) data are added to break the strong degeneracy between parameters in the extended models. In this paper, we forecast the cosmological bias due to local gravitational redshifts for a future WFIRST-like supernovae survey. We find that the local gravitational redshift effect remains negligible, provided that CMB data or some future redshift survey data are added to break the degeneracy between parameters.

We use the exact analytical solution of the radial part of the Klein–Gordon equation describing a charged massive scalar field in the electrically charged Garfinkle–Horowitz–Strominger dilaton black hole spacetime, given in terms of the confluent Heun functions, to study the physical phenomena related to resonant frequencies associated with this field, and also to examine some aspects related to its Hawking radiation. The special case of a Schwarzschild spacetime is also considered.

In this paper, we study an interacting new holographic dark energy model (NHDE) in DGP braneworld with a spatially flat FRW universe. Mainly, in this study we concentrate our attention on both interacting and noninteracting forms of the model. The study shows that the equation of state and the deceleration parameter depict an accelerated universe for all variety of interactions. On the other hand, the StateFinder analysis shows that the interacting and noninteracting behave similar to both quintessence and phantom dark energy and for the present value obey the behavior of quintessence. Moreover, the result of $Om$-diagnostic emphasizes on the result of the equation of state showing that the current model in high–$z$ stays in the quintessence era and in the late time has the Phantom-like behavior. By the use of the squared sound speed $v_s^2$ we find that the present mode has a good stability. In order to obtain the best fit values of the parameters in this work, we used the latest observational data (Pantheon, Boss DR12 and Planck 2015) implementing MCMC method by the use of EMCEE python package. We also employ AkaikeInformation Criterion (AIC) and Bayesian Information Criterion (BIC) model selection tools and comparethe model with both $\mathrm{\Lambda }$CDM and holographic Ricci dark energy as the reference models. We observe that the evidence against the interacting and noninteracting NHDE with consideration of both references is strongly positive and BIC rules out the NHDE model. Generally, the results of AIC and BIC state that the observational data do not favor the NHDE model.

We use the deep learning algorithm to learn the Reissner–Nordström (RN) black hole metric by building a deep neural network. Plenty of data are determined in boundary of AdS and we propagate them to the black hole horizon through AdS metric and equation of motion (e.o.m). We label these data according to the values near the horizon, and together with initial data they constitute a data set. Then we construct corresponding deep neural network and train it with the data set to obtain the Reissner–Nordström (RN) black hole metric. Finally, we discuss the effects of learning rate, batch-size and initialization on the training process.

Constraining the dark energy equation of state, $w_x(z)$, is one of the main issues of current and future cosmological surveys. In practice, this requires making assumptions about the evolution of $w_x$ with redshift $z$, which can be manifested in a choice of a specific parametric form where the number of cosmological parameters play an important role in the observed cosmic acceleration. Since any attempt to constrain the EoS requires some prior fixing in one form or the other, settling a method to constrain cosmological parameters is of great importance. In this paper, we provide a straightforward approach to show how cosmological tests can be improved via a parametric methodology based on cosmography. Using Supernovae Type IA samplers, we show how by performing a statistical analysis of a specific dark energy parametrization can give directly the cosmographic parameters values.

We consider the Kepler two-body problem in presence of the cosmological constant $\mathrm{\Lambda }$. Contrary to the classical case, where finite solutions exist for any angular momentum of the system $L$, in presence of $\mathrm{\Lambda }$ finite solutions exist only in the interval $0<L<L_{\mathrm{\text{lim}}}(\mathrm{\Lambda })$. The qualitative picture of the two-body motion is described, and critical parameters of the problem are found. Application is made to the relative motion of the Local Group and Virgo cluster.

Generally the Brans–Dicke (BD) theory reduces to general relativity (GR) in the limit $\omega \to \infty$ if the scalar field goes as $\varphi \propto 1/\omega$. However, it is also known that there are examples with $\varphi \propto 1/\sqrt{\omega }$ that does not tend to GR. We discuss another case: a homogeneous and isotropic universe filled with stiff matter. The power of time dependence of these solutions does not depend on $\omega$, and there is no GR limit even though we have $\varphi \propto 1/\omega$. A perturbative and a dynamical system analysis of this exotic case are carried out.

The logarithmic $R^2$-corrected $F(R)$ gravity is investigated as a prototype model of modified gravity theories with quantum corrections. By using the auxiliary field method, the model is described by the general relativity with a scalaron field. The scalaron field can be identified as an inflaton at the primordial inflation era. It is also one of the dark matter candidates in the dark energy (DE) era. It is found that a wide range of the parameters is consistent with the current observations of CMB fluctuations, DE and dark matter.

We derive an exact static solution in diverse dimension, without any constraints, to the field equations of $f(T)$ gravitational theory using a planar spacetime with two unknown functions, i.e. $b(r)$ and $b_1(r)$. The black hole solution is characterized by two constants, $c_1$ and $c_2$, one is related to the mass of the black hole, $c_1$, and the other is responsible to make the solution deviate from the teleparallel equivalent of general relativity (TEGR). We show that the analytic function $f(T)$ depends on the constant $c_2$ and becomes constant function when $c_2=0$ which corresponds to the TEGR case. The interesting property of this solution is the fact that it makes the singularity of the Kretschmann invariant much softer than the TEGR case. We calculate the energy of this black hole and show that it is equivalent to ADM mass. Applying a coordinate transformation, we derive a rotating black hole with nontrivial values of the torsion scalar and $f(T)$. Finally, we examine the physical properties of this black hole solution using the laws of thermodynamics and show that it has thermodynamical stability.

In this work, we study constant-roll inflation driven by a scalar field with nonminimal derivative coupling to gravity, via the Einstein tensor. This model contains a free parameter, $\eta$, which quantifies the nonminimal derivative coupling and a parameter $\alpha$ which characterizes the constant-roll condition. In this scenario, using the Hamilton–Jacobi-like formalism, an ansatz for the Hubble parameter (as a function of the scalar field) and some restrictions on the model parameters, we found new exact solutions for the inflaton potential which include power-law, de Sitter, quadratic hilltop and natural inflation, among others. Additionally, a phase-space analysis was performed and it is shown that the exact solutions associated to natural inflation and a “cosh-type” potential, are attractors.

Static black hole with the Power Maxwell invariant (PMI), Born–Infeld (BI), logarithmic (LN), exponential (EN) electromagnetic fields in three-dimensional spacetime with cosmological constant was studied. It was shown that the LN and EN fields represent the Born–Infeld type of nonlinear electrodynamics. It the framework of General Relativity the exact solutions of the field equations were obtained, corresponding thermodynamic functions were calculated and the $P-V$ criticality of the black holes in the extended phase-space thermodynamics was investigated.

We investigate the cosmological dynamics of interacting dark energy models in which the interaction function is nonlinear in terms of the energy densities. Considering explicitly the interaction between a pressureless dark matter and a scalar field, minimally coupled to Einstein gravity, we explore the dynamics of the spatially flat FLRW universe for the exponential potential of the scalar field. We perform the stability analysis for three nonlinear interaction models of our consideration through the analysis of critical points and we investigate the cosmological parameters and discuss the physical behavior at the critical points. From the analysis of the critical points we find a number of possibilities that include the stable late-time accelerated solution, $w$CDM-like solution, radiation-like solution and moreover the unstable inflationary solution.

We address the quantum estimation of parameters encoded into the initial state of two modes of a Dirac field described by relatively accelerated parties. By using the quantum Fisher information (QFI), we investigate how the weak measurements performed before and after the accelerating observer, affect the optimal estimation of information encoded into the weight and phase parameters of the initial state shared between the parties. Studying the QFI, associated with weight parameter $𝜗$, we find that the acceleration at which the optimal estimation occurs may be controlled by weak measurements. Moreover, it is shown that the post-measurement plays the role of a quantum key for manifestation of the Unruh effect. On the other hand, investigating the phase estimation optimization and assuming that there is no control over the initial state, we show that the weak measurements may be utilized to match the optimal $𝜗$ to its predetermined value. Moreover, in addition to determination of a lower bound on the QFI with the local quantum uncertainty (LQU), we unveil an important upper bound on the precision of phase estimation in our relativistic scenario, given by the maximal steered coherence (MSC). We also obtain a compact expression of the MSC for general X states.