Physics of the Dark Universe最新文献

We analyse the orbital period decay in compact binary systems influenced by a fifth force and ultralight particle radiation, considering a general eccentric Keplerian orbit. The analysis provides constraints on the axion decay constant when orbital period decay involves axionic fifth force and axion radiation. The bound on axion coupling improves by an order of magnitude for high eccentricity binaries like the Hulse–Taylor binary. These bounds become stronger when considering both axion mediation and radiation. We also derive constraints on the strengths of the fifth force and radiation from GW170817 by measuring the Chirp mass, which depends on initial eccentricity. The coalescence time increases with higher initial eccentricity compared to the gravity-only scenario, highlighting the importance of accurately selecting initial eccentricity for setting bounds on fifth force searches in precision gravitational wave detection. Additionally, we provide model-independent estimates for dark matter capture by a binary system. The derived constraints can be further strengthened with the use of second and third generation gravitational wave detectors.

In this paper, we propose a model including four scalar fields coupled with general gravity theories, which is a generalization of the two-scalar model proposed in Phys. Rev. D 103 (2021) no.4, 044055, where it has been shown that any given spherically symmetric static/time-dependent spacetime can be realized by using the two-scalar model. We show that by using the four-scalar model, we can construct a model that realizes any given spacetime as a solution even if the spacetime does not have a spherical symmetry or any other symmetry. We also show that by imposing constraints on the scalar fields by using the Lagrange multiplier fields, the scalar fields become non-dynamical and they do not propagate. This tells that there does not appear any sound which is usually generated by the density fluctuation of the fluid. In this sense, the model with the constraints is a most general extension of the mimetic theory in JHEP 11 (2013), 135, where there appears an effective dark matter. The dark matter is non-dynamical and it does not collapse even under gravitational force. Our model can be regarded as a general extension of any kind of fluid besides dark matter. We may consider the case that the potential of the scalar fields vanishes and the model becomes a non-linear $\sigma$ model. Then our formulation gives a mapping from the geometry of the spacetime to the geometry of the target space of the non-linear $\sigma$ model via gravity theory although the physical meaning has not been clear. We also consider the application of the model to $f\left(Q\right)$ gravity theory, which is based on a non-metricity tensor and $Q$ is a scalar quantity constructed from the non-metricity tensor. When we consider the $f\left(Q\right)$ gravity in the coincident gauge where the total affine connections vanish, when $f\left(Q\right)$ is not a linear function of $Q$, spherically symmetric spacetime cannot be realized except in the case that $Q$ is a constant. The situation does not change if we use the two-scalar model, as we show. If we use the four-scalar model in this paper, however, spherically symmetric spacetime can be realized in the framework of $f\left(Q\right)$ gravity with the coincident gauge.

An ultralight gauge boson could address the missing cosmic dark matter, with its transverse modes contributing to a relevant component of the galactic halo today. We show that, in the presence of a coupling between the gauge boson and neutrinos, these transverse modes affect the propagation of neutrinos in the galactic core. Neutrinos emitted from galactic or extra-galactic supernovae could be delayed by $\delta t=\left(10^{-8}\text{–}10^1\right)$  s for the gauge boson masses $m_{A^{\prime }}=\left(10^{-23}\text{–}10^{-19}\right)$  eV and the coupling with the neutrino $g=10^{-27}\text{–}10^{-20}$. While we do not focus on a specific formation mechanism for the gauge boson as the dark matter in the early Universe, we comment on some possible realizations. We discuss model-dependent current bounds on the gauge coupling from fifth-force experiments, as well as future explorations involving supernovae neutrinos. We consider the concrete case of the DUNE facility, where the coupling can be tested down to $g\simeq 10^{-27}$ for neutrinos coming from a supernova event at a distance $d=10$  kpc from Earth.

In this study, we investigate the greybody factor of a (3+1)-dimensional black hole solution in the context of alternative $f\left(Q\right)$ gravity with minimum scalar field coupling. We obtain the radial equation by applying the Klein–Gordon equation and transforming it into a Schrodinger wave equation using the tortoise coordinate. This transformation enables us to determine the effective potential and its graphical behavior for different values of the coupling constant and relevant physical parameters. We obtain two solutions for the radial equation corresponding to the event and cosmological horizons. To determine the greybody factor and its behavior, we combine these two solutions in the intermediate regime. The greybody factor increases with an increase in radius and coupling constant. This indicates that in alternative gravity, the larger black hole will die sooner as compared to cosmic gravity.

We study the dynamics of homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker cosmological models with positive spatial curvature within the context of mimetic gravity theory by employing dynamical system techniques. Our analysis yields phase-space trajectories that describe physically relevant solutions, capturing various stages of cosmic evolution. We also employ Bayesian statistical analysis to constrain the cosmological parameters of the models, utilizing data from Type Ia supernovae and Hubble parameter data sets. The observational data sets provide support for the viability of mimetic gravity models, which can effectively describe the late-time accelerated expansion of the universe.

We analyze the orbital and oscillatory motion of test particles in the vicinity of a non-commutative black hole submerged in perfect fluid dark matter and derive analytical solutions for the specific angular momentum and radial profiles of energy. Using the effective potential approach, we discuss the stability of circular orbits. Furthermore, we calculate the innermost stable circular orbits. The effective force acting on particles has also been discussed. We find the expressions for frequencies of radial and latitudinal harmonic oscillations as a function of the black hole mass and the model’s parameters. The key features of quasi-periodic oscillations of test particles near the stable circular orbits in an equatorial plane of the black hole are discussed. Furthermore, Periastron precession has been discussed. We demonstrate that the parameters of the model have a strong influence on particle motion around black holes. By using the observational data of four different X-ray binary systems GRO J1655-40, XTE J1550-564, XTE J1859+226, and GRS 1915+105, within the scope of Monte Carlo Markov Chain, we constrain the involved parameters $\alpha$ and $\beta$. It is necessary to mention that our presented investigations through graphical behavior are viable with required physical behavior.

We investigate a modified cosmological model aimed at addressing the Hubble tension, considering revised dynamics in the late Universe. The model introduces a parameter $c$ affecting the evolution equations, motivated by a modified Poisson algebra inspired by effective Loop Quantum Cosmology. Our analysis includes diverse background datasets such as Cosmic Chronometers, Pantheon+ Type Ia Supernovae (with and without the SH0ES calibration), SDSS, DESY6 and DESI Baryon Acoustic Oscillations, and background information of the Cosmic Microwave Background. We find that the model alleviates the Hubble tension in most of the dataset combinations, with cases reducing discrepancies to below $1\sigma$ when including SH0ES. However, the model exhibits minimal improvement in the overall fit when compared to $\Lambda$CDM, and Bayesian evidence generally favors the standard model. Theoretical foundations support this approach as a subtle adjustment to low-redshift dynamics, suggesting potential for further exploration into extensions of $\Lambda$CDM. Despite challenges in data fitting, our findings underscore the promise of small-scale modifications in reconciling cosmological tensions.

The orbital and oscillatory motion of test particles around a non-rotating, conformally coupled charged black hole with scalar hair is studied in this work. The impact of the black hole parameters on particle motion is investigated. The stable circular orbits, specific angular momentum, and radial profiles with specific energy are computed using an analytical approach. We discuss the stability of circular orbits using the effective potential technique. We also compute the effective force and innermost stable circular orbits around a conformally connected charged black hole with scalar hair. In addition, we display the trajectories of particles around a conformally connected charged black hole with scalar hair and numerically integrate the equations of motion for the test particle. Additionally, we determine the formulae for the frequencies of latitudinal and radial harmonic oscillations about the mass of the black hole and the model’s parameters. The main characteristics of quasi-periodic oscillations close to stable circular orbits in the black hole’s equatorial plane are examined for test particles. Furthermore, the Periastron precession process is explored. We show particle motion around black holes strongly depends on the model parameters. It is important to note that the graphical behavior describing our findings is viable.

This paper finds an exact singular black hole solution in the presence of nonlinear electrodynamics as the source of matter field surrounded by a cloud of strings in $4D$ $AdS$ spacetime. Here, the presence of the cloud of string, the usual Bardeen solution, becomes singular. The obtained black hole solution interpolates with the $AdS$ Letelier black hole in the absence of both the deviation parameter and magnetic charge and interpolates with the $AdS$ Bardeen black hole in the absence of the deviation parameter and a cloud of strings parameter. We analyse the horizon structure and thermodynamics properties, including the stability of the resulting black hole, numerically and graphically. Thermodynamical quantities associated with the black hole get modified due to the nonlinear electrodynamics and cloud of strings. Moreover, we study the effect of a cloud of strings parameter, magnetic charge and deviation parameter on critical points and phase transition of the obtained black hole where the cosmological constant is treated as the thermodynamics pressure. The critical radius increases with increasing deviation parameter values and magnetic charge values. In contrast, the critical pressure and temperature decrease with increasing deviation parameters and magnetic charge values.