Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDirect couplings of mimetic dark matter and their cosmological effects
159
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The original mimetic model was proposed to take the role of dark matter. In this paper we consider possible direct interactions of the mimetic dark matter with other matter in the universe, especially the standard model particles such as baryons and photons. By imposing shift symmetry, the mimetic dark matter field can only have derivative couplings. We discuss the possibilities of generating baryon number asymmetry and cosmic birefringence in the universe based on the derivative couplings of the mimetic dark matter to baryons and photons.
rate research
Read More
It has been shown that the nonthermal spectrum of Hawking radiation will lead to information-carrying correlations between emitted particles in the radiation. The mutual information carried by such correlations can not be locally observed and hence is dark. With dark information, the black hole information is conserved. In this paper, we look for the spherically symmetric black hole solution in the background of dark matter in mimetic gravity and investigate the radiation spectrum and dark information of the black hole. The black hole has a similar spacetime structure to the Schwarzschild case, while its horizon radius is decreased by the dark matter. By using the statistical mechanical method, the nonthermal radiation spectrum is calculated. This radiation spectrum is very different from the Schwarzschild case at its last stage because of the effect of the dark matter. The mimetic dark matter reduces the lifetime of the black hole but increases the dark information of the Hawking radiation.
We study spherically symmetric solutions with a scalar field in the shift-symmetric subclass of the Horndeski theory. Constructing an effective energy-momentum tensor of the scalar field based on the two-fluid model, we decompose the scalar field into two components: dark matter and dark energy.We find the dark-matter fluid is pressure-less, and its distribution of energy density obeys the inverse-square law. We show the scalar field dark matter can explain the galaxy rotation curve and discuss the time evolution of the dark matter in the cosmic background.
Phenomenological implications of the Mimetic Tensor-Vector-Scalar theory (MiTeVeS) are studied. The theory is an extension of the vector field model of mimetic dark matter, where a scalar field is also incorporated, and it is known to be free from ghost instability. In the absence of interactions between the scalar field and the vector field, the obtained cosmological solution corresponds to the General theory of Relativity (GR) with a minimally-coupled scalar field. However, including an interaction term between the scalar field and the vector field yields interesting dynamics. There is a shift symmetry for the scalar field with a flat potential, and the conserved Noether current, which is associated with the symmetry, behaves as a dark matter component. Consequently, the solution contains a cosmological constant, dark matter and a stiff matter fluid. Breaking the shift symmetry with a non-flat potential gives a natural interaction between dark energy and dark matter.
The cosmological energy density $rho_{_{_Lambda}}$ at the Planck scale $M_{rm pl}$ drives inflation and simultaneously reduces its value to create the pair-energy density $rho_{_{_M}}$ via the continuous pair productions of massive fermions and antifermions. The decreasing $rho_{_{_Lambda}}$ and increasing $rho_{_{_M}}$, in turn, slows down the inflation to its end when the pair production rate $Gamma_M$ is larger than the Hubble rate $H$ of inflation. A large number of massive pairs is produced and reheating epoch starts. In addition to the Einstein equation and energy-conservation law, we introduce the Boltzmann-type rate equation describing the number of pairs produced from (annihilating to) the spacetime, and reheating equation describing massive unstable pairs decay to relativistic particles and thermodynamic laws. This forms a close set of four independent differential equations uniquely determining $H$, $rho_{_Lambda}$, $rho_{_M}$ and radiation-energy density $rho_{_R}$, given the initial conditions at inflation end. Numerical solutions demonstrate three episodes of preheating, massive pairs dominate and genuine reheating. Results show that $rho_{_Lambda}$ can efficiently convert to $rho_{_M}$ by producing massive pairs, whose decay accounts for reheating $rho_{_R}$, temperature and entropy of the Big-Bang Universe. The stable massive pairs instead account for cold dark matter. Using CMB and baryon number-to-entropy ratio measurements, we constrain the effective mass of pairs, Yukawa coupling and degeneracies of relativistic particles. As a result, the obtained inflation $e$-folding number, reheating scale, temperature and entropy are in terms of the tensor-to-scalar ratio in the theoretically predicated range $0.042lesssim r lesssim 0.048$, consistently with current observations.
The recent observation of the the gravitational wave event GW170817 and of its electromagnetic counterpart GRB170817A, from a binary neutron star merger, has established that the speed of gravitational waves deviates from the speed of light by less than one part in $10^{15}$. As a consequence, many extensions of General Relativity are inevitably ruled out. Among these we find the most relevant sectors of Horndeski gravity. In its original formulation, mimetic gravity is able to mimic cosmological dark matter, has tensorial perturbations that travel exactly at the speed of light but has vanishing scalar perturbations and this fact persists if we combine mimetic with Horndeski gravity. In this work, we show that implementing the mimetic gravity action with higher-order terms that break the Horndeski structure yields a cosmological model that satisfies the constraint on the speed of gravitational waves and mimics both dark energy and dark matter with a non-vanishing speed of sound. In this way, we are able to reproduce the $Lambda$CDM cosmological model without introducing particle cold dark matter.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
