No Arabic abstract
In this paper, we discuss the equation of state for nonlinear spinor gases in the context of cosmology. The mean energy momentum tensor is similar to that of the prefect fluid, but an additional function of state $W$ is introduced to describe the nonlinear potential. The equation of state $w(a)lesssim -1$ in the early universe is calculated, which provides a natural explanation for the negative pressure of dark matter and dark energy. $W$ may be also the main origin of the cosmological constant $Lambda$. So the nonlinear spinor gases may be a candidate for dark matter and dark energy.
The axion arises in well-motivated extensions of the Standard Model of particle physics and is regarded as an alternative to the weakly interacting massive particle paradigm to explain the nature of dark matter. In this contribution, we review theoretical aspects of dark matter axions, particularly focusing on recent developments in the estimation of their relic abundance. A closer look at their non-thermal production mechanisms in the early universe reveals the possibility of explaining the observed dark matter abundance in various mass ranges. The mass ranges predicted in various cosmological scenarios are briefly summarized.
Dark matter effects may be attributed to interactions between the Machian strings connecting every pair of elementary particles in the observable Universe. A simple model for the interaction between Machian strings is proposed. In the early Universe, the Machian strings of a density perturbation had a spherically symmetric distribution and the interaction with the Machian strings of a test particle is found to give a multiple of the Newtonian gravitational acceleration. In a strong gravitational field, the interaction between Machian strings tends to a constant limit in order to ensure the absence of dark matter effects in the Solar System. Dark matter effects on a galactic scale may be attributed to a change in the distribution of the Machian strings around a galaxy during the process of galaxy formation. The interaction between the Machian strings of a test mass and the Machian strings of a galaxy is considered in detail and the MOND phenomenology for galaxy rotation curves is obtained.
We analyze the potential of accelerator-based neutrino experiments, such as the Deep Underground Neutrino Experiment Near Detector, to constrain a five dimensional operator mediating a beyond standard model interaction between mass dimension one fermion fields, labeled elko, and neutrinos. We identify the parameter space where the fermion with mass dimension one is a viable dark matter candidate.
QCD is the fundamental theory to describe the strong interaction, where quarks and gluons have the color degrees of freedom. However, a single quark or gluon can not be separated out and all observable particles are color singlet states. Color confinement or quark confinement conjecture can be proved by considering not only the strong interaction but also the electroweak interaction which is $SU(3)_c$ invariant. Any measurable state has to be color singlet is the direct consequence of the common symmetry of the standard model. Color non-singlet objects are created from the big bang when the interaction breaks $SU(3)_c$ symmetry based on the nonlocal Lagrangian. There is nearly no interaction between colored objects and color singlet universe when the momentum transfer is not large enough. Colored objects are reasonable candidates of dark matter and the missing of anti-matter in the universe can also be easily explained. Dark matter can be produced in the laboratory which can be tested by measuring the energy loss and baryon number change in the extremely high energy collisions of particles and anti-particles.
Distortions of CMB temperature and polarization maps caused by gravitational lensing, observable with high angular resolution and sensitivity, can be used to constrain the sterile neutrino mass, m_s, from CMB data alone. We forecast m_s>1.75 keV from Planck and m_s>4.97 keV from Inflation Probe at 95% CL, by using the CMB weak lensing extraction.