Dark matter evidence and candidates There exists several pieces of evidence (see [60, 61] for a review) which indicate the existence of dark matter (DM). Xxxxx stated first, is that of Xxxx and Xxxxx’x [62] discovery in the 1970’s, and later evidence by Xxxxx [63] and Xxxxx et al [64],
Dark matter. Using the laws of particle physics, combined with Xxxxxxxx’x gravity we can model the evolution of the Universe and see in much detail how its current state has emerged from very simple initial conditions. In the modern era of precision cosmology detailed predictions of this picture are confirmed with high accuracy using astronomical ob- servations of various types [37]. Ironically, this success revealed one of the greatest mysteries of modern science: 95% of the total energy density of our Universe is com- posed of entities of unknown nature, see Fig. 1.2. In particular, we see that most of the matter in the Universe does not emit any light – dark matter. Indeed, numerous independent tracers of the gravitational potential (observations of the motion of stars in galaxies and galaxies in clusters; emissions from hot ionized gas in galaxy groups and clusters; 21 cm line in galaxies; both weak and strong gravitational lensing mea- surements) demonstrate that the dynamics of galaxies and galaxy clusters cannot be explained by the Newtonian potential created by visible matter only. Moreover, cosmological data (analysis of the cosmic microwave background anisotropies and of the statistics of galaxy number counts) show that the large scale structure of the Universe started to develop much before the decoupling of photons at the time of recombination of hydrogen and, therefore, much before ordinary matter could start clustering (for reviews see e.g. [38–40]). This body of evidence points at the existence of a new substance, distributed in objects of all scales and providing a contribution to the total energy density of the Universe at the level of about 25%. Various attempts to explain this phenomenon by the presence of macroscopic compact objects (such as, for example, old stars) or by modifications of the laws of gravity (or of dynamics) failed to provide a consistent description of all the above phenomena [41]. Therefore, a microscopic origin of the dark matter phenomenon (i.e., a new particle or particles) remains the most plausible hypothesis. Neutrinos are the only electrically neutral and long-lived particles in the Xxxx- dard Model. As the experiments show that neutrinos have mass, they could play the role of dark matter particles. Neutrinos are involved in weak interactions that keep these particles in the early Universe in thermal equilibrium down to temperatures of a few MeV. At lower temperatures, the interaction rate of weak reactions drops below the ...
Dark matter. The second puzzle of modern cosmology is the nature of dark matter. Similar to its dark energy counterpart, the presence of this component is necessary to explain a plethora of observations, but the details of its nature are still unknown. As opposed to dark energy, it should be noted that the existence of invisible material capable of interacting only gravitationally has never been a controversial statement. For most of the history of modern cosmology, however, it was assumed that this invisible material was simply extinguished stars, cool dim gas or microscopic bodies akin to asteroids. Only in the 1990s, with the advent of early Universe observations, it became apparent that the fraction of traditional matter formed in the primordial Universe was insucient, and a new, unfamiliar kind was needed. Before the era of precision gravitational xxxxxxx, xxx existence of dark matter could only be inferred through the motion of luminous matter in its gravitational potentials. Pioneering observations of these phenomena, performed by Xxxxx Xxxxxx (Xxxxxx, 1933), Xxxx Xxxxx (Xxxxx and Xxxx, 1970) and many others, eventually became the pri- mary justication behind the present-day paradigm of dark matter. Its fundamental principles are simple: dark matter should be cold and non-interacting. These two prop- erties are required to reproduce the observed distribution of structure in the Universe and match simulated data. In this context, cold represents the opposite of relativistic. Examples of relativistic species in the Universe are radiation and neutrinos, for which the majority of the energy is in the form of momentum instead of rest mass. This re- sults in high velocities that help relativistic particles stream away from gravitational potentials and makes them unable to form small structures. In the case of dark mat- ter, this suppression is not observed. The second property is connected to the fact that dark matter appears to interact only through gravitational forces. The argument behind this principle is also linked to the distribution of matter in the Universe. The existence of additional interactions would lead to more compact structures since kinetic energy would be dissipated into random motion more eciently than through gravitational interactions alone. Once again, this phenomenon is not observed in the real Universe. Finally, the non-interacting property of dark matter refers also to its inability to interact with baryons. Because the standard model of pa...
Dark matter electron scattering formalism Calculating precisely the predicted energy-dependent scattering event rate is crucial in constraining the scattering cross section in any direct detec- tion experiment as it improves discrimination of dark matter events against
