المادة المظلمة و الطاقة المظلمة

It is well established by recent observations that the universe is made up of 74 per cent dark energy and 22 per cent dark matter while the rest is ordinary baryonic matter.  The nature and origin of dark energy and dark matter are still hotly debated. This is a vast interdisciplinary topic which is of paramount importance to modern particle physics, cosmology  and astrophysics. 

The most important model for dark energy is the cosmological constant. This is the energy of the vacuum in the presence of gravity. From the more fundamental particle physics (field and string theories) point of view the basic problem of dark energy and dark matter is reducible (at least in principle) to the problem of quantum gravity. At the current state of affairs only string theory has a quantum theory of gravity and thus can potentially address this problem in a consistent way. Unfortunately this is not easy to do in practice and thus we should content ourselves (at least at this stage) with simpler approaches. It seems that supersymmetry (or more precisely supergravity) is in all cases the first step in the right direction. We should also mention here that there is also a new proposed theory of quantum gravity known as Horava-Lifshitz gravity which is for many reasons more realistic than string theory.

Supersymmetry, now we mean minimal supersymmetric standard model (MSSM), is also potentially relevant to the issue of dark matter.  Although dark matter does not emit or absorb electromagnetic radiations at all energy scales its gravitational interactions dominate on all cosmological scales.  An excellent candidate for dark matter is neutralino which is the lightest supersymmetric stable particle formed from a linear combination of the supersymmetric partners of the photon, W^0 and the Higgs boson. Let us recall that in any supersymmetric theory to each boson we associate a fermion and to each fermion we associate a boson. In other words every particle has a super partner with the same mass but with a spin which differ by half a unit. As it turns out the neutralino can interact weakly with ordinary matter and it has mass of the order of Tev with a cosmological abundance equal Omega=1 in the current epoch of the universe and thus it can be identified with dark matter in the universe.

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