Light dark matter
Light dark matter, in astronomy and cosmology, are dark matter weakly interacting massive particles (WIMPS) candidates with masses less than 1 GeV. These particles are heavier than warm dark matter and hot dark matter, but are lighter than the traditional forms of cold dark matter, such as Massive Compact Halo Objects (MACHOs). The Lee-Weinberg bound limits the mass of the favored dark matter candidate, WIMPs, that interact via the weak interaction to 
  
    
      
        ≈
        2
      
    
    {\displaystyle \approx 2}
   GeV. This bound arises as follows. The lower the mass of WIMPs is, the lower the annihilation cross section, which is of the order 
  
    
      
        ≈
        
          m
          
            2
          
        
        
          /
        
        
          M
          
            4
          
        
      
    
    {\displaystyle \approx m^{2}/M^{4}}
  , where m is the WIMP mass and M the mass of the Z-boson.