doi:10.1038/nindia.2015.168 Published online 16 December 2015
By analysing a new particle physics model, Indian physicists have thrown light on the identity of dark matter, the invisible stuff that far outweighs the visible matter such as stars, gas and dust in the universe1.
Using the model, they prove mathematically and computationally that the dark matter consists of a neutral particle much heavier than a proton.
“This Insight into the particle nature of dark matter will pave the development of new physics beyond the known realm of fundamental particle physics,” says researcher Debasish Majumdar, who worked with Kamakshya Prasad Modak from the Astroparticle Physics and Cosmology Division of Saha Institute of Nuclear Physics.
“This knowledge will help better understand the formation of cosmic structures such as galaxies and galaxy clusters in the universe where dark matter acts as the seed for mass accumulation,” Modak told Nature India.
The Standard Models of the universe and particle physics explain how elementary particles such as quarks, leptons, photons, electrons and positrons popped into existence in the early hot universe. As the universe began to cool, these elementary particles interacted with each other and coalesced to form atoms of various elements which eventually gave rise to visible matter such as stars and galaxies.
Physicists speculate that dark matter contributes to the formation of galaxies and cluster of galaxies. But, the Standard Model of particle physics does not incorporate dark matter that makes up five-sixths of the matter of the universe.
To fill this gap, the researchers proposed an extra inert Higgs doublet – one charged particle and two neutral particles in the new model known as Inert Higgs Doublet Model (IHDM). Using this model, they theoretically proved that the lighter of the two neutral particles is the dark matter particle, 63.5 times heavier than a proton.
The researchers say that the gamma rays originating from the annihilation of the dark matter particles can suitably explain the observed excess gamma ray flux emanating from the centre of the Milky Way galaxy and elsewhere in the universe.
Besides reshaping the current knowledge of particle physics, this study elucidates the nature of symmetries present in the early universe fractions of a second after its birth, Modak points out.
The research analyses all possible gamma ray sources that contribute to the extragalactic gamma ray signals, says physicist Venkatesh Singh, who studies dark matter at the Banaras Hindu University. Since Inert Higgs Doublet Model is an effective and viable model for particle dark matter, this model can be put to further test with data on indirect dark matter signals from future experimental results, Singh adds.
1. Modak, K. P. et al. Confronting galactic and extragalactic γ-ray observed by Fermi-LAT with annihilating dark matter in Inert Higgs Doublet Model. Astrophys. J. Suppl. 219, 37 (2015) doi: 10.1088/0067-0049/219/2/37