Exploring Cold Dark Matter with Unstable WIMPs

Dark matter is one of the biggest mysteries in modern physics. It is a form of matter that does not interact with light or ordinary matter, but influences the gravitational dynamics of the universe. Scientists estimate that dark matter makes up about 85% of the total matter in the universe, but its nature and origin remain unknown. One of the leading candidates for dark matter is the Weakly Interacting Massive Particle (WIMP), which arises naturally in some extensions of the standard model of particle physics. However, despite decades of searching, WIMPs have not been detected in laboratory experiments or astronomical observations. A new study by researchers from the Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology (DST), suggests that relaxing some of the assumptions about WIMPs could shed more light on the nature of cold dark matter (CDM), a subclass of dark matter that moves slowly compared to the speed of light.

Unstable WIMPs and cold dark matter

The study, published in the journal Physical Review D , was led by Professor Shiv Sethi from RRI and his collaborator Abineet Parichha, a former student at the Indian Institute of Science Education and Research, Mohali. The researchers considered the possibility that WIMPs are unstable and decay over time, instead of being stable as usually assumed. They showed that this scenario can satisfy all the existing constraints from cosmology and particle physics, and also make testable predictions for future observations. The researchers used a combination of analytical and numerical methods to explore the implications of unstable WIMPs for the evolution and structure of the universe. They found that unstable WIMPs can produce the correct amount of CDM in the early universe, as well as explain some of the anomalies in the cosmic microwave background (CMB), the relic radiation from the Big Bang. They also showed that unstable WIMPs can affect the formation and distribution of galaxies and clusters, and leave distinctive signatures in the cosmic neutrino background (CNB), the relic neutrinos from the Big Bang.

Implications and challenges

The study opens up a new perspective on dark matter and its possible connection to particle physics. It also challenges the conventional wisdom that WIMPs must be stable and massive, and provides a novel way to test the nature of CDM with cosmological data. However, the study also faces some challenges and limitations. For instance, the decay rate of WIMPs must be fine-tuned to match the observations, and the decay products must be compatible with other constraints from particle physics. Moreover, the study does not address the origin or mechanism of WIMP decay, which remains an open question for future research.


Dark matter is one of the most intriguing and elusive phenomena in physics. By relaxing some of the assumptions about WIMPs, a popular candidate for dark matter, researchers from RRI have found a new way to explore CDM, a major component of the universe. Their study shows that unstable WIMPs can explain various cosmological observations and make testable predictions for future experiments. Their study also challenges some of the established notions about WIMPs and CDM, and opens up new avenues for further investigation.

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