In the realm of astrophysics and particle physics, a team of researchers from the Indian Institute of Technology Guwahati, including M. Bhuyan, Jeet Amrit Pattnaik, S. K. Patra, and Sudhanwa Patra, has been delving into the mysteries of dark matter and its potential impact on neutron stars. Their recent study, published in the journal Physical Review D, explores how the fundamental nature of dark matter particles could influence the structure and observables of these ultra-dense stellar objects.
Dark matter, a mysterious and invisible form of matter that makes up approximately 27% of the universe, remains one of the most enigmatic components of the cosmos. One key question that has puzzled scientists is whether dark matter particles are Dirac or Majorana fermions. This distinction is crucial as it affects the internal degrees of freedom of these particles and, consequently, their behavior and interactions. Dirac fermions have four degrees of freedom, while Majorana fermions have only two. Understanding this fundamental characteristic could significantly impact dark-sector phenomenology and detection strategies.
The researchers focused their investigation on neutron stars, which are among the densest objects in the universe, offering extreme conditions that can provide unique insights into the properties of dark matter. By considering a scenario where fermionic dark matter is admixed with nuclear matter within neutron stars, the team examined how this admixture could modify the equation of state—the relationship between pressure, density, and energy—which in turn affects observable quantities such as the mass-radius relation and tidal deformability.
Using a relativistic mean-field framework extended by a scalar (or Higgs-like) portal coupling between dark matter and nucleons, the researchers constructed self-consistent equations of state for both Dirac and Majorana dark matter scenarios. They then solved the Tolman-Oppenheimer-Volkoff equations to obtain stellar configurations. Their findings revealed that, due to the difference in internal degrees of freedom, Dirac dark matter generally softens the equation of state more strongly than Majorana dark matter. This leads to neutron stars with smaller radii and lower maximum masses in the case of Dirac dark matter.
The study also identified the parameter space consistent with current constraints from the Neutron star Interior Composition Explorer (NICER) and gravitational-wave observations. This highlights the potential of compact-star observations to discriminate between Dirac and Majorana dark matter, providing a valuable tool for astrophysicists and particle physicists in their quest to unravel the mysteries of dark matter.
For the energy sector, understanding the fundamental nature of dark matter and its interactions with ordinary matter could have profound implications. Dark matter research is closely tied to the development of advanced detection technologies and the exploration of new energy sources. Insights gained from studies like this one could pave the way for innovative energy solutions and a deeper comprehension of the universe’s fundamental forces and particles.
Source: Physical Review D, “Dirac vs. Majorana Dark Matter Imprints on Neutron Star Observables”
This article is based on research available at arXiv.