Anisotropic Particle Creation from the T-Vacuum in the Radiation-Dominated Universe

We further investigate novel features of the T-vacuum state, originally defined in the context of quantum field theory in a (1+1)-dimensional radiation-dominated universe. Here, we extend the previous work to a realistic (3+1)-dimensional setup and show that the T-vacuum gives rise to an anisotropic particle creation phenomenon in the radiation-dominated early universe. Unlike the Hawking or Unruh effect, where the particle content is thermal and asymptotically defined, here, it is non-thermal and instantaneous. This novel example of particle creation is interesting because these particles are detected in the frame of physical or cosmological observers, who envision the T-vacuum as a particle-excited state. Such results have the potential to be eventually compared with the observed anisotropies from the early universe and may provide new insights into cosmological particle creation.