| Friday 19 April 2024 | |
| Events for day: Tuesday 29 September 2020 |
| 14:00 - 15:00 Weekly Seminar HEPCo Group Effective theories for a nonrelativistic field in an expanding universe: Induced self-interaction, pressure, sound speed, and viscosity School PHYSICS Abstract: A massive, nonrelativistic scalar field in an expanding spacetime is usually approximated by a pressureless perfect fluid, which leads to the standard conclusion that such a field can play the role of cold dark matter. In this paper, we systematically study these approximations, incorporating subleading corrections. We provide two equivalent effective descriptions of the system, each of which offers its own advantages and insights: (i) A nonrelativistic effective field theory (EFT) with which we show that the relativistic corrections induce an effective self-interaction for the nonrelativistic field. As a byproduct, o ... 17:00 - 19:00 IPM-SUT Joint IRQM Webinars on Quark matter and Relativistic hydrodynamics Kinetic theory and hydrodynamics for spin-1/2 particles with nonlocal collisions School PARTICLES AND ACCELERATORS Abstract: We study the Wigner function for massive spin-1/2 particles up to first order in the Planck constant ?. First considering the collisionless limit, we derive a generalized Boltzmann equation in which the force exerted by an inhomogeneous electromagnetic field on the particle dipole moment arises naturally. Furthermore, a kinetic equation for this dipole moment is derived. Carefully taking the massless limit we find agreement with previous results. We then derive the collision term in the Boltzmann equation using the equation of motion for the Wigner function. To next-to-lowest order in ? it contains a nonlocal contribution, which is ... |