Abstract
In a collision of strongly coupled quantum matter we find that the dynamics of the collision produces regions where a local rest frame cannot be defined because the energy-momentum tensor does not have a real time-like eigenvector. This effect is purely quantum mechanical, since for classical systems, a local rest frame can always be defined. We study the relation with the null and weak energy condition, which are violated in even larger regions, and compare with previously known examples. While no pathologies or instabilities arise, it is interesting that regions without a rest frame are possibly present in heavy ion collisions.
Highlights
Local rest frame and energy conditionsIn a system consisting of gas of classical, on-shell particles with mass m having a nonnegative particle distribution function f , the energy-momentum tensor is given by1
JHEP10(2014)110 rest frame for the energy-momentum tensor in certain regions
Note that for systems that are close to thermal equilibrium, this velocity would correspond to the local fluid velocity, but, as long as there is a local rest frame, it is a well-defined quantity even far away from thermal equilibrium where fluid dynamics does not apply
Summary
In a system consisting of gas of classical, on-shell particles with mass m having a nonnegative particle distribution function f , the energy-momentum tensor is given by1 Such a system has a local rest frame if there exists a frame with no momentum flow, i.e. T0i = 0. In that case the LRF condition is more difficult to violate than the NEC, and the rest frame velocity is in opposite direction of the flux. If the potential is bounded from below and normalized so that U (φ) = 0 at its minimum, the WEC is satisfied For both examples, a gas of classical particles and a system of classical fields, a local rest frame may always be defined, and the weak energy condition is never violated
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