Instability of global de Sitter space to particle creation

Abstract

We show that global de Sitter space is unstable to particle creation, even for a massive free field theory with no self-interactions. The O(4, 1) de Sitter invariant state is a definite phase coherent superposition of particle and anti-particle solutions in both the asymptotic past and future, and therefore is not a true vacuum state. In the closely related case of particle creation by a constant, uniform electric field, a time symmetric state analogous to the de Sitter invariant one is constructed, which is also not a stable vacuum state. We provide the general framework necessary to describe the particle creation process, the mean particle number, and dynamical quantities such as the energy-momentum tensor and current of the created particles in both the de Sitter and electric field backgrounds in real time, establishing the connection to kinetic theory. We compute the energy-momentum tensor for adiabatic vacuum states in de Sitter space initialized at early times in global S 3 sections, and show that particle creation in the contracting phase results in exponentially large energy densities at later times, necessitating an inclusion of their backreaction effects, and leading to large deviation of the spacetime from global de Sitter space before the expanding phase can begin. * anderson@wfu.edu † emil@lanl.gov arXiv:1310.0030v1 [gr-qc]

Schwinger effect in 4D de Sitter space and constraints on magnetogenesis in the early universe

“…Such a behavior of the current is analogous to that from the Schwinger process in flat space [13,14]. On the other hand, with weak electric fields, i.e.…”

“…is to study the expectation value of the induced current, as in [7,[9][10][11][12][13][14]. This allows us to analyze cases where even the adiabatic vacuum does not exist in the asymptotic future, in other words, regimes where the scalar mass and electric force are much smaller than the Hubble scale and thus the scalar excitations are not well described as particles.…”

Massive scalar field evolution in de Sitter

“…For quantized theories de Sitter space has been analyzed in terms of back-reaction of cosmological fluctuations in [7][8][9] quantum gravity in [10][11][12][13] and quantum fields on a classical curved background in . In [29,30] a thorough investigation of de Sitter space in a global coordinate system was presented and as the main finding it was stated that the global de Sitter space with a quantized scalar field is unstable thus reinforcing the arguments made already in [14].…”

“…As we are interested in the massive case we assume γ 1 throughout. As discussed in [29,30], in de Sitter the general mode solutions of the mode equation (2.4) have two special classes, which are not orthogonal, the "in" and the "out" modes…”

“…To see this, first we note that the mode expansions (2.6) and (2.7) can be connected via a Bogolubov transformation [29,30] …”