https://doi.org/10.1140/epjc/s10052-022-10783-2
Regular Article - Theoretical Physics
Unitarity problems for an effective field theory description of early universe cosmology
1
Department of Physics, McGill University, H3A 2T8, Montreal, QC, Canada
2
Department of Physics, Bu-Ali Sina (Avicenna) University, 65178 016016, Hamedan, Iran
3
School of Physics, Institute for Research in Fundamental Sciences (IPM), 19538-33511, Tehran, Iran
Received:
10
April
2022
Accepted:
5
September
2022
Published online:
15
September
2022
In the context of Effective Field Theory, the Hilbert space of states increases in an expanding universe. Hence, the time evolution cannot be unitary. The formation of structure is usually studied using effective field theory techniques. We study the constraints on effective field theory analyses of early universe models which come from demanding that the factor of the space of states corresponding to length scales where the primordial fluctuations are manifest does not suffer from the unitarity problem. For bouncing and emergent cosmologies, no constraints arise provided that the energy scale of the bounce or emergent phases is smaller than the ultraviolet (UV) cutoff scale. On the other hand, in the case of the inflationary scenario, non-trivial upper bounds on the energy scale of inflation arise.
© The Author(s) 2022
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