https://doi.org/10.1140/epjp/s13360-020-00362-3
Regular Article
Density fluctuations and single-mode thermal states in the FRW universe
1
Department of Physics, Malaviya National Institute of Technology Jaipur, Jaipur, 302017, India
2
Department of Physics, Dayanand Sagar University, Bangalore, India
* e-mail: kvkamma.phy@mnit.ac.in
Received:
3
February
2020
Accepted:
24
March
2020
Published online:
15
April
2020
Using single-mode squeezed and coherent thermal states formalism, we analyzed the validity of the semiclassical Einstein equation (SCEE) in the flat Friedmann–Robertson–Walker universe by analyzing the density fluctuations in terms of a massive inflaton. In a single-mode squeezed thermal states the density fluctuations are too large; consequently, the semiclassical theory of gravity (SCTG) does not hold good, for squeezing parameter greater than unity, i.e., 
; however, the theory is valid when this related squeezing parameter is smaller than the unity, i.e., 
and 
. Also, it is noted that the SCEE is dependable on coherent thermal state formalism. The current study provides a description of the density fluctuations as a result of the quantum and thermal effects in the SCTG.
© Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature, 2020
