TY - JOUR

T1 - Gravitational wave signals in an Unruh-DeWitt detector

AU - Prokopec, Tomislav

PY - 2023/2/2

Y1 - 2023/2/2

N2 - We firstly generalize the massive scalar propagator for planar gravitational waves propagating on Minkowski space obtained recently in van Haasteren and Prokopec (2022 arXiv:2204.12930 [gr-qc]). We then use this propagator to study the response of a freely falling Unruh-DeWitt detector to a gravitational wave background. We find that a freely falling detector completely cancels the effect of the deformation of the invariant distance induced by the gravitational waves, such that the only effect comes from an increased average size of scalar field vacuum fluctuations, the origin of which can be traced back to the change of the surface in which the gravitational waves fluctuate. The effect originates from the quantum interference between propagation on off-shell detector's trajectories which probe different spatial gravitational potential induced by the gravitational backreaction from gravitational waves, and it is therefore purely quantum. When resummed over classical graviton insertions, gravitational waves generate cuts on the imaginary axis of the complex ?T-plane (where ?tau = tau - tau ' denotes the difference of proper times), and the discontinuity across these cuts is responsible for a continuum of energy transitions induced in the Unruh-DeWitt detector. Not surprisingly, we find that the detector's transition rate is exponentially suppressed with increasing energy and the mass of the scalar field. What is surprising, however, is that the transition rate is a non-analytic function of the gravitational field strain. This means that, no matter how small is the gravitational field amplitude, expanding in powers of the gravitational field strain cannot approximate well the detector's transition rate. We present numerical and approximate analytical results for the detector's transition rate both for circularly polarized and for polarized monochromatic, unidirectional, gravitational waves.

AB - We firstly generalize the massive scalar propagator for planar gravitational waves propagating on Minkowski space obtained recently in van Haasteren and Prokopec (2022 arXiv:2204.12930 [gr-qc]). We then use this propagator to study the response of a freely falling Unruh-DeWitt detector to a gravitational wave background. We find that a freely falling detector completely cancels the effect of the deformation of the invariant distance induced by the gravitational waves, such that the only effect comes from an increased average size of scalar field vacuum fluctuations, the origin of which can be traced back to the change of the surface in which the gravitational waves fluctuate. The effect originates from the quantum interference between propagation on off-shell detector's trajectories which probe different spatial gravitational potential induced by the gravitational backreaction from gravitational waves, and it is therefore purely quantum. When resummed over classical graviton insertions, gravitational waves generate cuts on the imaginary axis of the complex ?T-plane (where ?tau = tau - tau ' denotes the difference of proper times), and the discontinuity across these cuts is responsible for a continuum of energy transitions induced in the Unruh-DeWitt detector. Not surprisingly, we find that the detector's transition rate is exponentially suppressed with increasing energy and the mass of the scalar field. What is surprising, however, is that the transition rate is a non-analytic function of the gravitational field strain. This means that, no matter how small is the gravitational field amplitude, expanding in powers of the gravitational field strain cannot approximate well the detector's transition rate. We present numerical and approximate analytical results for the detector's transition rate both for circularly polarized and for polarized monochromatic, unidirectional, gravitational waves.

KW - Unruh-DeWitt detector

KW - Gravitational waves

KW - Quantum field theory in curved spaces

UR - https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=d7dz6a2i7wiom976oc9ff2iqvdhv8k5x&SrcAuth=WosAPI&KeyUT=WOS:000926559300001&DestLinkType=FullRecord&DestApp=WOS

U2 - 10.1088/1361-6382/acabf5

DO - 10.1088/1361-6382/acabf5

M3 - Article

SN - 0264-9381

VL - 40

JO - Classical and Quantum Gravity

JF - Classical and Quantum Gravity

IS - 3

M1 - 035007

ER -