Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E16: Quantum Field Theory in Curved SpacetimeLive

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Sponsoring Units: DGRAV Chair: Gabriela Gonzalez, Louisiana State University 
Saturday, April 17, 2021 3:45PM  3:57PM Live 
E16.00001: Semiclassical Approximation for 1+1 Quantum Electrodynamics I: Backreaction, energy transfer and particle number. Silvia Pla Garcia, Jose NavarroSalas, Paul R. Anderson, Robert S. Link, Ian M. Newsome We analyze solutions to the backreaction equations in 1+1 dimensional semiclassical electrodynamics when a strong, timevarying and homogeneous electric field coupled to either a quantized scalar field or a quantized spin $\frac{1}{2}$ field. Details of the particle production process are shown along with the transfer of energy between the electric field and the particles. Special attention will be given for the limit in which the mass of the created particles is zero. The validity of the semiclassical approximation will be discussed. [Preview Abstract] 
Saturday, April 17, 2021 3:57PM  4:09PM Live 
E16.00002: Semiclassical Approximation for 1+1 Quantum Electrodynamics II: Validity of the Semiclassical Approximation Ian Newsome, Paul R. Anderson, Robert S. Link, Silvia Pla, Jose NavarroSalas The validity of the semiclassical approximation in 1+1 quantum electrodynamics (QED) can be analyzed using a criterion which states the semiclassical approximation will break down if any linearized gauge invariant quantity constructed from solutions to the linear response equation grows rapidly for some time interval. A numerical solution to the linear response equation will be presented for the case of a quantized spin $\frac{1}{2}$ field coupled to a classical spatially homogeneous background electric field in 1+1 QED. This will be compared with two nearby solutions to the semiclassical backreaction equation whose difference acts as an approximate solution to the linear response equation. Special attention will be given to the critical scale for the Schwinger effect $E\sim E_{crit}=m^{2}/q$, as well as the extreme limits $q\,E/m^2 \ll 1$ and $q\,E/m^2 \gg 1$. [Preview Abstract] 
Saturday, April 17, 2021 4:09PM  4:21PM Live 
E16.00003: Stressenergy Tensor for a Quantized Scalar Field When a Black Hole in Four Dimensions Forms From the Collapse of a Null Shell Shohreh Gholizadeh Siahmazgi, Paul R. Anderson, Raymond D. Clark, Alessandro Fabbri A method has been developed to compute the stressenergy tensor for a quantized massless minimally coupled scalar field in a spacetime where a black hole forms from the collapse of a spherically symmetric null shell in four dimensions. This method involves taking the difference between the stressenergy tensor for the "in" state in the collapsing null shell spacetime and that for the Unruh state in the Schwarzschild spacetime. The construction of the modes that define the invacuum state and Unruh state will be discussed. Two different checks on the construction of the modes for the "in" state will be presented and the numerical computation of the stressenergy tensor will be discussed. [Preview Abstract] 
Saturday, April 17, 2021 4:21PM  4:33PM Live 
E16.00004: Preinflationary RadiationDominated Era from Scalar, Fermion, and Gauge Fields Taylor Ordines, Eric Carlson A radiationdominated preinflationary era is essential in many inflationary models that attempt to reproduce the anomalously low quadrupole moment in the CMB power spectrum. Despite its importance, the radiationdominated era is often just an assumption, and few arguments are ever given for its presence. Semiclassical gravity provides a context for examining the behavior of quantum fields in such a preinflationary era. In previous work, we demonstrated that for scalar fields a radiationdominated era naturally arises if the Universe started near zero size. In our current work, we extend this argument to fermion and gauge fields. [Preview Abstract] 
Saturday, April 17, 2021 4:33PM  4:45PM Live 
E16.00005: Backreaction effects in initially contracting models of Universe with different order reduction methods applied Leda Gao, Paul R. Anderson, Robert S. Link The effects of particle production due to a quantized massive conformally coupled scalar field on the evolution of the Universe are considered for models in which there is a positive cosmological constant and the Universe initially is in a contracting de Sitter phase. Different adiabatic in states for the field are considered. The stressenergy tensor for the massive scalar field is renormalized using adiabatic regularization. This introduces higher derivative terms in the semiclassical backreaction equations which result in extra solutions that can often be physically unrealistic. Several methods similar to that of order reduction are used to eliminate these extra solutions and a comparison of the results is made. [Preview Abstract] 
Saturday, April 17, 2021 4:45PM  4:57PM Live 
E16.00006: Horizons and Correlation Functions in $2D$ Schwarzschildde Sitter Spacetime Paul R. Anderson, Jennie Traschen It is shown that the twopoint correlation function for a massless minimally coupled scalar field in the Unruh state in $2D$ Schwarzschildde Sitter spacetime grows linearly in terms of a particular time coordinate that is good throughout the spacetime. The rate of growth is equal to the sum of the black hole plus cosmological horizon surface gravities. Similar growth is found to occur for the Unruh state in $2D$ Schwarzschild spacetime and some other $2D$ spacetimes with horizons. There is no such growth for the velocity twopoint function, but in many cases a correlation peak is found when the time coordinates for the two points are the same and the space coordinates are separated by one or both horizons [Preview Abstract] 
Saturday, April 17, 2021 4:57PM  5:09PM Live 
E16.00007: Unitarity in Quantum Fields Theory in Curved Spacetimes Ivan Agullo, Abhay Ashtekar The goal of this talk is to describe an aspect of quantum field theory in time dependent, globally hyperbolic spacetimes which is not commonly appreciated: dynamics is not unitary in the standard sense. This point will be illustrated with a simple cosmological spacetime. I will then shown that a generalized notion of unitarity does hold. This generalized notion allows one to correctly pass to the Schr\"{o}dinger picture starting from the Heisenberg picture used in the textbook treatments. [Preview Abstract] 
Saturday, April 17, 2021 5:09PM  5:21PM Live 
E16.00008: Local and Covariant Flow Relations for OPE Coefficients in Curved Spacetime Mark Klehfoth In the limit all their points approach one another, the npoint functions of a local quantum field theory may be approximated to arbitrary precision by their socalled operator product expansions (OPEs). The coefficients of these expansions are ordinary cnumber distributions which contain a wealth of information about the theory's causal, algebraic, and dynamical structure. In flat Euclidean spacetime, Hollands et al. have derived "flow equations" which govern how OPE coefficients depend on the theory's interaction parameters. These flow equations were rigorously proven to hold orderbyorder in perturbation theory, but they remain mathematically welldefined under very general modelindependent assumptions and provide a potential avenue for defining the interacting OPE coefficients nonperturbatively. However, there exist serious obstacles to generalizing the Hollands flow equations to curved Lorentzian spacetimes in a manner compatible with locality and covariance. In this talk, I describe these issues and present our resolutions to them for a solvable toy model: KleinGordon theory on curved spacetime with the mass viewed as an "interaction parameter". The techniques I describe are expected to apply, more generally, to Lorentzian QFTs with nonlinear interactions. [Preview Abstract] 
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