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SUMMARY:An Open System Approach to Cosmology - Enrico Pajer (DAMTP)
DTSTART:20251118T143000Z
DTEND:20251118T153000Z
UID:TALK236863@talks.cam.ac.uk
CONTACT:Steven Brereton
DESCRIPTION:Cosmological models and predictions rely extensively on the we
 ll-established field theory framework of particle physics. However\, a qua
 litatively new challenge arises: cosmological systems inherently contain s
 ubstances with poorly constrained macroscopic properties and entirely unkn
 own microphysics\, such as the inflaton sector\, dark matter\, and dark en
 ergy. This results in a rich array of novel phenomena\, including dissipat
 ion\, stochastic fluctuations\, out-of-equilibrium dynamics\, and non-unit
 ary macroscopic evolution. Moreover\, since gravitational observables are 
 of primary interest\, and gravity universally couples to all forms of matt
 er\, a close system approach requires precise description of all cosmic co
 nstituents—something feasible only in the simplest toy models. To addres
 s these challenges\, I propose an open system approach to cosmology. I beg
 in with a pedagogical introduction to open quantum systems. Then\, I prese
 nt the open effective field theory of inflation as a general class of theo
 ries of single-field inflation in the presence of an unknown medium. This 
 local\, dissipative theory yields a new class of predictions for cosmologi
 cal correlators\, generalizing existing models. I then tackle the challeng
 e of formulating general relativity in the presence of an unspecified medi
 um. As a warmup\, I present a formulation of electromagnetism in a medium\
 , incorporating dissipation and fluctuations while ensuring a consistent t
 reatment of gauge symmetries. Building on these results\, I introduce the 
 general and systematic construction of dissipative extensions of general r
 elativity and explore their implications for modeling open dark matter\, d
 ark energy and the late-time evolution of the universe. Finally\, I study 
 the implications for the dissipative propagation of gravitational waves th
 rough the dark sector medium.
LOCATION:Hoyle Lecture Theatre\, Institute of Astronomy (In-person/Streame
 d)
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