Supported by a mini-grant from the Foundational Questions Institute.

- Mustapha Amin
- Feraz Azhar
- Daniel Baumann
- Jonathan Braden
- Anthony Challinor
- Jens Chluba (AM only)
- George Efstathiou
- Steven Gratton
- Antony Lewis
- Paul McFadden
- Daniel Mortlock
- Hiranya Peiris
- Andrew Pontzen
- Eva Silverstein
- Anze Slosar

- 9:30am-10:15am: Arrive: Tea/Coffee, Doughnuts and Cookies outside the room
- 10:15am: Start
- 10:15-11:15am: Inflation
- Inflation from the top down (DB)

- 11:15-11:30am: Tea/Coffee outside the room
- 11:30am-1:15pm: Eternal Inflation and Measures
- Stochastic Eternal Inflation (SG)
- Infinities in Cosmology (GPE)

- 1:30-2:45pm: Lunch at The Plough, Coton
- 3pm-4:15pm: Statistical Mechanics and Entropy
- Describing ensembles (AP)
- Entropy in preheating (JB)

- 4:15-4:30pm: Tea/Coffee outside the room
- 4:30-6:45pm: Inference, other and more inflation
- Inference and Models (DM)
- BBN (AS)
- Negative temperatures and phantom models (AL)
- Predictions for classes of Inflation models (HP)

- 7pm: Dinner at Restaurant 22

Starting from a pure state, how does a nonequilibrium quantum field theory generate entropy and decohere into an effectively classical statistical ensemble? This has cosmological applications to the initial density perturbations, (p)reheating, and bubble nucleation in first order phase transitions. If there are no additional environmental degrees of freedom that the field couples to, then the standard mechanism of environment-induced decoherence cannot be used. Instead, the field must decohere itself in some way. One obvious way for this to occur is that high-order correlation functions may serve as an environment for the low-order correlators. This also provides a natural coarse-graining of the fields and thus creates an effective non-pure state with non-zero entropy. However, if coherent field configurations (such as topological defects, bubbles, oscillons, etc.) emerge as part of the dynamics, then it is clear that additional some additional information about correlations between different Fourier modes must be included. As well, in the strongly nonlinear regime, the field theory may be more easily described in terms of some collective variables instead of the fundamental scalars. This leaves open interesting questions as to what the correct collective variables are, which correlations should be used, how these are dynamically selected during the time-evolution, and what is the time-scale for the effective decoherence of the system.

Readings:

Two challenges:

- Extra Fields
- Extra Scales

See Sec. 3 of a recent conference talk.

Potential New Methodologies for studying many field inflation scenarios motivated by fundamental physics...

Further reading:- Easther, Frazer, Peiris, Price, Phys. Rev. Lett. 112, 161302 (2014) pdf here
- Price, Peiris, Frazer, Easther, Phys. Rev. Lett. 114, 031301 (2015) pdf here
- Price, Frazer, Xu, Peiris, Easther, JCAP, 03, 005 (2015) pdf here

Negative temperature imply negative pressures, but are only possible in particular constrained quantum systems and may be unstable. Is there any way to get and maintain such a quantum system for dark energy or inflation (or re-interpret existing models in terms of negative temperatures?)

Readings:When we make arguments in statistical mechanics, we typically maximize the entropy of some distribution of particles subject to constraints. We can maximize, for instance, the entropy of the distribution of particles in different buckets i subject to fixed mean energy and particle number. However the actual number of particles in a given phase space volume ni is a physically real thing, and so from the Jaynes perspective this seems like the wrong sort of argument. We seem to be slightly confusing our subjective probabilities for the distribution vs the actual frequency of particles in different states within the real system.

We ought to be maximizing our uncertainty about the situation, which would amount to maximizing the uncertainty in the probability distribution function p(n), not in the occupation numbers themselves.

This point was made in a recent paper by Carron & Szapudi, in which they claimed that one ends up with a different version of statistical mechanics by "fixing" the problem. However I have some calculations which show how to recover normal statistical mechanics from the extended version. So, beyond showing where the Carron & Szapudi made the wrong assumptions, is this approach useful for anything? One can, for example, calculate typical fluctuations around the equilibrium with apparently fewer ad hoc assumptions than normally made. But are there more fundamental issues lurking here?

The mini-grant will cover food, non-alcoholic drinks and hopefully any reasonable travel expenses those coming from outside of Cambridge may incur!