We recomputed the primordial tensor spectrum for this model and derived the tensor-to-scalar ratio. Using BICEP’s current bound, r < 0.036, we placed an upper limit on noise sourcing tensors during inflation [24/25]

The main novelty is that we can now study gravitational waves propagating through a medium — featuring non-trivial speed, dissipation, noise, and even birefringence [22/25]

This effect appears clearly in the modified continuity equation [20/25]

We derived the modified Einstein equations in this framework. Assuming homogeneity and isotropy, we get the modified Friedmann equations below — describing cosmic evolution influenced by a dissipative matter sector [19/25]

The scalar clock emerges explicitly after performing two Stückelberg tricks — one for each branch of the path integral [17/25]

Once the symmetry breaking pattern is set, we can build the most general effective action compatible with these symmetries — organized order by order in a derivative expansion. At lowest order, the functional looks like this: [16/25]

To construct an open theory of single clock cosmology, we start by doubling the fields — giving two copies of diffeomorphism invariance in the Schwinger-Keldysh path integral. Dissipation and noise then break this down to the diagonal subgroup [15/25]

To tackle this, we need to understand what makes cosmology — if not unique — at least different from particle physics or condensed matter [5/25]

These correlators are computed using the principles of finite-time QFT. Instead of the usual path integral used in particle physics, we work with the Schwinger-Keldysh contour, which looks like this [4/14]

In cosmology, we aim to compare the observed statistics of galaxies in the sky with theoretical predictions, known as cosmological correlators [3/14]

These correlators are computed using the principles of finite-time QFT. Instead of the usual path integral used in particle physics, we work with the Schwinger-Keldysh contour, which looks like this [4/14]

In cosmology, we aim to compare the observed statistics of galaxies in the sky with theoretical predictions, known as cosmological correlators [3/14]