Huge thanks to Xi and Zhehan for this collaboration β itβs been a real pleasure.
Iβve learned a ton, from deep conceptual discussions to the nitty-gritty of the computation.
Stay tuned: the open cosmological collider signal could be just around the corner! π₯π [10/10]
This case study clarified several subtleties in integrating out heavy fields in the early universe.
I hope it will also be useful to others, and help guide which EFTs we should write in cosmology when the UV physics is unknown [9/10]
As in flat space, the EFT coefficients controlling this open EFT are generally non-analytic, exhibiting branch cuts. Expanding in the heavy mass recovers the asymptotic nature of de Sitter EFTs (arxiv.org/abs/2505.17820) [8/10]
Dissipation is always subleading, suppressed exponentially by the heavy mass. This provides a clear open-system perspective on the cosmological collider signal [7/10]
In de Sitter, cosmological dynamics bring additional complications. Interestingly, different sectors of the EFT produce distinct physical signals: in parity-preserving theories, the non-local signal comes from stochastic operators, while the local signal arises from the unitary sector [6/10]
The relevant EFT coefficients are generically non-analytic in momenta. In flat space, this non-analyticity appears as a series of folded poles. Imposing a mass hierarchy smooths these features and allows one to recover a local open EFT [5/10]
Working in the SchwingerβKeldysh formalism already brings a few surprises.
Reproducing the flat-space signal requires more than a unitary EFT: dissipative and stochastic operators for the massless field must also be included [4/10]
We proceed in three steps. We decompose the signal and study its physical origin, integrate out the massive scalar to obtain a non-local EFT, and finally recast this non-locality as non-analytic EFT coefficients β which smooth out once a scale hierarchy is imposed [3/10]
In this work, we study the exchange of a massive scalar, probed through the trispectrum β the in-in analogue of 2β2 scattering β of a massless scalar [2/10]
EFTs in de Sitter spacetime hide a number of conceptual subtleties. In this paper we present a concrete case study where some of these issues appear in a particularly clear way. #cosmology #collider #physics [1/10]
arxiv.org/abs/2512.07941
More lecture notes from the Disordered Universe Summer School are on the way! Topics include:
π Ξ > 0 universes (D. Anninos)
π Out-of-equilibrium systems (T. Anous)
π Amplitudes & correlators (A. McLeod)
Stay tuned! Details: indico.sns.it/event/91/ove...
Last summer I taught at the Disordered Universe Summer School β an interdisciplinary program on de Sitter physics, cosmology, holography, scattering amplitudes, and open/disordered systems. I prepared lecture notes on Open Effective Field Theories, now on arXivπ arxiv.org/abs/2510.00140
Itβs been a real pleasure collaborating with physicists outside cosmology on this project. Huge thanks to Alessio, Ana, and MichaΕ for the countless hours of discussions and the effort to bridge quantum information and cosmology πβοΈ[20/20]
...weβre effectively stuck probing a classical probability distribution β one that hides clear quantum signatures [19/20]
Even though the quantum states of cosmological inhomogeneities may show strong non-classical traits, our limited observational access during inflation means... [18/20]
This tension highlights a key puzzle about quantum perturbations in the early universe [17/20]
It would require accessing the decaying mode of inflationary perturbations β something thatβs extremely challenging and may still fall short of true optimality [16/20]
But β and itβs a big but β this measurement is far beyond the reach of current observations [15/20]
The conclusions are twofold: first, there is an optimal measurement strategy that can constrain the tensor-to-scalar ratio extremely well [14/20]
Our main result: there is a huge gap between the classical and quantum Fisher information β one that grows exponentially with the duration of inflation [13/20]
For concreteness, we focus on the tensor-to-scalar ratio β a key observational target in upcoming experiments [12/20]
To understand how much information we lose due to limited access to early-universe data, we contrast the quantum Fisher information β the best-case scenario β with the classical Fisher information extracted from measurements of the Gaussian curvature perturbations alone [11/20]
This limited observational access makes it much harder to reconstruct the quantum state produced by inflation [10/20]
Key features β like non-Gaussianities in scalar perturbations, primordial gravitational wave statistics, or momentum correlations β are either weakly constrained or not measured at all [9/20]
Unfortunately, our window into the early Universe is still pretty narrow [8/20]
It sets the ultimate limit on how precisely we could measure a parameter β if we had ideal access to the early Universeβs quantum state [7/20]
So how do we approach this? We bring in quantum metrology β specifically, the quantum Fisher information β and apply it to the state of cosmological fluctuations right after inflation [6/20]
This raises two deep questions:
Β· How well can we infer a given parameter?
Β· Whatβs the best way to do it? [5/20]
I've always found it wild that we just collect photons with telescopes β and somehow extract things like the dark matter abundance or the Universeβs expansion rate [4/20]
In cosmology, this process shapes nearly everything we know about the Universe: its composition, its history, its fate [3/20]
