Open gravitational dynamics offers an alternative perspective on the dark sector. This model fits current data and predicts correlated signatures in GW, galaxy clustering and weak lensing, offering multiple observational tests in upcoming surveys. Exciting prospects ahead!🌜
The model predicts enhanced structures at low z compared to Lambda-CDM. This enhancement places this minimal scenario outside the observationally allowed range, though precise bounds would require scanning over cosmological parameters and a precise inclusion of baryons
Scalar perturbations also change. We predict a modification of the Bardeen potentials, producing a non-trivial gravitational slip, η = Φ / Ψ. This deviates from Lambda-CDM model where η = 1, and is rather constrained by DESI results
In our model, dissipative effects modify the propagation of GWs. The GW luminosity distance hence differs from the electromagnetic one. The predicted effect is consistent with current constraints from LVK and could be tested with future observations
The model is made of a single open dark fluid whose effective EOS can be chosen to reproduces BAO + CMB best-fit expansion history, similar to a CPL dark-energy parametrization. But importantly, the acceleration arises without violating the null energy condition
If gravity interacts with an environment, its dynamics can be treated as an open system. Using Schwinger-Keldysh formalism, we developed a general framework for open gravitational dynamics. In this paper we study a minimal model that account for late-time cosmic acceleration
Phenomenology of an Open EFT of Dark Energy 🌌
đź“„https://arxiv.org/abs/2603.12321
All current evidence for dark matter and dark energy is purely gravitational. Hence, we treat the dark sector as the medium through which the spacetime metric propagates #cosmology #darkenergy
Thread 👇
📢Registration open for Contours 2026 — EFTs Meet the Schwinger–Keldysh Formalism!
📅 29 June – 3 July 2026
đź“Ť DAMTP, University of Cambridge
Join us for a conference on non-equilibrium EFTs across #hydrodynamics, #blackholes, #holography & #cosmology
Submit abstracts: indico.global/event/16432/...
Huge thanks to Xi and Zhehan for this collaboration — it’s been a real pleasure.
I’ve 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! 💥🌌 [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 Schwinger–Keldysh 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 — 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 — the in-in analogue of 2→2 scattering — 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:
🌌 Λ > 0 universes (D. Anninos)
đź“Š Out-of-equilibrium systems (T. Anous)
🔍 Amplitudes & correlators (A. McLeod)
Stay tuned! Details: indico.sns.it/event/91/ove...
Last summer I taught at the Disordered Universe Summer School — 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 arXiv📜 arxiv.org/abs/2510.00140
It’s been a real pleasure collaborating with physicists outside cosmology on this project. Huge thanks to Alessio, Ana, and Michał for the countless hours of discussions and the effort to bridge quantum information and cosmology 🌌⚛️[20/20]
...we’re effectively stuck probing a classical probability distribution — 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 — something that’s extremely challenging and may still fall short of true optimality [16/20]
But — and it’s a big but — 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 — one that grows exponentially with the duration of inflation [13/20]
For concreteness, we focus on the tensor-to-scalar ratio — 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 — the best-case scenario — with the classical Fisher information extracted from measurements of the Gaussian curvature perturbations alone [11/20]