Constraining Effective Field Theories without Lorentz

Contribution List

12. Positivity bounds: electromagnetic properties of media, and more / Simple properties of Green's function without Lorentz invariance

Ahmadullah Zahed, Borna Salehian

7/7/25, 10:00 AM

Part 1: I will start talking about the constraints imposed on the electromagnetic response of media by microcausality (commutators of local fields vanish outside the light cone) and positivity of the imaginary parts (the medium can only absorb energy from the external field). Modeling the medium as composed of small polarizable particles, one finds that similar positivity bounds apply to their...

2. The hydrohedron: rigorous bounds on transport from causality

Benjamin Withers

7/7/25, 2:30 PM

As an effective theory constructed in a gradient expansion, relativistic hydrodynamics is fixed by symmetries up to a set of transport coefficients. I will utilise bootstrap techniques to rule out theories that are inconsistent with microscopic causality. What remains is a universal convex geometry in the space of transport coefficients, "the hydrohedron”. I will also discuss the necessary...

7. Analyticity and causality in Lorentz-breaking backgrounds: scattering vs correlators

Alessandro Podo, Shengjia Zhou

7/7/25, 4:00 PM

We will describe the analytic structure and positivity properties of the perturbative S-matrix of excitations in a relativistic phi^4 superfluid. Motivated by this, we will then discuss how microcausality implies non-perturbative analyticity properties of correlators in a mixed (t,k) representation. This result applies to generic relativistic QFTs in homogeneous and isotropic backgrounds,...

10. Positivity from thermodynamics

Riccardo Penco

7/8/25, 10:00 AM

I will discuss the extent to which thermodynamic considerations can be leveraged to derive positivity bounds on low energy effective theories.

5. Dressing and Screening in de Sitter

Lorenzo Di Pietro

7/8/25, 2:30 PM

For a gauge theory in dS, I will discuss how to define and compute properly dressed late-time correlation functions of charged fields, and an analogue of Debye screening that affects the late-time decay of the electric field. I will briefly review the use of conformal symmetry to reveal analyticity and positivity properties of late-time correlation functions, and discuss these properties in...

8. An Open System Approach to Gravity and Cosmology

Enrico Pajer

7/9/25, 10:00 AM

Cosmological models and predictions rely extensively on the well-established field theory framework of particle physics. However, a qualitatively new challenge arises: cosmological systems inherently contain substances with poorly constrained macroscopic properties and entirely unknown microphysics, such as the inflaton sector, dark matter, and dark energy. This results in a rich array of...

1. Bispectrum Islands

Sadra Jazayeri

7/9/25, 2:30 PM

Motivated by the success story of the modern S-matrix bootstrap in mapping out the space of scattering amplitudes consistent with fundamental principles, I explore how a similar framework can be applied to cosmological correlators generated during inflation. In particular, I focus on the bispectrum of curvature perturbations sourced by interactions with a generic hidden sector during...

9. Graviton loops and negativity

Julio Parra-Martinez

7/10/25, 10:00 AM

I will explain some challenges introduced by loop corrections to gravitational EFT bounds on Wilson coefficients and how they can be overcome. Time permitting, I will show that bounds without IR divergences from massless graviton exchange can be obtained under certain reasonable assumptions.

11. All but bounds on Love numbers

Giulia Isabella

7/10/25, 2:30 PM

I will discuss the EFT describing compact objects, characterized by Wilson coefficients knowns as Love numbers. I will present a method for computing this gravitational EFT to high orders and highlight the challenges involved in placing bounds on these coefficients.

16. Effective field theories of hydrodynamics and magnetohydrodynamics

Saso Grozdanov

7/11/25, 10:00 AM

I will discuss recent advances in constructing and analysing effective field theories (EFTs) that capture the dynamics of collective thermal systems, in particular of dissipative fluids and plasmas described by hydrodynamics and magnetohydrodynamics. I will begin by reviewing how these EFTs, which encode the global symmetries of the underlying microscopic dynamics, are formulated within the...

3. IFPU Colloquium: Spontaneously broken spacetime symmetries and a quantum bound on transparency

Alberto Nicolis

7/11/25, 11:30 AM

I will show how the low-energy dynamics of different phases of matter---different "materials"---can be conveniently described within the framework of relativistic quantum field theory, in particular in terms of spontaneous symmetry breaking, Goldstone excitations, and effective field theory. As an application of the formalism, I will show how to derive an absolute bound on how transparent a...

17. Asymptotic Superluminality

Warin Patrick McBlain

15. Discussion session: Condensed matter

Angelo Esposito, Subham Dutta Chowdhury

13. Discussion session: Cosmology

Diptimoy Ghosh, Lam Hui, Paolo Creminelli

14. Discussion session: Targets and Synergies

Joan Elias Miro, Julio Parra-Martinez, Luca Santoni