Constraining Effective Field Theories without Lorentz

Jul 7, 2025, 9:00 AM → Jul 11, 2025, 4:20 PM Europe/Rome

Room D (IFPU)

Effective Field Theories (EFTs) are the cornerstone of modern theoretical physics. In the last fifteen years it has been widely appreciated that “not anything goes” in EFTs: fundamental principles such as unitarity and causality place strong constraints on the space of possible theories. The question of how to extend this observation to contexts where Lorentz invariance is spontaneously broken is attracting increased attention. Several approaches have been put forward, each with its own advantages and drawbacks. Time is ripe to bring together experts to share viewpoints and debate recent developments. This workshop will host a diverse group of international researchers, with complementary perspectives and expertise, to discuss open questions and define theoretical targets across different fields, with the ultimate goal of learning what is allowed—and what is not—in our Universe.

 

Organizers: 

Paolo Creminelli (ICTP)

Alessandro Podo (IHES, Bures-sur-Yvette)
Borna Salehian (ETH, Zurich)


 

This workshop is an IFPU Focus Week, organized at the IFPU institute.
The institute is located next to ICTP, in the Miramare campus at Via Beirut 2, Trieste, Italy. You can find information on how to reach it at this webpage: https://www.ifpu.it/how-to-reach-us/

 

Mon, July 7

Welcome

Seminar: Borna Salehian/Ahmadullah Zahed

Coffee break

Free discussion

Lunch

1 The hydrohedron: rigorous bounds on transport from causality

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 role played by non-hydrodynamic degrees of freedom in achieving causality. Based on 2212.07434 and 2305.07703.

Speaker: Benjamin Withers

Coffee break

Seminar: Alessandro Podo/Shengjia Zhou

Tue, July 8

Seminar: Riccardo Penco

Coffee break

Free discussion

Lunch

Seminar: Lorenzo Di Pietro

Coffee break

Free discussion

Social Dinner

Wed, July 9

Seminar: Enrico Pajer

Coffee break

Free discussion

Lunch

2 Bispectrum Islands

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 inflation, and I show that the result must obey a set of positivity constraints stemming from the interplay between unitarity and de Sitter isometries. While I assume certain broad features of the hidden sector, I remain agnostic about its microscopic details. As a result, the derived positivity bounds are broadly applicable to a wide range of inflationary UV completions—whether the bispectrum arises from the exchange of weakly coupled fields, such as Kaluza-Klein modes or moduli in extra-dimensional models, or from operators with continuous spectra, as in conformal field theories.

Speaker: Sadra Jazayeri

Coffee break

Discussion session: Cosmology

Thu, July 10

Seminar: Julio Parra-Martinez

Coffee break

Free discussion

Lunch

Seminar: Giulia Isabella

Coffee break

Discussion session: Targets and Synergies

Social Dinner

Fri, July 11

Seminar: Saso Grozdanov

Coffee break

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

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 material can be.

Speaker: Alberto Nicolis

Lunch

Discussion session: Condensed Matter