Eric Braaten
Ohio State University

Nora Brambilla
Technische Universität München

Thomas Schäfer
North Carolina State University

Antonio Vairo
Technische Universität München

Program Coordinator:
Kimberlee Choe
(206) 685-3509

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INT Program INT-18-1b

Multi-Scale Problems Using Effective Field Theories
May 7 - June 1, 2018


There are many interesting open problems at the frontiers of nuclear and particle physics that are characterized by the existence of a separation of scales that can be exploited using effective field theories (EFTs). The EFT method treats the low-energy degrees of freedom as dynamical fields, and takes into account higher-energy scales systematically through matching conditions. The choice of the low-energy degrees of freedom that remain dynamical depends on the physical observables we wish to describe.

Many state-of-the-art applications of EFT involve multiple effective field theories to deal with several different scales. Examples include sequences of EFTs in which the dynamical degrees of freedom have increasingly lower energies. Other applications involve very different EFTs that are combined in innovative ways to systematically separate the scales.

EFT methods developed in high energy and nuclear physics have been applied successfully in other fields, such as atomic, molecular, and solid state physics. Many-body systems involving multiple scales are of interest to physicists from many backgrounds, and new avenues for studying these systems in very clean settings have recently emerged in condensed matter physics and especially in atomic physics. This interdisciplinary program will focus on addressing multi-scale problems in various areas of physics using multiple effective field theories with the aim to bring together EFTs practitioners from a large span of physical problems. An innovative and original aspect of our program is the synergy created by bringing together scientists working in diverse areas of physics using the unifying methodology of EFTs.


It is clear that progress in many of these areas is critically dependent on bringing together EFT practitioners with overlapping interests but different specialized expertise, which is the goal of our program. In addition to spinning off results from EFTs in nuclear and particle physics to related problems in atomic, molecular and condensed matter physics, we want to develop EFT descriptions for nonperturbative physics in collaboration with lattice gauge theorists.


The program seeks to bring together researchers with diverse backgrounds in nuclear, particle, atomic, and condensed matter physics, as well as quantum optics and computational physics. The program will have around 16 participants at any given time. Participants will be invited to present their work during informal morning talks. Each morning, we will arrange two talks by researchers from different fields introducing physically related topics from different perspectives. In addition, we will organize two weekly afternoon discussions with subjects related to the presentations.

We specify below a focus for each of the four weeks of the program. Each focus represents a specific multi-scale application of EFT where we believe significant progress can be made. We hope to attract multiple participants actively working on the focus area each week. However the program each week will maintain an emphasis on the broad applicability of effective field theories.

    Week 1: Transport

    There is a hierarchy of scales in real-time correlation functions that can be used to connect an underlying microscopic field theory to kinetic theory and fluid dynamics. Questions on this framework include: can we perform the required matching calculations in higher order, and can we define them non-perturbatively? What is the role of real-time classical simulations? Can we view dissipative, stochastic fluid dynamics as an EFT?

    Week 2: Dark matter

    The physics of dark matter may well involve multiple scales. The important scales for wimps include the wimp mass, the weak boson masses, and wimp mass splittings, and they can differ by orders of magnitude. The important scales for axions involve its decay constant, its mass, and its width, and they can differ by tens of orders of magnitude. EFT can be used to separate the scales in order to simplify theoretical treatments and sharpen phenomenological predictions. EFT can also provide model-independent frameworks for addressing dark-matter problems. This focus week will highlight recent progress in applying EFT to dark matter and hopefully stimulate further progress on constraining the nature of the dark-matter particle.

    Week 3: Open quantum systems

    Non-equilibrium processes appear in a large span of physical problems ranging from high energy physics and cosmology, to heavy ion physics and atomic and condensed matter physics. Examples include the loss of ultracold trapped atoms due to highly inelastic reactions, the evolution of quarkonium in the Quark Gluon Plasma fireball, the decay of heavy Majorana neutrinos in the hot environment of the early universe. Recently an open quantum system approach based on the underlying effective field theory and on Lindblad equations have been developed in some cases. This focus week will highlight the recent progress and promote new ideas and further development with an interdisciplinary discussion bringing together various physics communities.

    Week 4: Exotic states

    In hadron and nuclear physics, resonances and composite objects with various natures and with interactions at the pion scale are very prominent in experiments and in theory discussions. The X, Y, Z states observed at collider experiments are good examples. They include tetraquark mesons and pentaquark baryons, whose constituents include a heavy quark and antiquark. Nonrelativistic EFTs have been developed to describe such hadrons whose masses are well below the heavy-meson pair threshold. The threshold region is more challenging, because it introduces additional scales. A promising approach is based on the EFT of the Born-Oppenheimer expansion, which has been extremely successful in atomic and molecular physics.

    We will also discuss the development of novel EFTs for such systems, together with related lattice calculations, in a cross talk among atomic, molecular, nuclear and particle physicists.