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Instanton

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QCD worldsheet axion from the bootstrap

Andrea Guerrieri, Victor Gorbenko

The worldsheet axion plays a crucial role in the dynamics of the Yang-Mills confining flux tubes. According to the lattice measurements, its mass is of order the string tension and its coupling is close to a certain critical value. Using the S-matrix Boots ...

New York2024

, ,

We present a nonperturbative recipe for directly computing the S-matrix in strongly-coupled QFTs. The method makes use of spectral data obtained in a Hamiltonian framework and can be applied to a wide range of theories, including potentially QCD. We demons ...

SPRINGER2023

Nonperturbative aspects of scattering amplitudes

Miguel Alexandre Ribeiro Correia

In this thesis we study how physical principles imposed on the S-matrix, such as Lorentz invariance, unitarity, crossing symmetry and analyticity constrain quantum field theories at the nonperturbative level. We start with a pedagogical introduction to the ...

EPFL2023

Bounds on scattering of neutral Goldstones

Andrea Guerrieri, Denis Karateev, Kelian Philippe Häring

We study the space of

2\to 2

scattering amplitudes of neutral Goldstone bosons in four space-time dimensions. We establish universal bounds on the first two non-universal Wilson coefficients of the low energy Effective Field Theory (EFT) for such particl ...

2023

Bounds on multiscalar CFTs in the epsilon expansion

Matthijs Jan Hogervorst

We study fixed points with N scalar fields in 4 - epsilon dimensions to leading order in epsilon using a bottom-up approach. We do so by analyzing O(N) invariants of the quartic coupling lambda(ijkl) that describes such CFTs. In particular, we show that la ...

SPRINGER2021

Standard model meets gravity: Electroweak symmetry breaking and inflation

Andrey Shkerin, Sebastian Zell

We propose a model for combining the Standard Model (SM) with gravity. It relies on a nonminimal coupling of the Higgs field to the Ricci scalar and on the Palatini formulation of gravity. Without introducing any new degrees of freedom in addition to those ...

AMER PHYSICAL SOC2021

Nonperturbative Mellin Amplitudes

João Pedro Alves Da Silva

Conformal field theory lies at the heart of two central topics in theoretical high energy physics: the study of quantum gravity and the mapping of quantum field theories through the renormalization group. In this thesis we explore a technique to study conf ...

EPFL2021

Instanton theory of ground-state tunneling splittings with general paths

Christophe Louis Joseph Jean-Luc Vaillant, Mihael Erakovic

We derive a multidimensional instanton theory for calculating ground-state tunneling splittings in Cartesian coordinates for general paths. It is an extension of the method by Mil'nikov and Nakamura [J. Chem. Phys. 115, 6881 (2001)] to include asymmetric p ...

2020

Accurate Description of Nuclear Quantum Effects with High-Order Perturbed Path Integrals (HOPPI)

Michele Ceriotti, Venkat Kapil

Imaginary time path-integral (PI) simulations that account for nuclear quantum effects (NQE) beyond the harmonic approximation are increasingly employed together with modern electronic-structure calculations. Existing PI methods are applicable to molecules ...

AMER CHEMICAL SOC2020

Nonperturbative Mellin amplitudes: existence, properties, applications

Alexander Zhiboedov, João Pedro Alves Da Silva

We argue that nonperturbative CFT correlation functions admit a Mellin amplitude representation. Perturbative Mellin representation readily follows. We discuss the main properties of nonperturbative CFT Mellin amplitudes: subtractions, analyticity, unitari ...

SPRINGER2020

Bounds on scattering of neutral Goldstones

Andrea Guerrieri, Denis Karateev, Kelian Philippe Häring

We study the space of

2\to 2

2023