Quantum Fields and Strings

Quantum field theory was originally developed as the extension of quantum mechanics needed to accommodate the principles of special relativity. Today quantum field theory is the modern paradigm with which we understand particle physics, condensed matter systems, and many aspects of early universe cosmology, and it is used to describe the interactions of elementary particles, the dynamics of many body systems and critical phenomena, all with exquisite accuracy. Currently, Perimeter researchers are producing world-leading advances in the study of integrability and scattering amplitudes in quantum field theories. String theory is a theoretical framework which was proposed to produce a unified description of all particles and forces in nature, including gravity. It is based on the idea that at very short distances, all particles should in fact be seen to be extended one-dimensional objects, i.e., ‘strings.’ Modern string theory has grown to be a broad and varied field of research with strong connections to quantum gravity, particle physics and cosmology, as well as mathematics. An exciting new framework known as ‘holography’ has emerged from string theory whereby quantum gravity is formulated in terms of quantum field theory in one less dimension. This symbiosis between quantum field theory and quantum gravity has been a focus of many Perimeter researchers. This has led to the development of exciting new methods to study the quantum dynamics of gauge theories and in the application of these techniques to new domains, such as nuclear physics and condensed matter physics

Analyticity and Unitarity for Cosmological Correlators

Lorenzo Di Pietro University of Trieste

We consider quantum field theory on a rigid de Sitter space. We show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. We use this to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function, to derive an OPE expansion, and to constrain the operator spectrum. Generically, dimensions and OPE coefficients do not obey the usual CFT notion of unitarity.

Flavon Inflation

Stefan Antusch Max-Planck Gesellschaft
A new class of particle physics models of inflation is presented which is based on the phase transition associated with the spontaneous breaking of family symmetry responsible for the generation of the effective quark and lepton Yukawa couplings. We show

Moduli stabilization and flavor structure in 5D SUGRA with multi moduli

Moduli stabilization, SUSY breaking and flavor structure are discussed in 5D gauged supergravity models with two vector-multiplet moduli fields. One modulus field makes the fermion mass hierarchy while the other is relevant to the SUSY breaking mediation. We analyse the potential for the moduli from the viewpoint of the 4D effective theory to obtain the stabilized values of the moduli and their F-terms.

Gravitational Radiation from Preheating

John Giblin Kenyon College
Parametric resonance, also known as preheating, is a plausible mechanism for bringing about the transition between the inflationary phase and a hot, radiation dominated universe. This epoch results in the rapid production of heavy particles far from thermal equilibrium and has the potential to source a significant stochastic background of gravitational radiation. Here, I present a numerical algorithm for computing the contemporary power spectrum of gravity waves generated in this post-inflationary phase transition for a large class of scalar-field driven inflationary models.

Summing over geometries in string theory

Lorenz Eberhardt Institute for Advanced Study (IAS)

I discuss the question how string theory achieves a sum over bulk geometries with fixed asymptotic boundary conditions. I analyze this problem with the help of the tensionless string on AdS3xS3xT4 (with one unit of NS-NS flux) that was recently understood to be dual to the symmetric orbifold of T4. I argue that large stringy corrections around a fixed background can be interpreted as different semiclassical geometries, thus making a sum over semi-classical geometries superfluous.

The standard model, left/right symmetry, and the "magic square"

Latham Boyle Perimeter Institute for Theoretical Physics
Recently, an intriguing connection between the exceptional Jordan algebra h_3(O) and the standard model of particle physics was noticed by Dubois-Violette and Todorov (with further interpretation by Baez). How do the standard model fermions fit into this story? I will explain how they may be neatly incorporated by complexifying h_3(O) or, relatedly, by passing from RxO to CxO in the so-called "magic square" of normed division algebras.

Crossing Symmetry in the Planar Limit

Sebastian Mizera Institute for Advanced Study (IAS) - School of Natural Sciences (SNS)

Crossing symmetry asserts that particles are indistinguishable from anti-particles traveling back in time. In quantum field theory, this statement translates to the long-standing conjecture that probabilities for observing the two scenarios in a scattering experiment are described by one and the same function. Why could we expect it to be true? In this talk we examine this question in a simplified setup and take steps towards illuminating a possible physical interpretation of crossing symmetry.