Talks

Apart from Einstein, Paul Dirac was probably the greatest theoretical physicist of the twentieth century. Dirac, co-inventor of the most revolutionary theory for 150 years 'quantum mechanics' is now best known for conceiving of anti-matter in his head and also for his deeply eccentric behaviour. For him, the most important attribute of a fundamental theory was its mathematical beauty, an idea that he said was 'almost a religion' to him. In this talk, Farmelo will argue that this obsession originated in his early life and training as an engineer and mathematician. An examination of Dirac's character will show why he was sometimes called 'the strangest man' in the modern history of physics.

To study the continuum limit of a microscopic model of gravity we need microscopic observables that have a clear interpretation in terms of continuum geometry. In general the construction of such observables is notoriously difficult. In the model of causal dynamical triangulations (CDT) it is clear what the microscopic observables are, but at present the only known well-behaved observables with a continuum interpretation are spatial volumes. In this talk I will demonstrate what it takes to go beyond these by introducing the moduli as observables for CDT in 2+1 dimensions with spatial topology of the torus. Measurements of these observables using computer simulations provide valuable clues concerning the effective action describing CDT in the continuum. In particular I will present numerical evidence indicating that the effective kinetic term is well described by a modified Wheeler-De Witt metric like the one appearing in Horava-Lifshitz gravity.

Paul Dirac has been called ‘the first truly modern theoretical physicist’. In the latter part of his life, he was obsessed by the idea that the fundamental laws of nature must have mathematical beauty. This was ‘almost a religion to him’, he said. In this talk, I shall trace the origins of his fascination with this idea (going back to his school education) and question the account he gave of his contribution to quantum mechanics and field theory, which he often said emerged from his aesthetic perspective. I shall also give some insights into the extraordinary character of this man, whom Niels Bohr called ‘the strangest man’ who ever visited his Institute in Copenhagen.

The description of non-Fermi liquid metals is one of the central problems in the theory of correlated electron systems. I present a holographic theory which builds on general features of the thermal entropy density and the entanglement entropy. Remarkable connections emerge between the holographic approach, and the postulated strong-coupling behavior of the field-theoretic approach.

We show that a baryon asymmetry can be generated by dissipative effects during warm inflation via a supersymmetric two-stage mechanism, where the inflaton is coupled to heavy mediator fields that then decay into light species through B- and CP-violating interactions. In contrast with thermal GUT baryogenesis models, the temperature during inflation is always below the heavy mass threshold, simultaneously suppressing thermal and quantum corrections to the inflaton potential and the production of dangerous GUT relics. This naturally gives a small baryon asymmetry close to the observed value, although parametrically larger values may be diluted after inflation along with any gravitino overabundance. Furthermore, this process yields baryon isocurvature perturbations within the range of future experiments, making this an attractive and testable model of GUT baryogenesis.

What is everything in the universe made of? What was the universe like billions of years ago? These are eternal questions that humans have pondered throughout the ages. Today, we are on the verge of potentially making revolutionary breakthroughs in answering them. The Large Hadron Collider (LHC) at CERN is a 27-kilometre long underground experiment located on the Swiss-French border near Geneva. It smashes subatomic particles together at vast speeds in an effort to learn more about the fundamental building blocks that make up everything around you. It is the biggest, most ambitious scientific experiment in human history. On December 13, the LHC announced the latest findings in its search for the last undiscovered particle in our current model of subatomic particles. This particle is the near-mythical 'Higgs Boson' — the particle thought to be involved in giving other particles their mass. This educational event, geared towards high school students, teachers and the general public, followed CERN's announcement and discussed its findings and implications in clear, accessible language. Host Damian Pope and PI Researchers Natalia Toro, Philip Schuster, and experimental particle physicist Andy Haas of New York University participate in an informative and interactive discussion.

I will discuss some work on the collider phenomenology and cosmology of light gravitino dark matter, and will touch on some related issues concerning infrared divergences in charged-particle decay at finite temperature.
Light gravitinos, with mass in the eV to MeV range, are well-motivated in particle physics, but their status as dark-matter candidates is muddled by early-Universe uncertainties.

Both Tevatron experiments have recently reported an anomalous forward-backward asymmetry in top-antitop production. Their inclusive results are roughly 3 standard deviations larger than the standard model prediction and may be evidence of new physics that couples to the top quark. In this talk, I will present a weakly-coupled light axigluon model (< Mtop) with flavor universal couplings as a possible explanation. Surprisingly,a particle with these properties can generate a large ttbar asymmetry with model-parameters safe from dijet resonance searches, flavor changing neutral currents, and constraints from the Z pole.

Although the typical physical system achieves an ordered state at low temperatures, spin liquids stay disordered even in their ground state. In addition to an increasing number of experimental candidates for spin liquids, recent numerical work from Meng, et. al and Yan, et. al. has supplied strong numerical evidence for natural Hamiltonians having spin liquid ground states. Their featureless nature, though, makes  learning about these states particularly difficult. In this talk, we explore what variational ansatz can teach us about them. Additionally, we examine whether the canonical theoretical framework makes sense in the context of the best wave-functions. Finally, we look at what other tools we have to make sense of spin liquids.