Olivier Lennon

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Olivier Lennon

Student

I am a final year DPhil student in the Particle Theory group. I have been working on physics beyond the Standard Model under the supervision of John March-Russell.

Previously, I attended Imperial College London where I completed an MSci degree in Physics with Theoretical Physics.

Teaching

I have held the following teaching posts during my time at Oxford:

- Tutor for B4 Subatomic Physics (Scattering Theory, Nuclear and Particle Physics) at Lincoln College (22 contact hours)

- Tutor for CP3/CP4 Mathematical Methods (Calculus, Vectors and Matrices, Complex Numbers and ODEs) at Lincoln College (24 contact hours)

Before my time at Oxford, I was a tutor for A-Level students in Mathematics and Chemistry (56 contact hours).

Outreach

I believe that outreach is a tremendously worthwhile and necessary activity to attract the most gifted students from the most disadvantaged backgrounds to academia. The impact that we as physicists have goes further than our individual research metrics - the future students we inspire has the potential to dwarf our own personal contributions. I have partaken in outreach activities throughout all stages of my education. As a student from a disadvantaged background, I have often returned to my old school to give talks on what it takes to be successful in academic study. I have also volunteered as a tutor in physics, mathematics and chemistry at my previous school on numerous occasions throughout 2006 - 2016. I have also worked as an open day helper at both Oxford and my previous institution, Imperial College London.

Fundamental physics is at a crossroads. The Standard Model of particle physics is incredibly successful at describing three of the four known forces of nature (the electromagnetic, strong- and weak-nuclear forces), the elementary particles of matter (the quarks and leptons), and the generation of mass (via the Englert-Brout-Higgs-Guralnik-Hagen-Kibble mechanism), the latter of which the LHC confirmed during its first run by discovering the elusive Higgs boson. However, this is not the full story; the Standard Model leaves many questions unanswered: How do neutrinos acquire mass? What is the nature of dark matter? How is the hierarchy of masses stabilised? Did the universe enter a period of hyper expansion in its early history? Can we unify the four forces of nature into a single, consistent theory?

At the Planck scale (an energy of ~1019 GeV), the Standard Model breaks down as the effects of the fourth force, gravity, become important. There has been considerable effort in trying to construct a framework which supersedes the Standard Model at these energies. However, this energy scale is approximately sixteen orders of magnitude above the current limits of experiment, set by the second run of the LHC (~104 GeV), which commenced in 2015. In the intervening energies, it is believed that extensions to the standard model should begin to answer some of the long-standing questions postulated above. However, meaningful signals are noticeably absent, thus far.

My personal research has focussed on two themes: the existence of exotic objects, known as Q-balls, in theories beyond the Standard Model, and the origin of the missing mass in the Universe, the so-called "dark matter".

Q-balls are an example of a soliton, which is an extended object kept stable by some conservation law. In the case of Q-balls, these are composed of scalar fields and kept stable by a combination of energy conservation, and the conservation of Noether charge. The Standard Model does not admit these objects - the only scalars in the theory are the Higgs and the mesons of chiral symmetry breaking, and their potentials do not allow for the existence of Q-balls. However, extensions to the Standard Model can. My research has focussed on a particular extension, similar to mirror world constructions, where an almost exact copy of the Standard Model exists at a higher energy scale. This hidden sector interacts with the Standard Model through a Higgs portal interaction, due to mixing of fundamental scalars in both sectors. In analogy to chiral symmetry breaking in our world, the hidden sector also undergoes chiral symmetry breaking at parametrically lower scales. Q-balls can exist in the hidden sector which are, crucially, kept stable by the Standard Model Higgs! My research has focussed on the spectrum of these Q-balls, proving the existence of thick-wall and thin-wall types.

Not much is known about the dark matter which exists in our Universe. It makes up ~85% of the known matter content of the Universe. The mass of the dominant component of this matter is constrained to be within 90 (nine-zero) orders of magnitude! The self- and dark matter-Standard Model-interaction strengths are bounded from above and consistent with purely gravitational interactions. In light of this, my research focussed on the Hawking radiation of primordial black holes as a method to produce the relic abundance of dark matter. The creation of primordial black holes exists in a wide range of theories of the Early Universe. It was found that, for a large range of dark matter and black holes masses, this method is successful in reproducing our Universe.

Finally, I have a rapidly developing interest in the application of physics ideas to biological systems.