University of California-Berkeley
SPS Award for Outstanding Undergraduate Research
Simulating Cosmological Axions in Primordial Magnetic Field
I am a rising senior at the University of California, Berkeley studying Physics and Computer Science. My interests lie in the field of high energy physics and currently I do research with Prof. Benjamin Safdi to simulate cosmological axions in the early universe. I look forward to delving deeper into this field and plan on getting a PhD in particle physics. I attended several public lectures and talks by notable physicists and mathematicians while I was in high school which in turn led me to become passionate about physics. As a result, I decided to become the seminar chair of our SPS chapter to bridge the gap between the esoteric research that professors do and enthusiastic students who would like to learn more about it. I also help organize Undergraduate Seminars which provide an opportunity to students to know the research other undergraduates do, and get a chance themselves to practice formal presentations. In my free time, I like hiking, playing the guitar, and juggling the football (not the American kind)!
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. The axion, a particle billions of times lighter than the electron that was proposed in the 1970s to solve the strong CP problem in the neutron, is now proving to be a strong candidate to explain this missing mass in the universe. Even though their mass is extremely miniscule, axions are produced abundantly through the decay of strings formed during the Peccei-Quinn phase transition in the early universe after the big bang. Calculating this abundance precisely is the focus of the proposed work. Our goal is to measure the emission spectrum of axion radiation from the strings, which are topological defects generated by the axion field. This is because the axion radiation and its energy spectrum determine the dark matter abundance today. The string cores are regulated by ultraviolet physics (i.e., the Peccei-Quinn symmetry is restored), which we also must simulate. The simulations that have been run so far have not taken into account the effects of how an external magnetic field would affect the evolution of the axion strings which have been proposed to be superconducting. It is theorized that if a primordial magnetic field (PMF) exists in the early universe, a large current is induced on axion strings, creating a significant drag force from interactions with the surrounding plasma. This could significantly impact the dark matter density. For example, since the strings evolve with friction more of them could build up over time, leading to more axion radiation and thus more dark matter being produced. We compute this effect precisely using large-scale numerical simulations of superconducting axion strings in an expanding universe with primordial magnetic fields.Project leader:
Professor Benjamin Safdi