> "O God, I could be bounded in a nutshell and count myself a king of infinite space, were it not that I have bad dreams." > > (Hamlet contemplating Banach-Tarski, *Hamlet*, Act II, Scene II. One can only imagine his nightmare to be the Axiom of Determinacy.) Welcome to my site! I am a PhD student at Caltech (see [here](https://www.pma.caltech.edu/people/tasmin-chu) for a picture of me) working with [Omer Tamuz](https://tamuz.caltech.edu/) and [Tom Hutchcroft](https://www.its.caltech.edu/~thutch/). I completed my MSc in math under the supervision of [Louigi Addario-Berry](https://problab.ca/louigi/) and [Anush Tserunyan](https://www.math.mcgill.ca/atserunyan/) at McGill University. I also did my BSc in mathematics at McGill. Broadly, I'm interested in discrete probability, ergodic theory, and percolation theory. I also like descriptive and group-theoretic aspects of these fields. You can email me at tlchu[at]caltech[dot]edu. # More about me **Research Interests:** My research interests centre on the intersection of measurable group theory and ergodic theory with discrete probability and combinatorics. See e.g. Lyons' *Probability on Trees and Networks* for an idea of the kind of math I am interested in. I tend to like the conversation between geometric/algebraic invariants of countable graphs and the stochastic behaviour of various models defined on said graphs. Right now I'm working on a root reconstruction problem for the Susceptible-Infected model on Bienaymé trees and on randomly sampled graphs with fixed degree sequences. This is joint work with Sasha Bell, Louigi Addario-Berry, and Théodore Conrad-Frenkiel. **Preprints and publications:** 2. **Heavy repulsion of clusters in Bernoulli percolation**, with Sasha Bell, Owen Rodgers, Grigory Terlov, and Anush Tserunyan. First appeared on ArXiv 2025. Preprint. *ArXiv* link [here](https://arxiv.org/abs/2509.10631). *Abstract*: We study Bernoulli$(p)$ percolation on (non)unimodular quasi-transitive graphs and prove that, almost surely, for any two heavy clusters $C$ and $C'$, the set of vertices in $C$ within distance one of $C'$ is light, i.e. it has finite total weight. This is a significant step towards resolving a longstanding question posed by Häggström, Peres, and Schonmann, and a generalization of a theorem of Timár, who proved the same result in the unimodular setting. 1. **Oscillating and nonsummable Radon-Nikodym cocycles along the forward geodesic of measure-class-preserving transformations**, with Sasha Bell and Owen Rodgers. Published (online first) in [*Groups, Geometry, and Dynamics*](https://ems.press/journals/ggd/articles/14298613) in 2025. *ArXiv* link [here](https://arxiv.org/abs/2407.16967). *Abstract*: We consider the least-deletion map on the Cantor space, namely the map that changes the first 1 in a binary sequence to 0, and construct product measures on $2^\mathbb{N}$ so that the corresponding Radon-Nikodym cocycles oscillate or converge to zero nonsummably along the forward geodesic of the map. These examples answer two questions of Tserunyan and Tucker-Drob. We analyze the oscillating example in terms of random walks on $\mathbb{Z}$, using the Chung-Fuchs theorem. **Service work and mentorship:** I was an organizer and photographer for SUMM 2024 (Seminars in Undergraduate Mathematics in Montreal). See [here](https://www.flickr.com/photos/199862491@N06/) for some pictures. I also helped organize McGill's 2023 summer [undergraduate research seminar](https://docs.google.com/spreadsheets/d/1CPBZnN05_sns4YwlCe9hhX-8Iwyipnv3b7w4QelLcKU/edit#gid=0) with Carl Kristof-Tessier. I like organizing reading groups when I have to learn something new; you can see a list in my Past Seminars folder on the left. I volunteer for a nonprofit called the [The Prison Mathematics Project](https://www.prisonmathproject.org/) which supports math circles within prisons and connects incarcerated individuals to math mentors. We recently fundraised over $2500 thanks to word of mouth and social media fundraising. I used to run the Twitter account, where I raised the Twitter follower count from 200 to over 2000. I now spearhead an initiative to mail out monthly mathematical problem sets (with solutions) to participants: you can write and submit [your own problem set here](https://forms.gle/qEFpc9ec4HVCaiKG8). I volunteer myself as a math mentor at the Prison Mathematics Project. I am teaching calculus over email to my amazing mentee Kevin. I was a mentor in the 2025 run of McGill's [[DRP Mentorship |Directed Reading Program]], which pairs undergraduate students with graduate student mentors. **Teaching:** At Caltech, I am currently TAing Ma 140 (Graduate Probability), taught by Omer Tamuz, for the fall quarter. At McGill: I was a TA for MATH 141, Calculus 2 for the Winter 2025 semester. I was a TA for MATH 133, Linear Algebra for the Fall 2024 semester. **Awards**: My master's was funded by a NSERC Canada Graduate Scholarship-Master's (CGS-M), worth $23,834 and partial concurrent funding from Fonds de Recherche du Quebec (FRQNT), (total award is worth $40 000 but I only received part of it). During the summer of 2023, I was awarded a $9000 Science Undergraduate Research Award (SURA) to do research. I received the J.W. McConnell scholarship from McGill for 2 years and the David Tat-Chi Lin scholarship for 1 year, for a total of $9000. **Seminar talks:** **Oct 2024**, McMaster University, BioDataLunch. *Abstract*: How do we find the origin of a rumour or patient 0 in a pandemic? This can be thought of as finding the root of a graph generated in a certain infectious way. We give new root reconstruction algorithms on two graph models (Bienaymé trees and the configuration model). This is joint work with Louigi Addario-Berry, Sasha Bell, and Théodore Conrad-Frenkiel. **Feb 2024,** McGill University, Descriptive Dynamics and Combinatorics Seminar. *Abstract:* Let $(X, \mu)$ be a standard probability space. We say a (not necessarily proper) colouring of a graph $G \subseteq X^2$ is $\kappa$-domatic, for $\kappa$ a cardinal, if each vertex $x \in G$ sees exactly $\kappa$ many different colours among its neighbours. We sketch a result of Edward Hou, 2022, which says any $\mu$-preserving $\omega$-regular Borel graph $G \subseteq X^2$ admits a $\mu$-measurable $\omega$-domatic colouring. This talk was given jointly with Owen Rodgers. Joint results of mine have also been presented at the **August 2024** Frontiers of Statistical Mechanics and Theoretical Computer Science (by Louigi Addario-Berry) and at the McGill Descriptive Dynamics and Combinatorics Seminar in **October 2023** (by Sasha Bell and Owen Rodgers). For my work history, check out my [LinkedIn](https://www.linkedin.com/in/tasmin-chu-5769aa1b4/). ### Recent attended conferences - [PIMS Probability Summer School](https://secure.math.ubc.ca/Links/ssprob25/schedule.php) at University of British Columbia (June 2025) - [Probability, Dynamics, and the Geometry of Groups](https://www.uni-muenster.de/Stochastik/workshop/probdynamics2024/) at University of Münster (September 2024) - [Workshop on Measurable Combinatorics](https://erdoscenter.renyi.hu/events/workshop-measurable-combinatorics) at Rényi Institute (June 2024) - [Young Set Theory Workshop](https://erdoscenter.renyi.hu/events/young-set-theory-workshop) at Rényi Institute (June 2024) You will find me talking about nonunimodular graphs at [PIEROGY 2026](https://pierogy.matinf.uj.edu.pl/home). Please say hi! # Equity in math I strongly believe that anyone who wants to do math belongs in math. Too often, we place an emphasis on "innate talent" or "genius" in mathematics. This disproportionately leads to minorities and women [disqualifying themselves](https://www.science.org/content/article/belief-some-fields-require-brilliance-may-keep-women-out) from participating in mathematics in the first place. Definitely, people from nontraditional and underrepresented backgrounds should feel empowered to study math. #### \{Collaborators\} - [Owen Rodgers](https://sites.google.com/view/owenrodgers/home) - [Sasha Bell](https://sites.google.com/view/sasha-bell) - [Anush Tserunyan](https://www.math.mcgill.ca/atserunyan/index.html) - [Grigory Terlov](https://sites.google.com/view/gterlov/home) #### \{Friends\} \ \{Collaborators} - [Caelan Atamanchuk](https://caelanatamanchuk.com/) - [Jessie Meanwell](https://sites.jessiemeanwell.com/) - [Antoine Poulin](https://antoinegpoulin.github.io/) - [Jacob Reznikov](https://axiomofchoice.dev/) - [Sam Murray](https://sam-murr.github.io/) - [Sophia Howard](https://sophiahoward22.github.io/) - [Chris Karpinski](https://sites.google.com/view/chris-karpinski/home?authuser=0) - [Marcel Goh](https://marcelgoh.ca/) - (and others without websites...) Montreal has a great scene of people working in the intersection of descriptive set theory, logic, discrete probability, and geometric group theory. You can find a list of people, reading groups, seminar, and colloquia [here](https://www.math.mcgill.ca/dcl/).