The High Energy Particle Physics journal club meets weekly to present on recent research published in the field. Graduate students who are studying high energy physics at OU are expected to participate.
The seminar and journal club are being temporarily combined, to be held on Tuesdays at 1:00 pm in Lin Hall 105 on the OU Norman campus.
Title: "A Collider-, Cosmology-, and Astrophysics-Testable Curvaton"
Abstract: We show that the primordial curvature perturbations can be realized by a light spectator field, the curvaton, that decays through a superrenormalizable interaction with the Higgs. The favored parameter space can be probed by proposed searches for light Higgs-mixed scalars, as well as by cosmological and astrophysical observations.
Title: "The Origin of Supermassive Black Holes from Pop III.1 Seeds and Implications for Particle Physics and Cosmology"
Abstract: The origin of supermassive black holes (SMBHs) is a key open question for contemporary astrophysics and cosmology. I review various formation scenarios for SMBHs and then discuss the predictions of the Pop III.1 model, i.e., seeding via metal-free stars forming in locally isolated dark matter minihalos, where dark matter annihilation has a chance to alter the structure of the star allowing growth to supermassive scales (Banik, Tan & Monaco 2019; Singh, Monaco & Tan 2023; Cammelli et al. 2025; Sanati et al. 2025a,b; Nandal et al. 2026; for a review see Tan et al. 2024 and this project page: http://cosmicorigins.space/smbh). The model predicts that all SMBHs form very early in the Universe (i.e., by z = 20) with a spatial distribution that is initially relatively unclustered. It also makes predictions for SMBH occupation fractions, host galaxy properties, frequency of binary SMBHs and the gravitational wave background. These predictions are compared to latest results from the Hubble Space Telescope, James Webb Spact Telescope and pulsar timing array observations. Another key prediction is an early phase of “flash” ionization of the universe at z~20, which can help alleviate cosmological tensions (Hubble tension, dynamical dark energy, negative neutrino masses) (Tan 2025; Tan & Komatsu 2026; Aggarwal et al. 2026). Finally, since the Pop III.1 mechanism relies on the process of WIMP dark matter self-annihilation, there are implication for the nature of the dark matter particle.
Title: "The String Axiverse Under Pressure: Mapping Moduli Space with Cosmological Observations"
Abstract: String theory generically predicts many axion-like fields, but their properties are not arbitrary: their masses, interaction strengths, and cosmic abundances depend on the geometry of the extra dimensions. I will explain this connection for axions arising from the C4 field in type IIB string theory, using explicit Calabi–Yau compactifications from the Kreuzer–Skarke database and the computational package CYTools.
I will first discuss ultralight “fuzzy” axions, which can behave as wave-like dark matter, and the other relics that accompany them in these compactifications. The main focus will then be a Bayesian framework for connecting the underlying geometry to cosmological observations. A key advance is our ability to systematically sample the Kähler cone—the allowed region of parameters describing the sizes of internal cycles—using Markov chain Monte Carlo methods. This opens the way to exploring how axion predictions vary as the geometry changes, rather than restricting attention to a few selected examples. Repeating the analysis across compactifications allows us to construct and compare string-derived axion priors and determine which regions of geometric parameter space are compatible with observations.
Finally, I will discuss the consistency conditions that must be satisfied by the nonperturbative effects responsible for generating axion potentials. These include flux quantization and rigidity requirements, which help determine whether a proposed axion potential can actually arise in a given compactification.
Title: "On the Virtue of Ignorance: Hadrons and the Minimum Free Energy Principle"
Abstract: I show that the mass and the parton distribution functions (PDFs) of ground-state mesons and baryons in various confining gauge theories in 1+1 spacetime dimensions minimize an appropriate measure of free energy. To demonstrate this, I introduce a variational method for solving the Schrodinger equation that governs the light-cone wavefunctions of these hadrons. The template wavefunction used in this method minimizes a suitable free energy functional associated with the hadron. Operationally, this conjecture transforms the problem of solving an integro-differential eigenvalue equation into a simple one-parameter optimization problem. I also discuss intuitive arguments that motivate why such a minimum free energy principle might emerge in confining theories. Applying this method, I reproduce known analytic and numerical results in the literature for hadron masses and meson PDFs in 1+1 confining theories. In addition, the framework yields new predictions for baryon PDFs that could be tested in future lattice calculations. This success suggests that the conjecture may capture a broader organizing principle for hadron structure, motivating its exploration in other confining theories, particularly in higher spacetime dimensions.
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