Left panel shows a wine-bottle potential well with residual azimuthal symmetry corresponding to a pseudo Nambu-Goldstone boson (the axion). Right panel shows some relevant terms in the axion Lagrangian of axions, as well as the Jeans length associated with axions

Axions are hypothetical particles, the pseudo Nambu-Goldstone bosons of new global symmetry (as shown in the figure above to the left). They may solve the strong-CP problem of the standard model, and furnish an attractive candidate for either cold dark matter or a sub-dominant hot dark matter component. At low masses, axions could also comprise some of the dark energy. Axions may arise naturally in string theory due to compactification of higher-form gauge fields, and there may indeed be many axions in nature! I am interested in astrophysical probes of axions, either through their two-photon coupling (as shown by the proportionality in the above figure to the right) or their gravitational imprint (as parameterized by the axion Jeans scale in the last equation above. In the future, I hope to explore the implications of upcoming measurements of weak gravitational lensing of the CMB for allowed axion parameter space, and to understand in detail the formation of galaxies and other non-linear cosmological structure in axion (or axion-like) dark matter and dark energy models.

Ultra-light axions, the axiverse, and the energy scale of inflation

Axions are a hypothetical new particle introduced to explain why there is not more charge-parity symmetry violation in the theory of the strong interaction. Depending on precise parameters, ultra-light axions () can act as dark matter or dark energy. For masses , axions behave more like dark energy, while if , axions behave more like […]

Constraints to axions in modified thermal histories

I showed that if the radiation domination era began not long before big-bang nucleosynthesis (a novel but empirically allowed possibility), constraints to thermally produced axions are significantly relaxed. Results published in arXiv:0711.1352 (Phys. Rev. D 77, 085020). Collaborators: Tristan Smith and Prof. Marc Kamionkowski. Most experimental searches for axions and astrophysical constrains depend on their […]

Telescope searches for decaying thermal relic axions in the galaxy cluster RDCS 1252

I successfully proposed ~20 hours of observation time to look for decaying relic axions in the high-z galaxy cluster RDCS 1252. The resulting upper limits are the best in existence in the mass window from 8-14 eV. In the course of project, I mentored Princeton undergraduate student Kai Zhong Khor (shown below). Collaborators: Kai Zong […]

Telescope searches for decaying thermal relic axions in the galaxy clusters A2667/A2390

In this work, I led a team that used spectra of the galaxy clusters A2667 and A2390 obtained at the VLT in Chilé using the VIMOS IFU to look for thermally-produced axions in the 4.5-7.7 eV mass window, using their monochromatic decays to photons. If extant, such axions would produce a line signature in the […]