Research

Research Interests

 I am also thinking more about the nature of dark energy (DE), which we know even less about, other than the facts that it (1) makes up the majority of the energy in the universe and (2) causes the expansion of space today to accelerate. Recent data (see below) has shown a preference for a deviation from the standard picture of a cosmological constant (Lambda), where the energy density of DE remains constant while the universe expands. I am trying to understand the landscape of models of DE which can accommodate the recent data, and what this would-be discovery can tell us about the nature of DE concretely.

Other areas of interest to me include the rich phenomenology of axions, both as dark matter candidates and as sources for other new physics. Axions (the QCD axion, Ultra-light axions, and axion-like particles), originally proposed as a solution to the Strong CP problem of QCD,  are light scalar particles which have a range of applications in modern cosmology, astrophysics, and particle physics. I have been studying models of the QCD axion in particular, a well-motivated particle outside of the DM problem. I have worked on ways to modify the window of viable DM axion parameters to search for ways in which the axion can be the DM and a solution to other problems that arise from both theoretical motivations and observational findings. More recently I have explored the nature of axion perturbations in the early universe, diving into the differences and similarities axions have with other DM candidates. I am actively exploring more aspects of the phenomenology of axions and related models/theories.

Another interest of mine is the pursuit of a more complete understanding of the history of the universe, searching for a cosmological concordance model. In recent years, the "standard" model of cosmology, the original concordance model known as LambdaCDM, has been challenged by a number of discrepant observations. Much attention has been given to the so-called Hubble Tension, a disagreement between early-universe measurements (cosmic microwave background (CMB) data from Planck, ACT, SPT) and some late-universe measurements (specifically Cepheid-variable-calibrated supernovae luminosities from the SH0ES collaboration) of the present rate of the universe's expansion, the Hubble constant. The Hubble constant seems to be well-determined down to nearly percent-level precision by each of these methods, as well as other complementary methods, but their results disagree at varying levels, some claiming greater than 5 sigma (even 7 sigma!) disagreement. Since the CMB data rely on a  cosmological model to extrapolate the value of the Hubble constant today,  a promising approach to understanding this discrepancy lies in trying to adjust the LambdaCDM model. Other such tensions have gained recent interest. For instance, Baryon Acoustic Oscillations (BAO) data from DESI have recently placed an upper bound on the total mass of standard model neutrinos within the LambdaCDM model which is discrepant with lower bounds from neutrino oscillation experiments. In addition, the combination of DESI data along with uncalibrated supernovae distances (such as those from the DES, Pantheon, and Union3 compilations) have shown a preference for DE which is not constant in time as assumed in LambdaCDM, but dynamical instead. These anomalies, and others, are both puzzling and exciting as they provide the blueprints for hunting for new physics phenomena in cosmology. 

Recently, I have worked to uncover how many of the Cosmic Tensions are correlated with the measurements of the CMB sensitive to the Epoch of Reionization. Specifically, the optical depth to reionization τ, which measures the effects of the ionized plasma of the late universe on the photons of the CMB, has a correlation with many of the parameters involved in these tensions. The smallness of τ, as measured by the large-scale polarization measurements of the CMB by Planck, seems to exacerbate these tensions by decreasing the value of the Hubble constant, tightening the upper bound on neutrino mass, and increasing the preference for dynamical dark energy. While this correlation is likely indirect, relying on the remaining parameters and various physical effects, I find this relationship interesting and am continuing to explore the implications of this finding.

Beyond what I have outlined above, I am always looking out for new ways to use cosmological and astrophysical observations to hunt for new physics phenomena.