Particle Physics

Detecting ultralight axion dark matter has recently become one of the benchmark goals of future direct detection experiments. I will discuss a new idea to detect such particles whose mass is well below the micro-eV scale, corresponding to Compton wavelengths much greater than the typical size of tabletop experiments. The approach involves detecting axion-induced transitions between two quasi-degenerate resonant modes of a superconducting accelerator cavity. Compared to more traditional setups, the sensitivity is parametrically enhanced for ultralight axions, allowing for the exploration of vast new areas of parameter space relevant to the QCD axion and astrophysically long-ranged fuzzy dark matter.

The Muon g-2 experiment at Fermilab has recently confirmed Brookhaven's earlier measurement of the muon anomalous magnetic moment aμ. This new result increases the discrepancy Δaμ with the Standard Model (SM) prediction and strengthens its "new physics" interpretation as well as the quest for its underlying origin. In this talk I will review the SM prediction of the muon g-2, focusing on some of the latest developments, and discuss the connection of the discrepancy Δaμ to precision electroweak predictions via their common dependence on hadronic vacuum polarization effects.

It is known that constraints imposed by causality and unitarity of four-particle scattering amplitudes lead to non-trivial requirements on the low energy effective field theory coefficients. We introduce families of linear and nonlinear inequalities resulting from a systematic study of positive geometry structure hidden in those constraints.

The dark photon is a well-motivated extension of the Standard Model which can mix with the regular photon. This mixing is enhanced whenever the dark photon mass matches the primordial plasma frequency, leading to resonant conversions between photons and dark photons. These conversions can produce observable cosmological signatures, including distortions to the cosmic radiation background. In this talk, I will discuss a new analytic formalism for these conversions that can account for the inhomogeneous distribution of matter in our universe, leading to new and revised limits on the mixing parameter of light dark photons derived from the COBE/FIRAS measurement of the cosmic microwave background spectrum. I will then describe some ongoing work on a dark sector model that can explain the longstanding ARCADE radio background excess through resonant conversions of dark photons.

Far-infrared spectroscopy can reveal secrets of galaxy evolution and heavy-element enrichment throughout cosmic time, and astronomers worldwide are designing cryogenic space telescopes for far-IR spectroscopy. The most challenging aspect is a far-IR detector which is both exquisitely sensitive (limited by the zodiacal-light noise in a narrow band (lambda/delta lambda ~1000)) and array able to tens of thousands of pixels. The quantum capacitance detector (QCD) being developed at MDL, is a 50mK device adapted from quantum computing applications in which photon-produced free electrons in a superconductor tunnel into a small capacitive island embedded in a resonant circuit. The QCD has optically-measured noise equivalent power (NEP) of 2x10-20 W Hz-1/2 at 1.5THz under 10-19W of optical loading, making it the most sensitive far-IR detector ever demonstrated. The QCD has further demonstrated individual far-IR photon counting, confirming the exquisite sensitivity and suitability for cryogenic space astrophysics. In this lecture, the development of the Quantum Capacitance detector will be highlighted, from inception through proof of concept devices, culminating with the demonstration of single photon detection. Current development efforts will be discussed.