My research spans a broad range of topics in particle physics that covers the cosmic, intensity, and energy frontiers. I am generally interested in physics beyond the Standard Model of particle physics, especially dark matter, dark sectors, LHC phenomenology Higgs physics, supersymmetry, and supersymmetry breaking. One of my main goals is to develop the theoretical foundation for novel strategies and experiments to search for dark matter, new forces, and other new particles. I am also very interested in the theoretical implications of the data being collected at various experiments, including those searching for dark matter, high-intensity beam experiments, and the Large Hadron Collider (LHC). Moreover, although I am a theorist, I actively contribute to several experiments.
My experimental activities include:
I am a co-spokesperson of the SENSEI Collaboration. SENSEI (Sub-Electron Noise Skipper CCD Experimental Instrument) is a new dark matter direct-detection experiment with unprecedented sensitivity to several types of dark matter particles including dark-photons and axion like particles. The target material consists of 100-grams of silicon charge-coupled device (CCD) with a novel readout -- a skipper CCD (developed at Lawrence Berkeley National Laboratory MicroSystems Lab). For the first time, the number of electrons in each pixel, across a large CCD consisting of millions of pixels, can be counted precisely (see our paper here ). This is irrespective if the pixel contains only zero or one electron, or if it contains more than 1000 electrons.
The skipper CCDs have several applications. One particularly exciting application is to use them to search for dark matter particles as light as a few MeV that scatter off electrons. Such tiny dark matter-electron interactions typically would produce only a few electrons in a pixel, something which can now be measured with the new skipper CCDs. SENSEI can also probe for dark matter as light as a few eV that is absorbed by electrons. For both scattering and absorption, SENSEI will probe orders of magnitude of unexplored dark matter parameter space. The picture on the right shows a prototype ~0.2-gram Skipper CCD operating at the MINOS facility at Fermilab (I took this picture on May 24, 2017). The 100-gram SENSEI experiment is supported by Fermilab and a grant to Stony Brook University from the Heising-Simons Foundation (PI: Essig, Co-I: Tiffenberg). Our first dark matter search results from using this prototype detector appeared in April 2018 on the arxiv here.
I am a co-spokesperson of the APEX collaboration. APEX (A' EXperiment) will search for a new vector boson A' (a "dark photon") with very weak coupling to electrons in the mass range from 65 MeV to 550 MeV. New vector bosons with such small couplings arise naturally from a small kinetic mixing of the "dark photon" A' with the photon -- one of the very few ways in which new forces can couple to the Standard Model -- and have received considerable attention as an explanation of various dark matter related anomalies. A' bosons are produced by radiation off an electron beam, and could appear as narrow resonances with small production cross-section in the QED e+e- spectrum. The figure to the right shows existing constraints on dark photons as well as projections from APEX and HPS.
I am a member of the HPS collaboration. HPS (Heavy Photon Search) will, like APEX, also search for a new vector boson A' with very weak coupling to electrons. APEX and HPS probe largely complementary parameter space. HPS is also sensitive to displaced vertices, allowing it to probe smaller couplings than other fixed-target experiment, but larger couplings than beam-dump experiments.
Fermi Gamma-ray Space Telescope
I am an Affiliated Scientist of the Fermi Large Area Telescope (Fermi-LAT) collaboration. I have contributed to several papers by the collaboration on the indirect detection of dark matter.