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Open access publications by faculty, postdocs, and graduate students in the Department of Physics and Astronomy.
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- ItemNew Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength Problem(Physical Review Letters, 2022-12-05) Kühn, Steffen; Cheung, Charles; Oreshkina, Natalia S.; Steinbrügge, René; Togawa, Moto; Bernitt, Sonja; Berger, Lukas; Buck, Jens; Hoesch, Moritz; Seltmann, Jörn; Trinter, Florian; Keitel, Christoph H.; Kozlov, Mikhail G.; Porsev, Sergey G.; Gu, Ming Feng; Porter, F. Scott; Pfeifer, Thomas; Leutenegger, Maurice A.; Harman, Zoltán; Safronova, Marianna S.; López-Urrutia, José R. Crespo; Shah, ChintanOne of the most enduring and intensively studied problems of x-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of crucial value for plasma diagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power 2.5 times and the signal-to-noise ratio thousandfold compared with our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio Rexp=f3C/f3D=3.51(2)stat(7)sys agrees with our state-of-the-art calculation of Rth=3.55(2), as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of 3C and 3D transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.
- ItemTurbulent Energy Transfer and Proton–Electron Heating in Collisionless Plasmas(Astrophysical Journal, 2022-12-19) Roy, S.; Bandyopadhyay, R.; Yang, Y.; Parashar, T. N.; Matthaeus, W. H.; Adhikari, S.; Roytershteyn, V.; Chasapis, A.; Li, Hui; Gershman, D. J.; Giles, B. L.; Burch, J. L.Despite decades of study of high-temperature weakly collisional plasmas, a complete understanding of how energy is transferred between particles and fields in turbulent plasmas remains elusive. Two major questions in this regard are how fluid-scale energy transfer rates, associated with turbulence, connect with kinetic-scale dissipation, and what controls the fraction of dissipation on different charged species. Although the rate of cascade has long been recognized as a limiting factor in the heating rate at kinetic scales, there has not been direct evidence correlating the heating rate with MHD-scale cascade rates. Using kinetic simulations and in situ spacecraft data, we show that the fluid-scale energy flux indeed accounts for the total energy dissipated at kinetic scales. A phenomenology, based on disruption of proton gyromotion by fluctuating electric fields that are produced in turbulence at proton scales, argues that the proton versus electron heating is controlled by the ratio of the nonlinear timescale to the proton cyclotron time and by the plasma beta. The proposed scalings are supported by the simulations and observations.
- ItemDirect detection of ultralight dark matter bound to the Sun with space quantum sensors(Nature Astronomy, 2022-12-05) Tsai, Yu-Dai; Eby, Joshua; Safronova, Marianna S.Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks.
- ItemDetection of astrophysical tau neutrino candidates in IceCube(The European Physical Journal C, 2022-11-15) IceCube Collaboration; Abbasi, R.; Ackermann, M.; Adams, J.; et al.High-energy tau neutrinos are rarely produced in atmospheric cosmic-ray showers or at cosmic particle accelerators, but are expected to emerge during neutrino propagation over cosmic distances due to flavor mixing. When high energy tau neutrinos interact inside the IceCube detector, two spatially separated energy depositions may be resolved, the first from the charged current interaction and the second from the tau lepton decay. We report a novel analysis of 7.5 years of IceCube data that identifies two candidate tau neutrinos among the 60 “High-Energy Starting Events” (HESE) collected during that period. The HESE sample offers high purity, all-sky sensitivity, and distinct observational signatures for each neutrino flavor, enabling a new measurement of the flavor composition. The measured astrophysical neutrino flavor composition is consistent with expectations, and an astrophysical tau neutrino flux is indicated at 2.8σ significance.
- ItemResonances and near field heat transfer of finite structures(European Physical Society Letters, 2022-12-02) Chui, S. T.; Lin, Zhifang; Zi, JianWe describe a formulation for near field heat transfer for a finite size system so that the heat conductance can be expressed as sums of contributions from the resonances of the combined structure of the “receiver” and the “source”. Our work opens the door to investigating near field heat transfer between finite systems and in particular metamaterials whose resonances have been well studied. We illustrated our results with an analytically tractable example of energy transfer between two split ring resonantors separated by a distance d on top of each other. When the cuts of the two rings are opposite each other, the heat conductance is smaller than when the cuts of the two rings are on top of each other. This result can only come from a finite system calculation.