Plasma Astrophysicist | HAPI Research Associate
We discovered a new resonant gravitational instability driven by the relative drift between baryons and dark matter after decoupling. When the projected dark matter drift is subsonic, baryon sound waves resonate with Doppler-shifted dark matter modes, producing exponential growth that exceeds the intrinsic dark matter growth rate. The instability operates on short timescales (years to Myr) across all scales — from planets to galaxy clusters — and naturally explains long-standing puzzles: the persistence of spiral arms in galaxies, the heating of the intracluster medium (cooling flow problem), turbulence in molecular clouds, and high-frequency solar oscillations.
First comprehensive analysis of a new instability that alters the standard picture of gravitational structure formation, unifying subsonic enhancement and supersonic suppression of baryon perturbations.
arXiv:2604.22665 (submitted to ApJ)From driving spiral arms in galaxies to heating the intracluster medium and seeding Population III stars — the instability provides a new lens on dark matter–baryon interactions across all scales.
My research focuses on understanding the microphysics of cosmic ray transport and their significant impact on astrophysical environments, from the interstellar medium to galaxy clusters. I have discovered a novel CR-driven instability at intermediate scales that fundamentally changes how cosmic rays interact with surrounding plasma.
A newly discovered cosmic-ray-driven instability that grows significantly faster than previously known instabilities, with profound implications for CR transport and electron acceleration in galactic halos.
ApJ 2021 JPP Letter 2023Developing predictive frameworks for nonlinear saturation of CR-driven instabilities which dictate their transport properties in realistic astrophysical conditions.
ApJ 2025Using particle-in-cell (PIC) simulations with the SHARP code, I study the microphysics of electron-ion collisionless shocks relevant to supernova remnants, galaxy clusters, and other astrophysical environments. This work elucidates the mechanism by which shocks efficiently accelerate particles to suprathermal energies.
By varying the Alfvénic Mach number, we show that shocks where the intermediate-scale instability operates achieve substantially higher electron acceleration efficiency.
Read PaperStudy demonstrating that simulations using the realistic mass ratio m_i/m_e = 1836 are essential for drawing accurate physical conclusions about shock dynamics.
ApJL 2024 View SimulationsInvestigation of how ion magnetization affects parallel electron-ion collisionless shocks. Strongly magnetized shocks exhibit lower compression ratios and suppressed particle acceleration.
ApJ 2025 View SimulationsAs the primary developer of the SHARP (Spectral Highly Accurate Relativistic PIC) code, I have created a highly accurate plasma dynamics simulator that enables previously intractable simulations of astrophysical plasmas. The code features up to 5th-order spline interpolation, achieving three-order-of-magnitude improvements in energy conservation.
Implemented up to 5th-order spline interpolation for field gathering and particle scattering, dramatically improving energy conservation over standard PIC methods.
ApJ 2017Integrated kinetic, ideal fluid, and Landau-fluid plasma descriptions in a unified framework enabling multi-scale astrophysical simulations.
JPP 2024I investigate the nonlinear evolution of beam-plasma instabilities in diverse astrophysical environments, from solar radio bursts to the intergalactic medium. These instabilities are critical for constraining the strength of intergalactic magnetic fields and understanding energy dissipation in cosmic voids.
Investigation of nonlinear saturation mechanisms of beam-plasma instabilities and their impact on constraints on cosmic magnetic field origins.
ApJ 2017Using particle-in-cell simulations, we re-examine and overturn all previous cosmological constraints on dark photon dark matter by demonstrating that its resonant conversion into ordinary plasma is highly inefficient, saturating at very low levels due to nonlinear plasma dynamics. This work shows that constraints are weakened by factors of 3,000 to 10 million, rendering dark photon dark matter effectively undetectable by current and near-future cosmological observations.
Hook, Huang & Shalaby (2025): Comprehensive study of dark photon dark matter resonant conversion in the early universe, showing saturation due to nonlinear plasma effects.
arXiv:2510.13956 View Simulations