Astro-particle physics

An interesting question arises: if we could create a new particle using colliders, would it signal particle dark matter?The answer is no. Like the story of the “Blind Men and an Elephant”, any new particle created in colliders must not only match the relic density but also provide a clear signal from our universe, as current evidence for dark matter comes from astrophysical and cosmological measurements.Assuming dark matter particles are everywhere, we might detect their collisions with Standard Model particles, and identify the products of their interactions with Standard Model particles rather than the dark matter itself.Therefore, dark matter direct detection (DD) and indirect detection (ID) methods are designed to explore these signals.DD aims to directly measure dark matter collisions with nucleons or electrons in Earth-based experiments like Xenon1T, PandaX, and LZ. In contrast, ID uses telescopes such as the Fermi gamma-ray telescope, AMS-02, DAMPE, and the IceCube neutrino observatory to search for these products, helping to constrain the annihilation cross-section for annihilating dark matter and the lifetime of decaying dark matter.

First, WIMPs are a well-studied dark matter candidate in DD experiments. Many theoretical models include WIMPs, but their variety complicates comparisons with detection data. To address this, an effective theory has been developed for the non-relativistic limit, simplifying dark matter-nucleon interactions and facilitating the study of nuclear response functions. In Ref¹, we use this framework for spin-1/2 dark matter and combine likelihood functions from the latest PandaX, LUX, and XENON1T data to provide joint limits on effective couplings, accounting for astrophysical uncertainties in dark matter distribution. We also discuss isospin-violating interactions and provide updated limits on new physics mass scales for both dimension-five and dimension-six effective theories above the electroweak scale.

Dark matter in the universe might directly produce antimatter. Our team at Purple Mountain Observatory (PMO) particularly focuses on detecting dark matter annihilation signals in the AMS02 antiproton measurement. Although astrophysical processes, such as inelastic collisions between cosmic rays and interstellar matter, also generate antimatter particles, they form the background for detecting dark matter signals. The fluxes of antimatter particles from astronomical processes are much lower than that of corresponding matter particles, providing better sensitivity for detecting antimatter produced by dark matter annihilation. Using precise measurements of cosmic ray nuclei and antiprotons from AMS-02, our team improved the expected antiproton spectrum from astronomical background models. Comparing the observed antiproton fluxes with the expected background, we found an excess that can be explained by dark matter annihilation models. Importantly, the parameter regions used to explain the antiproton excess, the gamma-ray excess from the Galactic center, and the faint gamma-ray excess observed in some dwarf spheroidal galaxies are highly consistent. As presented in Fig 5, our Bayesian analysis revealed a notable confidence level for a new antiproton component, potentially from dark matter.

In work², we reevaluate the potential for detecting dark matter annihilation signals in the Galactic Center, focusing on velocity-dependent dynamics within a dense spike near the supermassive black hole (SgrA). We examine three annihilation processes—p-wave, resonance, and forbidden annihilation—under semi-relativistic velocities, using gamma-ray data from the Fermi and DAMPE telescopes. Through comprehensive six-dimensional integration, we accurately calculate DM-induced gamma-ray fluxes near SgrA, taking into account the velocity and positional dependencies of the annihilation cross-section and photon yield spectra. Our results emphasize the resonance and forbidden annihilation scenarios, where larger coupling can impact spike density, potentially producing detectable gamma-ray line spectra within the energy resolution of Fermi and DAMPE.

The standard DD strategy involves measuring the recoil energy from dark matter-nucleon interactions. As the Earth moves through the local virialized halo, Maxwell-Boltzmann distributed dark matter particles collide with the detector. Due to their non-relativistic velocities, these particles do not produce detectable recoil energy for masses under 5 GeV in xenon detectors and are ineffective in the coannihilation region, where their small kinetic energy cannot excite particles to the next lightest state. To address this, we have studied detecting accelerated virialized dark matter by considering collisions with high-energy cosmic ray protons³. These collisions can accelerate dark matter particles with masses below a few GeV to relativistic speeds, allowing them to be detected underground with kinetic energies above the designed threshold. This method can reveal dark matter masses previously undetectable with the standard approach. Similarly, light dark matter can be detected with neutrino telescopes⁴ or through inelastic scattering with heavy cosmic rays⁵. Additionally, collisions between cosmic ray protons and dark matter might produce neutrinos and gamma rays⁶.

Finally, because the signals from DD and ID both include astrophysical and particle physical information, our team aims to separate particle dark matter information from astronomical data by pre-calculating and tabulating astronomical uncertainties, resulting in a likelihood function for the residual flux. To achieve this, we developed the numerical tool LikeDM⁷¹. This software bridges dark matter theoretical models and observational data, allowing users unfamiliar with data processing and astronomical backgrounds to easily test their models with observational data.