<p>Millicharged particles are well-motivated dark matter candidates arising in many extensions of the standard model. We show that, despite their tiny coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>e</mi><mi>m</mi></msub></math> to photons, millicharged dark matter (mDM) in the Earth’s geomagnetic field can generate a quasistatic, monochromatic magnetic signal with angular frequency twice the mDM mass. Using null results from the SuperMAG and SNIPE Hunt collaborations, we constrain the effective charge of bosonic mDM in the mass range <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>18</mn></mrow></msup><mo>−</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>14</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>. The resulting upper bounds exceed stellar cooling constraints by over 13 orders of magnitude, demonstrating the power of this method.</p>

China

Ariel Arza

Yuanlin Gong

Jing Shu

Lei Wu

Qiang Yuan

Bin Zhu

Geomagnetic Constraints on Millicharged Dark Matter

Primordial black holes (PBHs), originating from the gravitational collapse of large overdensities in the early Universe, emerge as a compelling dark matter (DM) candidate across a broad mass range. Of particular interest are ultra-light PBHs with masses around 10$^{14}$ to 10$^{17}$ g, which are typically probed by searching their evaporation products. Using the soft X-ray signal measured by the XMM telescopes, we derive constraints on the fraction of PBHs dark matter with masses in the range 10$^{15}$-10$^{16}$ g. We find that observations exclude fraction <math><mi>f</mi><mo>&gt;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>6</mn></mrow></msup></math> at 95% C.L. for mass <math><msub><mrow><mi>M</mi></mrow><mrow><mi>PBH</mi></mrow></msub><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>15</mn></mrow></msup></math> g.

Jun Guo

Probing ultralight primordial black hole dark matter with XMM telescopes

We search for stochastic gravitational wave background emitted from cosmic strings using the Parkes Pulsar Timing Array data over 15 years. While the common power-law excess revealed by several pulsar timing array experiments might be accounted for by the gravitational wave background from cosmic strings, the lack of the characteristic Hellings-Downs correlation cannot establish its physical origin yet. The constraints on the cosmic string model parameters are thus derived with the conservative assumption that the common power-law excess is due to unknown background. Two representative cosmic string models with different loop distribution functions are considered. We obtain constraints on the dimensionless string tension parameter <math><mi>G</mi><mi>μ</mi><mo>&lt;</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>11</mn></mrow></msup><mi>–</mi><msup><mn>10</mn><mrow><mo>−</mo><mn>10</mn></mrow></msup></math>, which is more stringent by two orders of magnitude than that obtained by the high-frequency LIGO-Virgo experiment for one model, and less stringent for the other. The results provide the chance to test the grand unified theories, with the spontaneous symmetry breaking scale of <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> being two-to-three orders of magnitude below <math><msup><mn>10</mn><mn>16</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. The pulsar timing array experiments are thus entirely complementary to the LIGO-Virgo experiment in probing the cosmic strings and the underlying beyond standard model physics in the early Universe.

Ligong Bian

Bo Wang

Junchao Zong

Searching for cosmic string induced stochastic gravitational wave background with the Parkes Pulsar Timing Array

We report a novel search for the cosmic-ray boosted dark matter using the <math><mrow><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>tonne</mi><mo>·</mo><mi>day</mi></mrow></math> full dataset of the PandaX-II detector located at the China Jinping Underground Laboratory. With the extra energy gained from the cosmic rays, sub-GeV dark matter particles can produce visible recoil signals in the detector. The diurnal modulations in rate and energy spectrum are utilized to further enhance the signal sensitivity. Our result excludes the dark matter–nucleon elastic scattering cross section between <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>31</mn></mrow></msup></mrow></math> and <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>28</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> for dark matter masses from <math><mrow><mn>0.1</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> to <math><mrow><mn>0.1</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></math>, with a large parameter space previously unexplored by experimental collaborations.

Xiangyi Cui

Abdusalam Abdukerim

Zihao Bo

Wei Chen

Xun Chen

Yunhua Chen

Chen Cheng

Yunshan Cheng

Yingjie Fan

Deqing Fang

Changbo Fu

Mengting Fu

Lisheng Geng

Karl Giboni

Linhui Gu

Xuyuan Guo

Ke Han

Changda He

Jinrong He

Di Huang

Yanlin Huang

Zhou Huang

Ruquan Hou

United States

Xiangdong Ji

Yonglin Ju

Chenxiang Li

Mingchuan Li

Shu Li

Shuaijie Li

Qing Lin

Jianglai Liu

Xiaoying Lu

Lingyin Luo

Wenbo Ma

Yugang Ma

Yajun Mao

Yue Meng

Nasir Shaheed

Xuyang Ning

Ningchun Qi

Zhicheng Qian

Xiangxiang Ren

Changsong Shang

Guofang Shen

Lin Si

Wenliang Sun

Andi Tan

Yi Tao

Anqing Wang

Meng Wang

Qiuhong Wang

Shaobo Wang

Siguang Wang

Zhou Wang

Wei Wang

Xiuli Wang

Mengmeng Wu

Weihao Wu

Jingkai Xia

Mengjiao Xiao

Xiang Xiao

Pengwei Xie

Binbin Yan

Xiyu Yan

Jijun Yang

Yong Yang

Chunxu Yu

Jumin Yuan

Ying Yuan

Dan Zhang

Minzhen Zhang

Peng Zhang

Tao Zhang

Li Zhao

Qibin Zheng

Jifang Zhou

Ning Zhou

Xiaopeng Zhou

Yong Zhou

Shao-Feng Ge

Search for Cosmic-Ray Boosted Sub-GeV Dark Matter at the PandaX-II Experiment

The fast developments of radio astronomy open a new window to explore the properties of Dark Matter (DM). The recent direct imaging of the supermassive black hole (SMBH) at the center of M87 radio galaxy by the Event Horizon Telescope (EHT) collaboration is expected to be very useful to search for possible new physics. In this work, we illustrate that such results can be used to detect the possible synchrotron radiation signature produced by DM annihilation from the innermost region of the SMBH. Assuming the existence of a spike DM density profile, we obtain the flux density due to DM annihilation induced electrons and positrons, and derive new limits on the DM annihilation cross section via the comparison with the EHT integral flux density at 230 GHz. Our results show that the parameter space can be probed by the EHT observations is largely complementary to other experiments. For DM with typical mass regions of being weakly interacting massive particles, the annihilation cross section several orders of magnitude below the thermal production level can be excluded by the EHT observations under the density spike assumption. Future EHT observations may further improve the sensitivity on the DM searches, and may also provide a unique opportunity to test the interplay between DM and the SMBH.

Guan-Wen Yuan

Zhan-Fang Chen

Zhao-Qiang Shen

Wen-Qing Guo

Ran Ding

Xiaoyuan Huang

Constraints on dark matter annihilation from the Event Horizon Telescope observations of M87*

In the first part of this Chapter the present state of knowledge from the observations of cosmic rays between 10$^{13}$ and 10$^{20}$ eV is summarized. This is not intended to be a complete review, but rather a broad overview of the relevant processes involving cosmic rays, including the astrophysical environments in which they take place. This overview mainly concerns experimental results and phenomenological aspects of their interpretation, therefore experiments’ description is not given but references to the vast bibliography are provided in the text. Some attempt is made to address the most popular explanations offered by theoretical models. The second part is devoted to the description of the LHAASO performance and of its capability to provide a response to several open questions, still unanswered, concerning cosmic rays above 10$^{13}$ eV, highlighting which major steps forward in this field could be taken from LHAASO observations.

Italy

Benedetto D’Ettorre Piazzoli

Si-Ming Liu

Switzerland

Domenico della Volpe

Zhen Cao

Andrea Chiavassa

Yi-Qing Guo

Russia

Leonid T. Ksenofontov

France

Olivier Martineau-Huynh

Diane Martraire

Ling-Ling Ma

Xin-Hua Ma

Yuri Stenkin

Hou-Dun Zeng

Shou-Shan Zhang

Yi Zhang

Hui Zhu

Chapter 4 Cosmic-Ray Physics  

Extra-galactic gamma-ray sources, such as gamma-ray bursts, active galactic nuclei, starburst galaxies, are interesting and important targets for LHAASO observations. In this chapter, the prospects of detecting these sources with LHAASO and their physical implications are studied. The upgrade plan for the Water Cherenkov Detector Array (WCDA), which aims to enhance the detectability of relatively lower energy photons, is also presented. In addition, a study on constraining the extragalactic background light with LHAASO observation of blazars is presented.

Xiang-Yu Wang

Xiao-Jun Bi

Piero Vallania

Han-Rong Wu

Da-Hai Yan

Chapter 3 Extra-galactic gamma-ray sources  

Several groups have reported a possible excess of primary electrons at high energies with the joint fit of the positron fraction and total electron/positron spectra. With the latest release of high-precision electron/positron spectra measured by AMS-02, we further confirm this excess by fitting ΔΦ (i.e., <math><msub><mrow><mi>Φ</mi></mrow><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></msub><mo>−</mo><msub><mrow><mi>Φ</mi></mrow><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></msub></math>) data in this work. Then we investigate the contribution of a single nearby supernova remnant to the primary electron excess and find that Monogem can reasonably account for this excess. Moreover, we predict that the electron spectrum may harden again at a few TeVs due to Vela's contribution. DAMPE, which can accurately measure electrons at TeV scale, is expected to provide the robust test of this new spectral feature in the near future. Finally, we fit the proton spectrum data of DAMPE with Monogem or Loop I. We find that both the primary electron excess and the proton spectral bump could be mainly generated by Monogem.

Tian-Peng Tang

Zi-Qing Xia

Lei Zu

Lei Feng

Yi-Zhong Fan

Jian Wu

Explanation of nearby SNRs for primary electron excess and proton spectral bump

The XENON1T collaboration reported an excess of the low-energy electron recoil events between 1 and 7 keV. We explore the possibility to explain such an anomaly by the MeV-scale dark matter (DM) heated by the interior of the Sun due to the same DM-electron interaction as in the detector. The kinetic energies of heated DM particles can reach a few keV, and can potentially account for the excess signals detected by XENON1T. We study different form factors of the DM-electron interactions, F(q) ∝ q  i  with q being the momentum exchange and i = 0, 1, 2, and find that for all these cases the inclusion of the Sun-heated DM component improves the fit to the XENON1T data. The inferred DM-electron scattering cross section (at q = αm  e  where α is the fine structure constant and m  e  is electron mass) is from ∼ 10 −38 cm2 (for i = 0) to ∼ 10 −42 cm2 (for i = 2). We also derive constraints on the DM-electron cross sections for these form factors, which are stronger than previous results with similar assumptions. We emphasize that the Sun-heated DM scenario relies on the minimum assumption on DM models, which serves as a general explanation of the XENON1T anomaly via DM-electron interaction. The spectrum of the Sun-heated DM is typically soft comparing to other boosted DM, so the small recoil events are expected to be abundant in this scenario. More sensitive direct detection experiments with lower thresholds can possibly distinguish this scenario with other boosted DM models or solar axion models.

Yifan Chen

Ming-Yang Cui

Xiao Xue

Sun heated MeV-scale dark matter and the XENON1T electron recoil excess

We point out a new type of diurnal effect for the cosmic ray boosted dark matter (DM). The DM-nucleon interactions not only allow the direct detection of DM with nuclear recoils but also allow cosmic rays to scatter with and boost the nonrelativistic DM to higher energies. If the DM-nuclei scattering cross sections are sufficiently large, the DM flux is attenuated as it propagates through the Earth, leading to a strong diurnal modulation. This diurnal modulation provides another prominent signature for the direct detection of boosted sub-GeV DM, in addition to signals with higher recoil energy.

Diurnal Effect of Sub-GeV Dark Matter Boosted by Cosmic Rays