arXiv subjects

Xiao-Jun Bi

Publications and source records attributed to Xiao-Jun Bi.

At least 91 records · Page 5Linked to original sources

arXiv2020

DAMPE proton spectrum indicates a slow-diffusion zone in the nearby ISM

The hardening and softening features in the DAMPE proton spectrum are very likely to be originated from a nearby supernova remnant (SNR). The proton spectrum from the nearby SNR is required to be very hard below $\approx10$ TeV. To reproduce this feature, we illustrate that anomalously slow-diffusion zone for cosmic rays (CRs) must be existed in the local interstellar medium (ISM) after also taking the dipole anisotropy of CRs into account. Assuming that the diffusion coefficient is homogeneous in the nearby ISM, we show that the diffusion coefficient is constrained to the magnitude of $10^{26}$ cm$^2$ s$^{-1}$ when normalized to 1 GeV, which is about 100 times smaller than the average value in the Galaxy. We further discuss the spatial distribution of the slow diffusion and find two distinct possibilities. In one case, the SNR is several hundred of parsecs away from the solar system, meanwhile both the SNR and the solar system are required to be included in a large slow-diffusion zone. The homogeneous diffusion belongs to this case. In the other case, the SNR is very close with a distance of $\sim50$ pc and the slow-diffusion zone is only limited around the SNR. The required diffusion coefficient is further smaller in the latter case. This work provides a new way of studying the CR diffusion in the local ISM.

astro-ph.HE↗

arXiv2020

The implications of the axion like particle from the Fermi-LAT and H.E.S.S. observations of PG 1553+113 and PKS 2155-304

We investigate the axion like particle (ALP)-photon oscillation effect in the high energy $γ$-ray spectra of PG 1553+113 and PKS 2155-304 measured by Fermi-LAT and H.E.S.S.. The choice of extragalactic background light (EBL) model, which induces the attenuate effect in observed $γ$-ray spectra, would affect the ALP implication. For the ordinary EBL model that prefers a null hypothesis, we set constraint on the ALP-photon coupling constant at 95% C.L. as $g_{aγ}\lesssim 5\times 10^{-11} ~\rm{GeV}^{-1}$ for the ALP mass $\sim 10$ neV. We also consider the CIBER observation of the cosmic infrared radiation, which shows an excess at the wave wavelength of $\sim 1~μ$m after the substraction of foregrounds. The high energy gamma-rays from extragalactic sources at high redshifts would suffer from a more significant attenuate effect caused by this excess. In this case, we find that the ALP-photon oscillation would improve the fit to the observed spectra of PKS 2155-304 and PG 1553+113 and find a favored parameter region at 95% C.L..

astro-ph.HE↗

arXiv2019

Holographic Technicolor Model and Dark Matter

We investigate the strongly coupled minimal walking technicolor model (MWT) in the framework of a bottom-up holographic model, where the global $SU(4)$ symmetry breaks to $SO(4)$ subgroup. In the holographic model, we found that 125GeV composite Higgs particles and small Peskin-Takeuchi $S$ parameter can be achieved simultaneously. In addition, the model predicts a large number of particles at the TeV scale, including dark matter candidate Technicolor Interacting Massive Particles (TIMPs). If we consider the dark matter nuclear spin-independent cross-section in the range of $10^{-45}\sim 10 ^ {-48} $cm$^2$, which can be detected by future experiments, the mass range of TIMPs predicted by the holographic technicolor model is 2 $\sim$ 4 TeV.

hep-ph↗

arXiv2019

Prospect for dark matter signatures from dwarf galaxies by LHAASO

The Large High Altitude Air Shower Observatory (LHAASO) is a next-generation observatory for high energy gamma rays and cosmic rays with wide field of view. It will detect gamma rays with high sensitivity in the energy range from 300 GeV to 1 PeV. Therefore, it is promising for LHAASO to search for the high-energy gamma rays induced by dark matter (DM) self-annihilation in dwarf spheroidal satellite galaxies (dSphs), which are ideal objects for the DM indirect detection. In this work, we investigate the LHAASO sensitivity to DM self-annihilation signatures for 19 dSphs and take the uncertainties on the spatial DM distribution of dSphs into account. We perform a joint likelihood analysis for the 19 dSphs and find that the LHAASO sensitivity to the DM annihilation cross section will reach $\mathcal{O}(10^{-24})\sim \mathcal{O}(10^{-25})$ cm$^3$ s$^{-1}$ at the mass scale above TeV for several annihilation modes, which is larger than the canonical thermal relic cross section by a factor of 10 to 100.

astro-ph.HE↗

arXiv2019

Possible origin of the slow-diffusion region around Geminga

Geminga pulsar is surrounded by a multi-TeV $γ$-ray halo radiated by the high energy electrons and positrons accelerated by the central pulsar wind nebula (PWN). The angular profile of the $γ$-ray emission reported by HAWC indicates an anomalously slow diffusion for the cosmic-ray electrons and positrons in the halo region around Geminga. In the paper we study the possible mechanism for the origin of the slow diffusion. At first, we consider the self-generated Alfvén waves due to the streaming instability of the electrons and positrons released by Geminga. However, even considering a very optimistic scenario for the wave growth, we find this mechanism DOES NOT work to account for the extremely slow diffusion at the present day if taking the proper motion of Geminga pulsar into account. The reason is straightforward as the PWN is too weak to generate enough high energy electrons and positrons to stimulate strong turbulence at the late time. We then propose an assumption that the strong turbulence is generated by the shock wave of the parent supernova remnant (SNR) of Geminga. Geminga may still be inside the SNR, and we find that the SNR can provide enough energy to generate the slow-diffusion circumstance. The TeV halos around PSR B0656+14, Vela X, and PSR J1826-1334 may also be explained under this assumption.

astro-ph.HE↗

arXiv2019

Reanalyze the pulsar scenario to explain the cosmic positron excess considering the recent developments

As the TeV halos around Geminga and PSR B0656+14 have been confirmed by HAWC, slow diffusion of cosmic rays could be general around pulsars, and the cosmic positron spectrum from pulsars could be significantly changed. As a consequence, the most likely pulsar source of the positron excess, Geminga, is no more a viable candidate under the additional constraint from Fermi-LAT. Moreover, the latest measurement by AMS-02 shows a clear cutoff in the positron spectrum, which sets a strict constraint on the age of the pulsar source. Considering these new developments we reanalyze the scenario in this work. By checking all the observed pulsars under the two-zone diffusion scenario, we propose for the first time that PSR B1055-52 is a very promising source of the positron excess. B1055-52 can well reproduce both the intensity and the high-energy cut of the AMS-02 positron spectrum, and may also explain the H.E.S.S $e^-+e^+$ spectrum around 10 TeV. Moreover, if the slow diffusion is universal in the local interstellar medium, B1055-52 will be the unique reasonable source of the AMS-02 positron spectrum among the observed pulsars.

astro-ph.HE↗

arXiv2019

Time dependent solar modulation of cosmic rays from solar minimum to solar maximum

We study the time-dependent modulation effect and derive the local interstellar spectra (LIS) for the cosmic ray (CR) proton, helium, boron and carbon. A two-dimensional modulation model including the variation of the interplanetary environment with time is adopted to describe modulation process. The propagation equation of CRs in the heliosphere is numerically solved by the package Solarprop. We derive the LIS by fitting the latest results of several experiments, including Voyager 1, PAMELA, BESS-POLARII and ACE, during low solar activity periods. We further study the modulation in the polarity reversal periods with the PAMELA proton data. We find that the rigidity dependence of the diffusion coefficient is critical to explain the modulation effect during reversal periods. Our results also indicate a power law relation between the diffusion coefficient and the magnitude of the heliospheric magnetic field (HMF) at the Earth.

astro-ph.HE↗

arXiv2019

Investigating the dark matter signal in the cosmic ray antiproton flux with the machine learning method

We investigate the implications on the dark matter (DM) signal from the AMS-02 cosmic antiproton flux. Global fits to the data are performed under different propagation and hadronic interaction models. The uncertainties from the injection spectrum, propagation effects and solar modulation of the cosmic rays are taken into account comprehensively. Since we need to investigate extended parameter regions with multiple free parameters in the fit, the machine learning method is adopted to maintain a realistic time cost. We find all the effects considered in the fitting process interplay with each other, among which the hadronic interaction model is the most important factor affecting the result. In most hadronic interaction and CR propagation models no DM signal is found with significance larger than $2σ$ except that the EPOS-LHC interaction model requires a more than $3σ$ DM signal with DM mass around $1\,\mathrm{TeV}$. For the diffusive reacceleration propagation model there is a highly significant DM signal with mass around $100\,\mathrm{GeV}$. However, the signal becomes less than $1σ$ if we take a charge dependent solar modulation potential in the analysis.

astro-ph.HE↗

arXiv2019

Impact of Fermionic Electroweak Multiplet Dark Matter on Vacuum Stability with One-loop Matching

We investigate the effect of fermionic electroweak multiplet dark matter models on the stability of the electroweak vacuum using two-loop renormalization group equations (RGEs) and one-loop matching conditions. Such a treatment is crucial to obtain reliable conclusions, compared with one-loop RGEs and tree-level matching conditions. In addition, we find that the requirement of perturbativity up to the Planck scale would give strong and almost mass-independent constraints on the Yukawa couplings in the dark sector. We also evaluate these models via the idea of finite naturalness for the Higgs mass fine-tuning issue.

hep-ph↗

arXiv2018

Two-zone diffusion of electrons and positrons from Geminga explains the positron anomaly

The recent HAWC observations of very-high-energy $γ$-ray halo around Geminga and Monogem indicate a very slow diffusion of cosmic rays, which results in tiny contribution of positrons from these two pulsars to the local flux. This makes the cosmic positron excess anomaly observed by PAMELA and AMS-02 even more puzzling. However, from the Boron-to-Carbon ratio data one can infer that the average diffusion coefficient in the Galaxy should be much larger. In this work we propose a two-zone diffusion model that the diffusion is slow only in a small region around the source, outside of which the propagation is as fast as usual. We find that such a scenario can naturally explain the positron excess data with parameters even more reasonable than that in the conventional one-zone diffusion model. The reason is that during the life time of Geminga ($\sim 300$ kyr) the electrons/positrons have propagated too far away with a fast diffusion and lead to a low local flux. The slow diffusion region in the two-zone model helps to confine the electrons/positrons for a long time and lead to an enhancement of the local flux. So under the constraint of the HAWC observations, pulsars are still the probable origin of the cosmic-ray positron excess.

astro-ph.HE↗

arXiv2018

Discriminating Local Sources of High-Energy Cosmic Electrons and Positrons by Current and Future Anisotropy Measurements

The Fermi-LAT detects no significant anisotropy of the cosmic-ray (CR) electrons and positrons ($e^-+e^+$) with seven years of data, which provides the strongest restriction to the $e^-+e^+$ anisotropy up to now. As next generation CR observatory, HERD is expected to have a better capability of anisotropy detection than Fermi-LAT. In this paper, we discuss several models aimed to explain the AMS-02 data by the present and future anisotropy measurements. We find that the upper limits of Fermi-LAT disfavor Vela SNR as the dominant source in sub-TeV, while other cases that remain safe under the constraint of Fermi-LAT are expected to be distinguished from each other by HERD. We then discuss the possibilities of remarkable TeV spectral features, and test the corresponding anisotropies. We find the conditions under which the TeV model can have a prominent spectral feature and avoid the constraint of Fermi-LAT at the same time. Furthermore, the expected performance of HERD is sensitive enough to detect the anisotropies of all these TeV models, and even for the case of a featureless TeV spectrum. Thus HERD may play a crucial part in the study of the origin of cosmic electrons and positrons.

astro-ph.HE↗

arXiv2018

Constraint on the velocity dependent dark matter annihilation cross section from gamma-ray and kinematic observations of ultrafaint dwarf galaxies

Searching for gamma rays from dwarf spheroidal galaxies (dSphs) is a promising approach to detect dark matter (DM) due to the high DM densities and low baryon components in dSphs. The Fermi-LAT observations from dSphs have set stringent constraints on the velocity independent annihilation cross section. However, the constraints from dSphs may change in velocity dependent annihilation scenarios because of the different velocity dispersions in galaxies. In this work, we study how to set constraints on the velocity dependent annihilation cross section from the combined Fermi-LAT observations of dSphs with the kinematic data. In order to calculate the gamma ray flux from the dSph, the correlation between the DM density profile and velocity dispersion at each position should be taken into account. We study such correlation and the relevant uncertainty from kinematic observations by performing a Jeans analysis. Using the observational results of three ultrafaint dSphs with large J-factors, including Willman 1, Reticulum II, and Triangulum II, we set constraints on the p-wave annihilation cross section in the Galaxy as an example.

astro-ph.HE↗

arXiv2018

Exploring Fermionic Dark Matter via Higgs Boson Precision Measurements at the Circular Electron Positron Collider

We study the impact of fermionic dark matter (DM) on projected Higgs precision measurements at the Circular Electron Positron Collider (CEPC), including the one-loop effects on the $e^+e^-\to Zh$ cross section and the Higgs boson diphoton decay, as well as the tree-level effects on the Higgs boson invisible decay. As illuminating examples, we discuss two UV-complete DM models, whose dark sector contains electroweak multiplets that interact with the Higgs boson via Yukawa couplings. The CEPC sensitivity to these models and current constraints from DM detection and collider experiments are investigated. We find that there exist some parameter regions where the Higgs measurements at the CEPC will be complementary to current DM searches.

hep-ph↗

arXiv2018

Exploring triplet-quadruplet fermionic dark matter at the LHC and future colliders

We study the signatures of the triplet-quadruplet dark matter model at the LHC and future colliders, including the 100 TeV Super Proton-Proton Collider and the 240 GeV Circular Electron Positron Collider. The dark sector in this model contains one fermionic electroweak triplet and two fermionic quadruplets, which have two kinds of Yukawa couplings to the Higgs doublet. Electroweak production signals of the dark sector fermions in the $\text{monojet}+/\!\!\!\!E_\mathrm{T}$, disappearing track, and $\text{multilepton}+/\!\!\!\!E_\mathrm{T}$ channels at the LHC and the Super Proton-Proton Collider are investigated. Moreover, we study the loop effects of this model on the Circular Electron Positron Collider precision measurements of $e^+e^-\to Zh$ and $h\toγγ$. We find that most of the parameter regions allowed by the observed dark matter relic density will be well explored by such direct and indirect searches at future colliders.

hep-ph↗

arXiv2018

Searching for Gamma-Ray Emission from Reticulum II by Fermi-LAT

Recently, many new dwarf spheroidal satellites (dSphs) have been discovered by the Dark Energy Survey (DES). These dSphs are ideal candidates for probing for gamma-ray emissions from dark matter (DM) annihilation. However, no significant signature has been found by the Fermi-LAT dSph observations. In this work, we reanalyze the Fermi-LAT Pass 8 data from the direction of Reticulum II, where a slight excess has been reported by some previous studies. We treat Reticulum II (DES J0335.6-5403) as a spatially extended source, and and that no significant gamma-ray signature is observed. Based on this result, we set upper-limits on the DM annihilation cross section.

astro-ph.HE↗

arXiv2018

Fermi Large Area Telescope detection of gamma-ray emission from the direction of supernova iPTF14hls

The remnant of supernova explosion is widely believed to be the acceleration site of high-energy cosmic ray particles. The acceleration timescale is, however, typically very long. Here we report the detection of a variable $γ$-ray source with the Fermi Large Area Telescope, which is positionally and temporally consistent with a peculiar supernova, iPTF14hls. A quasi-stellar object SDSS J092054.04+504251.5, which is probably a blazar according to the infrared data, is found in the error circle of the $γ$-ray source. More data about the $γ$-ray source and SDSS J092054.04+504251.5 are needed to confirm their association. On the other hand, if the association between the $γ$-ray source and the supernova is confirmed, this would be the first time to detect high-energy $γ$-ray emission from a supernova, suggesting very fast particle acceleration by supernova explosions.

astro-ph.HE↗

arXiv2018

Expectations of the Cosmic Antideuteron Flux

The cosmic antideuteron is a promising probe for the dark matter annihilation signature. In order to determine the DM signature, the background astrophysical antideuteron flux should be carefully studied. In this work we provide a new calculation of the secondary antideuteron flux, and pay special attention to the uncertainties from hadronic interaction models by using several Monte Carlo generators. The uncertainties from propagation effects are also carefully investigated for both the astrophysical background and DM annihilation signature in several scenarios, which are constrained by the latest B/C ratio measured by AMS-02. Considering these uncertainties, we find that the secondary antideuteron flux is hard to detect in the near future detectors. However, the antideuteron signature from dark matter annihilation will be detectable even considering the constraint from the AMS-02 observation of the $\bar{p}/p$ ratio.

astro-ph.HE↗

arXiv2017

Explanations of the DAMPE high energy electron/positron spectrum in the dark matter annihilation and pulsar scenarios

Many studies have shown that either the nearby astrophysical source or dark matter (DM) annihilation/decay is required to explain the origin of high energy cosmic ray (CR) $e^\pm$, which are measured by many experiments, such as PAMELA and AMS-02. Recently, the Dark Matter Particle Explorer (DAMPE) collaboration has reported its first result of the total CR $e^\pm$ spectrum from $25 \,\mathrm{GeV}$ to $4.6 \,\mathrm{TeV}$ with high precision. In this work, we study the DM annihilation and pulsar interpretations of the DAMPE high energy $e^\pm$ spectrum. In the DM scenario, the leptonic annihilation channels to $τ^+τ^-$, $4μ$, $4τ$, and mixed charged lepton final states can well fit the DAMPE result, while the $μ^+μ^-$ channel has been excluded. In addition, we find that the mixed charged leptons channel would lead to a sharp drop at $\sim$ $\mathrm{TeV}$. However, these DM explanations are almost excluded by the observations of gamma-ray and CMB, unless some complicated DM models are introduced. In the pulsar scenario, we analyze 21 nearby known pulsars and assume that one of them is the primary source of high energy CR $e^\pm$.Considering the constraint from the Fermi-LAT observation of the $e^\pm$ anisotropy, we find that two pulsars are possible to explain the DAMPE data. Our results show that it is difficult to distinguish between the DM annihilation and single pulsar explanations of high energy $e^\pm$ with the current DAMPE result.

astro-ph.HE↗