Diffuse flux of ultra-high energy photons from cosmic-ray interactions in the disk of the Galaxy and implications for the search for decaying super-heavy dark matter
An estimate of the expected photon flux above $10^{17}~$eV from the interactions of ultra-high energy cosmic rays with the matter in the Galactic disk is presented. Uncertainties arising from the distribution of the gas in the disk, the absolute level of the cosmic ray flux, and the composition of the cosmic rays are taken into account. Within these uncertainties, the integrated photon flux above $10^{17}~$eV is, averaged out over Galactic latitude less than $5^\circ$, between $\simeq 3.2{\times}10^{-2}~$km$^{-2}~$yr$^{-1}~$sr$^{-1}$ and $\simeq 8.7{\times}10^{-2}~$km$^{-2}~$yr$^{-1}~$sr$^{-1}$. The all-sky average value amounts to $\simeq 1.1{\times}10^{-2}~$km$^{-2}~$yr$^{-1}~$sr$^{-1}$ above $10^{17}~$eV and decreases roughly as $E^{-2}$, making this diffuse flux the dominant one from cosmic-ray interactions for energy thresholds between $10^{17}~$eV and $10^{18}$~eV. Compared to the current sensitivities of detection techniques, a gain between two and three orders of magnitude in exposure is required for a detection below $\simeq 10^{18}$~eV. The implications for searches for photon fluxes from the Galactic center that would be indicative of the decay of super-heavy dark matter particles are discussed, as the photon flux presented in this study can be considered as a floor below which other signals would be overwhelmed.
We consider scenario of the dark matter consisting of two fractions, stable part being dominant and a smaller unstable fraction, which has decayed after the recombination epoch. It has been suggested in Ref. [arxiv:1505.03644] that the above scenario may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (cepheid variables and SNe Ia, cluster counts) cosmological measurements. We derive constraints on the heavy relics branching to $q\bar{q}$, $e^+e^-$, $μ^+μ^-$, $τ^+τ^-$, $ν_e\bar{ν_e}$, $ν_μ\bar{ν_μ}$, $W^+W^-$ and $γγ$ in the above scenario by comparison of the seconda…
We estimate the sensitivity of LHAASO telescope for the large angular scale diffuse gamma-ray flux in multi-TeV - multi-PeV energy range. We discuss possible sources of the signal in this energy range including the guaranteed flux from cosmic ray interactions in the interstellar medium and possible flux from decaying dark matter. We show that LHAASO will be able to detect the diffuse cosmic ray induced gamma-ray flux up to high Galactic latitude regions thus providing firm identification of the Galactic cosmic ray component of the astrophysical neutrino signal detected by IceCube and clarifica…
Dwarf spheroidal galaxies are compact stellar objects with small or negligible astrophysical backgrounds, widely considered as promising targets to search for a signal from the dark matter decay and annihilation. We present constraints on the lifetime of the superheavy decaying dark matter branching to the $q\bar{q}$ channel in the mass range $10^{19} - 10^{25}$ eV based on the directional limits on the ultra-high-energy (UHE) gamma rays obtained by the Pierre Auger Observatory and the Telescope Array experiment. Attenuation effects during the propagation of UHE photons towards Earth are taken…
It is shown that the antiproton spectrum reported by the AMS02 collaboration can be accounted for by dark matter (DM) decay if the residence time in the Galactic halo is of order 90 Myr. The DM lifetime assumed, $ 5 \cdot 10^{27}$ s for DM particle mass of 3 TeV, is shown to be consistent with the constraints of diffuse gamma ray background. Alternative sources of antiprotons, such as those from compact objects, are shown to be strongly constrained by neutrino astronomy and therefore unlikely candidates.
We use the recent measurement of the isotropic $γ$-ray background (IGRB) by Fermi LAT and analysis of the contribution of unresolved point $γ$-ray sources to IGRB to build constraints on the models of ultra-high cosmic rays (UHECR) origin. We also calculate the minimal expected diffuse $γ$-ray flux produced by UHECR interactions with an interstellar photon background. Finally, for the subclass of dark matter (DM) models with decaying weakly interacting massive particles (WIMP), we build constraints on the particle decay time using minimal expected contributions to the IGRB from unresolved poin…
We performed the deepest search for an X-ray emission line between 0.5 and 7 keV from non-baryonic dark matter with the Suzaku XIS. Dark matter associated with the Milky Way galaxy was selected as the target to obtain the best signal-to-noise ratio. From the Suzaku archive, we selected 187 data sets of blank sky regions which were dominated by the X-ray diffuse background. The data sets were from 2005 to 2013. Instrumental responses were adjusted by multiple calibration data sets of the Crab Nebula. We also improved the technique of subtracting lines of instrumental origin. These energy spectr…
Cosmic rays accelerated to ultra-high energies (E>4x10^19 eV) in electric fields in accretion discs around supermassive black holes are discussed. Particle injection spectra are assumed to be harder than those formed in acceleration on shock fronts. It turned out that cosmic rays with injection spectra supposed contribute a little in the particle flux detected with ground-based arrays. But in the extragalactic space particle generate a noticeable flux of the diffuse gamma-ray emission compared with the data obtained with the Fermi LAT instrument (onboard the Fermi space observatory). The inten…
The diffuse $γ$-ray spectrum at sub-PeV energy region has been measured for the first time by the Tibet-AS$γ$ experiment. It will shed new light on the understanding of origin and propagation of Galactic cosmic rays at very high energies. It has been pointed out that the traditional cosmic ray propagation model based on low energy measurements undershoot the new data, and modifications of the model with new ingredients or alternative propagation framework is required. In this work, we propose that the hadronic interactions between freshly accelerated cosmic rays and the medium surrounding the …
Limit on the diffuse flux of ultra-high energy tau neutrinos with the surface detector of the Pierre Auger Observatory
在皮埃尔·俄歇天文台收集的数据被用来建立宇宙辐射中τ中微子扩散通量的上限。掠过地球的$ν_τ$可能在地壳中相互作用，并通过带电电流相互作用产生$τ$轻子。$τ$轻子可能从地球中出现，并在大气中衰变，产生一个具有典型特征的几乎水平的簇射，即使在非常大的大气深度也是一个持续的电磁分量。本文描述了在宇宙线引起的正常簇射背景下，选择由$τ$衰变引起的事件的搜索过程。详细介绍了计算随时间连续增长的探测器曝光量的方法。系统的不确定性，从探测器的曝光，分析和所涉及的物理进行了讨论。对于能量范围为$τ$ eV $< E_ν$ $<$ $2\times10^{19}$ eV的中微子，假设扩散谱的形式为$E_ν^{-2}$，2004年1月1日至2008年4月30日收集的数据产生了90%的置信度上限为$E_ν^{2} \mathrm{d}N_{ν_τ}/\mathrm{d}E_ν < 9 \times 10^{-8}$ GeV cm $^{-2}$ s $^{-1}$ sr $^{-1}$。
We suggest a possible mechanism of ultra diffuse galaxy formation: the UDGs may occur as a result of a central collision of galaxies. If the galaxies are young and contain a lot of gas, the collision may kick all the gas off the systems and thus strongly suppress any further star formation. As a result, the galaxies now have a very low surface brightness and other properties typical of the ultra diffuse galaxies. We use the Coma cluster (where numerous UDGs were recently discovered) to test the efficiency of the process. The mechanism works very well and can transform a significant fraction of…
The search for ultra-high energy downward-going and Earth-skimming cosmic neutrinos by the Surface Detector array of the Pierre Auger Observatory (PAO) is analyzed in the ADD model with n extra flat spatial dimensions. We assumed that the diffuse neutrino flux dN_nu/dE_nu$ is equal to k E_nu^(-20) in the energy range 10^(17) eV - 2.5 10^(19) eV. Taking into account that no neutrino events where found by the PAO, we have estimated an upper bound on a value of k. It is shown that this bound can be stronger than the upper bound on k recently obtained by the Pierre Auger Collaboration, depending o…
The diffuse $γ$-ray emission was measured up to $957$ TeV by the Tibet-AS$γ$ experiment recently. Assuming that it is produced by the hadronic interaction between cosmic ray nuclei and the interstellar medium, it requires that the cosmic ray nuclei should be accelerated well beyond PeV energies. Measurements of the cosmic ray spectra for different species show diverse results at present. The Tibet experiments showed that the spectrum of proton plus helium has an early knee below PeV. If this is correct, the diffuse $γ$-ray emission would suggest an additional component of Galactic cosmic rays …
Ultra-high-energy (UHE) neutrinos, with EeV-scale energies, carry with them unique insight into fundamental open questions in astrophysics and particle physics. For fifty years, they have evaded discovery, but maybe not for much longer, thanks to new UHE neutrino telescopes, presently under development. We capitalize on this upcoming opportunity by producing state-of-the-art forecasts of the discovery of a diffuse flux of UHE neutrinos in the next 10-20 years. By design, our forecasts are anchored in often-overlooked nuance from theory and experiment; we gear them to the radio array of the pla…
Electron-positron Annihilation Lines and Decaying Sterile Neutrinos
如果存在大量的惰性中微子，它们衰变为光子和/或电子-正电子对可能会引起可观察到的后果。我们考虑了MeV无菌中微子衰变导致银河系中心弥散正电子湮没线的可能性，并由此从相关的天体物理/宇宙学数据中得到了无菌中微子衰变率$Γ_e \ge 10^{-28}$ s $^{-1}$的界.此外，我们预计软伽马流量$1.2 \times 10^{-4}-9.7 \times 10^{-4}$ ph cm $^{-2}$ s $^{-1}$从银河系中心，显示为一个小MeV的颠簸在背景光子谱。此外，我们还估计了无菌中微子衰变产生的活动中微子穿过地球的通量为$0.02-0.1$ cm $^{-2}$ s $^{-1}$。
Current and Future Constraints on Dark Matter from Prompt and Inverse-Compton Photon Emission in the Isotropic Diffuse Gamma-ray Background
我们进行了详细的检查，从提示和逆康普顿发射光子，包括模型相关和模型无关的边界的湮灭和衰变暗物质模型的电流约束。我们还表明，所观察到的各向同性弥散伽马射线背景（DGRB），这提供了一个最保守的约束模型的湮灭弱尺度暗物质粒子，可能会提高其灵敏度的一个因素~2至3（95% C. L.）。因为费米-LAT实验通过五年的观测解决了DGRB贡献的blazar源。对于我们的预测，我们采用的结果约束的光度依赖的密度演化加上blazar光谱能量分布序列模型，这是由DGRB和blazar源计数分布函数的约束。
Diffuse radio emission at the centre of galaxy clusters has been observed both in merging clusters on scales of Mpc, called giant radio haloes, and in relaxed systems with a cool-core on smaller scales, named mini haloes. Giant radio haloes and mini haloes are thought to be distinct classes of sources. However, recent observations have revealed the presence of diffuse radio emission on Mpc scales in clusters that do not show strong dynamical activity. RX J1720.1+2638 is a cool-core cluster, presenting both a bright central mini halo and a fainter diffuse, steep-spectrum emission extending beyo…
