arXiv subjects

Qiang Yuan

Publications and source records attributed to Qiang Yuan.

215 records · Page 12Linked to original sources

arXiv2009

Dark matter annihilation and non-thermal Sunyaev-Zel'dovich effect: I. galaxy cluster

In this work we calculate the Sunyaev-Zel'dovich (SZ) effect due to the $e^+e^-$ from dark matter (DM) annihilation in galaxy clusters. Two candidates of DM particle, (1) the weakly-interacting massive particle (WIMP) and (2) the light dark matter (LDM) are investigated. For each case, we also consider several DM profiles with and without central cusp. We generally find smaller signals than previously reported. Moreover, the diffusion of electrons and positrons in the galaxy clusters, which was generally thought to be negligible, is considered and found to have significant effect on the central electron/positron distribution for DM profile with large spatial gradient. We find that the SZ effect from WIMP is almost always non-observable, even for the highly cuspy DM profile, and using the next generation SZ interferometer such as ALMA. Although the signal of the LDM is much larger than that of the WIMP, the final SZ effect is still very small due to the smoothing effect of diffusion. Only for the configuration with large central cusp and extremely small diffusion effect, the LDM induced SZ effect might have a bit chance of being detected.

astro-ph.CO↗

arXiv2009

Discriminating different scenarios to account for the cosmic $e^\pm$ excess by synchrotron and inverse Compton radiation

The excesses of the cosmic positron fraction recently measured by PAMELA and the electron spectra by ATIC, PPB-BETS, Fermi and H.E.S.S. indicate the existence of primary electron and positron sources. The possible explanations include dark matter annihilation, decay, and astrophysical origin, like pulsars. In this work we show that these three scenarios can all explain the experimental results of the cosmic $e^\pm$ excess. However, it may be difficult to discriminate these different scenarios by the local measurements of electrons and positrons. We propose possible discriminations among these scenarios through the synchrotron and inverse Compton radiation of the primary electrons/positrons from the region close to the Galactic center. Taking typical configurations, we find the three scenarios predict quite different spectra and skymaps of the synchrotron and inverse Compton radiation, though there are relatively large uncertainties. The most prominent differences come from the energy band $10^4\sim 10^9$ MHz for synchrotron emission and $\gtrsim 10$ GeV for inverse Compton emission. It might be able to discriminate at least the annihilating dark matter scenario from the other two given the high precision synchrotron and diffuse $γ$-ray skymaps in the future.

astro-ph↗

arXiv2009

On the e$^+$e$^-$ excesses and the knee of the cosmic ray spectra -- hints of cosmic rays acceleration at young supernova remnants

Supernova remnants have long been regarded as sources of the Galactic cosmic rays up to petaelectronvolts, but convincing evidence is still lacking. In this work we explore the common origin of the subtle features of the cosmic ray spectra, such as the knee of cosmic ray spectra and the excesses of electron/positron fluxes recently observed by ATIC, H.E.S.S., Fermi-LAT and PAMELA. Numerical calculation shows that those features of cosmic ray spectra can be well reproduced in a scenario with e$^+$e$^-$ pair production by interactions between high energy cosmic rays and background photons in an environment similar to the young supernova remnant. The success of such a coherent explanation serves in turn as an evidence that at least a portion of cosmic rays might be accelerated at young supernova remnants.

astro-ph.HE↗

arXiv2009

Perspective of Galactic dark matter subhalo detection on Fermi from the EGRET observation

The perspective of the detectability of Galactic dark matter subhaloes on the Fermi satellite is investigated in this work. Under the assumptions that dark matter annihilation accounts for the "GeV excess" of the Galactic diffuse $γ$-rays discovered by EGRET and the $γ$-ray flux is dominated by the contribution from subhaloes of dark matter, we calculate the expected number of dark matter subhaloes that Fermi may detect. We show that Fermi may detect a few tens to several hundred subhaloes in 1-year all sky survey. Since EGRET observation is taken as a normalization, this prediction is independent of the particle physics property of dark matter. The uncertainties of the prediction are discussed in detail. We find that the major uncertainty comes from the mass function of subhaloes, i.e., whether the subhaloes are "point like" (high-mass rich) or "diffuse like" (low-mass rich). Other uncertainties like the background estimation and the observational errors will contribute a factor of $2\sim 3$.

astro-ph↗

arXiv2009

Parameters in a Class of Leptophilic Dark Matter Models from PAMELA, ATIC and FERMI

In this work we study a class of leptophilic dark matter models, where the dark matter interacts with the standard model particles via the $U(1)_{L_i-L_j}$ gauge boson, to explain the $e^{\pm}$ excess in cosmic rays observed by ATIC and PAMELA experiments, and more recently by Fermi experiment. There are three types of $U(1)_{L_i-L_j}$ models: a) $U(1)_{L_e - L_μ}$, b) $U(1)_{L_e - L_τ}$, and c) $U(1)_ {L_e-L_τ}$. Although ATIC or Fermi data is consistent with PAMELA data separately, ATIC and Fermi data do not agree with each other. We therefore aim to identify which of the three models can explain which data set better. We find that models a) and b) can give correct dark matter relic density and explain the ATIC and PAMELA data simultaneously recur to the Breit-Wigner enhancement. Whereas model c) with a larger $Z^\prime$ mass can explain Fermi and PAMELA data simultaneously. In all cases the model parameters are restricted to narrow regions. Future improved data will decide which set of data are correct and also help to decide the correct dark matter model.

hep-ph↗

arXiv2009

Non-Thermal Production of WIMPs, Cosmic $e^\pm$ Excesses and $γ$-rays from the Galactic Center

In this paper we propose a dark matter model and study aspects of its phenomenology. Our model is based on a new dark matter sector with a U(1)' gauge symmetry plus a discrete symmetry added to the Standard Model of particle physics. The new fields of the dark matter sector have no hadronic charges and couple only to leptons. Our model can not only give rise to the observed neutrino mass hierarchy, but can also generate the baryon number asymmetry via non-thermal leptogenesis. The breaking of the new U(1)' symmetry produces cosmic strings. The dark matter particles are produced non-thermally from cosmic string loop decay which allows one to obtain sufficiently large annihilation cross sections to explain the observed cosmic ray positron and electron fluxes recently measured by the PAMELA, ATIC, PPB-BETS, Fermi-LAT, and HESS experiments while maintaining the required overall dark matter energy density. The high velocity of the dark matter particles from cosmic string loop decay leads to a low phase space density and thus to a dark matter profile with a constant density core in contrast to what happens in a scenario with thermally produced cold dark matter where the density keeps rising towards the center. As a result, the flux of gamma rays radiated from the final leptonic states of dark matter annihilation from the Galactic center is suppressed and satisfies the constraints from the HESS gamma-ray observations.

hep-ph↗

arXiv2009

Testing Lorentz Invariance with Ultra High Energy Cosmic Ray Spectrum

The GZK cutoff predicted at the Ultra High Energy Cosmic Ray (UHECR) spectrum as been observed by the HiRes and Auger experiments. The results put severe constraints on the effect of Lorentz Invariance Violation(LIV) which has been introduced to explain the absence of GZK cutoff indicated in the AGASA data. Assuming homogeneous source distribution with a single power law spectrum, we calculate the spectrum of UHECRs observed on Earth by taking the processes of photopion production, $e^+e^-$ pair production and adiabatic energy loss into account. The effect of LIV is also taken into account in the calculation. By fitting the HiRes monocular spectra and the Auger combined spectra, we show that the LIV parameter is constrained to $ξ=-0.8^{+3.2}_{-0.5}\times10^{-23}$ and $0.0^{+1.0}_{-0.4}\times10^{-23}$ respectively, which is well consistent with strict Lorentz Invariance up to the highest energy.

astro-ph↗

arXiv2009

The diffuse GeV-TeV $γ$-ray emission of the Cygnus region

Recently the Milagro experiment observed diffuse multi-TeV gamma-ray emission in the Cygnus region, which is significantly stronger than what predicted by the Galactic cosmic ray model. However, the sub-GeV observation by EGRET shows no excess to the prediction based on the same model. This TeV excess implies possible high energy cosmic rays populated in the region with harder spectrum than that observed on the Earth. In the work we studied this theoretical speculation in detail. We find that, a diffuse proton source with power index $α_p\lesssim 2.3$, or a diffuse electron source with power index $α_e\lesssim2.6$ can reproduce the Milagro's observation without conflicting with the EGRET data. Further detections on neutrinos, a diagnostic of the hadronic model, and hard X-ray synchrontron radiation, a diagnostic of the lepton model, help to break this degeneracy. In combination with the gamma ray observations to several hundred GeV by Fermi, we will be able to understand the diffuse emission mechanisms in the Cygnus region better.

astro-ph↗

arXiv2009

Signatures of the Baryon Acoustic Oscillations on the Convergence Power Spectrum of Weak lensing by Large Scale Structure

We employ an analytical approach to investigate the signatures of Baryon Acoustic Oscillations (BAOs) on the convergence power spectrum of weak lensing by large scale structure. It is shown that the BAOs wiggles can be found in both of the linear and nonlinear convergence power spectra of weak lensing at about $40\le l\le600$, but they are weaker than that of matter power spectrum. Although the statistical error for LSST are greatly smaller than that of CFHT and SNAP survey especially at about $30<l<300$, they are still larger than the their maximum variations of BAOs wiggles. Thus, the detection of BAOs with the ongoing and upcoming surveys such as LSST, CFHT and SNAP survey confront a technical challenge.

astro-ph↗

arXiv2008

Reconstruction of Gas Temperature and Density Profiles of the Galaxy Cluster RX J1347.5-1145

We use observations of Sunyaev-Zel'dovich effect and X-ray surface brightness to reconstruct the radial profiles of gas temperature and density under the assumption of a spherically symmetric distribution of the gas. The method of reconstruction, first raised by Silk & White, depends directly on the observations of the Sunyaev-Zel'dovich effect and the X-ray surface brightness, without involving additional assumptions such as the equation of state of the gas or the conditions of hydrostatic equilibrium. We applied this method to the cluster RX J1347.5-1145, which has both the Sunyaev-Zel'dovich effect and X-ray observations with relative high precision. It is shown that it will be an effective method to obtain the gas distribution in galaxy clusters. Statistical errors of the derived temperature and density profiles of gas were estimated according to the observational uncertainties.

astro-ph↗

arXiv2008

Cosmological Constraints from Hubble parameter $H(z)$ and SN Ia observations

In this paper, we use a set of observational $H(z)$ data (OHD) to constrain the $Λ$CDM cosmology. This data set can be derived from the differential ages of the passively evolving galaxies. Meanwhile, the $\mathcal {A}$-parameter, which describes the Baryonic Acoustic Oscillation (BAO) peak, and the newly measured value of the Cosmic Microwave Background (CMB) shift parameter $\mathcal {R}$ are used to present combinational constraints on the same cosmology. The combinational constraints favor an accelerating flat universe while the flat $Λ$CDM cosmology is also analyzed in the same way. We obtain a result compatible with that by many other independent cosmological observations. We find that the observational $H(z)$ data set is a complementarity to other cosmological probes.

astro-ph↗

arXiv2008

PAMELA data and leptonically decaying dark matter

Recently PAMELA released their first results on the positron and antiproton ratios. Stimulated by the new data, we studied the cosmic ray propagation models and calculated the secondary positron and antiproton spectra. The low energy positron ratio can be consistent with data in the convection propagation model. Above $\sim 10$ GeV PAMELA data shows a clear excess on the positron ratio. However, the secondary antiproton is roughly consistent with data. The positron excess may be a direct evidence of dark matter annihilation or decay. We compare the positron and anti-proton spectra with data by assuming dark matter annihilates or decays into different final states. The PAMELA data actually excludes quark pairs being the main final states, disfavors gauge boson final states. Only in the case of leptonic final states the positron and anti-proton spectra can be explained simultaneously. We also compare the decaying and annihilating dark matter scenarios to account for the PAMELA results and prefer to the decaying dark matter. Finally we consider a decaying neutralino dark matter model in the frame of supersymmetry with R-parity violation. The PAMELA data is well fitted with neutralino mass $600\sim 2000$ GeV and life time $\sim 10^{26}$ seconds. We also demonstrate that neutralino with mass around 2TeV can fit PAMELA and ATIC data simultaneously.

hep-ph↗

arXiv2008

The diffuse Galactic gamma-rays from dark matter annihilation

The diffuse Galactic $γ$-rays from EGRET observation shows excesses above 1 GeV in comparison with the expectations from conventional Galactic cosmic ray (CR) propagation model. In the work we try to solve the "GeV excess" problem by dark matter (DM) annihilation in the frame of supersymmetry (SUSY). Compared with previous works, there are three aspects improved in this work: first, the direction-independent "boost factor" for diffuse $γ$-rays from dark matter annihilation (DMA) is naturally reproduced by taking the DM substructures into account; second, there is no need for renormalization of the diffuse $γ$-ray background produced by CRs; last but not the least, in this work our new propagation model can give consistent results of both diffuse $γ$-rays and antiprotons, by directly adding the signals from DMA to the diffuse $γ$-ray background. This is a self-consistent model among several possible scenarios at present, and can be tested or optimized by the forthcoming experiments such as GLAST, PAMELA and AMS02.

astro-ph↗

arXiv2008

Diffuse $γ$-rays and $\bar{p}$ flux from dark matter annihilation -- a model for consistent results with EGRET and cosmic ray data

In this work we develop a new propagation model for the Galactic cosmic rays based on the GALPROP code, including contributions from dark matter annihilation. The model predicts compatible Galactic diffuse $γ$ ray spectra with EGRET data in all sky regions. It also gives consistent results of the diffuse $γ$ ray longitude and latitude distributions. Further the results for B/C, $^{10}$Be/$^9$Be, proton, electron and antiproton spectra are also consistent with cosmic ray measurements. In the model we have taken a universal proton spectrum throughout the Galaxy without introducing large fluctuation for the proton energy loss is negligible. The dark matter annihilation signals are `boosted' after taking the contribution from subhalos into account. Another interesting feature of the model is that it gives better description of the diffuse $γ$ rays when taking the source distribution compatible with supernova remnants data, which is different from previous studies.

astro-ph↗

arXiv2008

Constraints on the Dark Matter Annihilations by Neutrinos with Substructure Effects Included

Dark matter (DM) annihilations in the Galaxy may produce high energy neutrinos, which can be detected by the neutrino telescopes, for example IceCube, ANTARES and Super-Kamiokande. The neutrinos can also arise from hadronic interaction between cosmic ray and atmosphere around the Earth, known as atmospheric neutrino. Current measurements on neutrino flux is consistent with theoretical prediction of atmospheric neutrino within the uncertainties. In this paper, by requiring that the DM annihilation neutrino flux is less than the current measurements, we obtain an upper bound on the cross section of dark matter annihilation $ < {σv} >$. Compared with previous investigations, we improve the bound by including DM substructure contributions. In our paper, two kinds of substructure effects are scrutinized. One is the substructure average contribution over all directions. The other is point source effect by single massive sub-halo. We found that the former can improve the bound by several times, while the latter can improve the bound by $ 10^1 \sim 10^4$ utilizing the excellent angular resolution of neutrino telescope IceCube. The exact improvement depends on the DM profile and the sub-halo concentration model. In some model, IceCube can achieve the sensitivity of $ < {σv} > \sim 10^{- 26} cm^3 s^{- 1} $.

astro-ph↗

arXiv2008

Scaling Relation between Sunyaev-Zel'dovich Effect and X-ray Luminosity and Scale-Free Evolution of Cosmic Baryon Field

It has been revealed recently that, in the scale free range, i.e. from the scale of the onset of nonlinear evolution to the scale of dissipation, the velocity and mass density fields of cosmic baryon fluid are extremely well described by the self-similar log-Poisson hierarchy. As a consequence of this evolution, the relations among various physical quantities of cosmic baryon fluid should be scale invariant, if the physical quantities are measured in cells on scales larger than the dissipation scale, regardless the baryon fluid is in virialized dark halo, or in pre-virialized state. We examine this property with the relation between the Compton parameter of the thermal Sunyaev-Zel'dovich effect, $y(r)$, and X-ray luminosity, $L_{\rm x}(r)$, where $r$ being the scale of regions in which $y$ and $L_{\rm x}$ are measured. According to the self-similar hierarchical scenario of nonlinear evolution, one should expect that 1.) in the $y(r)$-$L_x(r)$ relation, $y(r)=10^{A(r)}[L_{\rm x}(r)]^{α(r)}$, the coefficients $A(r)$ and $α(r)$ are scale-invariant; 2.) The relation $y(r)=10^{A(r)}[L_{\rm x}(r)]^{α(r)}$ given by cells containing collapsed objects is also available for cells without collapsed objects, only if $r$ is larger than the dissipation scale. These two predictions are well established with a scale decomposition analysis of observed data, and a comparison of observed $y(r)$-$L_x(r)$ relation with hydrodynamic simulation samples. The implication of this result on the characteristic scales of non-gravitational heating is also addressed.

astro-ph↗

arXiv2007

The Galactic positron flux and dark matter substructures

In this paper we calculate the Galactic positron flux from dark matter annihilation in the frame of supersymmetry, taking the enhancement of the flux by existence of dark matter substructures into account. The propagation of positrons in the Galactic magnetic field is solved in a realistic numerical model GALPROP. The secondary positron flux is recalculated in the GLAPROP model. The total positron flux from secondary products and dark matter annihilation can fit the HEAT data well when taking a cuspy density profile of the substructures.

astro-ph↗