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Models and Searches Particle Dark Matter Observations
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Customers who bought this item also bought. Stock Image. New Paperback Quantity Available: 1. Seller Rating:. Particle Dark Matter Gianfranco Bertone editor of compilation. Published by Cambridge University Press , Cambridge New paperback Quantity Available: New Quantity Available: 1. The window functions are shown in Figure 3. The left panel refers to the particle DM cases and shows the redshift dependence of the window functions for the radio, X-ray, and gamma-ray emissions, in both annihilating and decaying scenarios.
The plot shows that a multi-wavelength approach can be quite powerful. Indeed, the different emissions exhibit rather different window functions: each one therefore can provide different and complementary information. In particular, the radio case is more peaked at low redshift, while the X-ray window function has a flatter shape, with the gamma-ray case being somewhat in between.
We also notice that the decaying and annihilating DM cases produce very similar window functions for radio emission, while for X-rays and gamma-rays the window function is flatter in the annihilating case as compared to the decaying case. This occurs because of the effect of clustering, which enhances the signal at larger redshifts.
Figure 3. Window functions. Right: Window functions vs.
Particle Dark Matter : Observations, Models and Searches
They have quite different shapes, as a consequence of the different redshift evolution of the relevant tracers which produce the observed signal. Comparing the two panels of Figure 3 allows to understand which cross-correlation combinations could be optimal although experimental limitations may occur, like limited statistics in one observational channel or angular resolutions.
The weak-lensing shear is peaked at intermediate-low redshift, which makes this observables a good candidate for cross-correlation with particle DM signals, as proposed in Ref. The CMB window function instead extends over a very wide range of redshift in principle, up to the last scattering : this is also why it appears significantly lower, as compared to the other cases in Figure 3 , since we have normalized all window functions to the total average intensity i. In the following, we also normalize all the angular PS to the total averaged intensity, as reported in Equation 5 , in order to make the various cases more easily comparable.
The angular power spectra of annihilating DM are presented in the left panels of Figures 4 — 6 , while the decaying cases are reported in the right panels of the same figures.
Figure 4 shows the auto- and cross-correlations of the electromagnetic signals. The most anisotropic cases involve the radio emission. This is because the radio window function is peaked at low-redshift: the signal therefore comes from a relatively low number of halos and thus is quite anisotropic. The flatter window function of X-rays implies that in this case the number of objects contributing to the intensity field is larger, thus making the emission smoother and the ensuing PS smaller. The gamma-rays case is intermediate to radio and X-rays: as shown by its window function in Figure 3 , the gamma-rays emission is peaked at low-to-intermediate redshifts and this implies a relatively larger anisotropy in the intensity, as compared to X-rays.
The flattening is therefore again related to the redshift distribution. Indeed the inner structure of closer objects, which are more important in the radio case, is resolved at larger angular scale with respect to more distant objects which contribute to the bulk of the emission in the gamma and X-ray cases. Figure 4. Angular PS of radio, X-ray, and gamma-ray emissions auto- and cross-correlations from annihilating DM left panel and decaying DM right panel.
The computation is performed using the 3D PS models reported in Figure 1 and the window functions shown in Figure 3. For the radio-radio case, we also show with the thinner dotted line the effect of a cored DM profile replacing the NFW distribution as a possible results of particle diffusion. The thick and thin dotted lines in the left panel of Figure 4 show the case with an NFW and cored distribution, respectively. The difference is not dramatic notice that this can also be seen as an estimate for the case where the DM distribution itself is cored, although the power spectrum we have been using is based on results of N-body simulations, thus fully consistent only with a cuspy profile.
Summarizing the behavior of the auto- and cross-correlation power spectra of the electromagnetic signals among themselves, we can state that the radio emission exhibits the strongest anisotropy, both among the auto-correlation signals and in combination with the other emissions. These general features occur both for the annihilating and decaying DM signals, with more power at large multipoles for annihilating DM as compared to the decaying case, and with slightly more separation among the different cases again for annihilating DM as compared to decaying DM.
Since we are dealing here with angular power spectra normalized to the average intensity, the actual feasibility of detection will depend also on the absolute normalization level accessible by the different detectors, which is detector specific. Being concerned in this paper with the theoretical properties of the auto- and cross-correlation signals and with the assessment of their mutual impact, we are not adopting here any specific experimental figure of merit: results shown in Figures 4 — 6 can then be folded with the individual detector capabilities.
In fact, the experimental ability to disentangle an anisotropy signal will also depend on the specific features of the detectors and on the astrophysical backgrounds, which also produce an anisotropic electromagnetic emission. Photon detectors at different wavelengths have intrinsically different angular resolution: e. On the other hand, at lower multipoles gamma-rays detector may be more suitable than interferometric radio telescopes.
The combination of the information coming from the auto-correlation signal at different wavelengths, as well as cross-correlations of different signals, may therefore be a relevant tool to identify and characterize a DM signal. Concerning astrophysical backgrounds, a large number of electromagnetic emitters are present, like e. The physical location of these astrophysical sources is to some extent correlated to the DM structures: nevertheless, they possess different properties both in redshift distribution relevant for the ensuing window functions and in spectral features.
These differences can be potentially used to attempt a separation between these backgrounds and the DM signals discussed in this paper. In this paper we are concerned on assessing the size and the relative impact of DM signals. A detailed analysis of the background sources is beyond the scope of the present paper, and for the cases for which studies are present we refer to the quoted references.
The cross-correlation of the gamma and radio emissions with gravitational tracers is shown in Figures 5 , 6 , respectively. This can be again understood by looking at the redshift dependence of the window functions. To have a good overlapping with the electromagnetic DM source, the gravitational tracer has to be peaked at relatively low redshift.
Moreover, as we already discussed, the closer is the emission the more anisotropic it appears and the ensuing angular PS flattens sooner, as a function of the multiple l. From the window function behavior of Figure 3 , we see that the radio signal and the 2MASS tracer are both strongly peaked at very low redshifts: this fact enhances the cross-correlation both because of the large overlap and because closer sources are fewer and therefore more anisotropic.
In the left panel of Figure 6 we show again the effect of a cored distribution, which is even milder than for the auto-correlation PS this occurs because this effect does not affect the LSS tracers and so now modifies only one of the two fields entering in the PS computation. This is again due to the good overlap of the gamma-rays and 2MASS window functions, nevertheless to a lower extent than in the radio case.
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Figure 5. The computation is performed using the 3D PS models reported in Figure 2 and the window functions shown in Figure 3. Figure 6. In the left panel, we also show with thinner lines the case of a cored DM distribution as a possible results of particle diffusion. In the case of cross-correlation with the cosmic-shear, a tomographic approach is feasible, and represents an unique opportunity to test the different redshift scaling we have been discussing Camera et al. The cross-correlation with the CBM lensing observable is the smallest, due to the fact that CMB-lensing sources are distributed in a much deeper interval of redshift, as compared to the electromagnetic emitters.
Summarizing the behavior of the cross-correlation power spectra of the electromagnetic signals with the gravitational tracers, we can state that again the radio emission exhibits the strongest anisotropy signal. The largest effect occurs both for radio and gamma-rays in the cross-correlation to the low-redshift 2MASS population: the angular PS spectrum in this case is about one order of magnitude stronger than the cross-correlations with cosmic shear and NVSS, and about three orders of magnitude larger than the cross-correlation with the CMB-lensing observable.
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We caution again that, however, such differences do not straightforwardly translate into the actual experimental capabilities. In this paper we have discussed extragalactic anisotropies in the electromagnetic emission produced by DM annihilation or decay as a promising tool to search for a DM signal. We have first reviewed the formalism needed to compute a generic 2-point angular power spectrum by following the halo-model description of clustering of structures in the Universe.
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This formalism was then applied to realize estimates involving relevant emissions induced by particle DM annihilations or decays. We have discussed the features and the relative size of the various auto- and cross-correlation angular power spectra that can be envisaged for anisotropy studies. From the side of DM signals we have considered the full multi-wavelength spectrum, including the synchrotron emission at radio frequencies, the IC radiation in the X-ray and gamma-ray bands, as well as the prompt emission of gamma-rays. The angular power spectra of auto-correlation of each of these signals and of the cross-correlation between any pair of them is presented.
As a way to enhance the capability of detection of such non-gravitational signals of DM and to improve their disentanglement from other astrophysical backgrounds we introduce their cross-correlation with maps tracing the gravitational potential. We have analyzed this possibility studying specific gravitational tracers of DM distribution in the Universe: weak-lensing cosmic shear, LSS matter distribution and CMB-lensing. We have shown that cross-correlating a multi-wavelength DM signal which is a direct manifestation of its particle physics nature with a gravitational tracer which is a manifestation of the presence of large amounts of unseen matter in the Universe may offer a prime tool to demonstrate that what we call DM is indeed formed by an elementary particle.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Planck results. Cosmological parameters. CrossRef Full Text. Ando S, Komatsu E.
Anisotropy of the cosmic gamma-ray background from dark matter annihilation. Phys Rev D.