69 research outputs found

    DAMA and the self similar infall halo model

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    The annual modulation in the rate of WIMP recoils observed by the DAMA collaboration at high significance is often analyzed in the context of an isothermal Maxwell-Boltzmann velocity distribution. While this is the simplest model, there is a need to consider other well motivated theories of halo formation. In this paper, we study a different halo model, that of self similar infall which is characterized by the presence of a number of cold streams and caustics, not seen in simulations. It is shown that the self similar infall model is consistent with the DAMA result both in amplitude and in phase, for WIMP masses exceeding ≈\approx 250 GeV at the 99.7% confidence level. Adding a small thermal component makes the parameter space near mχm_\chi = 12 GeV consistent with the self similar model. The minimum χ2\chi^2 per degree of freedom is found to be 0.92(1.03) with(without) channeling taken into account, indicating an acceptable fit. For WIMP masses much greater than the mass of the target nucleus, the recoil rate depends only on the ratio σp/mχ\sigma_{\rm p}/m_\chi which is found to be ≈\approx 0.06 femtobarn/TeV. However as in the case of the isothermal halo, the allowed parameter space is inconsistent with the null result obtained by the CDMS and Xenon experiments for spin-independent elastic scattering. Future experiments with directional sensitivity and mass bounds from accelerator experiments will help to distinguish between different halo models and/or constrain the contribution from cold flows.Comment: Main conclusions unchanged. Text is expanded, figures and references added. Accepted for publication in Physical Review D, and this replacement reflects the final versio

    Caustics, cold flows, and annual modulation

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    We discuss the formation of dark matter caustics, and their possible detection by future dark matter experiments. The annual modulation expected in the recoil rate measured by a dark matter detector is discussed. We consider the example of dark matter particles with a Maxwell-Boltzmann velocity distribution modified by a cold stream due to a nearby caustic. It is shown that the effect of the caustic flow is potentially detectable, even when the density enhancement due to the caustic is small. This makes the annual modulation effect an excellent probe of inner caustics. We also show that the phase of the annual modulation at low recoil energies does not constrain the particle mass unless the velocity distribution of particles in the solar neighborhood is known.Comment: Minor corrections made, replaced to reflect the published versio

    Distinguishing standard reionization from dark matter models

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    The Wilkinson Microwave Anisotropy Probe (WMAP) experiment has detected reionization at the 5.5σ5.5 \sigma level and has reported a mean optical depth of 0.088±0.0150.088 \pm 0.015. A powerful probe of reionization is the large-angle EEEE polarization power spectrum, which is now (since the first five years of data from WMAP) cosmic variance limited for 2≤l≤62\le l \le6. Here we consider partial reionization caused by WIMP dark matter annihilation, and calculate the expected polarization power spectrum. We compare the dark matter models with a standard 2-step reionization theory, and examine whether the models may be distinguished using current, and future CMB observations. We consider dark matter annihilation at intermediate redshifts (z<60z<60) due to halos, as well as annihilation at higher redshifts due to free particles. In order to study the effect of high redshift dark matter annihilation on CMB power spectra, it is essential to include the contribution of residual electrons (left over from recombination) to the ionization history. Dark matter halos at redshifts z<60z<60 influence the low multipoles l<20l<20 in the EEEE power spectrum, while the annihilation of free particle dark matter at high redshifts z>100z>100 mainly affects multipoles l>10l>10.Comment: Minor corrections. Published in Phys. Rev. Replaced to reflect the published versio
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