Accurate calculations of the WIMP halo around the Sun and prospects for gamma ray detection

Weakly interacting massive particles (WIMPs) can be captured by heavenly objects, like the Sun. Under the process of being captured by the Sun, they will build up a population of WIMPs around it, that will eventually sink to the core of the Sun. It has been argued with simpler estimates before that this halo of WIMPs around the Sun could be a strong enough gamma ray source to be a detectable signature for WIMP dark matter. We here revisit the problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma ray flux. Compared to earlier estimates, we find that the gamma ray flux from WIMP annihilations in the Sun halo would be negligible and no current or planned detectors would even be able to detect this flux.Comment: 5 pages, 1 figure. To appear in the proceedings of the Identification of Dark Matter conference (IDM 2008), Stockholm, Sweden, 18-22 August, 200

Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection

Galactic weakly interacting massive particles (WIMPs) may scatter off solar nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs continue to lose energy by repeated scatters in the Sun, eventually leading to complete entrapment in the solar interior. While the density of the bound population is highest at the center of the Sun, the only observable signature of WIMP annihilations inside the Sun is neutrinos. It has been previously suggested that although the density of WIMPs just outside the Sun is lower than deep inside, gamma rays from WIMP annihilation just outside the surface of the Sun, in the so called WIMP halo around the Sun, may be more easily detected. We here revisit this problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma-ray flux. Compared to earlier simpler estimates, we find that the gamma-ray flux from WIMP annihilations in the solar WIMP halo would be negligible; no current or planned detectors would be able to detect this flux.Comment: 18 pages, 7 figures, latex, updated to match published version

Gamma rays from ultracompact primordial dark matter minihalos

Ultracompact minihalos have recently been proposed as a new class of dark matter structure. These minihalos would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute non-baryonic massive compact halo objects (MACHOs) today. We examine the prospect of detecting ultracompact minihalos in gamma-rays if dark matter consists of self-annihilating particles. We compute present-day fluxes from minihalos produced in the electron-positron annihilation epoch, and the QCD and electroweak phase transitions in the early Universe. Even at a distance of 100 pc, minihalos produced during the electron-positron annihilation epoch should be eminently detectable today, either by the Fermi satellite, current Air Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos formed in the QCD phase transition would have similar predicted fluxes to the dwarf spheroidal galaxies targeted by current indirect dark matter searches, so might also be detectable by present or upcoming experiments.Comment: 5 pages, 3 figures. Minor update to match published version of erratu

The Local Dark Matter Density from SDSS-SEGUE G-dwarfs

We derive the local dark matter density by applying the integrated Jeans equation method from Silverwood et al. (2016) to SDSS-SEGUE G-dwarf data processed and presented by B\"udenbender et al. (2015). We use the MultiNest Bayesian nested sampling software to fit a model for the baryon distribution, dark matter and tracer stars, including a model for the 'tilt term' that couples the vertical and radial motions, to the data. The $\alpha$-young population from B\"udenbender et al. (2015) yields the most reliable result of $\rho_{\rm DM} = 0.46^{+0.07}_{-0.09}\, {{\rm GeV\, cm}^{-3}} = 0.012^{+0.001}_{-0.002}\, {{\rm M}_\odot \, {\rm pc}^{-3}}$. Our analyses yield inconsistent results for the $\alpha$-young and $\alpha$-old data, pointing to problems in the tilt term and its modelling, the data itself, the assumption of a flat rotation curve, or the effects of disequilibria.Comment: 17 pages, 10 figures, submitted to MNRA

A non-parametric method for measuring the local dark matter density

We present a new method for determining the local dark matter density using kinematic data for a population of tracer stars. The Jeans equation in the $z$-direction is integrated to yield an equation that gives the velocity dispersion as a function of the total mass density, tracer density, and the tilt term that describes the coupling of vertical and radial motions. We then fit a dark matter mass profile to tracer density and velocity dispersion data to derive credible regions on the vertical dark matter density profile. Our method avoids numerical differentiation, leading to lower numerical noise, and is able to deal with the tilt term while remaining one dimensional. In this study we present the method and perform initial tests on idealised mock data. We also demonstrate the importance of dealing with the tilt term for tracers that sample $\gtrsim 1$ kpc above the disc plane. If ignored, this results in a systematic underestimation of the dark matter density.Comment: V2: Improved tracer density description; increased number of mocks to explore outliers; corrected sign error in the (R, z) velocity dispersion; main conclusions unchanged. 19 pages, 14 figure

Erratum: Observational constraints on supermassive dark stars

No abstract is available for this article

Finding high-redshift dark stars with the James Webb Space Telescope

The first stars in the history of the Universe are likely to form in the dense central regions of 10^5-10^6 Msolar cold dark matter halos at z=10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that dark stars at z>6 are intrinsically too faint to be detected by JWST. However, by exploiting foreground galaxy clusters as gravitational telescopes, certain varieties of cool (Teff < 30000 K) dark stars should be within reach at redshifts up to z=10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least 1 percent of the total stellar mass in such objects.Comment: 12 pages, 7 figures; v2: matches published versio

The WIMP capture process for dark stars in the early universe

The first stars to form in the universe may have been dark stars, powered by dark matter annihilation instead of nuclear fusion. The initial amount of dark matter gathered by the star gravitationally can sustain it only for a limited period of time. It has been suggested that capture of additional dark matter from the environment can prolong the dark star phase even to the present day. Here we show that this capture process is ineffective to prolong the life of the first generation of dark stars. We construct a Monte-Carlo simulation that follows each Weakly Interacting Massive Particle (WIMP) in the dark matter halo as its orbit responds to the formation and evolution of the dark star, as it scatters off the star's nuclei, and as it annihilates inside the star. A rapid depletion of the WIMPs on orbits that cross the star causes the demise of the first generation of dark stars. We suggest that a second generation of dark stars may in principle survive much longer through capture. We comment on the effect of relaxing our assumptions.Comment: 13 pages, 6 figure

Observational constraints on supermassive dark stars

Some of the first stars could be cooler and more massive than standard stellar models would suggest, due to the effects of dark matter annihilation in their cores. It has recently been argued that such objects may attain masses in the 10^4--10^7 solar mass range, and that such supermassive dark stars should be within reach of the upcoming James Webb Space Telescope. Notwithstanding theoretical difficulties with this proposal, we argue here that some of these objects should also be readily detectable with both the Hubble Space Telescope and ground-based 8--10 m class telescopes. Existing survey data already place strong constraints on 10^7 solar mass dark stars at z~10. We show that such objects must be exceedingly rare or short-lived to have avoided detection.Comment: 6 pages, 4 figures. v3: erratum incorporate