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Search Results: 1 - 10 of 340362 matches for " Annika H. G. Peter "
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Dark matter bound to the Solar System: consequences for annihilation searches
Annika H. G. Peter
Physics , 2009,
Abstract: One method to search for particle dark matter is to hunt down its annihilation products. In the Solar System, three potential types of signals of annihilation have been identified: neutrinos and gamma-rays from the Sun, and neutrinos from the Earth. Each of these signals depends sensitively on the orbital evolution of dark matter once it becomes bound to the Solar System. I will review progress on characterizing these signals based on recent improvements in the determination of the properties of the bound dark matter population.
Dark matter in the solar system I: The distribution function of WIMPs at the Earth from solar capture
Annika H. G. Peter
Physics , 2009, DOI: 10.1103/PhysRevD.79.103531
Abstract: The next generation of dark matter (DM) direct detection experiments and neutrino telescopes will probe large swaths of dark matter parameter space. In order to interpret the signals in these experiments, it is necessary to have good models of both the halo DM streaming through the solar system and the population of DM bound to the solar system. In this paper, the first in a series of three on DM in the solar system, we present simulations of orbits of DM bound to the solar system by solar capture in a toy solar system consisting of only the Sun and Jupiter, assuming that DM consists of a single species of weakly interacting massive particle (WIMP). We describe how the size of the bound WIMP population depends on the WIMP mass, spin-independent cross section, and spin-dependent cross section. Using a standard description of the Galactic DM halo, we find that the maximum enhancement to the direct detection event rate, consistent with current experimental constraints on the WIMP-nucleon cross section, is < 1% relative to the event rate from halo WIMPs, while the event rate from neutrinos from WIMP annihilation in the center of the Earth is unlikely to meet the threshold of next-generation, km^3-sized (IceCube, KM3NeT) neutrino telescopes.
Dark matter in the solar system III: The distribution function of WIMPs at the Earth from gravitational capture
Annika H. G. Peter
Physics , 2009, DOI: 10.1103/PhysRevD.79.103533
Abstract: In this last paper in a series of three on weakly interacting massive particle (WIMP) dark matter in the solar system, we focus on WIMPs bound to the system by gravitationally scattering off of planets. We present simulations of WIMP orbits in a toy solar system consisting of only the Sun and Jupiter. As previous work suggested, we find that the density of gravitationally captured WIMPs at the Earth is small and largely insensitive to the details of elastic scattering in the Sun. However, we find that the density of gravitationally captured WIMPs may be affected by external Galactic gravitational fields. If such fields are unimportant, the density of gravitationally captured WIMPs at the Earth should be similar to the maximum density of WIMPs captured in the solar system by elastic scattering in the Sun. Using standard assumptions about the halo WIMP distribution function, we find that the gravitationally captured WIMPs contribute negligibly to direct detection event rates. While these WIMPs do dominate the annihilation rate of WIMPs in the Earth, the resulting event rate in neutrino telescopes is too low to be observed in next-generation neutrino telescopes.
Dark matter in the solar system II: WIMP annihilation rates in the Sun
Annika H. G. Peter
Physics , 2009, DOI: 10.1103/PhysRevD.79.103532
Abstract: We calculate the annihilation rate of weakly interacting massive particles (WIMPs) in the Sun as a function of their mass and elastic scattering cross section. One byproduct of the annihilation, muon neutrinos, may be observed by the next generation of neutrino telescopes. Previous estimates of the annihilation rate assumed that any WIMPs from the Galactic dark halo that are captured in the Sun by elastic scattering off solar nuclei quickly reach thermal equilibrium in the Sun. We show that the optical depth of the Sun to WIMPs and the gravitational forces from planets both serve to decrease the annihilation rate below these estimates. While we find that the sensitivity of upcoming km^3-scale neutrino telescopes to ~100 GeV WIMPs is virtually unchanged from previous estimates, the sensitivity of these experiments to ~10 TeV WIMPs may be an order of magnitude less than the standard calculations would suggest. The new estimates of the annihilation rates should guide future experiment design and improve the mapping from neutrino event rates to WIMP parameter space.
Mapping the allowed parameter space for decaying dark matter models
Annika H. G. Peter
Physics , 2010, DOI: 10.1103/PhysRevD.81.083511
Abstract: I consider constraints on a phenomenological decaying-dark-matter model, in which two weakly-interacting massive particle (WIMP) species have a small mass splitting, and in which the heavier particle decays to the lighter particle and a massless particle on cosmological timescales. The decay parameter space is parameterized by $v_k$, the speed of the lighter particle in the center-of-mass frame of the heavier particle prior to decay, and the decay time $\tau$. Since I consider the case in which dark-matter halos have formed before there has been significant decay, I focus on the effects of decay in already-formed halos. I show that the $v_k-\tau$ parameter space may be constrained by observed properties of dark-matter halos. I highlight which set of observations is likely to yield the cleanest constraints on $v_k-\tau$ parameter space, and calculate the constraints in those cases in which the effect of decay on the observables can be calculated without N-body simulations of decaying dark matter. I show that for $v_k \gtrsim 5\times 10^3$ km s$^{-1}$, the z=0 galaxy cluster mass function and halo mass-concentration relation constrain $\tau \gtrsim$ 40 Gyr, and that precise constraints on $\tau$ for smaller $v_k$ will require N-body simulations.
Getting the astrophysics and particle physics of dark matter out of next-generation direct detection experiments
Annika H. G. Peter
Physics , 2009, DOI: 10.1103/PhysRevD.81.087301
Abstract: The next decade will bring massive new data sets from experiments of the direct detection of weakly interacting massive particle (WIMP) dark matter. The primary goal of these experiments is to identify and characterize the dark-matter particle species. However, mapping the data sets to the particle-physics properties of dark matter is complicated not only by the considerable uncertainties in the dark-matter model, but by its poorly constrained local distribution function (the "astrophysics" of dark matter). In this Letter, I propose a shift in how to do direct-detection data analysis. I show that by treating the astrophysical and particle physics uncertainties of dark matter on equal footing, and by incorporating a combination of data sets into the analysis, one may recover both the particle physics and astrophysics of dark matter. Not only does such an approach yield more accurate estimates of dark-matter properties, but may illuminate how dark matter coevolves with galaxies.
WIMP astronomy and particle physics with liquid-noble and cryogenic direct-detection experiments
Annika H. G. Peter
Physics , 2011, DOI: 10.1103/PhysRevD.83.125029
Abstract: Once weakly-interacting massive particles (WIMPs) are unambiguously detected in direct-detection experiments, the challenge will be to determine what one may infer from the data. Here, I examine the prospects for reconstructing the local speed distribution of WIMPs in addition to WIMP particle-physics properties (mass, cross sections) from next-generation cryogenic and liquid-noble direct-detection experiments. I find that the common method of fixing the form of the velocity distribution when estimating constraints on WIMP mass and cross sections means losing out on the information on the speed distribution contained in the data and may lead to biases in the inferred values of the particle-physics parameters. I show that using a more general, empirical form of the speed distribution can lead to good constraints on the speed distribution. Moreover, one can use Bayesian model-selection criteria to determine if a theoretically-inspired functional form for the speed distribution (such as a Maxwell-Boltzmann distribution) fits better than an empirical model. The shape of the degeneracy between WIMP mass and cross sections and their offset from the true values of those parameters depends on the hypothesis for the speed distribution, which has significant implications for consistency checks between direct-detection and collider data. In addition, I find that the uncertainties on theoretical parameters depends sensitively on the upper end of the energy range used for WIMP searches. Better constraints on the WIMP particle-physics parameters and speed distribution are obtained if the WIMP search is extended to higher energy (~ 1 MeV).
Dark Matter: A Brief Review
Annika H. G. Peter
Physics , 2012,
Abstract: From astronomical observations, we know that dark matter exists, makes up 23% of the mass budget of the Universe, clusters strongly to form the load-bearing frame of structure for galaxy formation, and hardly interacts with ordinary matter except gravitationally. However, this information is not enough to identify the particle specie(s) that make up dark matter. As such, the problem of determining the identity of dark matter has largely shifted to the fields of astroparticle and particle physics. In this talk, I will review the current status of the search for the nature of dark matter. I will provide an introduction to possible particle candidates for dark matter and highlight recent experimental astroparticle- and particle-physics results that constrain the properties of those candidates. Given the absence of detections in those experiments, I will advocate a return of the problem of dark-matter identification to astronomy, and show what kinds of theoretical and observational work might be used to pin down the nature of dark matter once and for all. This talk is intended for a broad astronomy audience.
Comments on recent work on dark-matter capture in the Solar System
Joakim Edsjo,Annika H. G. Peter
Physics , 2010,
Abstract: Recently, several papers have appeared that examine the process of capturing dark-matter particles from the Galactic halo to orbits bound to the Solar System. The authors of these papers predict large enhancements to the local dark-matter density via gravitational three-body interactions with planets. However, these conclusions are wrong; these papers do not include the inverse process to capture, namely the ejection of dark-matter particles by three-body gravitational encounters. We emphasize previous work that shows that by including both capture and ejection of dark matter from the Solar System, the density of dark matter bound to the Solar System is small compared to the local Galactic dark-matter density.
Dynamics of WIMPs in the solar system and implications for direct and indirect detection
Annika H. G. Peter,Scott Tremaine
Physics , 2008,
Abstract: Semi-analytic treatments of the evolution of orbits of weakly interacting massive particles (WIMPs) in the solar system suggest that the WIMPs bound to the solar system may enhance the direct detection rate relative to that of the unbound population by up to a factor of order unity, and boost the flux of neutrinos from WIMP annihilation in the Earth by up to two orders of magnitude. To test these important but uncertain results, we perform a suite of numerical orbit integrations to explore the properties of the bound WIMP population as a function of the WIMP mass and the scattering cross section with baryonic matter. For regions of WIMP parameter space presently allowed by experiments, we find that (i) the bound WIMP population enhances the direct detection rate by at most ~1% relative to the rate from unbound halo WIMPs; (ii) it is unlikely that planned km^3-scale neutrino telescopes will detect neutrinos from WIMP annihilation in the Earth; (iii) the event rate from neutrinos produced by WIMP annihilation in the Sun may be much smaller than implied by the usual calculations, which assume that WIMPs scattered onto bound orbits are rapidly thermalized in the Sun.
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