Gerard Jungman

Supersymmetric dark matter

There is almost universal agreement among astronomers that most of the mass in the Universe and most of the mass in the Galactic halo is dark. Many lines of reasoning suggest that the dark matter consists of some new, as yet undiscovered, weakly-interacting massive particle (WIMP). There is now a vast experimental effort being surmounted to detect WIMPS in the halo. The most promising techniques involve direct detection in low-background laboratory detectors and indirect detection through observation of energetic neutrinos from annihilation of WIMPs that have accumulated in the Sun and/or the Earth. Of the many WIMP candidates, perhaps the best motivated and certainly the most theoretically developed is the neutralino, the lightest superpartner in many supersymmetric theories. We review the minimal supersymmetric extension of the Standard Model and discuss prospects for detection of neutralino dark matter. We review in detail how to calculate the cosmological abundance of the neutralino and the event rates for both direct- and indirect-detection schemes, and we discuss astrophysical and laboratory constraints on supersymmetric models. We isolate and clarify the uncertainties from particle physics, nuclear physics, and astrophysics that enter at each step in the calculation. We briefly review other related dark-matter candidates and detection techniques.

Cosmological-parameter determination with microwave background maps

The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe (Ω), the baryon density, the Hubble constant (h), the cosmological constant (Λ), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with 0.5° angular resolution and a noise level of 15 μK per pixel can determine Ω, h, and Λ with standard errors of ±0.1 or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the underlying cosmological model is discussed.

Weighing the universe with the cosmic microwave background

Variations in Ω, the total density of the Universe, leave an imprint on the power spectrum of temperature fluctuations in the cosmic microwave background (CMB). We evaluate the precision with which Ω can be determined by a CMB map as a function of sky coverage, pixel noise, and beam size. Assuming only that the primordial density perturbations were adiabatic and with no prior information on the values of any other cosmological parameters, a full-sky CMB map at 0.5° angular resolution and a noise level of 15 μK per pixel can determine Ω with a standard error of 5%. If all other cosmological parameters are fixed, Ω can be measured to better than 1%.

Systematic Uncertainties in the Analysis of the Reactor Neutrino Anomaly

We examine uncertainties in the analysis of the reactor neutrino anomaly, wherein it is suggested that only about 94% of the emitted antineutrino flux was detected in short baseline experiments. We find that the form of the corrections that lead to the anomaly are very uncertain for the 30% of the flux that arises from forbidden decays. This uncertainty was estimated in four ways, is as large as the size of the anomaly, and is unlikely to be reduced without accurate direct measurements of the antineutrino flux. Given the present lack of detailed knowledge of the structure of the forbidden transitions, it is not possible to convert the measured aggregate fission beta spectra to antineutrino spectra to the accuracy needed to infer an anomaly. Neutrino physics conclusions based on the original anomaly need to be revisited, as do oscillation analyses that assumed that the antineutrino flux is known to better than approximately 4%.

Model independent comparison of direct versus indirect detection of supersymmetric dark matter

We compare the rate for scattering of neutralinos from nuclei with the flux of muons induced by energetic neutrinos from neutralino annihilation in the Sun and Earth. We consider scalar and spin interactions of neutralinos. We find that the event rate in a kg of Ge is roughly equivalent to that in a 10^5–1^07-m^2 muon detector for a neutralino with primarily scalar coupling to nuclei. For a spin-coupled neutralino, the event rate in a 50-g H detector is roughly that in a 10–500-m^2 muon detector. Expected backgrounds favor forthcoming elastic-scattering detectors for scalar couplings while neutrino detectors are favored for spin couplings.

Neutrinos from particle decay in the Sun and Earth

Weakly interacting massive particles (WIMPs) may be indirectly detected by observation of upward muons induced by energetic neutrinos from annihilation of WIMPs that have accumulated in the Sun and/or Earth. Energetic muon neutrinos come from the decays of \ensuremath{\tau} leptons, c, b, and t quarks, gauge bosons, and Higgs bosons produced by WIMP annihilation. We provide analytic expressions, suitable for computing the flux of upward muons, for the neutrino energy spectra from decays of all these particles in the center of the Sun and Earth. These analytic expressions should obviate the need for Monte Carlo calculations of the upward-muon flux. We investigate the effects of polarization of the gauge bosons on the neutrino spectra, and find that they are small. We also present simple expressions for the second moments of the neutrino distributions which can be used to estimate the rates for observation of neutrino-induced muons from WIMP annihilation.

Cosmic-ray antiprotons from neutralino annihilation into gluons.

We estimate the flux of cosmic-ray antiprotons expected from the annihilation of neutralinos in the galactic halo. The antiproton signal may offer an important alternative detection scheme in the case that neutralino annihilation proceeds mainly to the two-gluon final state.

Possible origins and implications of the shoulder in reactor neutrino spectra

We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments. We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra. In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from

Neutralino annihilation into gluons

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The inflationary perturbation spectrum.

U. We consider several possible origins of the shoulder, and find possible explanations. For example, there could be a problem with the measured aggregate beta spectra, or the harder neutron spectrum at a light-water power reactor could affect the distribution of beta-decaying isotopes. In addition to the fissile actinides, we find that