Edward A. Baltz

DarkSUSY: Computing Supersymmetric Dark Matter Properties Numerically

The question of the nature of the dark matter in the Universe remains one of the most outstanding unsolved problems in basic science. One of the best motivated particle physics candidates is the lightest supersymmetric particle, assumed to be the lightest neutralino—a linear combination of the supersymmetric partners of the photon, the Z boson and neutral scalar Higgs particles. Here we describe DarkSUSY, a publicly available advanced numerical package for neutralino dark matter calculations. In DarkSUSY one can compute the neutralino density in the Universe today using precision methods which include resonances, pair production thresholds and coannihilations. Masses and mixings of supersymmetric particles can be computed within DarkSUSY or with the help of external programs such as FeynHiggs, ISASUGRA and SUSPECT. Accelerator bounds can be checked to identify viable dark matter candidates. DarkSUSY also computes a large variety of astrophysical signals from neutralino dark matter, such as direct detection in low-background counting experiments and indirect detection through antiprotons, antideuterons, gamma-rays and positrons from the galactic halo or high-energy neutrinos from the centre of the Earth or of the Sun. Here we describe the physics behind the package. A detailed manual will be provided with the computer package.

Positron propagation and fluxes from neutralino annihilation in the halo

Supersymmetric neutralinos are one of the most promising candidates for the dark matter in the Universe. If they exist, they should make up some fraction of the Milky Way halo. We investigate the fluxes of positrons expected at the Earth from neutralino annihilation in the halo. Positron propagation is treated in a diffusion model including energy loss. The positron source function includes contributions from both continuum and monochromatic positrons. We find that, for a {open_quotes}canonical{close_quotes} halo model and propagation parameters, the fluxes are generally too low to be visible. Given the large uncertainties in both propagation and halo structure, it is however possible to obtain observable fluxes. We also investigate the shapes of the positron spectra, including fits to a feature indicated by the results of the HEAT experiment. {copyright} {ital 1998} {ital The American Physical Society}

Pre-launch estimates for GLAST sensitivity to dark matter annihilation signals

We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) for indirectly detecting weakly interacting massive particles (WIMPs) through the γ-ray signal that their pair ann ...

Determination of Dark Matter Properties at High-Energy Colliders

If the cosmic dark matter consists of weakly-interacting massive particles, these particles should be produced in reactions at the next generation of high-energy accelerators. Measurements at these accelerators can then be used to determine the microscopic properties of the dark matter. From this, we can predict the cosmic density, the annihilation cross sections, and the cross sections relevant to direct detection. In this paper, we present studies in supersymmetry models with neutralino dark matter that give quantitative estimates of the accuracy that can be expected. We show that these are well matched to the requirements of anticipated astrophysical observations of dark matter. The capabilities of the proposed International Linear Collider (ILC) are expected to play a particularly important role in this study.

Markov Chain Monte Carlo Exploration of Minimal Supergravity with Implications for Dark Matter

We explore the full parameter space of Minimal Supergravity (mSUGRA), allowing all four continuous parameters (the scalar mass m_0, the gaugino mass m_1/2, the trilinear coupling A_0, and the ratio of Higgs vacuum expectation values tan beta) to vary freely. We apply current accelerator constraints on sparticle and Higgs masses, and on the b -> s gamma branching ratio, and discuss the impact of the constraints on g_mu-2. To study dark matter, we apply the WMAP constraint on the cold dark matter density. We develop Markov Chain Monte Carlo (MCMC) techniques to explore the parameter regions consistent with WMAP, finding them to be considerably superior to previously used methods for exploring supersymmetric parameter spaces. Finally, we study the reach of current and future direct detection experiments in light of the WMAP constraint.

A Novel Antimatter Detector Based on X-Ray Deexcitation of Exotic Atoms

We propose a novel antiparticle detector. The gaseous antiparticle spectrometer (GAPS) effects particle identification through the characteristic X-rays emitted by antiparticles when they form exotic atoms in gases. GAPS obtains particularly high grasp (effective area-solid angle product) at lower particle energies, where conventional schemes are most limited in their utility. The concept is simple and lightweight, so it can be readily employed on balloon- and space-based missions. An extremely powerful potential application of GAPS is a space-based search for the neutralino through the detection of a neutralino annihilation by-product?the antideuteron. Paradoxically, this space-based search for the neutralino is capable of achieving comparable sensitivity to as yet unrealized third-generation, underground dark matter experiments. And GAPS can obtain this performance in a very modest satellite experiment. GAPS can also provide superior performance in searches for primary antiprotons produced via neutralino annihilation and black hole evaporation and in probing subdominant contributions to the antiproton flux at low energies. In a deep space mission, GAPS will obtain higher sensitivity for a given weight and power than BGO calorimeters.

Detection of neutralino annihilation photons from external galaxies

We consider neutralino annihilation in dense extragalactic systems known to be dominated by dark matter, in particular M87 and several local dwarf spheroidal galaxies. These annihilations can produce energetic gamma rays which may be visible to atmospheric Cerenkov telescopes. We explore the supersymmetric parameter space, and compute the expected flux of gamma--rays coming from these objects. It is shown that some parts of the parameter space lead to a signal observable with the next generation of Cerenkov telescopes, provided the supersymmetric dark matter has a clumpy structure, as may be expected in a hierarchical scenario for structure formation.

Analytic models of plausible gravitational lens potentials

Gravitational lenses on galaxy scales are plausibly modelled as having ellipsoidal symmetry and a universal dark matter density profile, with a Sersic profile to describe the distribution of baryonic matter. Predicting all lensing effects requires knowledge of the total lens potential: in this work we give analytic forms for that of the above hybrid model. Emphasising that complex lens potentials can be constructed from simpler components in linear combination, we provide a recipe for attaining elliptical symmetry in either projected mass or lens potential. We also provide analytic formulae for the lens potentials of Sersic profiles for integer and half-integer index. We then present formulae describing the gravitational lensing effects due to smoothly-truncated universal density profiles in cold dark matter model. For our isolated haloes the density profile falls off as radius to the minus fifth or seventh power beyond the tidal radius, functional forms that allow all orders of lens potential derivatives to be calculated analytically, while ensuring a non-divergent total mass. We show how the observables predicted by this profile differ from that of the original infinite-mass NFW profile. Expressions for the gravitational flexion are highlighted. We show how decreasing the tidal radius allows stripped haloes to be modelled, providing a framework for a fuller investigation of dark matter substructure in galaxies and clusters. Finally we remark on the need for finite mass halo profiles when doing cosmological ray-tracing simulations, and the need for readily-calculable higher order derivatives of the lens potential when studying catastrophes in strong lenses.

Darksusy - a numerical package for supersymmetric dark matter calculations

The question of the nature of dark matter in the Universe remains one of the most outstanding unsolved problems in basic science. One of the best motivated particle physics candidates is the lightest supersymmetric particle, assumed to be the lightest neutralino. We here describe DarkSUSY, an advanced numerical FORTRAN package for supersymmetric dark matter calculations. With DarkSUSY one can: (i) compute masses and compositions of various supersymmetric particles; (ii) compute the relic density of the lightest neutralino, using accurate methods which include the effects of resonances, pair production thresholds and coannihilations; (iii) check accelerator bounds to identify allowed supersymmetric models; and (iv) obtain neutralino detection rates for a variety of detection methods, including direct detection and indirect detection through antiprotons, gamma-rays and positrons from the Galactic halo or neutrinos from the center of the Earth or the Sun.

Strategies for Determining the Nature of Dark Matter

In this review, we discuss the role of the various experimental programs taking part in the effort to identify the particle nature of dark matter. In particular, we focus on electroweak-scale dark matter particles and discuss a wide range of search strategies that are being developed and utilized to detect them. These efforts include direct detection experiments, which attempt to observe the elastic scattering of dark matter particles with nuclei; indirect detection experiments, which search for photons, antimatter, and neutrinos produced as a result of dark matter annihilations; and collider searches for new teraelectronvolt-scale physics. Each of these techniques could potentially provide a unique and complementary set of information related to the mass, interactions, and distribution of dark matter. Ideally, these many different tools will be used together to conclusively identify the particle or particles that constitute the dark matter of the universe.