Galactic Searches for Dark Matter (1211.7090v1)

Abstract: For nearly a century, more mass has been measured in galaxies than is contained in the luminous stars and gas. Through continual advances in observations and theory, it has become clear that the dark matter in galaxies is not comprised of known astronomical objects or baryonic matter, and that identification of it is certain to reveal a profound connection between astrophysics, cosmology, and fundamental physics. The best explanation for dark matter is that it is in the form of a yet undiscovered particle of nature, with experiments now gaining sensitivity to the most well-motivated particle dark matter candidates. In this article, I review measurements of dark matter in the Milky Way and its satellite galaxies and the status of Galactic searches for particle dark matter using a combination of terrestrial and space-based astroparticle detectors, and large scale astronomical surveys. I review the limits on the dark matter annihilation and scattering cross sections that can be extracted from both astroparticle experiments and astronomical observations, and explore the theoretical implications of these limits. I discuss methods to measure the properties of particle dark matter using future experiments, and conclude by highlighting the exciting potential for dark matter searches during the next decade, and beyond.

• The paper unifies observational strategies and theoretical models to map dark matter distribution in the Milky Way.
• The paper shows that microlensing experiments rule out MACHOs and instead highlight WIMPs as promising dark matter candidates.
• The paper advocates for integrating collider data, galactic surveys, and next-generation detectors to refine dark matter detection methods.

An Overview of "Galactic Searches for Dark Matter"

The paper "Galactic Searches for Dark Matter" by Louis E. Strigari provides a comprehensive review of observational and theoretical strategies for detecting dark matter in the Milky Way galaxy. This essay aims to summarize the various avenues explored for identifying dark matter, the astrophysical and particle physics implications of these methodologies, and their contribution to our understanding of the universe.

Historical Context and Understanding Dark Matter

Dark matter has perplexed astronomers since it was first hypothesized to account for gravitational effects that cannot be explained by observable matter alone. This paper traces the historical trajectory of dark matter research, from Zwicky's measurements in the Coma cluster to more detailed assessments of nearby galaxies like M31 (Andromeda) and our own Milky Way. These observations collectively suggest a substantive mass component that is non-baryonic in nature.

The Nature of Galactic Dark Matter

The paper presents a synopsis of the methods used to map the dark matter in the Milky Way, highlighting its distribution in the galactic center, solar neighborhood, and far halo regions. Noteworthy are the detailed stellar kinematic surveys and halo modeling efforts like those that account for rotation curves and ellipsoidal density distributions. These methodologies unravel the mass profiles that cannot solely be accounted for by stars and gas. The synthesis of direct observation with theoretical predictions gives insight into the behavior and character of dark matter.

MACHOs and WIMPs

Two primary candidate explanations are evaluated: Massive Astrophysical Compact Halo Objects (MACHOs) and Weakly Interacting Massive Particles (WIMPs). The paper elucidates how microlensing experiments have essentially ruled out MACHOs as a dominant dark matter form, pivoting the focus onto the particle nature of dark matter. Conversely, WIMPs - hypothetical particles born out of extensions of the Standard Model - are spotlighted due to their rich theoretical backing and amenability to detection via non-gravitational methods such as scattering and annihilation.

Advances in Dark Matter Searches

Strigari explores both direct and indirect detection techniques crucial for understanding dark matter. Direct detection experiments are focused on observing dark matter interactions within terrestrial detectors, designed to identify rare scattering events between WIMPs and target nuclei.

Indirect detection strategies revolve around identifying the secondary particles produced by dark matter annihilation or decay in high-density regions, such as the Galactic center or dwarf spheroidal galaxies. Key to these methods are the interpretation of excesses or patterns in gamma-ray, neutrino, or cosmic-ray data against astrophysical background expectations.

Implications and Future Prospects

The paper posits that resolving the properties of dark matter will require integrating data from collider experiments, astroparticle observations, and cosmological measurements. Large-scale astronomical surveys and next-generation detector technologies promise to refine mass models and search parameters, improving our sensitivity to both anticipated dark matter signatures and potential deviations from theoretical predictions.

In anticipation of these advancements, Strigari suggests the potential for improved outcomes in dark matter research as methodological precision continues to increase and the interface between theoretical physics and observational astronomy strengthens.

The continuous evolution of observational techniques, combined with robust computational modeling, stands to significantly enhance our understanding of dark matter. This research is pivotal, not just for reconstructing galactic dynamics, but for informing high-energy physics and cosmology, deepening our grasp of fundamental cosmic structures and physics.