Dark Matter and Indirect Detection in Cosmic Rays

In the early years, cosmic rays contributed essentially to particle physics through the discovery of new particles. Will history repeat itself? As with the discovery of the charged pion, the recent discovery of a Higgs-like boson may portend a rich new set of particles within reach of current and near future experiments. These may be discovered and studied by cosmic rays through the indirect detection of dark matter.Comment: 8 pages, to appear in the Proceedings of Centenary Symposium 2012: Discovery of Cosmic Rays, Denver, Colorado, June 201

Non-WIMP Candidates

Non-WIMP dark matter candidates include particles motivated by minimality, candidates motivated by experimental anomalies, and exotic possibilities motivated primarily by the desire of clever iconoclasts to highlight how truly ignorant we are about the nature of dark matter. In this review, I discuss candidates that are not WIMPs, but nevertheless share the same theoretical motivations as WIMPs and also naturally have the correct relic density. There are two classes: superWIMP dark matter, where the desired relic density is inherited through decays, and WIMPless dark matter, where the dark matter's mass and couplings scale together to maintain the desired thermal relic density.Comment: 20 pages, published as Chapter 10, pp. 190-204, in Particle Dark Matter: Observations, Models and Searches, edited by Gianfranco Bertone (Cambridge University Press, 2010), available at http://cambridge.org/us/catalogue/catalogue.asp?isbn=978052176368

Dark Matter Implications for Linear Colliders

The existence of dark matter is currently one of the strongest motivations for physics beyond the standard model. Its implications for future colliders are discussed. In the case of neutralino dark matter, cosmological bounds do not provide useful upper limits on superpartner masses. However, in simple models, cosmological considerations do imply that for supersymmetry to be observable at a 500 GeV linear collider, some signature of supersymmetry must appear before the LHC.Comment: 4 pages, 2 figures, to appear in the proceedings of Linear Collider Workshop 2000, Fermilab, October 200

ILC Cosmology

Recent breakthroughs in cosmology pose questions that require particle physics answers. I review the problems of dark matter, baryogenesis, and dark energy and discuss how particle colliders, particularly the International Linear Collider, may advance our understanding of the contents and evolution of the Universe.Comment: 18 pages, Plenary Colloquium presented at the 2005 International Linear Collider Workshop, Stanford, California, USA, 18-22 March 200

Naturalness and the Status of Supersymmetry

For decades, the unnaturalness of the weak scale has been the dominant problem motivating new particle physics, and weak-scale supersymmetry has been the dominant proposed solution. This paradigm is now being challenged by a wealth of experimental data. In this review, we begin by recalling the theoretical motivations for weak-scale supersymmetry, including the gauge hierarchy problem, grand unification, and WIMP dark matter, and their implications for superpartner masses. These are set against the leading constraints on supersymmetry from collider searches, the Higgs boson mass, and low-energy constraints on flavor and CP violation. We then critically examine attempts to quantify naturalness in supersymmetry, stressing the many subjective choices that impact the results both quantitatively and qualitatively. Finally, we survey various proposals for natural supersymmetric models, including effective supersymmetry, focus point supersymmetry, compressed supersymmetry, and R-parity-violating supersymmetry, and summarize their key features, current status, and implications for future experiments.Comment: 38 pages, to appear in Annual Review of Nuclear and Particle Science; v2: fixed typos, updated Higgs results, added references and a parable, published versio

Dark Matter Phenomenology

I review recent developments in the direct and indirect detection of dark matter and new candidates beyond the WIMP paradigm.Comment: 6 pages, to appear in the Proceedings of the Tenth Conference on the Intersections of Particle and Nuclear Physics (CIPANP 2009), San Diego, California, 26-31 May 200

Impact of Resonance on Thermal Targets for Invisible Dark Photon Searches

Dark photons in the MeV to GeV mass range are important targets for experimental searches. We consider the case where dark photons $A'$ decay invisibly to hidden dark matter $X$ through $A' \to XX$. For generic masses, proposed accelerator searches are projected to probe the thermal target region of parameter space, where the $X$ particles annihilate through $XX \to A' \to \text{SM}$ in the early universe and freeze out with the correct relic density. However, if $m_{A'} \approx 2m_X$, dark matter annihilation is resonantly enhanced, shifting the thermal target region to weaker couplings. For $\sim 10\%$ degeneracies, we find that the annihilation cross section is generically enhanced by four (two) orders of magnitude for scalar (pseudo-Dirac) dark matter. For such moderate degeneracies, the thermal target region drops to weak couplings beyond the reach of all proposed accelerator experiments in the scalar case and becomes extremely challenging in the pseudo-Dirac case. Proposed direct detection experiments can probe moderate degeneracies in the scalar case. For greater degeneracies, the effect of the resonance can be even more significant, and both scalar and pseudo-Dirac cases are beyond the reach of all proposed accelerator and direct detection experiments. For scalar dark matter, we find an absolute minimum that sets the ultimate experimental sensitivity required to probe the entire thermal target parameter space, but for pseudo-Dirac fermions, we find no such thermal target floor.Comment: 17 pages, 2 figures; v2: improved agreement with existing non-resonant results, added extensive discussion of implications for direct detection experiment