# Unravelling Dark Matter

Conference Date:
Thursday, September 22, 2011 (All day) to Saturday, September 24, 2011 (All day)
Scientific Areas:
Cosmology
Particle Physics

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The nature of dark matter continues to be a mystery. However, recent experiments and observations are putting a new light on the spectra of theoretical possibilities. We are drawn to critically assess our present knowledge on the astrophysical side of the paradigm, to revise current theories of particle dark matter, and to look out for new observational windows. This workshop shall bring together leading theoretical particle and astro- physicists whose work is relevant in the direct and indirect detection of dark matter. What do we really know about dark matter on local, galactic, and cosmological scales and how confident are we in quantifying the uncertainties on this knowledge? What is new on the anomaly-driven observational forefront and how well can indirect astrophysical probes inform us about the particle nature of the dark matter sector? Finally, how well does the dark matter framework reconcile with the overall cosmological picture that observations present to us?

Niayesh Afshordi, Perimeter Institute

Haipeng An, Perimeter Institute

Brian Batell, University of Chicago

Latham Boyle, Perimeter Institute

Cliff Burgess, Perimeter Institute, McMaster University

Bei Cai, Queen's University

James Cline, McGill University

Juan Collar, University of Chicago, Kavli Institute

Ross Diener Perimeter Institute

Douglas Finkbeiner, Harvard University

Patrick Fox, Fermilab

Michael Hudson, University of Waterloo

Matthew Johnson, Perimeter Institute

Michael Kuhlen, University of California, Berkeley

Guilhem Lavaux, Perimeter Institute

Luis Lehner, Perimeter Institute

Robert Mann, Perimeter Institute, University of Waterloo

Reina Maruyama, University of Wisconsin Madison

David McKeen, University of Victoria

Daniel McKinsey, Yale University

John Moffat, Perimeter Institute

David Morrissey, TRIUMF

Leonidas Moustakas, JPL, Caltech

Guillaume Plante, Columbia University

Yosdanis Vazquez Ponce, Perimeter Institute

Maxim Pospelov, Perimeter Institute, University of Victoria

Steven Schramm, University of Toronto

Philip Schuster, Perimeter Institute

Yanwen Shang, Perimeter Institute

Kris Sigurdson, University of British Columbia

Tracy Slatyer, Institute for Advanced Study

Carlos Tamarit, Perimeter Institute

James Taylor, University of Waterloo

Daniel Terno, Perimeter Institute

Natalia Toro, Perimeter Institute

Michael Trott, Perimeter Institute

Mark Vogelsberger, Harvard Smithsonian Center for Astrophysics

Andrew Wayne, University of Guelph

Neal Weiner, New York University

Lawrence Widrow, Queen's University

Itay Yavin, New York University, Center for Cosmology and Particle Physics

Jesus Zavala, University of Waterloo

Niayesh Afshordi, Perimeter Institute

Structure in the Phase Space and Dark Matter Astronomy

Brian Batell, Perimeter Institute

Stabilizing Dark Matter

Stability on cosmological time scales constitutes one of the few robust guiding principles in the formulation of a theory of dark matter. This suggests the existence of a stabilizing symmetry associated to dark matter. I will explore several examples of stabilizing symmetries beyond the canonical Z_2 parity, such as Abelian Z_N discrete gauge symmetries, Non-Abelian discrete symmetries, and flavor symmetries.

Bei Cai, Queen's University

Dark matter search at SNOLAB with DEAP-3600

DEAP-3600 is a dark matter experiment using 3600 kg of liquid argon for direct WIMP search, with a target sensitivity to the spin-independent WIMP-nucleon cross-section of 10^{-46} cm^2.  The detector is currently under construction at SNOLAB, located 2 km underground in Sudbury. In this single-phase liquid argon experiment, discrimination of beta/gamma backgrounds from the WIMP-induced nuclear recoil signal will be achieved by analyzing the pulse shape of scintillation light. A prototype 7-kg liquid argon detector has been taking data at SNOLAB since 2007 and has allowed extensive background studies, including significant radon and surface contamination reduction. The status of the experiment and of background reduction studies will be presented.

James Cline, McGill University

Hidden Sector Dark Matter: Chasing the CoGeNT/DAMA/CRESST Ambulances

I discuss the challenges for building models of ~10 GeV dark matter that can accommodate the numerous astrophysical constraints that threaten to exclude them, as well as direct detection constraints.  A U(1)xU(1) hidden sector model with isospin violation, inelastic couplings, and annihilation into invisible products is suggested.  I will also discuss similar but simpler models that could simultaneously explain excess 511 keV gamma rays from the galactic center and direct detection of light dark matter.

Juan Collar, University of Chicago, Kavli Institute

Certainty And Uncertainty In Dark Matter Searches

Departing from the context of CoGeNT and COUPP, two direct searches for WIMP dark matter, we will inspect the recent landscape of anomalies observed by these and several other detectors. The aim of this talk is to communicate an appreciation for the subtleties inherent to experimental efforts in this field, and for the considerable difficulties that await for those trying to make sense of WIMP search observations (or lack thereof).

What Dark Matter Microhalos Can Tell us About Reheating

The expansion history of the Universe before big bang nucleosynthesis is unknown; in many models, the Universe was effectively matter-dominated between the end of inflation and the onset of radiation domination.  I will show how an early matter-dominated era leaves an imprint on the small-scale matter power spectrum.  This imprint depends on the origin of dark matter. If dark matter originates from the radiation bath after reheating, then small-scale density perturbations are suppressed, leading to a cut-off in the matter power spectrum.  Conversely, small-scale density perturbations are significantly enhanced if the dark matter was created nonthermally during reheating.  These enhanced perturbations trigger the formation of numerous dark matter microhalos during the cosmic dark ages.  The abundance of dark matter microhalos is therefore a new window on the Universe before nucleosynthesis.

Douglas Finkbeiner, Harvard University

Dark Matter Annihilation: From High Redshift to the Galactic Center

The existence of dark matter is hardly in doubt, yet astrophysicists continue to search in vain for any non-gravitational signals of it.  In the case of weakly interacting massive particle (WIMP) models, ongoing annihilation or decay of WIMPs to Standard Model particles could provide observable signals, e.g. as excess gamma rays in the center of the Milky Way or as excess ionization at high redshift.

I will present our latest results on the most rigorous constraint from astrophysics:  the effect of WIMP annihilation on the ionization history of the Universe, as recorded in the CMB.

Patrick Fox, Fermilab

A CoGeNT Modulation Analysis

We analyze the recently released CoGeNT data with a focus on their time-dependent properties. Using various statistical techniques, we confirm the presence of modulation in the data, and find a significant component at high (Eee \gtap 1.5 keVee) energies. We find that standard elastic WIMPs in a Maxwellian halo do not provide a good description of the modulation. We consider the possibility of non-standard halos, using halo independent techniques, and find a good agreement with the DAMA modulation for QNa ≈ 0.3, but disfavoring interpretations with QNa = 0.5. The same techniques indicate that CDMS-Ge should see an O(1) modulation, and XENON100 should have seen 10-30 events (based upon the modulation in the 1.5-3.1 keVee range), unless Leffis smaller than recent measurements. Models such as inelastic dark matter provide a good fit to the modulation, but not the spectrum. We note that tensions with XENON could be alleviated in such models if the peak is dominantly in April, when XENON data are not available due to noise.

Michael Kuhlen, University of California

Tidal Streams and Debris Flows: Dark Matter Velocity Substructure and Direct Detection

High resolution simulations of Galactic Cold Dark Matter halos reveal staggering amounts of substructure, both in configuration and velocity space. In this talk I will focus on the latter. In addition to spatially localized subhalos and streams, I will also discuss so-called debris flows -- incompletely phase-mixed material originating in numerous accretion and merging events that are the hallmark of the hierarchical build-up of the host halo. Finally, I will briefly discuss the presence and direct detection consequences of a dark disk in the Eris simulation, a cosmological simulation including baryonic physics of the formation of a realistic looking disk galaxy.

DM-Ice: a Direct Detection Experiment for Dark Matter at the South Pole

I will describe DM-Ice, a direct detection dark matter experiment at the South Pole.  The aim of the experiment is to test the claim for an observation of dark matter by the DAMA collaboration by carrying out an experiment with the same detector technology, but in the southern hemisphere.  By going to the opposite hemisphere, many of the suspected backgrounds would produce annual modulation with the opposite phase whereas the dark matter signature should stay the same. DMIce-17, a 17-kg detector was installed in the Antarctic ice at the South Pole in December 2010 at the depth of ~2200 m.w.e. and is currently taking data.  An experiment that can test DAMA's claim is currently being designed.  I will report on the status of DMIce-17 and the plans for the full-scale experiment.

David McKeen, University of Victoria

A Composite Model of Dark Matter

We describe a model of composite dark matter, bound by an asymptotically free gauge interaction.  This leads to a novel relic history and to an enhancement of the present-day dark matter annihilation cross section.  Potential indirect detection signals are discussed.

Daniel McKinsey, Yale University

Dark Matter Detection with Liquid Xenon and Liquid Helium

David Morrissey, TRIUMF

Signals of Hidden Antibaryonic Dark Matter

Many explanations have been proposed for the origin of dark matter  and the creation of the baryon asymmetry, but very few of them address both cosmological puzzles at once.  At the same time, the observed energy densities of dark matter and baryons are within a factor of five of each other hinting at a possible common origin.  In this talk I will present a novel mechanism that generates both densities at once, with the dark matter species carrying a net baryon number.  This gives rise to new and unusual dark matter signals such as the destruction of nucleons by dark matter scattering.  I will describe some of these signals, and discuss how they might be detected in current and upcoming experiments and astrophysical observations.

Leonidas Moustakas, Jet Propulsion Laboratory and California Institute of Technology

Revealing the Invisible: Strong Gravitational Lensing & Particle Dark Matter

The particular properties of different dark matter particle candidates can lead to different properties and distributions of sub-structure within galaxies; structure that may uniquely be probed through specific state of the art observations of galaxy-scale dark matter halos that happen to be acting as strong gravitational lenses. I will discuss how the matter power spectrum and non-linear evolution within galaxies depend on the specific properties of dark matter particle candidates, develop the types of strong gravitational lenses that lend themselves to probing substructure, and give both the current state of the art and the prospects for quantitative constraints in the near future.  Throughout, I will emphasize what cross-germination opportunities there are between such astrophysical structure measurements, and other exciting avenues of insight into the nature of dark matter.

Guillaume Plante, Columbia University

Status of the XENON100 Dark Matter Search

The XENON100 detector, currently taking data at the Laboratori Nazionali del Gran Sasso in Italy, is a dual-phase xenon time projection chamber used to search for dark matter by simultaneously measuring the scintillation and ionization signals produced by nuclear recoils. These two signals allow the three-dimensional localization of events with millimeter precision and the ability to fiducialize the target volume, yielding an inner core with a very low background. As the energy scale is based on the scintillation signal of nuclear recoils, the precise knowledge of the scintillation efficiency of nuclear recoils is of prime importance. I will briefly discuss the results of a new measurement of the relative scintillation efficiency of nuclear recoils in LXe, Leff, performed with a new single phase detector, designed and built specifically for this purpose. Finally, I will present the recent XENON100 results obtained from 100 live days of data acquired in 2010 and discuss the current status of the experiment and its evolution into XENON1T.

Maxim Pospelov, Perimeter Institute and University of Victoria

On the Relation Between the Invisible Higgs Decay and Dark Matter Scattering Cross Sections

The simplest singlet Higgs-portal dark matter model predicts large/dominant Higgs ->2 DM decay widths in the region of parameter space with m_DM < m_h/2, and Higgs mass below 140 GeV. On the other hand, the direct detection experiments such as Xenon100 put stringent constraints on the scattering DM-nucleon scattering cross section and seemingly exclude large part of the parameter space where the invisible Higgs decay dominates over visible modes. I analyze the robustness of this statement in the next-to-minimal models to show that the relation between invisible Higgs width and dark matter cross section does not hold in general. I discuss a number of theoretical scenarios where WIMP abundance is regulated by the Higgs portal, the direct detection signals are small AND Higgs decay width is dominated by the decay to dark matter.

Constraints on Dark Matter Models from a Fermi-LAT Search for Cosmic-Ray Electrons from the Sun

No known astrophysical mechanisms are expected to generate a significant high-energy flux of cosmic-ray electrons and positrons (CREs) from the Sun. However, some recently considered classes of dark matter models predict such a signal. We analyzed the CRE events collected by the Fermi-LAT during its first year of operation to search for a flux excess correlated with the Sun's direction, and found no evidence of a significant signal. I will discuss the constraints these results place on secluded dark matter models and inelastic dark matter models.

Kris Sigurdson, University of British Columbia

Wandering in the Dark

Tracy Slatyer, Institute for Advanced Study

Substructure, Sommerfeld, and CR Signals

Models of dark matter with Sommerfeld-enhanced annihilation have been proposed to explain the CR excess observed by the PAMELA and Fermi experiments. In such models, the local annihilation signal can easily be dominated by small, dense, cold subhalos, instead of by the smooth DM halo as usually assumed. I will discuss how such a "substructure+Sommerfeld" scenario modifies constraints from the CMB, limits on DM self-interaction, and bounds from measurements of inner-Galaxy gamma rays and the extragalactic diffuse background.

These constraints provide stringent limits on the usual smooth-halo scenario, robustly ruling out force carrier masses below ~200 MeV (in the context of explaining the PAMELA/Fermi signals) and causing tension for higher mediator masses, but in the presence of a modest amount of local substructure, force carrier masses down to 20 MeV or even lower can still be consistent with these bounds.

James Taylor, University of Waterloo

Our Self-Annihilating Neighbours

One of the most exciting, albeit slightly speculative, components of the Fermi mission is to search for evidence of energetic events related to dark matter decay or annihilation. The best targets for this search a regions where we suspect there is dark matter, but see few conventional gamma-ray sources such as molecular clouds, cosmic ray sources, or compact objects. Much emphasis has been placed on local dwarf satellites in particular, since many of these systems show evidence for relatively deep potential wells, but have few stars and no recent star formation. In this talk I will propose another possible target for indirect dark matter searches, among our nearby galactic neighbours.

Mark Vogelsberger, Harvard Smithsonian Center for Astrophysics

The Small-Scale Structure of Galactic Dark Matter

In my talk I will discuss the relevant astrophysical input for dark matter detection experiments, i.e. the expected distribution of dark matter at the solar position. Based on high resolution N-body simulations I will then show that the formation history of the galactic dark matter halo leaves imprints in the velocity and energy distribution. In the second part of my talk I will focus on the fine-grained dark matter structure and discuss the importance of caustics and streams for detection experiments.

Neal Weiner, New York University

A Tour of the Direct Detection Landscape

A wide range of results have led to a confusing situation in the area of direct WIMP detection. I'll review the status of these results. The features of the results imply that almost any explanation will require a departure from standard assumptions (Maxwellian halo, elastic WIMP scattering or otherwise) so I'll review the techniques to compare experiments without appealing to these assumptions. In particular, I'll comment on the status of light WIMPs and the iodine interpretations of DAMA (such as inelastic dark matter) in light of the most recent results.

Lawrence Widrow, Queen's University

Dark Matter Halos in 6D

I will describe various efforts to understand the phase space structure of dark matter halos.  Implications for dark matter detection experiments will also be discussed.

Jesus Zavala, University of Waterloo

Astrophysical Constraints on Dark Matter Annihilation with Sommerfeld Enhancement

Dark matter models with an annihilation cross section enhanced by a Sommerfeld mechanism have been proposed in the past years to explain a number of observed anomalies, such as the excess of high energy positrons in cosmic rays reported by PAMELA. However, this enhancement can not be arbitrarily large without violating a number of astrophysical measurements. In this talk, I will discuss the degree to which these measurements can constrain Sommerfeld-enhanced models. In particular, I will talk about constraints coming from the observed abundance of dark matter and the extragalactic background light measured at multiple wavelengths.

Jesus Zavala, University of Waterloo