Particle Physics

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.

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.

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.

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.

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.

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.

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

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.

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.

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).