The Search for Ultralight Bosonic Dark Matter

Description

A host of astrophysical measurements suggest that most of the matter in the Universe is an invisible, nonluminous substance that physicists call “dark matter.” Understanding the nature of dark matter is one of the greatest challenges of modern physics and is of paramount importance to our theories of cosmology and particle physics. This text explores one of the leading hypotheses to explain dark matter: that it consists of ultralight bosons forming an oscillating field that feebly interacts with light and matter. Many new experiments have emerged over the last decade to test this hypothesis, involving state-of-the-art microwave cavities, precision nuclear magnetic resonance (NMR) measurements, dark matter “radios,” and synchronized global networks of atomic clocks, magnetometers, and interferometers. The editors have gathered leading experts from around the world to present the theories motivating these searches, evidence about dark matter from astrophysics, and the diverse experimental techniques employed in searches for ultralight bosonic dark matter. The text provides a comprehensive and accessible introduction to this blossoming field of research for advanced undergraduates, beginning graduate students, or anyone new to the field, with tutorials and solved problems in every chapter. The multifaceted nature of the research – combining ideas and methods from atomic, molecular, and optical physics, nuclear physics, condensed matter physics, electrical engineering, particle physics, astrophysics, and cosmology – makes this introductory approach attractive for beginning researchers as well as members of the broader scientific community.   This is an open access book. Preface Contents Contributors Definitions of Commonly Used Acronyms and Mathematical Symbols Units and Conversion Factors 1 Introduction to Dark Matter 1.1 Why Do We Think There Is Dark Matter? 1.2 What Do (We Think) We Know About Dark Matter? 1.3 What Could Dark Matter Be? 1.4 Ultralight Bosonic Dark Matter 1.5 Conclusion References 2 Ultralight Bosonic Dark Matter Theory 2.1 Introduction 2.2 Bosonic Field Lagrangians 2.3 Why New Bosons Might Be Ultralight 2.4 Portals Between the Dark Sector and the Standard Model 2.4.1 Interactions Between Ultralight Bosonic Fields and Standard Model Particles 2.4.2 Axion-Photon Interaction 2.4.3 Axion-Fermion Interaction 2.5 Theoretical Motivations for Ultralight Bosons 2.5.1 Peccei-Quinn Solution to the Strong CP Problem and the QCD Axion 2.5.2 The Hierarchy Problem and the Relaxion 2.5.3 UBDM from Extra Dimensions 2.6 Non-thermal Production of UBDM 2.6.1 Vacuum Misalignment 2.6.2 Vector Field Misalignment 2.6.3 Scalar Field Misalignment References 3 Astrophysical Searches and Constraints 3.1 Astrophysical Search Channels 3.2 Gravitational Probes of UBDM 3.2.1 The CMB and Linear Structure Formation 3.2.2 Schrödinger–Poisson Equations 3.2.3 Galaxies and Nonlinear Structure 3.2.4 Black Hole Superradiance 3.2.5 Summary of Gravitational Constraints 3.3 Axion Compact Objects 3.3.1 Axion Stars 3.3.2 Miniclusters 3.4 Indirect Detection of UBDM 3.4.1 Stellar and Supernova Energy Loss 3.4.2 Axion–Photon Conversion References 4 Microwave Cavity Searches 4.1 Historical Introduction 4.2 Detection Principles 4.2.1 Signal Power 4.2.2 Noise Considerations 4.2.3 Scan Rate 4.3 Resonant Microwave Cavities 4.3.1 Resonant Cavity Modes 4.3.2 Quality Factor 4.3.3 Form Factor 4.3.4 Tuning and Mode Density 4.3.5 Multiple Cavity Systems 4.3.6 Testing Cavities 4.4 Amplifiers 4.4.1 Quantum-Limited Amplifiers 4.4.2 Sub-quantum Limited Amplifiers 4.5 Operational Experiments References 5 Solar Production of Ultralight Bosons 5.1 Production of Axions in the Sun 5.1.1 Solar Models and the Origin of Solar Axions 5.1.2 Non-Primakoff Solar Axions 5.1.3 Constraints on the Solar Axion Flux 5.1.4 Do Axions Escape from the Sun? 5.2 Axion-to-Photon Conversion Probability for Solar Axions 5.2.1 Coherence Condition and Conversion Probability in Vacuum 5.2.2 Coherence Condition and Conversion Probability in a Buffer Gas 5.2.2.1 Effective Mass of the Photon 5.2.2.2 Momentum Transfer 5.2.2.3 The Absorption of Photons in a Buffer Gas 5.2.2.4 Mass Range of Coherence 5.3 Expected Number of Photons from Solar Axion Conversion 5.4 Axion Helioscope Experiments 5.4.1 Concept of Axion Helioscopes 5.4.2 Current and Future Axion Helioscopes 5.4.2.1 The CERN Axion Solar Telescope (CAST) 5.4.2.2 The International Axion Observatory (IAXO) 5.4.2.3 Physics Prospects of IAXO 5.5 Alternative Experiments to Search for Solar Axions 5.5.1 Stationary Helioscopes 5.5.2 Crystalline Detectors Using Primakoff–Bragg Conversion 5.5.3 Non-Primakoff Effect Conversions References 6 Magnetic Resonance Searches 6.1 Searching for Axionlike Dark Matter via Nuclear Magnetic Resonance 6.1.1 Interactions with Nuclear Spins 6.1.1.1 The EDM Interaction with P,T-odd Moments of Nucleons and Nuclei 6.1.1.2 The Gradient Interaction 6.1.2 Interactions with Electron Spins 6.2 Basics of NMR 6.2.1 Nuclear Magnetism 6.2.2 Nuclear Spin Dynamics 6.2.3 Nuclear Spin Interactions 6.2.3.1 Chemical Shielding 6.2.3.2 Direct Dipole-Dipole Coupling 6.2.3.3 Indirect Spin-Spin Coupling 6.2.3.4 Quadrupolar Coupling 6.2.4 Zero-to-Ultralow-Field NMR 6.3 Detecting Spin Evolution due to Axionlike Dark Matter 6.3.1 Axion-Induced NMR Signals 6.3.2 Inductive Coil Detection 6.3.3 Superconducting Quantum Interference Devices 6.3.4 Atomic Vapor Sensors 6.3.4.1 Spin-Exchange-Collision-Free (SERF) Magnetometry 6.3.5 Magnetic Noise Suppression 6.4 Experimental Searches References 7 Dark Matter Radios 7.1 Hidden Photons 7.2 Hidden Photon Electrodynamics 7.3 Hidden Electric and Magnetic Fields as Dark Matter 7.4 Dark Matter Radio Experimental Scheme 7.4.1 Electric Field Due to Hidden Photons Within Shields 7.4.2 Magnetic Field Due to Hidden Photons Within Shields 7.4.3 DM Radio Inside a Cylindrical Shield 7.5 Out-of-Band Sensitivity 7.6 Sensitivity of Dark Matter Radio Experiments References 8 Laboratory Searches for Exotic Spin-Dependent Interactions 8.1 Introduction 8.1.1 Dark Matter and New Spin-Dependent Interactions 8.1.2 New Spin-Dependent Interactions 8.2 Spin-Dependent Interactions Mediated by Light Bosons: Classification 8.2.1 Interactions Mediated by Massive Spin-0 Bosons 8.2.1.1 Scalar-Scalar Interaction 8.2.1.2 Pseudoscalar-Scalar Interaction 8.2.1.3 Pseudoscalar-Pseudoscalar Interaction 8.2.2 Interactions Mediated by Massive Spin-1 Bosons 8.2.2.1 Vector-Vector Interaction 8.2.2.2 Axial-Vector-Vector Interaction 8.2.2.3 Axial-Vector-Axial-Vector Interaction 8.2.3 Interactions Mediated by Massless Spin-1 Bosons 8.2.3.1 Tensor-Tensor Interaction 8.2.3.2 Pseudotensor-Pseudotensor Interaction 8.2.3.3 Pseudotensor-Tensor Interaction 8.3 Searches for New Interactions Between Polarized Electrons and Unpolarized Nucleons 8.3.1 Torsion Pendulum Experiments 8.3.2 Electron-Spin Based Magnetometer Searches 8.3.3 Spectroscopic Constraints with Trapped Ions 8.4 Monopole-Dipole Searches with Polarized Nuclear Spins and Unpolarized Nucleons 8.4.1 Axion Searches with Comagnetometers 8.4.1.1 Noble Gas Comagnetometer 8.4.1.2 Noble Gas: Alkali Comagnetometer Searches 8.4.2 NMR-Based Spin-Dependent Searches 8.4.3 Resonant NMR-Based Spin-Dependent Interaction Search: ARIADNE 8.5 Spectroscopic Measurements of Spin-Spin Coupled Interactions 8.6 Outlook References 9 Light-Shining-Through-Walls Experiments 9.1 Introduction 9.1.1 UBDM Interaction with Photons in a Magnetic Field 9.1.2 Magnets 9.1.3 Light-Tightness 9.2 Boosting Sensitivity with a Production Cavity 9.2.1 Linear Cavity 9.2.2 Cavity Spatial Modes 9.2.3 Stabilization of Optical Cavities 9.2.4 Achieving High Finesse 9.2.5 High-Power Operation 9.3 Dual Cavity LSW Experiments 9.3.1 Dual Resonance 9.3.2 Spatial Overlap 9.3.3 Verification of the Resonance Condition and Spatial Overlap 9.4 Detection Techniques 9.4.1 Heterodyne Interferometry 9.4.2 Transition Edge Sensors 9.5 Conclusion References 10 Global Quantum Sensor Networks as Probes of the Dark Sector 10.1 Introduction 10.2 Portals Into Dark Sector 10.3 How Do Atomic Clocks and Magnetometers Work? 10.3.1 Atomic Clocks 10.3.2 Atomic Magnetometers 10.4 DM Searches with Network of Sensors 10.4.1 Overview of Existing Networks 10.4.2 Network-Based Searches for ``Wavy'' Dark Matter 10.4.3 Network-Based Searches for ``Clumpy'' Dark Matter 10.5 Putting It All Together 10.6 Summary References Solutions to Chapter Problems Solutions to Chapter Problems References Index