Max Planck Institute for Physics, Munich Solar Axions Supernova 1987A Early Universe Dark Matter Long-Range Force Axion Landscape Georg Raffelt Max Planck Institute for Physics, Munich

High- and Low-Energy Frontiers in Particle Physics 10 27 eV Planck mass GUT scale Electroweak QCD Cosmological constant 10 24 10 21 10 18 10 15 10 12 10 9 10 6 10 3 1 10 −3 10 −6 “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental par-ticle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider” P. Higgs F. Englert 2013 22 mg “for the discovery of neutrino oscillations, which shows that neutrinos have mass” T. Kajita A. McDonald 2015

High- and Low-Energy Frontiers in Particle Physics 10 27 eV Planck mass GUT scale Electroweak QCD Cosmological constant 10 24 10 21 10 18 10 15 10 12 10 9 10 6 10 3 1 10 −3 10 −6 𝒎 𝑫 𝒎 𝑫 𝟐 𝑴 𝑴 Heavy right-handed neutrinos (see-saw mechanism) WIMP dark matter (related to EW scale, perhaps SUSY) Axion dark matter (related to Peccei-Quinn symmetry) 𝒇 𝒂 𝒎 𝒂 ∼ 𝒎 𝝅 𝒇 𝝅 𝒇 𝒂 𝒎 𝝅 , 𝒇 𝝅

Bestiarium of Low-Mass Bosons Weakly Interacting Sub-eV Particles (WISPs) • Axion (1 parameter family 𝑚 𝑎 𝑓 𝑎 ∼ 𝑚 𝜋 𝑓 𝜋 ) Solves strong CP problem Could be dark matter • String axions (almost massless pseudoscalars in string theory) One of them may solve CP problem • Axion-like particles (ALPs) Generic two-photon vertex, could be dark matter (2 parameters 𝑚 𝑎 and 𝑔 𝑎𝛾 ) • Hidden photons Low-mass gauge bosons from 𝑈′(1) (kinetic mixing parameter 𝜒 and mass 𝑚 𝛾′ ) • Chameleons Scalars in certain models of scalar-tensor gravity Motivated by dark energy Environment-dependent properties

CP Violation in Particle Physics Discrete symmetries in particle physics C – Charge conjugation, transforms particles to antiparticles violated by weak interactions P – Parity, changes left-handedness to right-handedness T – Time reversal, changes direction of motion (forward to backward) CPT – exactly conserved in quantum field theory CP – conserved by all gauge interactions violated by three-flavor quark mixing matrix All measured CP-violating effects derive from a single phase in the quark mass matrix (Kobayashi-Maskawa phase), i.e. from complex Yukawa couplings Cosmic matter-antimatter asymmetry requires new ingredients M. Kobayashi T. Maskawa Physics Nobel Prize 2008

The CP Problem of Strong Interactions Real quark mass Phase from Yukawa coupling Angle variable CP-odd quantity ∼𝐄⋅𝐁 ℒ QCD = 𝑞 𝜓 𝑞 i𝐷− 𝑚 𝑞 𝑒 i 𝜃 𝑞 𝜓 𝑞 − 1 4 𝐺 𝜇𝜈𝑎 𝐺 𝑎 𝜇𝜈 −Θ 𝛼 s 8𝜋 𝐺 𝜇𝜈𝑎 𝐺 𝑎 𝜇𝜈 Remove phase of mass term by chiral transformation of quark fields 𝜓 𝑞 → 𝑒 −𝑖 𝛾 5 𝜃 𝑞 /2 𝜓 𝑞 ℒ QCD = 𝑞 𝜓 𝑞 i𝐷− 𝑚 𝑞 𝜓 𝑞 − 1 4 𝐺𝐺− Θ−arg det 𝑀 𝑞 −𝜋 ≤ Θ ≤+𝜋 𝛼 s 8𝜋 𝐺 𝐺 Θ can be traded between quark phases and 𝐺 𝐺 term No physical impact if at least one 𝑚 𝑞 =0 Induces a large neutron electric dipole moment (a T-violating quantity) Experimental limits: 𝚯 < 𝟏𝟎 −𝟏𝟏 Why so small?

Strong CP Problem QCD vacuum energy 𝑉(Θ) Λ QCD 4 Equivalent Equivalent Peccei-Quinn solution: Make 𝚯 dynamical, let system relax to lowest energy Θ −2𝜋 −𝜋 +𝜋 +2𝜋 • CP conserving vacuum has Θ=0 (Vafa and Witten 1984) • QCD could have any −𝜋≤Θ≤+𝜋, is “constant of nature” • Energy can not be minimized: Θ not dynamical

The Pool Table Analogy (Pierre Sikivie 1996) Gravity Pool table Symmetric relative to gravity Axis Symmetry dynamically restored (Peccei & Quinn 1977) New degree of freedom  Axion 𝚯 (Weinberg 1978, Wilczek 1978) fa Symmetry broken Floor inclined

37 Years of Axions

The Cleansing Axion “I named them after a laundry Frank Wilczek “I named them after a laundry detergent, since they clean up a problem with an axial current.” (Nobel lecture 2004)

Arthur Godfrey

Opportunities for detection Axion Bounds mPlanck fa 1018 1015 1012 109 106 GeV eV meV ma neV peV Astrophysical Bounds (Energy loss of stars) Supernova 1987A Globular Cluster Opportunities for detection

Experimental Tests of Invisible Axions Primakoff effect: Axion-photon transition in external static E or B field (Originally discussed for 𝜋 0 by Henri Primakoff 1951) Pierre Sikivie: Macroscopic B-field can provide a large coherent transition rate over a big volume (low-mass axions) Axion helioscope: Look at the Sun through a dipole magnet Axion haloscope: Look for dark-matter axions with a microwave resonant cavity Two-photon vertex generic for 𝜋 0 , 𝜂, axion-like particles (ALPs), gravitons

Search for Solar Axions Axion Helioscope (Sikivie 1983) Primakoff production Axion flux N a g a g Magnet S Axion-Photon-Oscillation Sun Tokyo Axion Helioscope (“Sumico”) (Results since 1998, up again 2008) CERN Axion Solar Telescope (CAST) (Data since 2003) Alternative technique: Bragg conversion in crystal Experimental limits on solar axion flux from dark-matter experiments (SOLAX, COSME, DAMA, CDMS ...)

CERN Axion Solar Telescope (CAST)

CAST Results

Parameter Space for Axion-Like Particles (ALPs) Two parameters: - ALP mass 𝑚 𝑎 - ALP-𝛾 coupling 𝑔 𝑎𝛾 Weinberg Wilczek “standard axion” Model dependence (KSVZ, DFSZ, …) broadens the “axion line” Γ 𝑎→𝛾𝛾 = 𝑔 𝑎𝛾 2 𝑚 𝑎 3 64𝜋

Parameter Space for Axion-Like Particles (ALPs) CAST exclusion range

Parameter Space for Axion-Like Particles (ALPs) ALPS-II at DESY

Shining TeV Gamma Rays through the Universe Figure from a talk by Manuel Meyer (Univ. Hamburg)

Next Generation Axion Helioscope (IAXO) at CERN Need new magnet w/ – Much bigger aperture: ~1 m2 per bore – Lighter (no iron yoke) – Bores at Troom • Irastorza et al.: Towards a new generation axion helioscope, arXiv:1103.5334 • Armengaud et al.: Conceptual Design of the International Axion Observatory (IAXO), arXiv:1401.3233

Parameter Space for Axion-Like Particles (ALPs) - Improvement by a factor of 30 - Leaping into uncharted territory Pushing generic ALP frontier QCD Axion meV frontier

Pie Chart of Dark Matter of the Universe Dark Energy 70% (Cosmological Constant) Neutrinos 0.1-0.4% Ordinary Matter 5% (of this only about 10% luminous) Dark Matter 25%

Creation of Cosmological Axions by Re-alignment 𝑻 ~ 𝒇 𝒂 (very early universe) UPQ(1) spontaneously broken Higgs field settles in “Mexican hat” Axion field sits fixed at 𝑎𝑖 =Θ𝑖 𝑓 𝑎 𝑎 𝑉(𝑎) 𝑻 ~ 𝟏 GeV (𝑯 ~ 𝟏𝟎 −𝟗 eV) Axion mass turns on quickly by thermal instanton gas Field starts oscillating when 𝑚𝑎 ≳ 3𝐻 Classical field oscillations (axions at rest) 𝑉(𝑎) 𝑎 Θ =0 Axions are born as nonrelativistic, classical field oscillations Very small mass, yet cold dark matter

Axion Cosmology in PLB 120 (1983)

Galactic WIMP vs Axion Dark Matter Local dark matter density around 0.4 GeV/cm3 WIMPs: Typical mass 100 GeV • Local number density: 𝟒𝟎𝟎𝟎 𝐦 −𝟑 𝟏𝟎𝟎 𝐆𝐞𝐕 𝒎 𝐖𝐈𝐌𝐏 Dilute gas of particles Axions: Typical mass 10 meV • Local number density: 𝟒×𝟏 𝟎 𝟏𝟗 𝐦 −𝟑 𝟏𝟎 𝛍𝐞𝐕 𝒎 𝒂 • Typical galactic virial velocity: 𝒗 𝐠𝐚𝐥 ∼𝟏 𝟎 −𝟑 𝒄 • Typical de Broglie wavelength (“localisation”) 𝝀∼ 𝟐𝝅 𝒎 𝒂 𝒗 𝐠𝐚𝐥 ∼𝟏𝟎𝟎 𝐦 𝟏𝟎 𝛍𝐞𝐕 𝒎 𝒂 • Typical occupation number 𝒇∼𝟏 𝟎 𝟐𝟓 𝟏𝟎 𝛍𝐞𝐕 𝒎 𝒂 𝟒 Highly degenerate Bose gas!

Axion Dark Matter Driving Oscillators Relic oscillations of QCD Q term • Drives oscillating neutron EDM • Drives oscillating E-field in microwave cavity w/ B-field +𝜋 −𝜋 Λ QCD 4 Θ=a/ f a n Axion-induced electric field oscillating with 𝝎= 𝒎 𝒂 External static B-field Neutron electric dipole moment oscillating with 𝝎= 𝒎 𝒂

Cold Axion Populations Scenario 1 • Cosmic inflation first • PQ symmetry breaking at 𝑇∼ 𝑓 𝑎 • Every causal patch has different random Θ 𝑖 • Topological defects at interfaces • Axion dark matter from - average re-alignment - cosmic-string (CS) & domain-wall (DW) decay Cosmic axion string Random Θ 𝑖 values 0.01 1.12 0.37 1.93 0.63 2.01 3.14 0.17 1.57 Scenario 2 • Cosmic inflation after PQ symmetry breaking • All axions from re-alignment of one random Θ i in our patch of the universe • Allows large 𝑓 𝑎 if Θ 𝑖 ≪1 (“anthropic” case) Θ 𝑖 =1.57 𝛺 𝑎 ℎ 2 =0.20 Θ 𝑖 2 𝑓 𝑎 10 12 GeV 1.184 =0.11 Θ 𝑖 2 10 𝜇eV 𝑚 𝑎 1.184

Axion Production by Domain Wall and String Decay Recent numerical studies of collapse of string-domain wall system Ω 𝑎 ℎ 2 = 8.4±3.0 𝑓 𝑎 10 12 GeV 1.19 × 𝑔 ∗,1 70 −0.41 Λ 400 MeV Implies a CDM axion mass of 𝑚 𝑎 ∼300 𝜇eV Hiramatsu, Kawasaki, Saikawa & Sekiguchi, arXiv:1202.5851 (2012) More recently by the same group 𝑚 𝑎 ∼90−140 𝜇eV Kawasaki, Saikawa & Sekiguchi, arXiv:1412.0789 (PRD 2015)

Axion Dark Matter Parameters mPlanck fa 1018 1015 1012 109 106 GeV eV meV ma neV peV kHz MHz GHz THz na Too much dark matter in re-aligment scenario with 𝚯 𝐢 =𝟏 Axion DM Astrophysical Bounds (Energy loss of stars) Too much dark matter in cosmic string and domain wall scenario Axion DM

Search for Galactic Axions (Cold Dark Matter) Dark matter axions Velocities in galaxy Energies therefore ma = 1-100 meV va  10-3 c Ea  (1  10-6) ma Microwave Energies (1 GHz  4 meV) Axion Haloscope (Sikivie 1983) Power Frequency ma Axion Signal Bext  8 Tesla Thermal noise of cavity & detector Microwave Resonator Q  105 Power of galactic axion signal Primakoff Conversion g 4× 10 −21 W 𝑉 0.22 m 3 𝐵 8.5 T 2 𝑄 10 5 × 𝑚 a 2𝜋 GHz 𝜌 𝑎 5× 10 −25 g/cm 3 a Cavity overcomes momentum mismatch Bext

Axion Dark Matter Experiment (ADMX) – Seattle Adapted from Gray Rybka

SQUID Microwave Amplifiers in ADMX Adapted from Gianpaolo Carosi

ADMX Gen 2

Axion Dark Matter Parameters mPlanck fa 1018 1015 1012 109 106 GeV eV meV ma neV peV kHz MHz GHz THz na Too much dark matter in re-aligment scenario with 𝚯 𝐢 =𝟏 Axion DM Astrophysical Bounds (Energy loss of stars) Too much dark matter in cosmic string and domain wall scenario Axion DM ADMX Taking data

Axion Dark Matter Search with Transition Radiation Dark matter axion field producing photons at dielectric interface (in B-field!) (Jaeckel & Redondo, PRD 88 (2013) 115002, arXiv:1308.1103) “Seed project” at MPI Physics: Test practical boost factor with a setup that contains up to five exchangeable discs (diameter ~200 mm) with high-ε material that can be positioned using motor drives with a precision of a few μm

Center for Axion and Precision Physics (CAPP) Yannis Semertzidis 15 Oct 2013 The plan is to launch a competitive Axion Dark Matter Experiment in Korea, participate in state-of-the-art axion experiments around the world, play a leading role in the proposed proton electric-dipole-moment (EDM) experiment and take a significant role in storage-ring precision physics involving EDM and muon g–2 experiments. http://capp.ibs.re.kr

Searching for Axions in the Anthropic Window CASPEr experiment Precise magnetometry to measure tiny deviations from Larmor frequency Graham & Rajendran, arXiv:1101.2691 Budker, Graham, Ledbetter, Rajendran & Sushkov, arXiv:1306.6089

ARIADNE: Axion Resonant InterAction DetectioN Experiment NMR Experiment ARIADNE: Axion Resonant InterAction DetectioN Experiment A.Geraci, A.Arvanitaki, A.Kapitulnik, Chen-Yu Liu, J.Long, Y.Semertzidis, M.Snow (to be supported by NSF and/or DoE?)

Axion Searches mPlanck fa 1018 1015 1012 109 106 GeV eV meV ma neV peV kHz MHz GHz THz na Taking data IAXO CASPEr ARIADNE Astrophysical Bounds (Energy loss of stars)

Axion and Axion-Like Particle Searches ARIADNE Center for Axion & Precision Physics (Daejon, Korea) WISP DMX (DESY) MAGIC ADMX-HF (Yale) Axion Dark Matter Experiment (UW, Seattle) H.E.S.S. IAXO Proposal (CERN) CASPEr, perhaps @ HIM (Mainz) Fermi LAT CAST @ CERN

Dow Jones Index of Axion Physics It’s a bull market, buy shares! Dow Jones Index of Axion Physics inSPIRE: Citation of Peccei-Quinn papers or title axion (and similar)