Theory Overview: Why are Long-lived parcticles important? Satoshi Shirai (Kavli IPMU) 1. Long-lived Particles Standard Model Examples 2. Symmetry and Cosmology Minimal dark matter SUSY Coannihlation dark matter Freeze-in DM and Baryogenesis 3. Summary 2 Long-lived Particles 3 Long-life? • Visible displacement of track or vertex • >O(10) μm decay length 4 Lifetime of Particles Decay Rate Typically Decay length Naively, particles are short-lived. 5 To Live a Long Life. Something special happens on long-lived particles Limited Channel： Some Symmetry? Weak Coupling：Approximate Symmetry Violation, High-scale Physics? Small Mass Dimension: Small mass difference with daughter particles? 6 In Standard Model 7 Stable Particles Symmetry Conservation law • Proton ● Lightest particle with baryon number • Electron ● Lightest particle with EM charge • Neutrino ● Lightest particles with Fermion/lepton number 8 Metastable particle: Muon Mass: 105 MeV, Lifetime: 2.2 μs, Decay length: 660 m Weak force: High-scale physics 9 Metastable particle: Neutron Mass: 939.56 MeV, Lifetime: 886 s, Decay length: 1011 m Weak force: High-scale physics Mass degeneracy: mp =938.27 MeV, mn – mp – me= 0.8 MeV 10 Metastable particle: Neutron Why Mass degenerated? up: 2-3 MeV, down 4-6 MeV Approximate SU(2) symmetry： isospin？ Stable nuclei needs small mass diff.: Anthropic? 11 Metastable particle: Neutron Neutron Mass&Lifetime Neutron abundance in BBN era Nuclei abundance 12 Metastable particle: Neutron Why Mass degenerated? up: 2-3 MeV, down 4-6 MeV Approximate SU(2) symmetry： isospin？ Stable nuclei needs small mass diff.: Anthropic? 13 Mesons... • K meson, charm meson, bottom meson ● Weak Interaction ● Flavor symmetry: Strangeness. ● CP symmetry: e.g., forbidden channel for KL 14 Long-lived particle implies • Weak interaction ● High-scale physics ● Symmetry and its breaking ● Tuning? ● … • Small Mass and Mass Difference ● Symmetry ● Accidental? ● … • Distinct observational signatures We learned basic concept of particle physics from LLPs 15 Long-lived Particles @ BSM 16 New physics needed! • Neutrino Mass • Seesaw • Dark Matter • SUSY • Baryon Number • Minimal Dark Matter • Quantum Gravity • Extra Dimension • Cosmological constant • String Landscape • Gauge hierarchy • Relaxion • U(1) quantization • Gauge extension • Strong CP • Mirror world • Flavor Structure • Axion •…. • Flavon •…. 17 Dark Matter and its Stability • Neutraino and Gravitino DM ● R-parity • Axion ● Small Mass from Nambu-Goldston Theorem • Minimal 5-plet Dark Matter ● Forbidden Channel • Mirror Matter ● Mirror baryon number 18 Metastable Particles • Neutraino NLSP + Gravitino LSP ● R-parity + High-scale physics (SUSY breaking) • Axion-like Particle ● Small Mass + High-scale physics (PQ’ symmetry breaking) [Shu-Yu’s talk] • Isospin partner of EW interacting DM(wino, higgsino…) ● Small mass difference from SU(2)L symmetry 19 Metastable Particles with Tuning? • Right-handed neutrino ● Small interaction for small neutrino mass [Arindam’s talk] • Coannihilating Dark Matter, e.g., gluino-bino ● Small mass difference for correct DM abundance • Freeze-in DM/Baryogenesis mechanism ● Small interaction for correct DM/Baryon abundance [Shintaro and Sreemanti’s talk] 20 BSM and Cosmology Standard Cosmology is almost perfect, if • Enough Temperature > O(1) MeV • Density fluctuation (seed of structure) • Baryon number • Dark Matter 21 BSM and Cosmology Standard Cosmology is almost perfect, if Inflation • Enough Temperature > O(1) MeV • Density fluctuation (seed of structure) • Baryon number Still unclear. So many models.. • Dark Matter 22 Origin of DM and Baryon • When and How? Inflation Hot Universe Standard Cosmology Start Now T=MeV 23 Origin of DM and Baryon • When and How? BSM sector Inflation Hot Universe Standard Cosmology Start Now T=MeV 24 Origin of DM and Baryon • When and How? BSM sector Inflation Hot Universe Standard Cosmology Start Now T=MeV Axion WIMP Leptogensis Dirac Universe Freeze-in DM 25 Origin of DM and Baryon • When and How? BSM sector Inflation Hot Universe Standard Cosmology Start Now T=MeV Axion WIMP Leptogensis Dirac Universe Freeze-in DM Thermal Plasma DM/Baryon number reaction rate 26 Reaction Rate Hubble Parameter [GeV] Hubble Radius[m] Temperature [GeV] 27 BSM mass scale Reaction Rate Freeze-out, WIMP Hubble Parameter [GeV] Hubble Radius[m] Temperature [GeV] 28 Reaction Rate Hubble Parameter [GeV] Hubble Radius[m] Freeze-in e.g., Temperature [GeV] 29 Reaction Rate Hubble Parameter [GeV] Hubble Radius[m] Freeze-in e.g., Temperature [GeV] 30 Summary • Long-lived particles @ BSM are never exotic • LLP may have connection to more fundamental theory ● Symmetry breaking • Connection to other observation, ● Neutrino mass and DM/Baryon 31 Summary • There is no All-purpose experiments for LLPs. ● Detection significantly depends on Lifetime, Mass, Decay mode, Production mode.. ● Choice of physics target is crucial. • Making models with LLPs is very easy. ● Theorists can predict anything…. • I hope we can share theoretical idea beyond “signal building.” 32 Gravitino LSP MSSM NLSP is unstable NLSP → gravitino + SM particle TOF and stopping Signatures Mass and lifetime → Planck scale measurement@LHC [Buchmuller, Hamaguchi, Ratz, Yanagida, 04] 33 BSM mass scale Reaction Rate Freeze-out, WIMP Hubble Parameter [GeV] Hubble Radius[m] Freeze-in e.g., Temperature [GeV] 34.