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