Ever wondered why there's more matter than antimatter in the universe? Baryogenesis and leptogenesis explain this mystery. These processes, occurring in the early universe, created an imbalance between matter and antimatter, leading to our matter-dominated cosmos.

Understanding baryogenesis and leptogenesis is crucial for grasping the universe's evolution. These concepts connect particle physics with cosmology, offering insights into fundamental laws of nature and the origins of matter. They're key pieces in the puzzle of our universe's composition.

Baryogenesis and Cosmology

Origin and Significance of Baryogenesis

• Baryogenesis produced excess of baryons (matter) over antibaryons (antimatter) in early universe led to matter-dominated universe
• Baryon asymmetry quantified by baryon-to-photon ratio (η) approximately 6 × 10^-10 based on cosmic microwave background and primordial nucleosynthesis observations
• Explains existence of matter in universe prevented annihilation of equal amounts of matter and antimatter
• Connects particle physics with cosmology provides insights into fundamental laws of nature and universe evolution
• Various models propose different mechanisms for generating observed baryon asymmetry
  • GUT baryogenesis
  • Electroweak baryogenesis
  • Affleck-Dine baryogenesis

Quantifying and Observing Baryon Asymmetry

• Baryon-to-photon ratio (η) measures baryon asymmetry of universe
• Cosmic microwave background observations provide evidence for baryon asymmetry
• Primordial nucleosynthesis predictions align with observed light element abundances supports baryon asymmetry theory
• Matter-dominated universe observable through large-scale structure formation (galaxies, clusters)
• Absence of large-scale antimatter regions in observable universe supports asymmetry hypothesis

Sakharov Conditions for Baryogenesis

Fundamental Requirements for Baryogenesis

• Andrei Sakharov proposed three necessary conditions in 1967 fundamental to understanding matter-antimatter asymmetry origin
• Baryon number violation allows processes changing net baryon number of universe
  • Example: proton decay in Grand Unified Theories
• C-symmetry and CP-symmetry violation ensures matter and antimatter creation processes occur at different rates
  • Example: neutral kaon decay exhibits CP violation
• Departure from thermal equilibrium prevents reverse reactions from erasing generated asymmetry
  • Example: phase transitions in early universe (electroweak transition)

Implications and Challenges of Sakharov Conditions

• Conditions must be satisfied simultaneously in early universe for successful baryogenesis
• Standard Model of particle physics partially satisfies conditions but fails to produce sufficient baryon asymmetry
• Beyond Standard Model physics necessary to fully explain observed baryon asymmetry
• Experimental searches for baryon number violation (proton decay experiments)
• Investigations of CP violation in particle physics experiments (B-factories, neutrino oscillation experiments)
• Theoretical models exploring novel mechanisms for departure from thermal equilibrium (cosmic inflation, topological defects)

CP Violation and Matter-Antimatter Asymmetry

Fundamentals of CP Violation

• CP violation asymmetry between particles and antiparticles under combined charge conjugation (C) and parity (P) transformations
• Crucial for baryogenesis allows different interaction rates between matter and antimatter leads to net excess of baryons
• Standard Model includes CP violation through CKM matrix in quark sector and potentially through PMNS matrix in lepton sector
• Magnitude of CP violation in Standard Model insufficient to account for observed baryon asymmetry
• Additional sources of CP violation in new physics models needed to explain matter-antimatter asymmetry

Experimental Searches and Theoretical Extensions

• Experimental searches for CP violation provide insights into potential baryogenesis mechanisms
  • B meson decays (Belle, BaBar experiments)
  • Neutrino oscillations (T2K, NOvA experiments)
• Theories extending Standard Model introduce new sources of CP violation
  • Supersymmetry
  • Extra dimensions
  • Leptoquarks
• CP violation in strong interactions (strong CP problem) potential connection to axions and dark matter
• Future experiments aim to measure CP violation in neutrino sector (DUNE, Hyper-Kamiokande)

Leptogenesis and Neutrino Physics

Leptogenesis Mechanism and Neutrino Connection

• Leptogenesis generates baryon asymmetry through lepton processes converted to baryon asymmetry via sphaleron processes
• Common scenario involves decay of heavy right-handed neutrinos in early universe
  • Produces lepton asymmetry
  • Later converted to baryon asymmetry
• Naturally arises in theories explaining small neutrino masses through seesaw mechanism
• Neutrino oscillations and mixing parameters provide crucial inputs for leptogenesis models
• CP violation in lepton sector potentially observable in neutrino oscillation experiments related to CP violation required for successful leptogenesis

Experimental Implications and Future Prospects

• Leptogenesis models make predictions for absolute neutrino mass scale and nature of neutrinos (Dirac or Majorana)
• Future experiments aim to test leptogenesis predictions
  • Neutrinoless double beta decay searches (LEGEND, nEXO)
  • Cosmological constraints on neutrino masses (Euclid, CMB-S4)
• Connection between leptogenesis and neutrino physics offers potential explanation for matter origin and observed neutrino properties
• Sterile neutrino searches (short-baseline neutrino experiments) could provide insights into leptogenesis mechanisms
• Precision measurements of neutrino mixing parameters and CP violation (DUNE, Hyper-Kamiokande) crucial for testing leptogenesis models