← Graph View All Domains

A topic in the Open Knowledge Graph — a free, open map of 15,290 topics and the order to learn them in.

Physics › Particle Physics

Leptogenesis and Baryogenesis

Research Depth 190 in the knowledge graph ☐ I know this ☆ Set as goal
1,276prerequisites beneath it
See this on the map →
CP ViolationNeutrino Masses and Oscillations+1 more→
baryogenesis leptogenesis matter-antimatter-asymmetry sakharov-conditions

Core Idea

The observed universe contains far more matter than antimatter (baryon-to-photon ratio eta ~ 6 x 10-10), an asymmetry that cannot be explained by the Standard Model alone. Baryogenesis mechanisms must satisfy the three Sakharov conditions: baryon number violation, C and CP violation, and departure from thermal equilibrium. Leptogenesis -- generating a lepton asymmetry from the decay of heavy right-handed neutrinos, which is then partially converted to a baryon asymmetry by electroweak sphalerons -- is one of the most compelling scenarios.

Explainer

The matter-antimatter asymmetry of the universe is one of the most profound puzzles in physics. The observed baryon-to-photon ratio eta ~ 6 x 10-10, measured from Big Bang nucleosynthesis and the CMB, means that for every billion antiprotons in the early universe, there were one billion and one protons. This tiny excess survived after all the matter-antimatter pairs annihilated, leaving the residual baryons that make up all visible matter today. Generating this asymmetry dynamically (baryogenesis) requires physics beyond the Standard Model.

Electroweak baryogenesis attempts to generate the asymmetry at the electroweak phase transition (~100 GeV). If the transition were strongly first-order, expanding bubbles of the broken phase would provide the out-of-equilibrium condition, and CP-violating interactions of particles with the bubble walls would produce a baryon asymmetry through sphaleron processes. However, in the SM with m_H = 125 GeV, the transition is a smooth crossover, not first-order. Extensions of the Higgs sector (additional scalars, as in the two-Higgs-doublet model or NMSSM) can make the transition first-order, but these models are constrained by Higgs coupling measurements and direct searches. Electroweak baryogenesis also requires new sources of CP violation beyond the CKM phase.

Leptogenesis is the leading alternative, elegantly connecting the baryon asymmetry to neutrino physics. In the type-I seesaw mechanism, heavy right-handed Majorana neutrinos N_i with masses M_i ~ 109-15 GeV generate tiny left-handed neutrino masses through m_nu ~ m_D2/M_N. These same heavy neutrinos, decaying out of equilibrium in the early universe with CP-violating asymmetry, produce a lepton asymmetry that sphalerons partially convert to a baryon asymmetry. The elegance of leptogenesis is that it uses particles (right-handed neutrinos) already motivated by neutrino masses and requires CP violation already hinted at by neutrino oscillation data.

Testing leptogenesis is challenging because the right-handed neutrinos are typically too heavy to produce at colliders. However, the connection to low-energy neutrino parameters provides indirect tests: the CP phase delta_CP measured in oscillation experiments is related (though not identical) to the high-energy CP violation driving leptogenesis. Resonant leptogenesis (where M_1 ~ M_2, enhancing the CP asymmetry) and ARS (Akhmedov-Rubakov-Smirnov) leptogenesis (using GeV-scale sterile neutrinos) offer scenarios testable at the LHC or future experiments like SHiP. The discovery of neutrinoless double beta decay would confirm the Majorana nature of neutrinos, a necessary ingredient for the seesaw mechanism and standard leptogenesis.

Practice Questions 3 questions

Prerequisite Chain

Understanding Zero → The Number Zero → Counting to Five → Counting to 10 → One-to-One Correspondence → Counting a Set of Objects Up to 20 → Cardinality: The Last Number Counted → Matching Numerals to Quantities → Subitizing Small Quantities → Addition Within 10 → Making 10 as an Addition Strategy → Addition Within 20 → Doubles and Near Doubles → Doubles Facts Within 10 → Near Doubles Facts Within 20 → Mental Math Strategies for Addition → Mental Math: Adding and Subtracting Tens → Addition Within 100 → Repeated Addition as Multiplication → Multiplication as Equal Groups → Multiplication: Arrays → Basic Multiplication Facts (0s, 1s, 2s, 5s, 10s) → Multiplication Facts Within 100 → Division as Equal Sharing → Division as Grouping (Measurement Division) → Division: Grouping (Repeated Subtraction) Model → Division: Fair Sharing Model → Division as Equal Sharing → Division as Grouping → Basic Division Facts → Division Facts Within 100 → Multiplication and Division Fact Families → Relationship Between Multiplication and Division → Division Facts as Inverse of Multiplication → Remainders and Quotients in Division → Division Word Problems → Multi-Step Word Problems → Solving Multi-Step Word Problems → Multiplication Word Problems → Division Word Problems → Introduction to Long Division → Factors and Multiples → Prime and Composite Numbers → Equivalent Fractions → Relating Fractions and Decimals → Decimal Place Value → Integers and the Number Line → Comparing and Ordering Integers → Absolute Value → Adding Integers → Subtracting Integers → Multiplying Integers → Dividing Integers → Unit Rates → Proportions → Percent Concept → Converting Between Fractions, Decimals, and Percents → Operations with Rational Numbers → Two-Step Equations → Solving Multi-Step Equations → Equations with Variables on Both Sides → Angle Pairs: Complementary, Supplementary, and Vertical → Parallel Lines and Transversals → Corresponding Angles → Alternate Interior Angles → Triangle Angle Sum Theorem → Exterior Angle Theorem → Triangle Inequality Theorem → Similar Triangles: AA Similarity → Similar Triangles: SSS and SAS Similarity → Proportions in Similar Triangles → Right Triangle Trigonometry Introduction → Sine, Cosine, and Tangent Ratios → Trigonometric Ratios Review → Radian Measure → Converting Between Degrees and Radians → The Unit Circle → Graphing Sine and Cosine → Graphing Tangent and Reciprocal Trigonometric Functions → Derivatives of Trigonometric Functions → Antiderivatives → Iterated Integrals and Fubini's Theorem → Double Integrals in Cartesian Coordinates → Double Integrals in Polar Coordinates → Double Integrals in Polar Coordinates → Double Integrals: Definition and Setup → Iterated Integrals and Fubini's Theorem → Double Integrals over Rectangular Regions → Double Integrals over General Regions → Applications of Double Integrals: Area, Mass, and Moments → Triple Integrals in Cartesian Coordinates → Triple Integrals in Cylindrical and Spherical Coordinates → Change of Variables and the Jacobian Determinant → Applications of Triple Integrals: Volume and Mass → Vector Fields and Their Representations → Line Integrals of Vector Fields → Work and Circulation → Line Integrals of Scalar and Vector Functions → Fundamental Theorem for Line Integrals → Conservative Vector Fields → Conservative Vector Fields and Potential Functions → Curl and Divergence of Vector Fields → Curl and Divergence → Divergence Theorem → Electric Flux and Divergence Theorem → Gauss's Law: Integral Form and Meaning → Solving Problems with Gauss's Law → Conductors in Electrostatic Equilibrium → Capacitance and Capacitors → Dielectrics → Dielectric Constant and Relative Permittivity → Electric Field Inside Dielectric Materials → Dielectric Materials and Polarization → Dielectric Susceptibility and Permittivity → Energy Density in Electric Fields → Electric Current and Current Density → Electrical Resistance and Resistivity → Ohm's Law and Circuit Elements → Electromotive Force (EMF) and Batteries → Kirchhoff's Circuit Laws: Voltage and Current → DC Circuit Network Analysis Methods → Transient Response in RC Circuits → RC Circuits → LC and RLC Circuits → AC Circuits: Fundamentals → Impedance and Reactance → AC Power and Resonance → Electromagnetic Waves → Postulates of Special Relativity → Time Dilation → Length Contraction → Lorentz Transformation → Relativistic Velocity Addition → Relativistic Momentum and Energy → Mass-Energy Equivalence and E=mc² → Photons as Particles with Energy and Momentum → Planck-Einstein Relation: Energy and Frequency → Photoelectric Effect → The Photon: Light as Quanta → Compton Scattering → Wave-Particle Duality → de Broglie Wavelength → The Schrödinger Equation → State Vectors and Wavefunctions → Quantum Superposition → The Measurement Problem → Interpretations of Quantum Mechanics → Postulates of Quantum Mechanics → Observables and Quantum Operators → Commutators and Commutation Relations → Quantum Angular Momentum → Quantum Mechanical Treatment of Hydrogen → Solving the Schrödinger Equation for Hydrogen Atom → Quantum Numbers → Electron Configuration → Periodic Trends → Covalent Bonding → Electronegativity and Bond Polarity → Ionic Bonding → Lewis Structures → VSEPR Theory and Molecular Geometry → Molecular Geometry and Electron Pair Geometry → Molecular Polarity and Dipole Moments → Intermolecular Forces → States of Matter and Phase Changes: Melting, Boiling, and Sublimation → Gas Laws and the Ideal Gas Equation → Gas Stoichiometry and Volume-Volume Calculations → Thermochemistry and Enthalpy → Heat Capacity and Calorimetry → Entropy and Molecular Disorder → Spontaneity and ΔG → Entropy and Gibbs Free Energy → Chemical Equilibrium → Statistical Mechanics: Ensembles and the Boltzmann Distribution → Partition Function: Definition and Properties → Helmholtz Free Energy → Gibbs Free Energy → Phase Transitions: First Order and Second Order → Critical Phenomena and Critical Exponents → Landau Theory of Phase Transitions → Symmetry Breaking and Phase Transitions → Goldstone's Theorem and Gapless Modes → Goldstone Theorem → Higgs Mechanism → Electroweak Unification → Standard Model Overview → Collider Physics Methods → Cross Section Measurements → Higgs Boson Discovery and Properties → Beyond Standard Model (BSM) Overview → Leptogenesis and Baryogenesis

Longest path: 191 steps · 1276 total prerequisite topics

Prerequisites (3)

CP Violationhard Neutrino Masses and Oscillationshard Beyond Standard Model (BSM) Overviewsoft

Leads To (0)

No topics depend on this one yet.