12.3 Baryogenesis and leptogenesis
4 min read•august 1, 2024
Ever wondered why there's more matter than antimatter in the universe? and 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
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- Baryogenesis produced excess of baryons (matter) over antibaryons (antimatter) in early universe led to matter-dominated universe
- asymmetry quantified by (η) approximately 6 × 10^-10 based on 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
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
- proposed three necessary conditions in 1967 fundamental to understanding origin
- Baryon number violation allows processes changing net baryon number of universe
- Example: in Grand Unified Theories
- and CP-symmetry violation ensures matter and antimatter creation processes occur at different rates
- Example: neutral kaon decay exhibits
- Departure from prevents reverse reactions from erasing generated asymmetry
- Example: in early universe (electroweak transition)
Implications and Challenges of Sakharov Conditions
- Conditions must be satisfied simultaneously in early universe for successful baryogenesis
- 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, )
- 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
- CP violation in strong interactions () 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
- 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 and CP violation (DUNE, Hyper-Kamiokande) crucial for testing leptogenesis models
Key Terms to Review (27)
Affleck-Dine Baryogenesis: Affleck-Dine baryogenesis is a theoretical mechanism proposed to explain the generation of the baryon asymmetry in the universe, which refers to the observed imbalance between matter and antimatter. This process involves the dynamics of scalar fields in the early universe, which can lead to the production of baryons through a process involving supersymmetry and inflation. This theory suggests that as the universe expanded and cooled, these scalar fields could have developed non-zero expectation values that contributed to creating an excess of baryons over antibaryons.
Andrei Sakharov: Andrei Sakharov was a prominent Russian physicist and activist, known for his significant contributions to the development of thermonuclear weapons and his later advocacy for human rights and disarmament. His work in theoretical physics laid the groundwork for many aspects of modern particle physics, and he is particularly recognized for his role in the theories surrounding baryogenesis and leptogenesis, which explain the matter-antimatter asymmetry in the universe.
Antibaryon: An antibaryon is a type of subatomic particle that is the antimatter counterpart of baryons, which are particles made up of three quarks. Antibaryons contain three antiquarks, which have opposite properties to their corresponding quarks, resulting in unique characteristics. The existence and behavior of antibaryons play a crucial role in understanding processes like baryogenesis and leptogenesis, as they provide insights into the matter-antimatter asymmetry in the universe.
Baryogenesis: Baryogenesis refers to the theoretical processes that explain the observed asymmetry between baryons (particles like protons and neutrons) and antibaryons in the universe. This phenomenon is crucial because, according to current models, the universe contains significantly more matter than antimatter, which raises questions about the mechanisms that led to this imbalance, especially in relation to fundamental interactions and the evolution of the universe.
Baryon: A baryon is a type of subatomic particle that is composed of three quarks and is one of the building blocks of atomic nuclei. Baryons, such as protons and neutrons, are held together by the strong force, which is mediated by particles called gluons. These particles have a half-integer spin, classifying them as fermions, and are essential in understanding the structure of matter in the universe.
Baryon-to-photon ratio: The baryon-to-photon ratio is a fundamental parameter that quantifies the relative abundance of baryons, which are particles like protons and neutrons, to photons in the universe. This ratio plays a crucial role in understanding the evolution of the universe, particularly in scenarios such as baryogenesis and leptogenesis, where it helps explain the observed matter-antimatter asymmetry and the formation of large-scale structures.
C-symmetry: C-symmetry, or charge conjugation symmetry, refers to the property of physical laws being invariant under the transformation that replaces particles with their corresponding antiparticles. This concept is crucial in understanding how certain interactions in particle physics should behave if particles were replaced with their antiparticle counterparts, helping to illuminate the balance of matter and antimatter in processes like baryogenesis and leptogenesis.
Cosmic microwave background: The cosmic microwave background (CMB) is the faint radiation left over from the hot, dense state of the early universe, providing a snapshot of the cosmos approximately 380,000 years after the Big Bang. This relic radiation not only supports the Big Bang theory but also serves as crucial evidence for various unsolved problems in particle physics, such as the nature of dark matter and baryogenesis.
Cp violation: CP violation refers to the phenomenon where the combined symmetries of charge conjugation (C) and parity (P) are not conserved in certain particle interactions, particularly in weak decays. This violation suggests that the laws of physics are not the same for particles and their antiparticles, leading to observable differences in behavior, which has profound implications for our understanding of the universe.
Electroweak baryogenesis: Electroweak baryogenesis is a theoretical framework that explains the generation of the observed matter-antimatter asymmetry in the universe during the electroweak phase transition. This phenomenon links the behavior of fundamental forces, particularly the electroweak interaction, to the creation of a net baryon number, which is crucial for understanding why our universe is predominantly composed of matter rather than antimatter.
Extra dimensions: Extra dimensions refer to additional spatial dimensions beyond the familiar three-dimensional space that we experience in everyday life. In theoretical physics, especially in contexts like string theory and certain models of quantum gravity, these dimensions can help explain various phenomena and address limitations within the Standard Model of particle physics, such as unifying gravity with other fundamental forces and solving unsolved problems.
Gut baryogenesis: Gut baryogenesis is a theoretical framework that describes the generation of baryon asymmetry in the universe during the grand unification epoch, when the forces of the strong, weak, and electromagnetic interactions are thought to merge. This process is tied to the concept of baryogenesis, where an imbalance between baryons (matter) and antibaryons (antimatter) is created, leading to the observed predominance of matter in the universe today. It emphasizes the role of grand unified theories (GUTs) and high-energy physics in explaining how this asymmetry could arise shortly after the Big Bang.
Leptogenesis: Leptogenesis is a theoretical process that explains the observed asymmetry between matter and antimatter in the universe by proposing the generation of an excess of leptons over anti-leptons in the early universe. This process is closely related to CP violation, which allows for differences in behavior between particles and their antiparticles, and has implications for understanding the limitations of the Standard Model, as well as providing insights into baryogenesis, which involves the production of baryons like protons and neutrons.
Leptoquarks: Leptoquarks are hypothetical particles that can simultaneously couple to both leptons (such as electrons and neutrinos) and quarks (the building blocks of protons and neutrons). These particles are of interest in theoretical physics as they may help explain the connection between the two sectors of matter, potentially providing insights into baryogenesis and leptogenesis, which describe processes that could generate the matter-antimatter asymmetry in the universe.
Matter-antimatter asymmetry: Matter-antimatter asymmetry refers to the observed imbalance between matter and antimatter in the universe, where matter overwhelmingly dominates. This phenomenon is crucial for understanding why the universe contains more matter than antimatter, despite theories suggesting they should have been created in equal amounts during the Big Bang. This asymmetry relates closely to various fundamental symmetries in physics and plays a significant role in weak interactions, pointing towards limitations in our current understanding of particle physics.
Neutrino mass generation: Neutrino mass generation refers to the processes that allow neutrinos, which are nearly massless elementary particles, to acquire a small but non-zero mass. This phenomenon is crucial for understanding the behavior of neutrinos in particle physics and has significant implications for theories of baryogenesis and leptogenesis, as well as our understanding of the early universe.
Neutrino mixing parameters: Neutrino mixing parameters refer to the quantities that describe the mixing of different flavors of neutrinos, specifically how they transition from one type to another as they propagate through space. This phenomenon is crucial for understanding neutrino oscillation, which is a fundamental aspect of particle physics and relates directly to the processes of baryogenesis and leptogenesis, where neutrino interactions play a role in the asymmetry between matter and antimatter in the universe.
Neutrino oscillation experiments: Neutrino oscillation experiments study the phenomenon where neutrinos change from one flavor to another as they propagate through space. This process is crucial for understanding the properties of neutrinos, particularly their masses and the mixing angles between different types, which can hint at new physics beyond the Standard Model. By investigating these transformations, researchers also gain insights into fundamental questions like the nature of matter and the universe's evolution.
Out-of-equilibrium processes: Out-of-equilibrium processes refer to dynamic events that occur in systems not in thermal or chemical equilibrium, leading to non-standard behaviors and distributions of particles. These processes are critical for understanding phenomena like baryogenesis and leptogenesis, where the early universe was far from equilibrium, influencing the generation of matter and asymmetries that shaped the cosmos.
Phase Transitions: Phase transitions refer to the changes between different states of matter, such as solid, liquid, and gas, which can occur under varying temperature and pressure conditions. These transitions are not just physical changes; they also have significant implications in various fields, including cosmology and particle physics, particularly in understanding the early universe and processes like baryogenesis and leptogenesis.
Proton decay: Proton decay is a hypothetical process in which a proton, a fundamental component of atomic nuclei, spontaneously transforms into lighter particles, typically resulting in the emission of positrons and neutral pions. This phenomenon is a key prediction of certain Grand Unified Theories (GUTs), suggesting that protons are not as stable as previously thought. The implications of proton decay touch on unsolved issues in particle physics and contribute to our understanding of baryogenesis and leptogenesis, which are processes that explain the observed matter-antimatter asymmetry in the universe.
Sphaleron processes: Sphaleron processes are non-perturbative quantum tunneling events that occur in certain theories of particle physics, allowing for the conversion between baryons and leptons. These processes play a critical role in the understanding of baryogenesis and leptogenesis, as they can violate baryon and lepton number conservation, which is essential for explaining the observed matter-antimatter asymmetry in the universe.
Standard Model: The Standard Model is a well-established theoretical framework in particle physics that describes the fundamental particles and their interactions through three of the four known fundamental forces: electromagnetic, weak, and strong forces. It unifies various concepts in particle physics, explaining how particles like quarks and leptons interact through force-carrying particles known as gauge bosons.
Sterile Neutrinos: Sterile neutrinos are a hypothesized type of neutrino that do not interact through the standard weak interactions like regular neutrinos but instead only interact via gravity. This makes them elusive and difficult to detect, leading to their consideration in several unsolved problems in physics, as well as in theories explaining the asymmetry between matter and antimatter, and providing possible connections to beyond-standard model physics.
Strong cp problem: The strong CP problem refers to the question of why quantum chromodynamics (QCD), the theory of the strong interaction, does not exhibit the expected violation of charge parity (CP) symmetry. Despite theoretical predictions suggesting that QCD should result in significant CP violation, experimental evidence shows that such violations are exceedingly small or nonexistent, leading to a puzzling discrepancy that remains unresolved in our understanding of particle physics.
Supersymmetry: Supersymmetry is a theoretical framework in particle physics that posits a symmetry between bosons and fermions, suggesting that every known particle has a corresponding 'superpartner' with different spin characteristics. This concept aims to resolve several issues within the Standard Model and to provide a candidate for dark matter, while also offering insights into the fundamental nature of particles and forces.
Thermal equilibrium: Thermal equilibrium occurs when two systems in thermal contact cease to exchange heat, resulting in them reaching the same temperature. This state is crucial in understanding how energy distributes itself in physical systems and plays a significant role in the behavior of particles in various processes, particularly those involving fundamental forces and interactions.