Baryogenesis

Baryogenesis
NASA / WMAP Science Team · Public domain · source
Name	Baryogenesis
Field	Particle physics, Cosmology
Related	Big Bang, CP violation, Sakharov conditions

Baryogenesis Baryogenesis describes the processes hypothesized to produce the observed asymmetry between baryon matter and antimatter in the Universe after the Big Bang. It addresses why the present cosmos, observed via the Cosmic Microwave Background, Big Bang nucleosynthesis, and surveys like Sloan Digital Sky Survey and Planck (spacecraft), contains far more protons and neutrons than their antiparticles. Proposed explanations connect ideas from Quantum field theory, Grand Unified Theory, Electroweak theory, and models tested at facilities such as the Large Hadron Collider and observatories like Super-Kamiokande.

Introduction

The baryon asymmetry is quantified by the baryon-to-photon ratio measured by Planck (spacecraft), inferred from Big Bang nucleosynthesis constraints and observations at WMAP and COBE. Early proposals invoked physics beyond the Standard Model such as Grand Unified Theory transitions in SO(10), SU(5), or E6 frameworks, or mechanisms tied to Inflation (cosmology), reheating after Cosmic inflation, and phase transitions like the Electroweak phase transition. Historical contributors include Andrei Sakharov, Andrei D. Sakharov, Sakharov conditions, Andrei Linde, Alan Guth, and Steven Weinberg who connected symmetry breaking, CP-violation, and out-of-equilibrium dynamics to cosmological asymmetry.

Sakharov conditions

The minimal criteria for generating a net baryon number were articulated by Andrei Sakharov and involve processes violating baryon number symmetry, violations of charge conjugation symmetry and CP violation, and departures from thermal equilibrium such as those occurring during phase transitions. Examples of baryon number violation arise in Grand Unified Theory decays studied in Proton decay experiments, and nonperturbative processes like sphaleron transitions in Electroweak theory. CP violation measured in systems such as Kaons at the CERN NA31 experiment and B meson mixing at Belle (detector) and BaBar motivates model building, while out-of-equilibrium conditions are realized during reheating scenarios explored in Chaotic inflation models by Andrei Linde and at bubble walls in first-order phase transitions studied by Mikhail Shaposhnikov.

Baryogenesis mechanisms

Proposed mechanisms span a range including Electroweak baryogenesis, Leptogenesis, the Affleck–Dine mechanism, and models tied to Grand Unified Theory baryogenesis in SU(5) or SO(10). Each mechanism invokes different new particles or sectors—examples include heavy Majorana neutrinos in Seesaw mechanism models inspired by Minkowski, Peter, Yanagida, T., Gell-Mann, and Mohapatra, R. N.—or scalar condensates in supersymmetric frameworks explored by Edward Witten and James Bjorken. Alternative ideas involve asymmetric dark matter scenarios connected to searches at XENON1T, LUX, and Fermi Gamma-ray Space Telescope.

Electroweak baryogenesis

Electroweak baryogenesis exploits CP violation and departure from equilibrium during the Electroweak phase transition in Electroweak theory; viability depends on the transition being strongly first-order as might occur in extensions like the Minimal Supersymmetric Standard Model or two-Higgs-doublet models studied in the context of Higgs boson searches at ATLAS and CMS. Calculations incorporate nonperturbative sphaleron rates computed by groups including Donaldson, and transport equations developed in work by George Moore and Michael Dine. Collider constraints from LEP, Tevatron, and LHC on Higgs sector parameters, plus EDM limits from experiments such as ACME Collaboration and nEDM searches, restrict CP-violating sources described by theorists including A. Riotto and M. Trodden.

Leptogenesis

Leptogenesis generates a lepton asymmetry that is converted to a baryon asymmetry via sphaleron processes in Electroweak theory. Classic thermal leptogenesis involves out-of-equilibrium decays of heavy Majorana neutrinos as in the Seesaw mechanism and was developed in work by Masataka Fukugita and Tsutomu Yanagida. Variants include resonant leptogenesis explored by A. Pilaftsis, flavored leptogenesis analyzed by Sacha Davidson, and low-scale scenarios connected to sterile neutrino searches at MicroBooNE, DUNE, and NA62. Observational links tie neutrino mass measurements from KATRIN and mixing parameters from Super-Kamiokande and SNO to leptogenesis model building.

Affleck–Dine mechanism

The Affleck–Dine mechanism invokes scalar field condensates carrying baryon or lepton number in supersymmetric theories, introduced by Ian Affleck and Michael Dine. It operates in the context of Supersymmetry breaking, flat directions in the Minimal Supersymmetric Standard Model, and dynamics during Inflation (cosmology) and reheating; baryon number is stored in coherent oscillations and later decays into standard particles. Applications link to nonthermal dark matter production considered by Gianfranco Bertone and to gravitational wave signals potentially observable by detectors like LISA and Advanced LIGO if associated with first-order transitions.

Experimental and observational constraints

Constraints derive from cosmological probes such as Planck (spacecraft), WMAP, Big Bang nucleosynthesis abundances measured in Sloan Digital Sky Survey spectroscopic surveys, and large-scale structure mapped by Dark Energy Survey. Laboratory limits on baryon number violation come from Super-Kamiokande proton decay searches and neutron–antineutron oscillation experiments at facilities like European Spallation Source. CP-violation and electric dipole moment bounds from ACME Collaboration, nEDM, and Muon g-2 measurements, along with collider limits from LHC, LEP, and Tevatron, shape viable parameter space for mechanisms. Neutrino experiments including KATRIN, DUNE, NOvA, and IceCube inform leptogenesis, while gravitational wave observatories such as LISA and Advanced LIGO could probe phase transitions relevant to electroweak and Affleck–Dine scenarios.

Category:Cosmology