Electroweak phase transition
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| Electroweak phase transition | |
|---|---|
| Name | Electroweak phase transition |
| Field | Particle physics, Cosmology |
| Related | Electroweak symmetry breaking, Higgs mechanism, Standard Model, Baryogenesis |
Electroweak phase transition The electroweak phase transition is a cosmological epoch in the early Universe associated with the breaking of symmetry in the electroweak sector of the Standard Model and the emergence of the Higgs boson mass scale. It connects high-temperature regimes governed by unified electromagnetism–weak interaction behavior to low-temperature physics where W bosons, Z bosons, and the photon acquire distinct roles, influencing processes relevant to Big Bang nucleosynthesis and baryon asymmetry of the universe. Studies of this transition invoke tools developed at institutions such as CERN, Fermilab, and KEK and interfaces with research programs like the Large Hadron Collider and the Planck mission.
Introduction
The electroweak epoch follows the GUT era and precedes the epochs described by Big Bang nucleosynthesis and recombination in standard cosmology. Its characterization depends on the parameters of the Standard Model, notably the Higgs boson mass measured at Large Hadron Collider experiments and the values of gauge couplings tested at LEP and SLAC National Accelerator Laboratory. The possibility that this transition is first-order, second-order, or a crossover has major consequences for scenarios like electroweak baryogenesis and for the generation of primordial gravitational waves measurable by observatories envisioned by collaborations such as the LISA consortium.
Theoretical Background
Analyses employ quantum field theory formalisms developed in the context of Yang–Mills theory and perturbative expansions used in calculations by researchers at Princeton University, Harvard University, and Institute for Advanced Study. The underlying symmetry is the SU(2)×U(1) gauge group of the Standard Model broken via the Higgs mechanism first articulated by teams influenced by work from Peter Higgs, François Englert, and Robert Brout. Finite-temperature field theory methods trace to contributions from Yoichiro Nambu-inspired approaches and thermal loops calculated in studies at Brookhaven National Laboratory. Nonperturbative methods using lattice gauge theory and computational frameworks developed at CERN and Fermilab permit exploration of phase structure, with early lattice studies by groups associated with University of Cambridge and University of Oxford clarifying crossover behavior for the measured Higgs boson mass.
Dynamics of the Phase Transition
If first-order, the transition proceeds via nucleation of broken-phase bubbles studied with techniques refined by theorists at Massachusetts Institute of Technology, Stanford University, and University of Chicago. Bubble wall propagation, friction, and reheating calculations reference transport treatments developed alongside work at Los Alamos National Laboratory and Rutherford Appleton Laboratory. Sphaleron processes, first highlighted by investigations from Gerard 't Hooft and expanded by analyses at Max Planck Institute for Physics, control baryon-number violation rates in the symmetric phase. The competition between expansion rate governed by General relativity in the Friedmann–Lemaître–Robertson–Walker framework and microphysical reaction rates determines out-of-equilibrium conditions, a theme explored in collaborations involving NASA-funded cosmology groups and theoretical teams at Yale University.
Cosmological Implications
A strongly first-order transition can source stochastic gravitational waves through bubble collisions and magnetohydrodynamic turbulence, spectra potentially detectable by projects coordinated by the European Space Agency and the European Southern Observatory-linked community supporting LISA. Electroweak baryogenesis scenarios aim to explain the baryon asymmetry of the universe using CP violation beyond that of the Cabibbo–Kobayashi–Maskawa matrix tested at Belle (experiment) and BaBar (experiment), requiring inputs aligned with constraints from Planck measurements of the cosmic microwave background by teams at ESA and NASA. Magnetic field generation and primordial relics from the transition connect to searches conducted by collaborations at Square Kilometre Array and experiments coordinated through Max Planck Society initiatives.
Experimental and Observational Constraints
Collider measurements from ATLAS and CMS at the Large Hadron Collider fix the Higgs mass and couplings that determine the nature of the transition, while precision electroweak tests from LEP and SLC place limits on deviations. Flavor and CP-violation bounds come from experiments such as LHCb, Belle, and NA62, constraining baryogenesis model-building. Cosmological observations from Planck, WMAP, and large-scale structure surveys like Sloan Digital Sky Survey restrict relic abundances and gravitational-wave backgrounds, with near-future probes from LISA and ground-based detectors influenced by collaborations at LIGO and VIRGO poised to test predicted signals.
Extensions Beyond the Standard Model
Realizing a strongly first-order electroweak transition typically requires new states or interactions as proposed in frameworks developed at Princeton University, Perimeter Institute, and CERN. Popular extensions include the Minimal Supersymmetric Standard Model motivated by groups at Fermilab and University of California, Berkeley, singlet scalar extensions studied by teams at Yukawa Institute for Theoretical Physics, and two-Higgs-doublet models investigated by researchers at University of Michigan and University of California, Santa Barbara. These models introduce new CP-violating phases amenable to tests at Electric Dipole Moment experiments conducted at Argonne National Laboratory and Paul Scherrer Institute, and produce collider signatures searched for by CMS and ATLAS. Alternative approaches involving strong dynamics inspired by Technicolor proposals and holographic constructions using ideas from Juan Maldacena link to research programs at Rutgers University and Columbia University.