Electroweak epoch

A long time ago, the world was very hot. It was much hotter than a fire. All the parts of the world were joined together. Then, the world began to cool down. This helped things change. Tiny bits of stuff moved with much energy. This heat made many new, strange bits. As the world grew, it got cooler. The tiny bits stopped making the strange parts. The world kept growing and changing. It was a very busy time.

A long time ago, the universe was very hot. This was the electroweak epoch. It happened right after the Big Bang. At this time, forces were joined together. One force was electromagnetism. Another was the weak interaction. They were one single force. This was the electroweak interaction.

Tiny bits of stuff moved with great power. These bits made exotic particles. One kind was the Higgs boson. Other bits were called W and Z bosons. The universe grew and cooled down. This made the bits less energetic. By 10 to the power of -12 seconds, the W and Z bosons stopped making themselves.

These bosons fell apart very fast. Then, the weak interaction became a short-range force. The epoch ended with a phase transition. A phase transition is a big change in how things work. We do not know exactly how it happened. Some think it was a first order transition. This could make gravitational waves. But new studies show it was a crossover. A crossover is a smooth change instead of a sudden one. The Higgs boson mass is 125 GeV. This helps us understand this smooth change.

The early universe was a very different place. Scientists call a specific time the electroweak epoch. This happened right after the Big Bang. During this time, the universe was incredibly hot. Most forces we know today were not separate. Instead, electromagnetism and the weak interaction were merged. They worked together as one single electroweak interaction.

This epoch worked through changes in heat and energy. As the universe grew, it began to cool down. This cooling caused the forces to change. First, the strong force separated from the electronuclear interaction. The electroweak interaction stayed merged for a while longer. This lasted until the temperature dropped below a critical point. This point is about 159.5 GeV in the Standard Model.

Experts study when this period actually began. Some cosmologists say it started with the inflationary epoch. This was about 10 to the power of -36 seconds after the Big Bang. Others say it started at 10 to the power of -32 seconds. At that time, energy from the inflaton field was released. This filled the universe with a hot quark-gluon plasma.

Tiny particles were very active during this time. High energy created many exotic particles. These included W and Z bosons and Higgs bosons. When the universe was 10 to the power of -12 seconds old, things changed. W and Z bosons stopped being created at high rates. The remaining bosons decayed very quickly. This made the weak interaction a short-range force.

We are still learning how this epoch ended. This end is called an electroweak phase transition. In the 1990s, some thought it was a first-order transition. That kind of change might create gravitational waves. However, the Higgs boson mass is actually 125 GeV. This mass shows the change was a continuous crossover. A crossover is a smooth change rather than a sudden one.

The electroweak epoch is a vital period in the history of our universe. It occurred during the very early stages of cosmic evolution. During this time, the universe was incredibly hot and dense. This heat kept certain fundamental forces of nature joined together. Specifically, electromagnetism and the weak interaction were merged into one. Scientists call this single force the electroweak interaction. This era is important because it marks how forces began to separate. Understanding this epoch helps us learn how the modern universe formed.

The mechanism of this epoch relied on extreme temperatures. In the very beginning, the universe was too hot for forces to stay separate. As the universe expanded, it began to cool down. First, the strong force separated from the electronuclear interaction. However, the electroweak interaction stayed merged for a longer period. This lasted until the temperature fell below a critical threshold. In the Standard Model of particle physics, this temperature is 159.5±1.5 GeV. This value represents the point of electroweak symmetry breaking.

Cosmologists debate exactly when this epoch began. Some researchers place its start at the beginning of the inflationary epoch. This would be roughly 10⁻³⁶ seconds after the Big Bang. Other scientists suggest it started later, at about 10⁻³² seconds. This later timing coincides with the release of potential energy. This energy came from the inflaton field that drove cosmic inflation. This release filled the universe with a hot, dense quark–gluon plasma.

Particle activity during this epoch was extremely intense. The high energy levels allowed for the creation of exotic particles. These included Higgs bosons and the W and Z bosons. These particles are essential to our understanding of physics. As the universe continued to expand and cool, energy levels dropped. By the time the universe was 10⁻¹² seconds old, things changed. W and Z bosons were no longer created at observable rates. The remaining bosons decayed very quickly into other things.

The end of this era is known as the electroweak phase transition. For many years, scientists speculated about the nature of this transition. In the 1990s, some thought it might be a first-order transition. A first-order transition is a sudden, sharp change. If this were true, it could have caused baryogenesis. It might also have created a background of gravitational waves. These ideas depended on the Higgs boson energy being below 45 GeV.

Recent measurements have changed our understanding of this transition. The Standard Model and new measurements show a different reality. The Higgs boson mass was found to be 125 GeV. This mass is much higher than the 45 GeV limit. Because of this, the transition was not first-order or second-order. Instead, it was a continuous crossover. This means the change was smooth rather than sudden. The crossover width is approximately 5 GeV around the transition temperature.

This smooth crossover has specific scientific consequences. Because it was a crossover, there was no electroweak baryogenesis. It also means we do not see a gravitational wave background in the mHz range. However, many scientific models still explore different possibilities. Some extensions to the Standard Model suggest different outcomes. These include supersymmetry and the two-Higgs-doublet model. These models can allow for a first-order electroweak phase transition. They simply require additional CP violation to work.