# What is the Standard Model of Particle Physics?

The standard model of particle physics, which is usually referred to simply as the standard model, is a quantum field theory that describes elementary particles and the interaction between them. It was developed in 1970, and its antecedents are the field theory and quantum field theory, the gauge theory, and the atomic theory.

The standard model is based on the principle of symmetry, which states that the laws of physics must be invariant under certain transformations. The standard model considers elementary particles to be irreducible entities and quanta to have kinematics governed by the four known fundamental interactions, except gravity, which does not fit into the mathematical models of the quantum world. The other interactions are the strong nuclear force, the electromagnetic force, and the weak nuclear force.

The standard model is considered to be one of the greatest achievements of theoretical physics, and it has been confirmed by numerous experiments and observations performed in high-energy particle accelerators, such as the Large Hadron Collider (LHC). However, it cannot yet be considered a complete theory because of a set of certain shortcomings.

The alternative theories to the standard model are the string theory and loop quantum gravity.

## What are elementary particles?

The elementary particles are the smallest entities that constitute matter. They are divided into bosons and fermions. Fermions, in turn, are divided into quarks and leptons.

## What is a particle accelerator?

A particle accelerator is a scientific device used for applying electric or magnetic fields to charged particles to increase their kinetic energy. With this, it is possible to accelerate subatomic particles like electrons, protons, or ions at high speeds close to the speed of light in tubes or circular rings; these are called linear accelerators or circular accelerators.

The aim of particle accelerators is to experimentally explore the fundamental structure of matter and the forces acting between particles. Particle accelerators have enabled important discoveries in particle physics; for example, in 2012, the existence of the Higgs boson was confirmed, as predicted by the Standard Model. The Large Hadron Collider (LHC) is the largest and highest-energy particle accelerator in existence.

## What are the shortcomings of the standard model?

The standard model has made several experimental achievements that have established it within modern physics. One of the most recent and most significant milestones was precisely the experimental verification of the existence of the Higgs boson, which had been theoretical until then. However, there are still challenges for the model’s consolidation. These include:

• The model contains 19 arbitrary parameters whose values are chosen so that the predictions fit the experimental results; that is, they are not fundamental physical constants.
• It does not explain why there are no fractionally charged hadrons, although the quarks that constitute them do have this.
• It does not determine the origin of the masses of leptons and quarks.
• The violation of symmetry known as a CP violation, which tries to explain why there is more matter than antimatter in the known universe.
• It does not explain dark matter, dark energy, or gravity.