# Standard Model Explained

The standard model is a theoretical model that helps scientists and researchers get a close understanding of the universe in the best possible manner to date. The standard model typically belongs to the particle physics domain and does not have a real-life implementation till now. The foundation of the standard model is typically formed on the basis of symmetry principles, i.e., the principle of equivalence and gauge principles. It is a combination or collection of a set of mathematical formulae and equations that tend to describe the nature of the elementary particles and the type of interactive forces existing between them. A standard model tends to lay 17 building blocks that are responsible for the formation of almost all the objects existing in nature, namely, six quarks, six leptons, the Higgs boson, and four force-carrying particles. The standard model was initially developed during the early 1970s. At that time, the Higgs boson particle was not discovered. The voids that prohibited the standard model to link the existing knowledge and elements at that particular time served to be a prime motivation for the scientists to explore and discover the particle, now known as the Higgs boson. The elements in a periodic table are arranged on the basis of the nature and the characteristics of the atoms. In a similar manner, the standard model tends to categorize atoms of elements on the basis of the elementary particles, i.e., fermions and bosons. It typically aims at providing a reasonable explanation of three fundamental concepts of the universe, i.e., how everything that exists in nature is made up of 12 different types of meta particles, what are the three interactive forces acting between these particles, and which special force binds all the particles and interactive forces to each other; however, the standard model fails to establish a relationship between the basic particles that constitute each and every object in the universe. Here, all the force-carrying particles such as photons that are responsible to transfer the electromagnetic force, the W and Z bosons that convey the weak force, and the gluons that communicate the strong force from one position to the other are described in a similar manner as that of the matter particles. If you observe the graphical representation of a standard model, you may easily conclude that the centrality of the model relies on the Higgs boson. The Higgs boson is placed right next to the gluon and photon particles, but it must be noticed that the Higgs boson does not have any effect on those particles in real life. Also, the quadrants of the circle are not properly defined. For example, according to the standard model representation, the photon particle gets paired up only with the particle that it can touch; however, in the actual scenario, this is not the case. Practically, the standard model is compatible with most of the general experiments, but there are certain limitations of the standard model. For instance, it clearly explains that the Higgs boson gives mass to the W and Z bosons, quarks, and the charged leptons, but it fails to explain whether the Higgs boson gives mass to the neutrinos or not. The neutrinos are tiny and light-weighted particles that do not have any charge on them. They are generally produced due to the combination of nuclei of atoms or due to the breakdown of the nucleus. The neutrinos are also known as ghostly particles as they do not interact with other matter after being produced in nature. The inability of the standard model to include the fourth fundamental force, i.e., the gravitational force in its concepts serves to be yet another limitation. According to research, only 5% of the universe is made up of ordinarily matter, there rest 95% of the universe is made up of dark matter and dark energy. It is known that about 27% of the universe is made up of dark matter. The standard model is inefficient in correlating dark matter and dark energy with its theory of the universe, hence it is one of the major drawbacks of the model. The standard model has the potential to explain the reason behind the expansion of the universe and to estimate its rate of expansion. The reason why there is more matter than antimatter might also be explained with the help of the standard model in the near future.

## Explanation of Standard Model

According to the standard model, each and every object existing in nature is made up of two types of particles, namely, quarks and leptons. The quarks are responsible for the formation of protons and neutrons, while the leptons tend to form the electron or the negatively charged particles of an atom. It also explains the existence of the fundamental forces in nature and their influence on the quarks and leptons. There are basically four fundamental forces in nature that govern the entire universe, namely, the gravitational force, the strong force, the weak force, and the electromagnetic force. The gravitational force is the force of attraction that exists between the two objects. The magnitude of the force of attraction existing between two objects due to gravity is directly proportional to the product of the masses of the two objects and is inversely proportional to the square of the distance between them. Here, the constant of proportionality is known as the Gravitational constant. The gravitational force is, however, not included in the standard model. This is because the value of the magnitude of gravitational force at a microscopic level is significantly low thus, it has a negligible effect on the subatomic particles. Another reason for excluding gravitational force from the standard model is that currently there are no possible methods that allow us to incorporate the classical theory of general relativity into the quantum field of operation. The strong force is the interactive force that exists between the subatomic particles of matter. The strong force is typically responsible to maintain the stability of the atoms by binding the atomic nuclei together and is carried by gluons. Gluons are the elementary particles that tend to act as gauge bosons or exchange particles between the quarks. The weak force or the weak nuclear force is the interactive force carried by W and Z bosons that tends to control the decay of nuclei of certain unstable subatomic particles. It tends to form the basis of the radioactivity of elements. The weak force is also responsible to trigger nuclear reactions such as nuclear fission or nuclear fusion. The nuclear breakdown of various subatomic particles due to the weak force initiates a chain of reactions that are capable of radiating a huge amount of power into the surroundings. For instance, the light energy radiated into the surroundings by the large celestial bodies such as the sun and other stars works on the basis of a chain reaction of helium or other subatomic particles due to the existence of weak force. Electromagnetism or electromagnetic force is yet another fundamental force that has a huge impact and control on the existence of the universe and the working of laws of nature. The electromagnetic force is the interaction between two or more electrically charged particles. It is a combination of electric and magnetic forces and may be either a force of attraction or a force of repulsion by nature. According to the standard model of particle physics, all types of substances that exist in the universe and are made up of ordinary matter are mainly composed of three types of particles, namely, quarks, leptons, and bosons.

## Particles of Matter

According to the standard model, the fundamental particles that makeup matter can be broadly classified into two categories, namely, matter particles and force carriers.

### 1. Fermions

Fermions tend to form a group of matter particles. Fermions are the elements described by the standard model as particles that have the property by virtue of which no two fermions can occupy the same position at the same time. As per the standard model, the fermions are the building blocks of everything that exists in the universe. Everything, from atoms of the elements that are present on the surface of the earth to the atoms of heavy celestial bodies, is made up of fermions. The fermions can be further classified into two broad categories, namely quarks and leptons:

#### 1. Quarks

The fermion quarks tend to combine and form the protons and neutrons of a substance. The protons of an atom typically consist of one down and two up quarks. These quarks are bonded together with the help of a strong nuclear force.

#### 2. Leptons

The leptons are the matter particles that are responsible for the formation of electrons and neutrinos. The electrons are the negative particles that hover around the nucleus of the atoms. Neutrinos are particles that have a relatively small mass and do not possess any charge on them.

### 2. Bosons

Boson particles can be further classified into two types, namely the Higgs boson and the four force-carrying particles. The Higgs boson tends to describe the mass property of the matter, while the four force-carrying particles are responsible to bind the matter particles together. The structure and formation of the matter particles depend on the bosons. Bosons include photons, gluons, W and Z bosons, and Higgs particles. Photons are the particles contained by light radiations and are responsible to carry the electromagnetic force. Gluons are the particles that provide a strong nuclear force required to combine the quark particles together to form protons and neutrons. Likewise, the W and Z boson particles deal with weak nuclear force.

## Double Simplex Model of the Standard Model

A few years after the standard model was explained, Chris Quigg, a particle physicist at the Fermi National Accelerator Laboratory, Illinois, provided an alternative visual representation of the Standard model that ensures a better order and structure of the elements. Here, the right-handed particles and the left-handed particles tend to form a simplex or the generalization of the triangle, which is why this visual representation of the Standard model given by Chris Quigg is known as the double simplex representation. According to the double simplex model, the matter that exists in nature is made up of two particles, namely, leptons and quarks. Also, for every matter particle existing in nature, there exists an antimatter particle. The antimatter particle typically has the same mass as that of the matter particle but has an opposite arrangement of the additional characteristics. This means that the antimatter particle would form an inverted double simplex; however, for simplicity, the simplex formed by antimatter is not considered. Each type of matter particle described by the standard model exists in nature in three forms. These versions of the matter particles are identical to each other. The only difference is that each form of the particle is progressively heavier than the other. The three versions of the quarks are typically known as up and down quarks, charm and strange quarks, and top and down quarks. Similarly, the three versions of the leptons are called electron and electron neutrino, muon and muon neutrino, and tau and tau neutrino.

### 1. Quarks

As per Quigg’s scheme, there are basically two types of quarks in nature that make up the proton and neutron particles of an atomic nucleus, namely, up quark and down quark. The up quark possesses an approximately two-thirds portion of a unit electric charge. The down quark has a negative one-third charge. Both the up quarks as well as down quarks tend to spin or rotate along their axis in a clockwise or counterclockwise direction. On the basis of the direction of spinning, the up and down quarks can either be left-handed quarks or right-handed quarks. The left-handed up and down quarks are capable of transforming from one form to the other with the help of an interactive force known as the weak force. W-boson particle is the carrier particle that is typically responsible to commute the weak force. The quarks tend to exchange the W boson particle with an electric charge of either +1 or -1 while transforming from one form to the other. On the other hand, the right-handed up and down quarks are not able to undergo a transformation from one form to the other. This is because right-handed W bosons do not exist in nature, which is why the right-handed up and down quarks are unable to absorb or release W boson particles and commute the weak force. The type of charge possessed by the quarks is denoted by their colour. There are typically three colours that a quark can have, i.e., red, green, or blue. The colour of the quark is a measure of its sensitivity towards the strong force. Quarks of different colours combine to form protons and neutrons. The resultant composite particle is held together with the help of strong force and is colourless in nature. The colourless nature of such particles implies no net colour charge. The absorption or emission of the gluons causes the gluons to change colour. The gluons are the carriers of the strong force. Such particles tend to interact with each other as well as with the quarks. This is the reason why the interaction between the quarks and the gluons form the sides of a triangle.

### 2. Leptons

The objects present in the universe consist of yet another matter particle typically known as leptons. There are basically two types of lepton particles, namely electrons and neutrinos. The electrons are the negatively charged particles, while the neutrinos are electrically neutral in nature and do not possess any kind of charge on them. The mass of the neutrinos is relatively small than the rest of the particles. One of the key differences between quarks and leptons is that the leptons do not possess a colour charge. Unlike the quarks, the lepton particles tend to interact with each other with the help of a strong force and not with the help of a weak force. The left-handed up and down lepton particles, i.e., the electrons and the neutrinos are capable of transforming into each other with the help of weak interaction. The right-handed neutrinos have not yet been discovered and are presumed to be non-existing in nature.

### 3. Higgs Boson

The Higgs boson is the centre point of the standard model and plays a significant role in explaining the concept of the double simplex arrangement of the standard model. The primary function of the Higgs field is to join the left and the right-handed particles together. The Higgs boson is responsible for associating a property to all the particles existing in nature known as the mass. The mass of a particular particle tends to increase with an increase in the interaction between the particle and the Higgs boson.