Scalar boson

A scalar boson is a boson whose spin equals zero. Boson means that it has an integer-valued spin; the scalar fixes this value to 0.

The name scalar boson arises from quantum field theory. It refers to the particular transformation properties under Lorentz transformation.


See also


  1. ^ Peskin, Michael E.; Schroeder, Daniel V. (1995). An Introduction to Quantum Field Theory. Westview Press. ISBN 978-0-201-50397-5.
1964 PRL symmetry breaking papers

The 1964 PRL symmetry breaking papers were written by three teams who proposed related but different approaches to explain how mass could arise in local gauge theories. These three papers were written by

Robert Brout and François Englert,

Peter Higgs, and

Gerald Guralnik, C. Richard Hagen, and Tom Kibble (GHK),and are credited with the theory of the Higgs mechanism and the prediction of the Higgs field and Higgs boson. Together, these provide a theoretical means by which Goldstone's theorem (a problematic limitation affecting early modern particle physics theories) can be avoided. They show how gauge bosons can acquire non-zero masses as a result of spontaneous symmetry breaking within gauge invariant models of the universe.As such, these form the key element of the electroweak theory that forms part of the Standard Model of particle physics, and of many models, such as the Grand Unified Theory, that go beyond it. The papers that introduce this mechanism were published in Physical Review Letters (PRL) and were each recognized as milestone papers by PRL's 50th anniversary celebration. All of the six physicists were awarded the 2010 J. J. Sakurai Prize for Theoretical Particle Physics for this work, and in 2013 Englert and Higgs received the Nobel Prize in Physics.On 4 July 2012, the two main experiments at the LHC (ATLAS and CMS) both reported independently the confirmed existence of a previously unknown particle with a mass of about 125 GeV/c2 (about 133 proton masses, on the order of 10−25 kg), which is "consistent with the Higgs boson" and widely believed to be the Higgs boson.

Baryon number

In particle physics, the baryon number is a strictly conserved additive quantum number of a system. It is defined as

where nq is the number of quarks, and nq is the number of antiquarks. Baryons (three quarks) have a baryon number of +1, mesons (one quark, one antiquark) have a baryon number of 0, and antibaryons (three antiquarks) have a baryon number of −1. Exotic hadrons like pentaquarks (four quarks, one antiquark) and tetraquarks (two quarks, two antiquarks) are also classified as baryons and mesons depending on their baryon number.


In quantum mechanics, a boson (, ) is a particle that follows Bose–Einstein statistics. Bosons make up one of the two classes of particles, the other being fermions. The name boson was coined by Paul Dirac to commemorate the contribution of Indian physicist and professor of physics at University of Calcutta and at University of Dhaka, Satyendra Nath Bose in developing, with Albert Einstein, Bose–Einstein statistics—which theorizes the characteristics of elementary particles.Examples of bosons include fundamental particles such as photons, gluons, and W and Z bosons (the four force-carrying gauge bosons of the Standard Model), the recently discovered Higgs boson, and the hypothetical graviton of quantum gravity. Some composite particles are also bosons, such as mesons and stable nuclei of even mass number such as deuterium (with one proton and one neutron, atomic mass number = 2), helium-4, or lead-208; as well as some quasiparticles (e.g. Cooper pairs, plasmons, and phonons).An important characteristic of bosons is that their statistics do not restrict the number of them that occupy the same quantum state. This property is exemplified by helium-4 when it is cooled to become a superfluid. Unlike bosons, two identical fermions cannot occupy the same quantum space. Whereas the elementary particles that make up matter (i.e. leptons and quarks) are fermions, the elementary bosons are force carriers that function as the 'glue' holding matter together. This property holds for all particles with integer spin (s = 0, 1, 2, etc.) as a consequence of the spin–statistics theorem.

When a gas of Bose particles is cooled down to temperatures very close to absolute zero, then the kinetic energy of the particles decreases to a negligible amount, and they condense into the lowest energy level state. This state is called a Bose-Einstein condensate. It is believed that this property is the explanation of superfluidity.

Higgs boson

The Higgs boson is an elementary particle in the Standard Model of particle physics, produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory. It is named after physicist Peter Higgs, who in 1964, along with five other scientists, proposed the mechanism which suggested the existence of such a particle. Its existence was confirmed in 2012 by the ATLAS and CMS collaborations based on collisions in the LHC at CERN.

On December 10, 2013, two of the physicists, Peter Higgs and François Englert, were awarded the Nobel Prize in Physics for their theoretical predictions. Although Higgs's name has come to be associated with this theory (the Higgs mechanism), several researchers between about 1960 and 1972 independently developed different parts of it.

In mainstream media the Higgs boson has often been called the "God particle", from a 1993 book on the topic, although the nickname is strongly disliked by many physicists, including Higgs himself, who regard it as sensationalism.

Index of physics articles (S)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

Mathematical formulation of the Standard Model

This article describes the mathematics of the Standard Model of particle physics, a gauge quantum field theory containing the internal symmetries of the unitary product group SU(3) × SU(2) × U(1). The theory is commonly viewed as containing the fundamental set of particles – the leptons, quarks, gauge bosons and the Higgs particle.

The Standard Model is renormalizable and mathematically self-consistent, however despite having huge and continued successes in providing experimental predictions it does leave some unexplained phenomena. In particular, although the physics of special relativity is incorporated, general relativity is not, and the Standard Model will fail at energies or distances where the graviton is expected to emerge. Therefore, in a modern field theory context, it is seen as an effective field theory.

This article requires some background in physics and mathematics, but is designed as both an introduction and a reference.

Proton radius puzzle

The proton radius puzzle is an unanswered problem in physics relating to the size of the proton. Historically the proton radius was measured via two independent methods, which converged to a value of about 0.8768 femtometres (1 fm = 10−15 m). This value was challenged by a 2010 experiment utilizing a third method, which produced a radius about 5% smaller than this. The discrepancy remains unresolved, and is a topic of ongoing research.

Stop squark

In particle physics, a stop squark, symbol t͂, is the superpartner of the top quark as predicted by supersymmetry (SUSY). It is a sfermion, which means it is a spin-0 boson (scalar boson). While the top quark is the heaviest known quark, the stop squark is actually often the lightest squark in many supersymmetry models.The stop squark is a key ingredient of a wide range of SUSY models that address the hierarchy problem of the Standard Model (SM) in a natural way. A boson partner to the top quark would stabilize the Higgs boson mass against quadratically divergent quantum corrections, provided its mass is close to the electroweak symmetry breaking energy scale. If this was the case then the stop squark would be accessible at the Large Hadron Collider. In the generic R-parity conserving Minimal Supersymmetric Standard Model (MSSM) the scalar partners of right-handed and left-handed top quarks mix to form two stop mass eigenstates. Depending on the specific details of the SUSY model and the mass hierarchy of the sparticles, the stop might decay into a bottom quark and a chargino, with a subsequent decay of the chargino into the lightest neutralino (which is often the lightest supersymmetric particle).

Many searches for evidence of the stop squark have been performed by both the ATLAS and CMS experiments at the LHC but so far no signal has been discovered. In January 2019, the CMS Collaboration published findings excluding stop squarks with masses as large as 1230 GeV at 95% confidence level.

Yoshio Koide

Yoshio Koide (小出 義夫, Koide Yoshio, born May 16, 1942 in Kanazawa, Ishikawa) is a Japanese theoretical physicist specializing in particle physics. Koide is famous for his eponymous Koide formula, which some physicists think has great importance while other physicists contend that the formula is merely a numerical coincidence.

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