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In particle physics, weak isospin is a quantum number relating to the weak interaction, and parallels the idea of isospin under the strong interaction. Weak isospin is usually given the symbol ''T'' or ''I'' with the third component written as ''Tz'', ''T3'', ''I''z or ''I''3.〔Ambiguities: ''I'' is also used as sign for the 'normal' isospin, same for the third component ''I''3 aka ''I''z. ''T'' is also used as the sign for Topness. This article uses ''T'' and ''T''3.〕 Weak isospin is a component of the weak hypercharge, which unifies weak interactions with electromagnetic interactions. It can be understood as the eigenvalue of a charge operator. The weak isospin conservation law relates the conservation of ''T''3; all weak interactions must preserve ''T''3. It is also conserved by the other interactions and is therefore a conserved quantity in general. For this reason ''T''3 is more important than ''T'' and often the term "weak isospin" refers to the "3rd component of weak isospin". ==Relation with chirality== Fermions with negative chirality (also called left-handed fermions) have ''T'' = and can be grouped into doublets with ''T''3 = ± that behave the same way under the weak interaction. For example, up-type quarks (u, c, t) have ''T''3 = + and always transform into down-type quarks (d, s, b), which have ''T''3 = −, and vice versa. On the other hand, a quark never decays weakly into a quark of the same ''T''3. Something similar happens with left-handed leptons, which exist as doublets containing a charged lepton (, , ) with ''T''3 = − and a neutrino (, , ) with ''T''3 = . Fermions with positive chirality (also called right-handed fermions) have ''T'' = 0 and form singlets that do not undergo weak interactions. Electric charge, ''Q'', is related to weak isospin, ''T''3, and weak hypercharge, ''Y''W, by : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Weak isospin」の詳細全文を読む スポンサード リンク
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