共查询到20条相似文献,搜索用时 781 毫秒
1.
Ronald C. King 《Nuclear Physics B》1981,185(1):133-156
Generalisations of the SU(5) grand unified gauge theory are discussed. It is assumed that the gauge group is simple, and that the theory is both anomaly free and asymptotically free. All possible fundamental fermion representations are determined given that the fermions are massless at the unification level, but acquire mass at the level of the exact SU(3) × U(1) symmetry. No a priori restriction to standard colour SU(3) representations is made. It is found that E6, SO(10) and SU(n) with n ? 5 are the only acceptable gauge groups. Standard colour solutions are legion, but dull, incorporating at the SU(5) level, nothing other than p generations or copies of the familiar representation . Exotic colour solutions are sparse, but interesting. Nine of these, all associated with SO(10), can accomodate those quarks and leptons currently thought to be fundamental, along with such things as colour sextets and octets, as well as doubly charged leptons. 相似文献
2.
We extend the supersymmetric, confining theory of weak interactions to a left-right symmetric model. This model is based on the gauge group SU(M)SC×SU(2)R×SU(2)L×SU(3)c×U(1) and is more natural as far as supersymmetry breaking is concerned. Supersymmetry protects chiral symmetries from spontaneous breakdown and allows a solution to the strong CP problem. This model can accommodate at most three generations of quarks and leptons. 相似文献
3.
C. Wetterich 《Nuclear Physics B》1985,260(2):402-428
The number of chiral fermions may change in the course of spontaneous symmetry breaking. We discuss solutions of a six-dimensional Einstein-Yang-Mills theory based on SO(12). In the resulting effective four-dimensional theory they can be interpreted as spontaneous breaking of a gauge group SO(10) to . For all solutions, the fermions which are chiral with respect to form standard generations. However, the number of generations for the solutions with broken SO(10) may be different compared to the symmetric solutions. All solutions considered here exhibit a local generation group SU(2)G × U(1)G. For the solutions with broken SO(10) symmetry, the leptons and quarks within one generation transform differently with respect to SU(2)G × U(1)G. Spontaneous symmetry breaking also modifies the SO(10) relations among Yukawa couplings. All this has important consequences for possible fermion mass relations obtained from higher-dimensional theories. 相似文献
4.
We consider parity violating effects in the neutral sector of a left-right symmetric SU(2)L × SU(2)R × U(1) gauge model of weak and electromagnetic interaction. With four quarks and four leptons, the parity violating optical rotation in atoms is estimated to be about an order of magnitude smaller (and of opposite sign) compared to the Salam-Weinberg (SW) model prediction. However, with new quarks and leptons this effect can be arranged to be even smaller. Weak-electromagnetic interference effects are quantitatively different from those found in the SW model. A unified gauge theory which embeds the left-right symmetric gauge model is briefly discussed. 相似文献
5.
We consider a model of quarks and leptons as quasi-Goldstone fermions which is based on an underlying supersymmetric SU(2)HC × SU(2)′HC preon theory. The spontaneous breakdown of a global U(6) × U(6)′ × U(1) symmetry to U(4) × U(4)′ × SU(2)diag creates both quarks and leptons and at the same time allows for the possibility of having either residual or fundamental weak interactions. Effective lagrangians in the confining phase of the theory are compared to those emerging from a complementary picture and the problems connected with the nature of the weak interactions are discussed in this context also. 相似文献
6.
Masaki Yasuè 《Nuclear Physics B》1984,234(1):252-268
The masses of composite leptons and quarks are discussed in a “dynamical subquark model of pregauge interactions”. In this model, the leptons and quarks are made of a spinor and scalar subquark with equal mass, M, and the gauge bosons and Higgs scalar of the SU(3)c×SU(2)L×U(1)Y model are made of a subquark-antisubquark pair. The SU(2)L×U(1)Y symmetry is spontaneously broken by the composite Higgs scalar and the (scalar) subquark mass parameter is in turn bounded as is the Fermi coupling constant). The spontaneously generated mass of a lepton or quark, mi(n) (i = 1, 2; n = 1 ~ Ng), is calculated to be: are the parameters satisfying that 0 ? ri(n) ? 1 and Σ (ri(n))2 = 1;Ng is the total number of generations of the leptons and quarks; αe.m. is the fine structure constant. The appearance of light composite fermions is related to a specific mechanism of generating global chiral symmetries of the leptons and quarks. Global symmetries of scalar subquarks yield chiral symmetries of the leptons and quarks. Our model turns out to satisfy 't Hooft's anomaly conditions on massless composite fermions. 相似文献
7.
Yuval Neeman 《Physics letters. [Part B]》1979,81(2):190-194
We derive the Salam-Weinberg model by gauging an internal simple supergroup . The theory uniquely assigns the correct SU(2)L ? U(1) eigenvalues for all leptons, fixes θW = 30°, generates the W±σ, Z0σ and Aσ together with the Higgs-Goldstone scalar multiplets as gauge fields, and imposes the standard spontaneous breakdown of SU(2)L ? U(1). The masses of intermediate bosons and fermions are directly generated by universality, which also fixes the Higgs field coupling. 相似文献
8.
It is shown that the left-right symmetric gauge models based on the group = SU(2)L × SU(2)R × U(1)L × U(1)R can accommodate quite naturally the results of the recent SLAC experiment concerning parity violation in neutral currents. The possibility of finding a light neutral gauge boson in the PETRA-PEP energy range remains particularly interesting. 相似文献
9.
We compute in the standard model of SU(3)c×(SU(2)×U(1)) with massless quarks and leptons the two-loop anomalous dimensions of the four-fermion operators relevant to proton decay in process involving (u, d, e, νe). The calculation is carried out by the use of dimensional reduction, a variant of dimensional regularization. Our aim is to give a complete calculation within the SU(5) GUT model of the next-to-leading enhancement-suppression factor for nucleon decay due to renormalization effects arising from hard gluons, W's and B's in process which involve (u, d, e, νe). It turns out that the result is sensitive to the ratios x(i) = MH (i)/MX where MH(i) are the masses of the twelve superheavy Higgs scalars in the multiplet which breaks SU(5) → SU(3)×SU(2)×U(1). 相似文献
10.
Induced flavour-changing neutral currents (FCNC) in supersymmetric unified theories are investigated both in models with the standard SU(2)L × U(1) gauge symmetry and in models with an extra ?(1) gauge symmetry. Supersymmetric extension of the natural flavour conservation laws for neutral currents is obtained by adding a condition regarding the assumed type of supersymmetry breaking. This condition ensures no direct flavour-changing couplings of neutral gauge-Higgs fermions and at the same time is necessary and sufficient for the natural suppression of the induced FCNC. It is found that in the class of models satisfying the new condition the contribution of the scalar partners of quarks to the induced strangeness-changing neutral current is comparable to that of the quarks in , while it is negligibly small in KL ? KS mass difference. 相似文献
11.
S. Rajpoot 《Zeitschrift fur Physik C Particles and Fields》1991,50(1):43-46
The apparent anticorrelation between the solarneutrino flux and the sun-spot number can be explained if electron neutrino has a large magnetic moment. A model with SU(2) L ×SU(2) R ×U(1) B?l gauge interaction is presented in which the electron neutrino has a large magnetic moment. The ingredients of the model are (i) the absence of the usual discrete left-right symmetry, (ii) new fermions that are singlets under SU(2) L and SU(2) R and (iii) two doublets and a charged singlet of higgs. The model utilises the see-saw mechanism of Gell-Mann, Ramond and Slansky give masses to all quarks and leptons. The large magnetic moment of the electron neutrino is achieved through charged singlet higgs fields. 相似文献
12.
We study the possibility that theU(1) B global symmetry associated with baryon number is spontaneously broken. We present realistic examples implemented in the context of a suitably extended standardSU(2) L×U(1)×SU(3)c model and of a composite model of quarks and leptons. The globalU(1) B symmetry in both cases is spontaneously broken at a relatively low mass scale without any conflict with observations. The dominant baryon number nonconserving process in these models obeys the ΔB=2 selection rule. 相似文献
13.
C. Wetterich 《Nuclear Physics B》1984,244(2):359-380
We discuss a six-dimensional SO(12) gauge theory which can be obtained from pure gravity in 18 dimensions coupled to a Majorana-Weyl spinor, if the ground state is characterized by a noncompact internal space without boundary with small finite volume. The six-dimensional SO(12) theory spontaneously compactifies to a four-dimensional SO(10) theory with local generation group SU(2)G × U(1)G. We obtain an even number of chiral fermion generations transforming as () under SO(10) × SU(2)G × U(1)G. Adding a scalar field to the six-dimensional theory provides us with fields carrying all the quantum numbers needed for a realistic spontaneous symmetry breakdown to SU(3)c × U(1)e.m. 相似文献
14.
《Physics letters. [Part B]》1986,167(2):209-213
Heavy leptons with high weak isospin, predicted in a subcomponent model of quarks and leptons with SU(2)L × U(1) symmetry, are examined phenomenologically in connection with recently reported anomalous events and super high energy physics. In constructing the effective lagrangian based on the subcomponent structure, IW = 1 heavy leptons play a special role in the effective interaction. 相似文献
15.
《Physics letters. [Part B]》1987,194(2):231-235
We describe a simple N = 1 supersymmetric GUT based on the group SU(5)×U(1) which has the following virtues: the gauge group is broken down to the SU(3)C×SU(2)L×U(1)Y of the standard model using just 10, Higgs representations, and doublet-triplet mass splitting problem is solved naturally by a very simple missing-partner mechanism. The successful supersymmetric GUT prediction for sin2θw can be maintained, whilst there are no fermion mass relations. The gauge group and representation structure of the model may be obtainable from the superstring. 相似文献
16.
Haim Harari 《Physics Reports》1978,42(4):235-309
We review the physics of quarks and leptons within the framework of gauge theories for the weak and electromagnetic interactions. The Weinberg-Salam SU(2) × U(1) theory is used as a “reference point” but models based on larger gauge groups, especially SU(2)L × SU(2)R × U(1), are discussed. We distinguish among thre “generations” of fundamental fermions: The first generation (e?, νe, u, d), the second generation (μ?, νμ, c, s) and the third generation (τ?, ντ, t, b). For each generation we discuss the classification of all fermions, the charged and neutral weak currents, possible right-handed currents, parity and CP-violation, fermion masses and Cabibbo-like angles and related problems. We review theoretical ideas as well as experimental evidence, emphasizing open theoretical problems and possible experimental tests. The possibility of unifying the weak, electromagnetic and strong interactions in a grand unification scheme is reviewed. The problems and their possible solutions are presented, generation by generation, but a brief subject-index (following the table of contents) enables the interested reader to follow any specific topic throughout the three generations. 相似文献
17.
We present a grand unified model of the strong, electromagnetic and weak interactions based on a local SU(8)L×SU(8)R gauge theory which possesses a global U(8)L × U(8)R invariance. We break the symmetry down to the standard SU(3)C × SU(2)L × U(1) model, with the proton remaining stable and the left-handed neutrinos obliged to remain massless. A novel feature of our model is the simultaneous absence of both strong CP violations and of axions. 相似文献
18.
Yoav Achiman 《Physics letters. [Part B]》1977,70(2):187-191
A left-right symmetric SUL(3) × SUR(3) gauge model with leptons in the () representation is presented. The SUIL(2)×U(1) subgroup is practically the WS + GIM model for , with additional currents involving heavy leptons. μ→eγ is naturally suppressed and a new kind of oscillations is possible. τ and 3μ events can be related to one leptonic triplet. The model is naturally imbedded in exceptional groups. 相似文献
19.
《Physics letters. [Part B]》1988,206(1):51-56
Several models of non-abelian orbifolds have been constructed. There are models with three or four families of quarks and leptons, and gauge symmetry SU(3) × SU(2) × SU(2) × U(1)2 × SU(3)′ × SO(10)′ × U(1)′ or SU(3) × SU(2) × U(1)3 × SU(4)′ × SO(8)′ × U(1)′. 相似文献
20.
It is stressed that within the simplest model SU(4) of color, unifying quarks with leptons, where B L is a gauge symmetry, a spontaneous breaking of this symmetry leads naturally to baryonlepton decays like n→e?k+, e?K+, μ?π+, μ?K+ [in constant to SU(5) where B L is not gauged]. Our mechanism is crucially tied to the presence of the Higgs multiplet (2, 2, 15) of SU(2) × SU(2) × SU(4), which is needed to account for the observed quarklepton mass ratios. 相似文献