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1.
S K Soni 《Pramana》1980,14(1):75-96
In schemes with oneW boson and twoZ-bosons (mediating the charged and neutral current interactions involving ordinary fermions) based on the direct product and simple groups, SU(2) × U(1) ×u′(1) andG × U(1) (G is a simple group of rank two), the following two questions are discussed. (1) What are the necessary and sufficient conditions for minimal reducibility of the effective four-fermion neutral current interaction (involving νμ-hadron, electron-hadron and νμ-electron sectors) to the corresponding prediction of the standard model? (2) In what way are the masses of the twoZ-bosons constrained relative to the mass of the neutral boson of standard model? The answers to these questions are given first by keeping the underlying Higgs structure, responsible for gauge-boson (and fermion) mass generation, completely arbitrary (called Higgs-independent case) and then by making a specific choice for the Higgs structure resulting in a natural mass relation for theW andZ-bosons that is an exact counterpart toM W (S)/2 =M Z (S)/2 sec2 ? W for the standard model (called Higgs-dependent case). The distinction between these two cases is brought out clearly as also that between the direct product and simple groups. Whether or not any assumption is made about the Higgs structure, with either the direct product or the simple group, it is concluded that in general there is aZ-boson lighter than the neutral boson of the standard model.  相似文献   

2.
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 24 multiplet which breaks SU(5) → SU(3)×SU(2)×U(1).  相似文献   

3.
We discuss a grand unified theory in the framework ofSU(n, 1) minimal supergravity with the Planck mass as the only input mass scale.M W m 3/2 is fixed by radiative corrections to be naturally ?M P1. Due to the particular form of explicit soft supersymmetry breaking a light singlet can be used to obtain naturally light Higgs doublets and for a new mechanism for radiativeSU (2)×U(1) breaking. The low energy particle spectrum is very restricted withm 3/2≈104 GeV.  相似文献   

4.
The role of heavy fermions and heavy Higgs-scalars in the MW ? MZ relation resulting from the one-loop-corrected μ decay width Γ(1) and its experimental data Γexp is studied in the framework of the standard electroweak theory. Exact and approximate formulae are both given for these heavy particle effects. The quadratic dependence of Γ(1) on large fermion mass mheavy gives a positive contribution to the calculation of MW from Γ(1) = Γexp for a given MZ, and cancels the light fermion contributions of the form ~ αln(mlight/MW) at the value of mheavy ~ 200 GeV. On the other hand, the Higgs mass dependence of the calculation is, at best, logarithmic, and does not produce visible effects. Applications for deriving constraints for the top-quark mass (or heavier fermion mass) are discussed, and a concrete example is given of the relation between experimental uncertainties in measurements of MW,Z and the corresponding allowed region for mt.  相似文献   

5.
Formulae for the radiative corrections toe + e ?f \(\bar f\) andepeX,v e X′ are given for two Higgs doublets inSU(2)×U(1). The magnitude of deviations from the minimal model is discussed for theM W ?M Z mass correlation, thee + e ? forward-backward and polarization asymmetries and σ(e + e ? → hadrons) at LEP/SLC, and for σ(NC)/σ(CC), charge and polarization asymmetries in deep inelasticep scattering at HERA. Precision experiments can restrict the mass splitting between neutral and charged Higgs bosons to ?100 GeV. In the supersymmetric Higgs model the additional corrections remain unobservably small.  相似文献   

6.
A unified gauge model is built with Higgs in 210⊙126⊙10 representations and intermediate symmetry $$SU(3)_c \otimes SU(2)_L \otimes SU(2)_R \otimes U(1)_{B - L} .$$ . The vacuum of the210 is in a two-dimensional stratum. From the values sin2θ W (M W ) and \(\frac{\alpha }{{\alpha _s }}(M_W )\) one determines the high scales, with the result to predict leptoquarks heavier than 1015 GeV and Majorana masses for the right-handed neutrinos around 1011 GeV.  相似文献   

7.
We investigate the prospects for a low right-handed scale MR in the context of locally supersymmetric O(10), limiting ourselves to the most interesting case of a single breaking scale between the grand unified scale MX and the W-mass. It is found that supersymmetry seems to imply a unique solution as regards the Higgs content and the intermediate symmetry group if a low right-handed scale (less than 104 GeV) exist at all. Apart from a minimal set of representations providing the symmetry battern, the Higgs sector consist of a pair of 16 and 16 spinor representations ying at scale MR and the residual symmetry is SU(3)c × U(1)B?L × SU(2)L × U(1)R.  相似文献   

8.
We study general conditions for obtaining spontaneous breaking of local supersymmetry in N = 1 supergravity coupled to supersymmetric matter. We consider in particular the coupling of N = 1 supergravity to grand unified theories like SU(5) and study the conditions which must be met in order to obtain a realistic model. Specific models are built in which local supersymmetry is broken at a scale √MWmp ~ 1010 GeV. This breaking of supersymmetry is only detected at low energies through soft terms breaking explicitly the global supersymmetry. These soft terms (scalar masses, gaugino masses and trilinear scalar couplings) are renormalized at low energies according to the renormalization group. The (mass)2 of the Higgs doublet evolve towards negative values at low energies giving rise to SU(2) × U(1) breaking as a radiative effect of local supersymmetry breaking. We finally point out the possible relevance of non-renormalizable superpotentials for the problem of fermion masses.  相似文献   

9.
《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, 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   

10.
The main purpose of this work is to study the three weak boson vertex. We give explicit formulae for all polarization amplitudes of the processese + e ?W + W ? ande + e ?ZZ, with arbitrary couplings between the various intermediate vector bosons. Using these expressions we discuss possible signatures ofC, P andT violation in the three vector boson coupling, as well as the effects of anomalous magnetic dipole and electric quadrupole moments ofW ±. The amplitudes for the above processes in any SU(2) × U(1) and SU(2)L × SU(2)R × U(1) gauge theory are also given, while the special case of the Weinberg-Salam model is studied in detail.  相似文献   

11.
《Nuclear Physics B》1986,269(1):119-130
We propose a class of supersymmetric grand unified models where parity and SU(2)R breaking scales are widely separated and compatible with a low-lying mass for the right-handed gauge boson WR. The intermediate symmetry SU(4)c×SU(2)L×SU(2)R and Higgs content are uniquely fixed if mWR < 109 GeV. The unification scale lies within an order of magnitude below the Planck mass.  相似文献   

12.
The Cabibbo angle is introduced as a mixing angle of the gauge bosonsW ± andX ± in anO(4)?U(1) gauge model. Masses of gauge bosons are calculated to beM W=82 (input), \(M_z = \sqrt 2 M_W s\gamma = 130\) (γ is mixing angle, sin2 γ=0.21),M x=666, andM Y=660, in units GeV. TheW μ ± andZ μ 0 couple to the familiar charged and neutral currents, respectively. The effective neutrino oscillation angle is found to be the Cabibbo angle.  相似文献   

13.
We study the long-distance behaviour of pure unified SU(5) gauge theory in the limit when the electroweak subgroup is unbroken. We show that the symmetry breaking pattern SU(5)→SU(3)c×SU(2)×U(1)Y, with SU(3)c and SU(2) ×U(1)Y realized, respectively, in confining and coulombic phases, is a possible dynamical phase of the SU(5) theory. The proof relies on showing that the duality equation of 't Hooft, relating the electric and magnetic flux, is exactly satisfied for the above symmetry breaking pattern. The infrared structure of SU(5), broken down to SU(3)c×SU(2)×U(1)Y, is not self-dual.  相似文献   

14.
We establish the relation between κsin2θw to be found from neutral-current experiments and sin2θw(Q) for Q=MW predicted by grand unified theories. We then calculate sin2θW(MW) in the minimal SU(5) model taking the MW as well as Mx threshold effects into account. We find that these two threshold effects on sin2θW(MW) cancel with each other and sin2θW(MW)=0.211± 0.005.  相似文献   

15.
The half-life of the 89.83 keV level in152Eu was measured in the151Eu(n, γ)152Eu reaction to be 381±19 nsec. This results in the determination of the absolute transition probabilities of the 89.83 keVE1+M2 transition to the ground state, yielding hindrance factors relative to the Weisskopf estimateF W(E1)=(2.3 ± 0.4) × 106 andF W=0.20±0.08.  相似文献   

16.
We discuss the production of gauge bosons in polarized and unpolarized deep inelastice P-scattering in the context of the standard modelSU(3)×SU(2)×U(1) of the strong and electroweak interactions. We present results for the total and the differential cross sections as functions of the parameters of the outgoing lepton for energies available at HERA in the near future. Besides the γ-exchange diagrams we also have included the contributions ofW- andZ-exchange. We find that they cannot be neglected especially for the processe ? Pv e W ? X.  相似文献   

17.
We derive the Salam-Weinberg model by gauging an internal simple supergroup SU(21). 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 IL = 12 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 SU(21) universality, which also fixes the Higgs field coupling.  相似文献   

18.
We present a supersymmetricSU(5)×U(1) model. This model has the following features. The gauge hierarchy is naturally generated by the quadratically divergent nature of the Fayet-IliopoulosD term. TheSU(5)×U(1) gauge symmetry breaks uniquely intoSU(3) W ×SU(2) c ×U(1) y at an energy scale of 1017–18GeV. The non-vanishing vacuum expectation value of an auxiliary field component ofU(1) gauge vector multiplet induces the breaking ofSU(2) W ×U(1) y . It gives a mass of 102–3GeV to scalar quarks and scalar leptons at the tree level. The renormalization group analysis shows that the color fine structure constant α C (M W ) becomes somewhat small and the Weinberg angle sin2θ W (M W ) somewhat too large in a simple version of the model.  相似文献   

19.
The rate for the decay of a Z-boson into a Higgs boson and monochromatic photon is computed to leading order in the standard SU(2) × U(1) gauge theory. The coupling has contributions from fermion and W-boson loops. The W-boson loop dominates unless the number of heavy fermion generations exceeds six. The branching ratio computed from the W-boson loop contribution, B(Z→Hγ), is approximately 2 × 10?6(1?(MH2MZ2))3.  相似文献   

20.
We investigate the hierarchy of gauge boson masses in the maximal grand unified theory by studying the renormalization group equations for the running coupling constants associated with the symmetry breaking of SU(16)viaSU(12) q×SU(4) l×U(1) |B|?|L| chain. Particular attention is given to the contribution of Higgs scalars to these equations. It is found that the intermediate mass scale ML, associated with right-handed gauge bosons could be as low as 10 3 GeV only for sin 2θ w(M L) as high as 0.265 with α s(M L)=0.13. In this chain of symmetry breaking, we have also examined the lowest unification mass that is allowed by the low-energy data for sin 2θ w(M L) and the assumed gauge hierarchy. This has been done in two cases; first for the case where SU(3) c is vectorial, second, for the case where SU(3) c is axial. In both cases the lowest unification mass scales were found to be 10 13, 10 11, 10 8 and 10 7 GeV for sin 2θ w(M L) = 0.22, 0.24, 0.26,and0.265 respectively with α s(M L) = 0.13. The implication of these low unification masses on baryon non-conserving processes is also discussed.  相似文献   

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