Implications of the CERN LEP results for SO(10) grand unification

Abstract

We consider the breaking of the grand unification group SO(10) to the standard model gauge group through several chains containing one intermediate breaking scale. Using the values of the gauge coupling constants at the scale M z derived from recent data from the CERN ef e-collider LEP, we determine the intermediate and the unification scales using two-loop renormalization group equations with appropriate matching conditions. Some chains are ruled out from experimental constraints. For the allowed ones, the intermediate scale is high, in the range of 1 0~-1 0~~ GeV. PACS number(s): 12.10.Dm, 12.15.C~ Recently it has been emphasized [I, 21 that the precision of data from the CERN e+e-collider LEP allows the extraction of the three coupling constants of the standard model very accurately, and this enables an extrapolation to high energies with very small errors. In these papers it was shown that if one extrapolates the couplings without change of particle content (i.e., with three families of fermions and one doublet of Higgs boson) or the group structure in the intervening energy scale, these couplings do not come together at a single point. Although this result is not unexpected, the statistical significance has been greatly improved. For example, LEP data imply [3] where cui = g:/4~, and gl, gz, 93 denote the normalized gauge coupling constants for the U(l)y, S U (~) L , and SU(3), factors, respectively. Now, if we take the central values for crl and a 2 , we need cr,(Mz) cz 0.07 in order to achieve unification. This is more than seven standard deviations removed from the mean value.In Refs.[I] and [2] it was further pointed out that the minimal supersymmetric model, with the supersymmetry-breaking scale MsusY N

Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model

“…In fact, besides the evolution of the coupling constants, such contributions are expected to modify the evolution of the fermion masses and mixing, introducing relations among the Yukawa couplings at the same scale M I . We quantify the impact of using such new contributions in the renormalization group equations (RGEs) for fermion masses and mixings, considering an illustrative and simplified SO (10) model with a breaking chain given by [8]:…”

“…Here, Φ and ∆ R contribute to α 4C , Φ and Σ to α 2L , and all three of them to α 2R . At M I , we impose the relations [8]:…”

“…In the present work, we will study a non-supersymmetric extension of the SM model based on the gauge group SO (10), which has often been discussed in the previous literature [3][4][5][6][7][8][9][10][11][12][13]. The gauge group SO(10) has the clear advantage that all SM fermions, including right-handed neutrinos, belong to the same 16 representation.…”

The ATLAS diboson resonance in non-supersymmetric SO(10)

“…However, if the right-handed neutrino is a Majorana fermion, we expect almost the same numbers of events for each case. 12 In addition, such a Majorana right-handed neutrino is severely restricted by the ATLAS search for same-sign leptons plus dijet events [148]. To reconcile these experimental results, there are several possibilities for extending the neutrino sector that work, such as the inverse seesaw [149,150] or the linear seesaw [151][152][153] mechanisms which were discussed in the context of the diboson anomaly in refs.…”

“…Second, anomaly cancellation in the SM can be understood naturally since SO (10) is free from anomalies. Third, gauge coupling unification can be realized without relying on supersymmetry, if there are intermediate-scale gauge symmetries [8][9][10][11][12][13][14]. Majorana mass terms of right-handed neutrinos can be generated at an intermediate scale, which may explain the smallness of neutrino masses.…”