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Register a new userGauge Coupling Running in Minimal SU(3)xSU(2)xU(1) Superstring Unification
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We study the evolution of the gauge coupling constants in string unification schemes in which the light spectrum below the compactification scale is exactly that of the minimal supersymmetric standard model. In the absence of string threshold corrections the predicted values $sin^2theta _W=0.218$ and $alpha _s=0.20$ are in gross conflict with experiment, but these corrections are generically important. One can express the string threshold corrections to $sin^2theta _W$ and $alpha_s$ in terms of certain $modular$ $weights$ of quark, lepton and Higgs superfields as well as the $moduli$ of the string model. We find that in order to get agreement with the experimental measurements within the context of this $minimal$ scheme, certain constraints on the $modular$ $weights$ of the quark, lepton and Higgs superfields should be obeyed. Our analysis indicates that this $minimal$ $string$ $unification$
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The apparent unification of gauge couplings around 10^16 GeV is one of the strong arguments in favor of Supersymmetric extensions of the Standard Model (SM). In this contribution two new analyses of the gauge coupling running, the latter using in contrast to previous studies not data at the Z peak but at LEP2 energies, are presented. The generic SUSY scale in the more precise novel approach is 93 < M_SUSY < 183 GeV, easily within LHC, and possibly even within Tevatron reach.
The apparent unification of gauge couplings in Grand Unified Theories around 10$^{16}$ GeV is one of the strong arguments in favor of Supersymmetric extensions of the Standard Model. In this paper, an analysis of the measurements of the strong coupling running from the CMS experiment at the LHC is combined with a traditional gauge coupling unification analysis using data at the Z peak. This approach places powerful constraints on the possible scales of new physics and on the parameters around the unification scale. A supersymmetric analysis without GUT threshold corrections describes the CMS data well and provides perfect unification. The favored scales are $M_{SUSY} = 2820 +670 -540$ GeV and $M_{GUT} = 1.05 pm 0.06 cdot 10^{16}$ GeV. For zero or small threshold corrections the scale of new physics may be well within LHC reach.
$SO(5) times U(1) times SU(3)$ gauge-Higgs unification model inspired by $SO(11)$ gauge-Higgs grand unification is constructed in the Randall-Sundrum warped space. The 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Fermion multiplets are introduced in the bulk in the spinor, vector and singlet representations of $SO(5)$ such that they are implemented in the spinor and vector representations of $SO(11)$. The mass spectrum of quarks and leptons in three generations is reproduced except for the down quark mass. The small neutrino masses are explained by the gauge-Higgs seesaw mechanism which takes the same form as in the inverse seesaw mechanism in grand unified theories in four dimensions.
In the exploration of viable models of dynamical electroweak symmetry breaking, it is essential to locate the lower end of the conformal window and know the mass anomalous dimensions there for a variety of gauge theories. We calculate, with the Schrodinger functional scheme, the running coupling constant and the mass anomalous dimension of SU(2) gauge theory with six massless Dirac fermions in the fundamental representation. The calculations are performed on $6^4$ - $24^4$ lattices over a wide range of lattice bare couplings to take the continuum limit. The discretization errors for both quantities are removed perturbatively. We find that the running slows down and comes to a stop at $0.06 lesssim 1/g^2 lesssim 0.15$ where the mass anomalous dimension is estimated to be $0.26 lesssim gamma^*_m lesssim 0.74$.
We study the path from the string scale physics to the low-energy physics in the $SU(6) times SU(2)_R$ string-inspired model with the flavor symmetry ${bf Z}_M times {bf Z}_N times tilde{D}_4$. The flavor symmetry controls the mass spectra of heavy particles as well as those of quarks and leptons in the intermediate energy region ranging from the string scale ($sim 10^{18} {rm GeV}$) to the electroweak scale. In this paper we examine the mass spectra of heavy particles in detail in our model. The renormalization group evolution of the gauge couplings is studied up to two-loop order. A consistent solution of the gauge unification around the string scale is found by adjusting the spectra of the anti-generation matter fields.
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