Yukawa Coupling Constants Research Articles

Anomalous magnetic moment of the muon in the left-right model

The effect of Higgs bosons on the anomalous magnetic moment of the muon is considered within the model that is based on the SU(2)L×SU(2)R×U(1)B–L gauge group and which involves a bidoublet and two triplets of Higgs fields (left-right model). For the Yukawa coupling constants and the masses of Higgs bosons, the regions are found where the model leads to agreement with experimental results obtained at the Brookhaven National Laboratory (BNL) for the anomalous magnetic moment of the muon. In order to explore corollaries from the constraints obtained for the parameters of the Higgs sector, the processes e+e− → μ+μ−, τ+τ− and μ+μ− → μ+μ−, τ+τ− are considered both within the left-right model and within the model involving two Higgs doublets (two-Higgs-doublet model). It is shown that, if the mass of the lightest neutral Higgs boson does indeed lie in the range 3.1–10 GeV, as is inferred from the condition requiring the consistency of the two-Higgs-doublet model with the data of the BNL experiment, this Higgs boson may be observed as a resonance peak at currently operating e+e− colliders (VEPP-4M, CESR, KEKB, PEP-II, and SLC). In order to implement this program, however, it is necessary to reduce considerably the scatter of energy in the e+ and e− beams used, since the decay width of the lightest neutral Higgs boson is extremely small at such mass values. It is demonstrated that, in the case of the left-right model, for which the mass of the lightest neutral Higgs boson is not less than 115 GeV, the resonance peak associated with it may be detected at a muon collider.

Evolution of the universal seesaw mass matrices

We investigate the general features of the evolution of the Yukawa coupling constants in the universal seesaw model with det M F = 0. Especially, it is checked whether the model causes bursts of Yukawa coupling constants, because in the model not only the magnitude of the Yukawa coupling constant ( Y L u ) 33 in the up-quark sector but also that of ( Y L d ) 33 in the down-quark sector is of the order of one, i.e., ( Y L u ) 33 ∼ ( Y L d ) 33 ∼ 1. The requirement of the perturbative calculability puts some constraints on the values of the intermediate mass scales and tan β (in the SUSY model).

Solar neutrinos in models involving an extended Higgs sector

Neutrino oscillations in matter and in a magnetic field are investigated within models involving an extended Higgs sector. The left-right model containing a bidoublet and two triplets of Higgs fields (LRM) and the general two-Higgs-doublet model (GTHDM) are chosen by way of example. It is shown that the interaction of leptons with physical Higgs bosons can substantially change the pattern of oscillations in these models in relation to the predictions of the Standard Model (SM). Upper limits on the Yukawa coupling constants and on the Higgs boson masses are found in order to obtain maximum corrections to the SM solar-matter potential VSM. By using constraints on these parameters from the literature and those that are obtained here, it is possible to estimate corrections to VSM that come exclusively from charged Higgs bosons. The maximum value of these corrections is 40% of VSM within the LRM and 10% of VSM within the GTHDM. The entire body of information about the contributions of physical Higgs bosons to the solar-matter potential can be obtained by studying the Lorentz structure of the amplitudes for the reactions e−νl → e−νl′ at low energies.

Evolution of the Yukawa coupling constants and seesaw operators in the universal seesaw model

The general features of the evolution of the Yukawa coupling constants and seesaw operators in the universal seesaw model with det M_F=0 are investigated. Especially, it is checked whether the model causes bursts of Yukawa coupling constants, because in the model not only the magnitude of the Yukawa coupling constant (Y_L^u)_{33} in the up-quark sector but also that of (Y_L^d)_{33} in the down-quark sector is of the order of one, i.e., (Y_L^u)_{33} \sim (Y_L^d)_{33} \sim 1. The requirement that the model should be calculable perturbatively puts some constraints on the values of the intermediate mass scales and tan\beta (in the SUSY model).

Zee model and phenomenology of lepton sector

The virtual effects of the Zee charged scalar boson on the lepton-family-number (LFN) violating processes are studied. We obtain the constraints on the individual Yukawa coupling constants of the Zee boson to leptons. Using these constraints, we predict the upper bounds on the muonium-antimuonium conversion probability, the branching fractions of the LFN violating decays such as $\tau \to e\gamma$, $\tau \to \mu\gamma$, $\tau^- \to \mu^+e^-e^-$ and $\tau \to e^+\mu^-\mu^-$. The contribution of the Zee boson to the muon anomalous magnetic moment is also considered

Neutrino masses, muon g−2, and lepton-flavour violation in the supersymmetric see-saw model

In the light of the recent muon (g_mu-2) result by the E821 experiment at the Brookhaven National Laboratory, we study the event rates of the charged lepton-flavour-violating (LFV) processes in the supersymmetric standard model (SUSY SM) with the heavy right-handed neutrinos (SUSY see-saw model). Since the left-handed sleptons get the LFV masses via the neutrino Yukawa interaction in this model, the event rate of mu->e gamma and the SUSY-SM correction to (g_mu-2)/2 (\delta a_mu^{SUSY}) are strongly correlated. When the left-handed sleptons have a LFV mass between the first and second generations ((m^2_L)_{12}) in the mass matrix, it should be suppressed by \sim 10^{-3} ({10^-9}/\delta a_mu^{SUSY}) compared with the diagonal components (m_{SUSY}^2), from the current experimental bound on mu-> e gamma. The recent (g_mu-2) result indicates {\delta a_mu^{SUSY}}\sim 10^{-9}. The future charged LFV experiments could cover (m^2_L)_{12}/m_{SUSY}^2\gsim 10^{-(5-6)}. These experiments will give a significant impact on the flavour models and the SUSY-breaking models. In the SUSY see-saw model (m^2_L)_{12} is proportional to square of the tau-neutrino Yukawa-coupling constant. In the typical models where the neutrino-oscillation results are explained and the top-quark and tau-neutrino Yukawa couplings are unified at the GUT scale, a large LFV mass of (m^2_L)_{12}/m_{SUSY}^2\gsim 10^{-4} is generated, and the large LFV event rates are predicted. We impose a so-called no-scale condition for the SUSY-breaking parameters at the GUT scale, which suppresses the FCNC processes, and derive the conservative lower bound on mu-> egamma. The predicted Br(mu-> e gamma) could be covered at the future LFV experiments.

SO(10) Grand Unified Theory in Generalized Covariant Derivative Formalism

The SO(10) grand unified theory is reformulated in a new field theory with a unified field strength for both the gauge and Higgs fields, and the fine-tuning problem and the condition for the symmetry breakings are investigated. The unified field strength for the gauge and Higgs fields, which takes values in the Dirac algebra, is defined by means of the commutator of the generalized covariant derivative for a multi-spinor field describing all families of quarks and leptons. The bosonic Lagrangian is constructed from a general sum of quadratic invariants of the field strength. Among the Yukawa coupling constants and other parameters related to the Higgs field self-couplings, there exist additional relations that are interpreted as initial conditions for renormalization equations. The grand unified symmetry is broken down to the low energy symmetry by the 210-, 45-, 126- and 10-dimensional Higgs fields. The Higgs potential turns out to have a discrete symmetry among Higgs fields. This symmetry makes it subtle and difficult to solve the fine-tuning problem, which requires accurate adjustments of the parameters included in the generalized covariant derivative. It is shown that the 45-dimensional Higgs field plays an essential role to break the discrete symmetry and to solve the fine-tuning problem.

Lepton-flavor violation in the left-handed slepton production at future lepton colliders

The Super-Kamiokande atmospheric neutrino data suggest existence of the large lepton-flavor violating (LFV) interaction in the higher energy scale. If the minimal supersymmetric standard model is extended to have right-handed neutrinos, the left-handed sleptons in the second and third generations are expected to have the LFV masses in the minimal supergravity scenario. In this article we study the LFV signals in the left-handed slepton production at $\mu^+\mu^-$ colliders and $\e^+\e^-$ linear colliders (LC's), $\mu^+\mu^-(\e^+\e^-)\to\tau\mu +4jets + \E$ and $\mu^+\mu^-(\e^+\e^-)\to\tau\mu l+ 2jets+ \E$. The main background comes from decay of a tau lepton into a muon in the lepton-flavor conserving slepton pair production. They are significantly reduced by the energy and the impact parameter cuts for the muon. At $\mu^+\mu^-$ colliders (LC's) it may be possible to reach the mixing angle $\sin 2\theta_{\tilde{\nu}} \gsim 0.1(0.5)$ and the mass difference $\Delta m_{\tilde{\nu}}\gsim 0.1(0.4)$ GeV for the sneutrinos in the second and third generations at the statistical significance of $3\sigma$. Such small mass difference and a mixing angle may be induced radiatively even if the Yukawa coupling constant for the tau neutrino is of the order of 0.1.

Universal Seesaw Mechanism with Universal Strength for Yukawa Couplings

Hypotheses of the universal seesaw mechanism and the {\it universal strength for Yukawa couplings} are applied to explain one possible origin of quasi-democratic mass matrices of a special type in a left-right symmetric model with the gauge group $SU(3)_c\times SU(2)_L\times SU(2)_R\times U(1)$. Two kinds of Higgs doublets are postulated to mediate scalar interactions between the $i$-th generation of light fermion doublets and the $j$-th generation of heavy fermion singlets with relative Yukawa coupling constants of the exponential form $e^{i\phi_{ij}}$, where $\phi_{ij}$ are real phase constants. The lowest seesaw approximation results effectively in self-adjoint mass matrices which are quasi-democratic and have the same diagonal elements. A set of values for the parameters $\phi_{ij}$ is found which reproduces the present experimental data for the absolute values of the CKM matrix elements, the Jarlskog parameter and the Wolfenstein parameters.

Single and Double Universal Seesaw Mechanisms with Universal Strength for Yukawa Couplings

Single and double universal seesaw mechanisms and the hypothesis of universal strength for Yukawa couplings are applied to formulate a unified theory of fermion mass spectrum in a model based on an extended Pati-Salam symmetry. Five kinds of Higgs fields are postulated to mediate scalar interactions among electroweak doublets of light fermions and electroweak singlets of heavy exotic fermions with relative Yukawa coupling constants of exponential form. At the first-order seesaw approximation, quasi-democratic mass matrices with equal diagonal elements are derived for all charged fermion sectors and a diagonal mass matrix is obtained for the neutrino sector under an additional ansatz. Assuming the vacuum neutrino oscillation, the problems of solar and atmospheric neutrino anomalies are investigated.

Nonequilibrium inflaton dynamics and reheating. II. Fermion production, noise, and stochasticity

We present a detailed and systematic analysis of the coarse-grained, nonequilibrium dynamics of a scalar inflaton field coupled to a fermion field in the latter stages of the reheating period of inflationary cosmology. We derive coupled nonperturbative equations for the inflaton mean field and variance at two loops in a general curved spacetime, and show that the equations of motion are real and causal, and that the gap equation for the two-point function is dissipative due to fermion particle production. We then specialize to the case of Minkowski space and small-amplitude inflaton oscillations, and derive the perturbative one-loop dissipation and noise kernels to fourth order in the Yukawa coupling constant; the normal-threshold dissipation and noise kernels are shown to satisfy a zero-temperature fluctuation-dissipation relation. We derive a Langevin equation for the dynamics of the inflaton zero mode, and show that its variance is non-negligible during reheating. Stochastic evolution of the inflaton may have important astrophysical consequences.

Renormalization Group Analysis of the Higgs Boson Mass in a Noncommutative Geometry

Within one loop approximation, the renormalization group analysis of the Higgs boson mass is performed with an initial condition induced by $m_{_H}=\sqrt{2}m_{_W}$ which is presented in the new scheme of our noncommutative differential geometry for the reconstruction of the standard model. This initial condition holds at energy derived from $g^2=(5/3)g'^2$ with the running SU(2)$_{_L}$ and U(1)$_{_Y}$ gauge coupling constants. $\sin^2\theta_{_W}=3/8$ is obtained under same conditions. However, contrary to ${\rm SU(5)}$ GUT without supersymmetry, the grand unification of coupling constant is not realized in this scheme. The physical mass of the Higgs boson considerably depends on the top quark mass $m_{top}$ since the top quark Yukawa coupling constants gives a large negative contribution to $\beta$ function of the Higgs quartic coupling constant in wide range. The Higgs boson mass varies from 153.42GeV to 191.94GeV corresponding to $168{\rm GeV}\leq m_{top}\leq 192{\rm GeV}$. We find $m_{_H}=164.01$GeV for $ m_{top}=175$GeV and $m_{_H}=171.92$GeV for $ m_{top}=180$GeV.

Mass hierarchy from compositeness hierarchy in supersymmetric gauge theory

The possibility that the mass hierarchy is intimately associated with the compositeness level of the matters is proposed in supersymmetric gauge theory. This implies, for instance, that the preons constituting top quark consists of the ``prepreons'' binded by the same gauge force making the charm quark out of another preons. The exemplifying toy model illustrates how the hierarchy in the yukawa coupling constants in the up-quark sector is generated from the underlying gauge dynamics. It is also indicated that the incorporation of down-type quarks as elementary objects leads to unpleasant results generically. Thus all the quarks as well as the leptons must also be regarded as composite in the present approach.

Direct-transmission models of dynamical supersymmetry breaking

We systematically construct gauge-mediated supersymmetry- (SUSY-)breaking models with direct transmission of SUSY-breaking effects to the standard-model sector. We obtain a natural model with the gravitino mass ${m}_{3/2}$ smaller than $1 \mathrm{keV}$ as required from the standard cosmology. If all Yukawa coupling constants are of order one, the SUSY-breaking scale ${m}_{\mathrm{SUSY}}$ transmitted into the standard-model sector is given by ${m}_{\mathrm{SUSY}}\ensuremath{\simeq}0.1({\ensuremath{\alpha}}_{i}/4\ensuremath{\pi})\ensuremath{\Lambda}$ where $\ensuremath{\Lambda}$ is the original dynamical SUSY-breaking scale. Imposing ${m}_{\mathrm{SUSY}}\ensuremath{\simeq}{(10}^{2}$--${10}^{3})$ GeV, we get $\ensuremath{\Lambda}\ensuremath{\simeq}{(10}^{5}--{10}^{6})$ GeV, which yields the gravitino mass ${m}_{3/2}\ensuremath{\simeq}{(10}^{\ensuremath{-}2}$--1) keV.

Fermion masses in a strong Yukawa coupling model

For strong enough Yukawa coupling the electroweak standard model fermion finds it energetically advantageous to transform itself into a bound state in the hedgehog background of the Higgs field in the semiclassical approximation. By considering that the bound states give the masses for the lepton and quark, it is found that all fermion masses can be described by the strongly Yukawa coupling constants which tend to a unitary constant.

Fine-Tuning Problem in a Left-Right Symmetric Model and Sogami's Generalized Covariant Derivative Method

We study Sogami's generalized covariant derivative method for a $SU(2)_{L} \times SU(2)_{R} \times U(1)_{B-L} \times SU(3)_{c}$ model that contains bi-doublet and triplet Higgs bosons. In particular, a detailed study is made on the minimization conditions of the Higgs potential. It is known that a minimization condition and certain phenomenology for a extra gauge boson mass derive a restriction on potential parameters, which requires fine-tuning. We show that the restriction can be reduced to a condition of Yukawa coupling constants giving a heavy mass of the right-handed tau neutrino in our model. We also discuss the consistency among parameter restrictions of our model by taking phenomenology of the Higgs boson masses into account.

Could there be a fourth generation of quarks without more leptons?

We investigate the possibility of adding a fourth generation of quarks. We also extend the Standard Model gauge group by adding another SU(N) component. In order to cancel the contributions of the fourth generation of quarks to the gauge anomalies we must add a generation of fermions coupling to the SU(N) group. This model has many features similar to the Standard Model and, for example, includes a natural generalisation of the Standard Model charge quantisation rule. We discuss the phenomenology of this model and, in particular, show that the infrared quasi-fixed point values of the Yukawa coupling constants put upper limits on the new quark masses close to the present experimental lower bounds.

HIGGS BOSON MASSES IN NMSSM WITH SPONTANEOUS CP-VIOLATION

The Higgs boson mass problem is considered in the next-to-minimal supersymmetric standard model for the case of spontaneous CP-violation. The renormalization group equations for the gauge, Yukawa and scalar coupling constants, the effective Higgs potential and lower experimental bounds on Higgs boson and chargino masses are analyzed. The restrictions on the Higgs boson masses are found.

CP SYMMETRY AND FERMION MASSES IN O(10) GRAND UNIFICATION MODELS

O(10) grand unification models which do not necessarily have an extra global symmetry are discussed, taking the model with one 10-plet in the Yukawa sector as an example. A strong correlation between mass ratios and CP is found. The mass relation mt/mb=vu/vd is recovered when GW=0; and another special relation mt/mb=GE/GW appears when vd=0, where GE,W are Yukawa coupling constants and vu,d are vevs. To facilitate this discussion, a set of O(10) γ-matrices is offered based on a physical representation of the spinors and that of the vector of the SO(10) group. Flavor changing neutral currents in such models are also discussed.

Derivation of Renormalization Group Equations of Higgs-Dependent Coupling Constants in n-Generation Standard Model11The project supported partially by National Natural Science Foundation of China and by Grant No. LWTZ-1298 of The Chinese Academy of Sciences

An explicit derivation of the renormalization group equations of the fermion-Higgs Yukawa coupling constants and the Higgs-quartic coupling constant in the standard model with n generations of fermions is given in the Feynman gauge.