Scalar Doublet Field Research Articles

Higgs inflation in a radiative seesaw model

We investigate a simple model to explain inflation, neutrino masses and dark matter simultaneously. This is based on the so-called radiative seesaw model proposed by E. Ma in order to explain neutrino masses and dark matter by introducing a Z2-odd isospin doublet scalar field and Z2-odd right-handed neutrinos. We study the possibility that the Higgs boson as well as neutral components of the Z2-odd scalar doublet field can satisfy conditions from slow-roll inflation and vacuum stability up to the inflation scale. We find that a part of parameter regions where these scalar fields can play a role of an inflaton is compatible with the current data from neutrino experiments and those of the dark matter abundance as well as the direct search results. A phenomenological consequence of this scenario results in a specific mass spectrum of scalar bosons, which can be tested at the LHC, the International Linear Collider and the Compact Linear Collider.

Model of flavor with quaternion symmetry

We present a renormalizable fermion mass model based on the symmetry ${Q}_{4}$ that accommodates all fermion masses and mixing angles in both the quark and lepton sectors. It requires the presence of only four $SU(2)$ doublet scalar fields transforming nontrivially under the flavor symmetry and the assumption of an alignment between first and second generation Yukawa couplings. No right-handed neutrinos are present in the model and neutrino masses are generated radiatively through the introduction of two additional $SU(2)$ singlet fields charged under both hypercharge and lepton number.

Doubly-charged scalar bosons from the doublet

We consider the extended Higgs models, in which one of the isospin doublet scalar fields carries the hypercharge Y=3/2. Such a doublet field Φ3/2 is composed of a doubly charged scalar boson as well as a singly charged one. We first discuss a simple model with Φ3/2 (Model I), and study its collider phenomenology at the LHC. We then consider a new model for radiatively generating neutrino masses with a dark matter candidate (Model II), in which Φ3/2 and an extra Y=1/2 doublet as well as vector-like singlet fermions carry the odd quantum number for an unbroken discrete Z2 symmetry. We also discuss the neutrino mass model (Model III), in which the exact Z2 parity in Model II is softly broken. It is found that the doubly charged scalar bosons in these models show different phenomenological aspects from those which appear in models with a Y=2 isospin singlet field or a Y=1 triplet one. They could be clearly distinguished at the LHC.

Rotating boson stars in five dimensions

We study rotating boson stars in five spacetime dimensions. The boson fields consist of a complex doublet scalar field. Considering boson stars rotating in two orthogonal planes with both angular momenta of equal magnitude, a special ansatz for the boson field and the metric allows for solutions with nontrivial dependence on the radial coordinate only. The charge of the scalar field equals the sum of the angular momenta. The rotating boson stars are globally regular and asymptotically flat. For our choice of a sextic potential, the rotating boson star solutions possess a flat spacetime limit. We study the solutions in flat and curved spacetime.

DYNAMICAL ELECTROWEAK SYMMETRY BREAKING IN STRING MODELS WITH D-BRANES

The possibility of dynamical electroweak symmetry breaking by strong coupling gauge interaction in models with D-branes in String Theory is examined. Instead of elementary scalar Higgs doublet fields, the gauge symmetry with strong coupling (technicolor) is introduced. As the first step of this direction, a toy model, which is not fully realistic, is concretely analyzed in some detail. The model consists of D-branes and anti-D-branes at orbifold singularities in (T2 × T2 × T2)/Z3 which preserves supersymmetry. Supersymmetry is broken through the brane supersymmetry breaking. It is pointed out that the problem of large S parameter in dynamical electroweak symmetry breaking scenario may be solved by natural existence of kinetic term mixings between hypercharge U(1) gauge boson and massive anomalous U(1) gauge bosons. The problems to be solved toward constructing more realistic models are clarified in the analysis.

Gap equations and electroweak symmetry breaking

Recently, a new dynamical symmetry breaking model of electroweak interactions was proposed based on interacting fermions. Two fermions of different SUL(2) representations form a symmetry breaking condensate and generate the lepton and quark masses. The weak gauge bosons get their usual standard model masses from a gauge invariant Lagrangian of a composite doublet scalar field. The new fermion fields become massive by condensation. In this paper the gap equations are given in the linearized (mean field) approximation, and the conditions for symmetry breaking and mass generation are presented. We have shown that there is a region in the parameter space where electroweak symmetry breaking does occur. Perturbative unitarity constrains the self-couplings and the masses of the new fermions; a raw spectrum is given.

Basis-independent methods for the two-Higgs-doublet model. II. The significance oftanβ

In the most general two-Higgs-doublet model (2HDM), there is no distinction between the two complex hypercharge-one SU(2) doublet scalar fields, Phi_a (a=1,2). Thus, any two orthonormal linear combinations of these two fields can serve as a basis for the Lagrangian. All physical observables of the model must therefore be basis-independent. For example, tan(beta)=<Phi_2^0>/<Phi_1^0> is basis-dependent and thus cannot be a physical parameter of the model. In this paper, we provide a basis-independent treatment of the Higgs sector with particular attention to the neutral Higgs boson mass-eigenstates, which generically are not eigenstates of CP. We then demonstrate that all physical Higgs couplings are indeed independent of tan(beta). In specialized versions of the 2HDM, tan(beta) can be promoted to a physical parameter of the Higgs-fermion interactions. In the most general 2HDM, the Higgs-fermion couplings can be expressed in terms of a number of physical "tan(beta)--like" parameters that are manifestly basis-independent. The minimal supersymmetric extension of the Standard Model provides a simple framework for exhibiting such effects.

Fermion condensate model of electroweak interactions

A new dynamical symmetry breaking model of electroweak interactions is proposed based on interacting fermions. Two fermions of different SU_{L}(2) representations form a symmetry breaking condensate and generate the lepton and quark masses. The weak gauge bosons get their usual standard model masses from a gauge invariant Lagrangian of a doublet scalar field composed of the new fermion fields. The new fermion fields become massive by condensation. It is shown that the new charged fermions are produced at the next linear colliders in large number. The model is a low energy one which cannot be renormalized perturbatively. For the parameters of the model unitarity constraints are presented.

MASSIVE-QUARK BARYONS AS SKYRMIONS

Massive-quark baryons containing one or more charm (c) or bottom (b) quarks are described as massive scalar doublet fields "wrapped" by the soliton of the light (up and down) flavors. The spin-isospin transmutation that takes place to make the trapped scalar behave like heavy-flavored quarks is analogous to what happens to a scalar doublet in the presence of a 't Hooft–Polyakov monopole. The Wess–Zumino term plays a pivotal role here. This model predicts spectra that resemble closely those of quark models. This feature is interpreted in terms of an induced gauge (or Berry) structure associated with "fast" and "slow" degrees of freedom corresponding, respectively, to the massive- and light-flavor quarks involved in the baryon structure.

The Higgs to W-boson mass ratio in the standard SU(2) Higgs model

An upper bound of the Higgs to W-boson mass ratio is numerically estimated in the SU(2) Higgs model with one scalar doublet field at physical values of the gauge coupling. Finite volume effects are discussed.

A numerical estimate of the upper limit for the Higgs boson mass

TheSU (2) Higgs model with a scalar doublet field is studied by Monte Carlo calculations on 124 and 164 lattices. The gauge coupling is chosen to be similar in magnitude to the physical value in the standard model. The numerical results at large scalar self-coupling imply an upper limitm H /m W ≃9 for the ratio of the Higgs boson mass to the W-mass.

Expansions at the parameter space boundary in the standard Higgs model

The strong self-coupling expansion and weak gauge coupling expansion are discussed in the lattice regularized SU(2) Higgs model with scalar doublet field.

Finite temperature SU(2) Higgs model on a lattice

By means of Monte Carlo simulations we investigate the finite temperature SU(2) lattice Higgs model with a doublet scalar field at large but finite quartic self-coupling. The lattices are asymmetric in space and time extensions and their spatial size is varied in order to study finite size effects. The second order deconfinement transition at high temperature of the pure SU(2) gauge theory changes into a crossover when the scalar field is coupled to the gauge field. The Higgs phase transition at zero temperature also changes into a crossover when the temperature gets high enough. Its position shifts slightly to larger values of the hopping parameter. This means that in the Higgs region of the phase diagram the system passes through this crossover when the temperature is raised at fixed values of the coupling parameters, in analogy to the symmetry restoring transition of Kirzhnits, Linde and Weinberg in the standard model.

Weak gauge coupling expansion near the critical line in the standard SU(2) Higgs model

The behaviour of the lattice-regularized SU(2) Higgs model with a scalar doublet field is investigated near the critical line at vanishing gauge coupling. By the use of the expansion in the gauge coupling the determination of the renormalization group trajectories is reduced to a similar problem in the pure φ 4 model. The shape of the critical surface separating the confining and the Higgs phase can also be obtained by the weak gauge coupling expansion from the shape of the φ 4 critical line.

Strong self-coupling expansion in the lattice-regularized standard SU(2) Higgs model

Expectation values at an arbitrary point of the 3-dimensional coupling parameter space in the lattice-regularized SU(2) Higgs model with a doublet scalar field are expressed by a series of expectation values at infinite self-coupling ( λ = ∞). Questions of convergence of this “strong self-coupling expansion” (SSCE) are investigated. The SSCE is a potentially useful tool for the study of the γ-dependence at any value (zero or non-zero) of the bare gauge coupling.

Weak gauge coupling expansion in the lattice-regularized standard SU(2) Higgs model

The weak gauge coupling expansion is derived in the lattice-regularized SU(2) Higgs model with a scalar doublet field at an arbitrary point of the parameter space boundary with vanishing gauge coupling. Consequences of the triviality of the φ 4 component on gauge invariant Green's functions are formulated.

Correlations and static energies in the standard Higgs model

Correlations in the W-boson and Higgs boson channels and the static energy of an external SU(2) doublet charge pair are investigated by Monte Carlo calculations in the SU(2) lattice gauge theory with a scalar Higgs doublet field. The mass ratio m W/ m H and the shape of the static potential are used to obtain information on the renormalization group trajectories in the three-dimensional coupling constant space. As a function of an appropriately chosen varibale, the measured quantities are, within errors, independent from the scalar self-coupling (λ) in a wide range 0.1 ⩽ λ ⩽ ∝. In the Higgs phase, a lower bound m W/ m H ⩾ (1.0 ± 0.3) is obtained for the ratio of the Higgs boson mass to the W-boson mass.

Monte Carlo study of the standard SU(2) Higgs model

The SU(2) Higgs model with scalar doublet field is numerically investigated on lattices with size between 8 4 and 12 4. Masses and zero momentum couplings are determined at several points of the three-dimensional coupling parameter space. Particular interest is given to questions related to the order of the confinement-Higgs phase transition. It is shown that for non-perturbative scalar self-couplings numerical Monte Carlo calculations are possible in the region of weak gauge coupling approximately equal to the physical value in the standard SU(2) ⊗ U(1) electroweak theory. Our first exploratory results in such a point on 12 4 lattice give a Higgs mass to W-mass ratio 6.4 ± 0.8 and a Higgs-WW coupling roughly a factor 3 smaller than the tree-level value. The circumstances under which these numbers could have some phenomenological relevance are discussed. A possible strategy is outlined for future large scale Monte Carlo calculations in the strongly self-interacting standard Higgs model with weak gauge coupling.

Two-state signal at the confinement-higgs phase transition in the standard SU(2) higgs model

In a Monte Carlo Calculation, numerical evidence is found for metastable coexisting phases in the variable length ( λ=1.0) and fixed length ( λ=∞) SU(2) Higgs model with doublet scalar field. This supports earlier conjectures about the first order nature of the phase transition for finite gauge coupling (β) and an arbitrary scalar self-coupling (λ).

Spontaneous breaking of the left-right symmetry and quantum corrections

In this paper we study new features of spontaneous symmetry breaking (SSB) of the left-right (LR) symmetry based on a model with gauge symmetry SU(2) R × SU(2) L × U(1) B− L that arise when we include quantum corrections to the tree-level Higgs potential. First, an instructive toy model, with fermions remaining massless, is considered in which the gauge symmetry breaks via SU(2) L × U(1) Y down to U(1) EM through the vacuum expectation value (VEV) of just two scalar doublet fields φ L ∼ ( 2, 1, 1) and φ R ∼ ( 1, 2, 1) . We show that while the tree-level solution yields 〈 φ R〉 ≠ 0 and 〈 φ L〉 = 0, inclusion of quantum corrections can induce 〈 φ R〉≠ 0 and provide a hierarchy m W R > m W L ≠ 0 for masses of the left-handed and right-handed vector bosons. The striking prediction of the model, following from the minimization of the potential, is a result of R = m W R / m W L being bounded above the expression exp(1+ β/2 α 2 where α= g 2/4 π with g a gauge coupling constant and β depends on the tree-level Higgs potential parameter and β<O( α 2). Thus in this model there is a natural bound for R ≲ 2 to 4. The model also predicts a light neutral pseudo-Goldstone particle, which is indeed a Higgs particle of the Weinberg-Salam model, and whose mass cannot exceed 10 GeV. This approach represents a viable way for breaking a discrete LR symmetry by quantum corrections and evades a constraint which states: the symmetry of the VEV obtained at the tree level cannot be broken by quantum corrections unless some “accidental” symmetry is present at the tree-level Higgs potential. We also consider a realistic model where we include together with the doublet fields φ L,R, also the field ξ ∼ ( 2, 2, 0) giving Dirac masses to fermions. In this model we observe that the LR symmetry can be broken spontaneously at the tree level as before, but in contrast to the toy model, also SU(2) L symmetry is necessarily broken at the tree level consistent with a hierarchy requirement m W R > m W L ≠ 0. Including quantum corrections the ratio R is still found to be bound above by the same expression as the one obtained in the toy model. However, now β can range from |O( α 2| to |O( α)| which permits the ratio R to span the entire range from 2 to exp[|O(1/α)|]. Also, the spectrum of pseudo-Goldstone particles is studied, and it is found compatible with experiment.