arXiv subjects
Publications and source records attributed to Chian-Shu Chen.
To include the quark sector, the $A_{5}\equiv I$ (icosahedron) four generation lepton model is extended to a binary icosahedral symmetry $I'$ flavor model. We find the masses of fermions, including the heavy sectors, can be accommodated. At leading order the CKM matrix is the identity and the PMNS matrix, resulting from same set of vacua, corresponds to tribimaximal mixings.
We study the charged scalar contributions to the Higgs decay channels of $h\rightarrow γγ$ and $h\rightarrow Zγ$ in the Type-II seesaw neutrino model. In most of the allowed parameter space in the model, the new contribution to $h\rightarrow Zγ$ is positively correlated with that to $h\rightarrowγγ$. If the current excess of the $h\rightarrow γγ$ rate measured by the ATLAS Collaboration persists, the $h\rightarrow Zγ$ rate should be also larger than the corresponding standard model prediction. We demonstrate that the anti-correlation between $h\rightarrowγγ$ and $h\rightarrow Zγ$ only exists in some special region.
We calculate the Higgs decay rate of $h\to Zγ$ by including the contributions from new scalars with arbitrary quantum numbers of the weak isospin ($T$) and hypercharge ($Y$) in the standard model. We find that our general formula for the decay rate of $h\to Zγ$ matches with that for $h\to γγ$ in the limit of $m_Z=0$, but it is different from those in the literature. To illustrate our result, by taking the current $2σ$ excess of the $h\to γγ$ rate measured by the LHC, we examine the corresponding shift for the $Zγ$ decay channel due to the new scalar. We show that the enhancement or reduction of the $h\to Zγ$ rate only depends on the relative size of $T$ and the absolute value of $Y$. Explicitly, we predict $0.76<R_{Zγ}\equiv Γ(h\to Zγ)/Γ_{SM}(h\to Zγ)<2.05$ by imposing the observed range of $1.5<R_{γγ}\equiv Γ(h\to Zγγ)/Γ_{SM}(h\toγγ)<2$, which is independent of the number of multiplets and the couplings to the Higgs particle as long as the scalars are heavier than 200 GeV. This result provides a clear signature for the future LHC measurements to test physics beyond the standard model.
One natural way to understand the excess of the measured $H\toγγ$ rate over the standard model (SM) expectation at the Large Hadron Collider (LHC) is to have charged scalar bosons, existing in most of the SM extensions. Motivated by this LHC result, we explore if it also sheds light on solving the small neutrino mass generation problem. We concentrate on a class of models with high dimensional representations of scalars to realize Majorana neutrino masses at two-loop level without imposing any new symmetry. In these models, multi scalars with the electric charges higher than two are naturally expected, which not only enhance the $H\toγγ$ rate, but provide more searching grounds at the LHC. In particular, the rate of $H\to Zγ$ also changes similar to that of the diphoton channel.
Motivated by the discovery hint of the Standard Model (SM) Higgs mass around 125 GeV at the LHC, we study the vacuum stability and perturbativity bounds on Higgs scalar of the SM extensions including neutrinos and dark matter (DM). Guided by the SM gauge symmetry and the minimal changes in the SM Higgs potential we consider two extensions of neutrino sector (Type-I and Type-III seesaw mechanisms) and DM sector (a real scalar singlet (darkon) and minimal dark matter (MDM)) respectively. The darkon contributes positively to the $β$ function of the Higgs quartic coupling $λ$ and can stabilize the SM vacuum up to high scale. Similar to the top quark in the SM we find the cause of instability is sensitive to the size of new Yukawa couplings between heavy neutrinos and Higgs boson, namely, the scale of seesaw mechanism. MDM and Type-III seesaw fermion triplet, two nontrivial representations of $SU(2)_{L}$ group, will bring the additional positive contributions to the gauge coupling $g_{2}$ renormalization group (RG) evolution and would also help to stabilize the electroweak vacuum up to high scale.
We propose that a hierarchical spectrum of sterile neutrinos (eV, keV, $10^{13-15}$ GeV) is considered to as the explanations for MiniBooNE and LSND oscillation anomalies, dark matter, and baryon asymmetry of the universe (BAU) respectively. The scenario can also realize the smallness of active neutrino masses by seesaw mechanism.
In this paper, we investigate the idea that the decay of a curvaton is kinematically blocked and show that the coupling constant for curvaton decay can be as large as ${\cal O}(1)$. We also find in this case the lower bound of the Hubble parameter at horizon exit from big bang nucleosynthesis (BBN) is $H_\ast \gae 7.2 \times 10^{-9}M_P \sim 10^{10} {GeV}$. Similar to conventional curvaton scenario, the nonlinear parameter can be as large as $f_{NL}=100$.
In this paper, we show that the idea of growing neutrino can result in a modulated reheating effect and produce detectable non-Gaussianity in the model where the Higgs triplet from type II seesaw mechanism plays the role of the inflaton in chaotic inflation.
We consider the possibility to combine inflection point inflation and growing neutrino dark energy in a particular setup of bimodal/schizophrenic neutrino model in the framework of MSSM$\otimes U(1)_{B-L}$. In order to obtain a varying neutrino mass, we make an assumption that a soft mass of $\tilde{Z'}_{BL}$ depends on a scalar field which plays the role of a cosmon field. We also investigate the possible effects of the cosmon field in the early universe such as modulated reheating and found that the induced density perturbation is negligible.
We study the lepton sector of a four generations model based on the discrete flavor group $A_5$ (the even permutation of five objects). The best features of the three family $A_4$ model survive, including the tribimaximal pattern of three generation neutrino mixings. At leading order the three light neutrino mass relations of $m_{ν_1} = m_{ν_3}$ and $m_{ν_2} = 0$ are predicted. The splitting of the neutrino masses can be naturally obtained as a result of the breaking of $A_{5}$ down to $A_4$ and a degenerate spectrum is preferred in our model. In our $A_5$ model, the electron mass is zero at tree level, but calculable through quantum corrections.
In this paper, we consider a chaotic inflation model where the role of inflaton is played by the Higgs triplet in type II seesaw mechanism for generating the small masses of left-handed neutrinos. Leptogenesis could happen after inflation. This model is constructed without introducing supersymmetry (SUSY).
We study a model with Majorana neutrino masses generated through doubly charged scalars at two-loop level. We give explicit relationships between the neutrino masses and the same sign dilepton decays of the doubly charged scalars. In particular, we demonstrate that at the tribimaximal limit of the neutrino mixings, the absolute neutrino masses and Majorana phases can be extracted through the measurements of the dilepton modes at colliders.
We consider an effective theory with an $SU(2)\times U(1)\times A_{4}\times Z_{2}\times Z_{4}$ symmetry and investigate the possibility of a linking TeV-leptogenesis with a reactor angle $|U_{e3}|$ through spontaneous $A_{4}$ symmetry breaking which is at a scale higher than electroweak scale under the framework of radiative seesaw. It has been shown that tri-bimaximal(TBM) can be obtained by forging vacuum expectation value (VEV) alignment of the $A_{4}$. Especially, one $A_{4}$ triplet scalar field with cut-off scale $Λ$ is added in neutrino Yukawa sector, which is responsible for the deviation of the exact TBM, to explain leptogenesis as well as a non-zero $|U_{e3}|$. Above the scale of $Λ$ the leptonic Yukawa sectors will lead to the exact TBM. We analyze possible spectrums of light neutrinos and their flavor mixing angles corresponding to heavy Majorana neutrino mass ordering, and show that non-resonance leptogenesis at TeV-scale constrained by low energy data is achievable, both analytically as well as numerically. We show that only normal hierarchical spectrum of light neutrino would be strongly favored by the current Wilkinson Microwave Anisotropy Probe (WMAP) data, and also show that a relatively large $|U_{e3}|$ corresponds to the value of baryon asymmetry $6.2\times10^{-10}$.
Observational evidences of nonzero neutrino masses and the existence of dark matter request physics beyond standard model. A model with extra scalars and leptonic vector-like fermions is introduced. By imposing a Z_2 symmetry, the neutrino masses as well as anomalous muon magnetic moment can be generated via one-loop effects at TeV-scale. An effort of explaining dark matter, Lithium problem, and leptogenesis is presented. This scenario can be tested at LHC and/or future experiments.
We examine the same-sign single dilepton productions of $\ell_i^{\pm}\ell_j^{\pm} (\ell_{i,j}=e,μ)$ in high-energy proton-proton collisions at the Large Hadron Collider (LHC) in models with doubly charged Higgs scalars as well as heavy Majorana neutrinos. We demonstrate that these spectacular productions can be detected at the LHC for a class model in which the doubly charged Higgs scalars couple only to the right-handed charged leptons. The ranges of the possible doubly charged Higgs masses and mixings to observe the processes at the LHC are discussed.
We have investigated in detail a model that contains an additional SU(2) singlet and triplet scalar fields than the Standard Model (SM). This allows the radiative generation of Majorana neutrino masses at two-loop order with the help of doubly charged Higgs bosons that arise from the extended Higgs sector. We studied in detail the phenomenology of the Higgs and neutrino sectors of the model. We give the analytical form of the masses of scalar and pseudoscalar bosons and their mixings, and the structure of the active neutrino mass matrix. It is found that the model accommodates only normal neutrino mass hierarchy, and that there is a large parameter space where the doubly charged Higgs can be observed at the LHC, thereby making it testable at the LHC. Furthermore, the neutrino-less double beta ($\nonu$) decays arise predominantly from exchange processes involving the doubly charged Higgs, whose existence is thus unmistakable if $\nonu$ decays are observed. The production and decays of the doubly charged Higgs are analyzed, and distinct and distinguishing signals are discussed.
We study a model in which lepton number violation is solely triggered by a dimension 4 hard breaking term in the scalar potential. A minimal model which contains a SU(2) triplet with hypercharge Y=2, and a pair of singlet doubly charged scalar fields in addition to the Standard Model (SM) Higgs doublet is constructed. The model is technically natural in the sense that lepton number is preserved in the limit that the hard term vanishes. SM phenomenology restricts the vacuum expectation value of the triplet scalar field $v_T<5.78$ GeV. Neutrino masses controlled by $v_T$ are generated at the two loop level and are naturally to the sub-eV range. In general they exhibit normal hierarchy structure. Here the neutrino mass term does not dominate neutrinoless double beta decays of nuclei. Instead the short distance physics with doubly charged Higgs exchange gives the leading contribution. We expect weak scale singly and doubly charged Higgs bosons to make their appearances at the LHC and the ILC.
Little Higgs models with $T$-parity provide a stable neutral particle $A_H$, the lightest $T$-odd particle (LTP), which was recently proposed to explain the cold dark matter of the Universe. In the coannihilation region of the LTP with the Little Higgs partner of the light quark $Q_H$, we propose novel signatures for its detection at hadronic colliders by searching for monojet and dijet plus missing energy events due to the associated production of $Q_H A_H$ and direct production of $Q_H \bar{Q}_H$, respectively. Using the most recent WMAP data, we show that the coupling of $A_H$-$Q_H$-$q$ is tightly constrained in the coannihilation region. This implies that the monojet signal is too small to be discernible but the dijet plus missing energy signal is potentially measurable at the LHC.