Two Higgs doublet models at future colliders

The two Higgs doublet model (THDM) is a simple extension of the standard model, which can provide a low energy effective description of more fundamental theories. The model contains additional Higgs bosons, and predicts rich phenomenology especially due to the variation of Yukawa interactions. Under imposing a softly broken discrete symmetry, there are four independent types of Yukawa interactions in THDMs. In this review, we briefly summarize bounds from current experimental data on THDMs and implications at future collider experiments. We pay special attention to the collider phenomenology of the Type-X (lepton specific) THDM, and also discuss recent progress for $\tan\beta$ determination in THDMs.Comment: 7 pages, 6 eps files. Talk given at Toyama International Workshop on Higgs as a Probe of New Physics 2013, Toyama, Japan, February 13-16, 201

Optimal Quantization of Signals for System Identification

In this paper, we examine the optimal quantization of signals for system identification. We deal with memoryless quantization for the output signals and derive the optimal quantization schemes. The objective functions are the errors of least squares parameter estimation subject to a constraint on the number of subsections of the quantized signals or the expectation of the optimal code length for either high or low resolution. In the high-resolution case, the optimal quantizer is found by solving Euler-Lagrange's equations and the solutions are simple functions of the probability densities of the regressor vector. In order to clarify the minute structure of the quantization, the optimal quantizer in the low resolution case is found by solving recursively a minimization of a one-dimensional rational function. The solution has the property that it is coarse near the origin of its input and becomes dense away from the origin in the usual situation. Finally the required quantity of data to decrease the total parameter estimation error, caused by quantization and noise, is discussed.Comment: 33 page

Lepton flavor violation in Higgs boson decays

We discuss lepton flavor violation (LFV) associated with tau leptons in the framework of the two-Higgs-doublet model. Current data for rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large $\tan\beta$ region where $\tan\beta$ is the ratio of vacuum expectation values of the two Higgs doublets. We show that measuring the LFV Higgs boson decays $h \to \tau^\pm \mu^\mp$ at future colliders can be useful to further constrain the LFV couplings especially in the relatively small $\tan\beta$ region.Comment: 3 pages, 1 figure. Proceeding for "Summer Institute 2005", August 11-18, 2005, Fuji-Yoshida, Japa

Syndetic Extension of Baryon and Lepton Numbers: Proton Decay and Long-Lived Dark Matter

The well-known baryon and lepton numbers of the standard model of quarks and leptons are extended to include new fermions and bosons in a simple structure with several essential features. The usual heavy right-handed neutrino singlets (for neutrino mass and leptogenesis) are related to the axion which solves the strong CP problem. At the same time, baryon number is broken softly, allowing the proton to decay. Associated with this breaking, a long-lived dark-matter candidate (called the pseudo-sakharon) emerges. This new insight connects proton decay to a new component of dark matter.Comment: 10 pages, 2 figure

Measuring Higgs boson associated Lepton Flavour Violation in electron-photon collisions at the ILC

We study the LFV Higgs production processes $e^-\gamma\to\ell^-\phi\;(\ell=\mu,\tau; \phi=H, A)$ as a probe of Higgs mediated LFV couplings at an electron-photon collider, where $H$ and $A$ are extra CP even and odd Higgs bosons, respectively, in the two Higgs doublet model. Under the constraints from the current data of muon and tau rare decay, the cross section can be significantly large. It would improve the experimental upper bounds on the effective LFV coupling constants. In addition, the chirality nature of the LFV Higgs coupling constants can be measured by selecting electron beam polarizations.Comment: 6 pages, 4 eps files, Added references, The 8th general meeting of the ILC physics working group, 1/21, 200

Detecting Majorana nature of neutrinos in muon and tau decay

The Majorana nature of neutrinos can be detected by the precise measurement of muon decay. This possibility comes from the presence of charged Higgs boson interaction for Majorana neutrinos. We study the effects of the neutrino Yukawa interaction via charged Higgs bosons in muon decay processes such as $\mu\to e\nu\bar{\nu}$ and $\mu\to e\gamma$. The Higgs triplet model with small vacuum expectation value is of special importance whose neutrino Yukawa coupling can affect significantly muon decays. External neutrino lines in the Feynman diagrams of $\mu\to e\nu\bar{\nu}$ can be crossed because of its Majorana nature. This fact provides the interference contribution between the W boson exchange diagram and that of charged Higgs boson, which may be detectable in near future experiments.Comment: 4 pages, 1 figure; Added reference

The Higgs boson mixes with an SU(2) septet representation

We study a possibility of the Higgs boson, which consists of an SU(2) doublet and a septet. The vacuum expectation value of a septet with hypercharge Y=2 is known to preserve the electroweak rho parameter unity at the tree level. Therefore, the septet can give significant contribution to the electroweak symmetry breaking. Due to the mixing with the septet, the gauge coupling of the standard-model-like Higgs boson is larger than that in the standard model. We show the sizable VEV of the Higgs septet can be allowed under the constraint from the electroweak precision data. The signal strengths of the Higgs boson for the diphoton and a pair of weak gauge boson decay channels at the LHC are enhanced, while those for the fermonic decay modes are suppressed. The mass of additional neutral Higgs boson is also bounded by the current LHC data for the standard model Higgs boson. We discussed the phenomenology of the multiply charged Higgs bosons, which come from the septet.Comment: 14 pages, 13 eps file

Phenomenology of flavon fields at the LHC

We study low energy constraints from flavour violating processes, production and decay at the LHC of a scalar field varphi (flavon) associated to the breaking of a non-supersymmetric Abelian family symmetry at the TeV scale. This symmetry is constrained to reproduce fermion masses and mixing, up to O(1) coefficients. The non-supersymmetric gauged U(1) models considered are severely restricted by cancellation of anomalies and LEP bounds on contact interactions, consequently its phenomenology is out of the LHC reach. We therefore introduce an effective U(1) which is not gauged and it is broken explicitly by a CP odd term at the TeV scale. This helps us to explore flavour violating processes, production and decay at the LHC for these kind of light scalars. In this context we first study the constraints on the flavon mass and its vacuum expectation value from low energy flavour changing processes such as \mu -> e\gamma . We find that a flavon of about m_\phi <~ 150 GeV could be experimentally allowed. These kind of flavons could be significantly generated at the LHC via the gluon fusion mechanism and the single top production channel g u -> t \phi. The produced flavons can have characteristic decay modes such as t \bar{c} for m_\phi >~ m_t, and \tau \bar{\mu} for m_\phi <~ m_t, which could be effectively useful to detect flavons.Comment: 41 pages, 6 figures. Replacement that matches the published version, except some minor details about English style, with added references and minor corrections, one figure replaced

Phenomenology in the Higgs Triplet Model with the A_4 Symmetry

We discuss the phenomenology of doubly and singly charged Higgs bosons (of SU(2)_L-triplet fields) in the simplest A_4-symmetric version of the Higgs Triplet Model. Mass eigenstates of these Higgs bosons are obtained explicitly from the Higgs potential. It is shown that their decays into a pair of leptons have unique flavor structures which can be tested at the LHC if some of their masses are below the TeV scale. Sizable decay rates for tau to bar(mu) e e and tau to bar(e) mu mu can be obtained naturally while other tau to l l' l'', mu to bar(e) e e, and l to l' gamma are almost forbidden in this model. Contributions of these Higgs bosons to the non-standard interactions of neutrinos are also considered.Comment: 31 pages, typos correcte

Survey of Higgs interpretations of the diboson excesses

We investigate diboson signals in the Standard Model (SM) with an extended Higgs sector, motivated by the excesses in the diboson channels at the LHC. We begin with the unitarity sum-rules of the weak gauge boson scattering assuming the Higgs sector is extended. According to the sum-rules, we discuss the Higgs interpretations of the diboson signals and the consistency with the ATLAS diboson anomaly and other experimental constraints. As a concrete example, we propose a two-Higgs-doublet model where the Yukawa coupling of an extra CP-even scalar with up-type quark is relatively large. The diboson (WW and ZZ) signals can be explained by 2 TeV CP-even Higgs boson, while the partners, the CP-odd and the charged Higgs bosons in the extra doublet, are severely constrained by both the LHC direct search and the indirect search via flavor observables. Especially, in order to avoid the diboson resonance search in the Vh channel, further extensions of the model are required. The diboson excess is correlated with the SM Higgs signals in our framework, so that the precise measurement of the SM Higgs boson is also important to test the Higgs interpretation.Comment: 14 pages, 7 figure