We present possible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron star systems, which are the most promising targets for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5– requires at least three detectors of sensitivity within a factor of of each other and with a broad frequency bandwidth. When all detectors, including KAGRA and the third LIGO detector in India, reach design sensitivity, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.

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Upper bounds for neutral as well as charged Higgs boson masses in a two-doublet model are obtained on the basis of tree unitarity conditionsà la Lee, Quigg and Thacker. A wide variety of scattering processes are considered so extensively that our bounds are more restrictive than those obtained previously for neutral Higgs bosons and are also of a new kind for charged Higgs boson. It is argued that at least one of the Higgs bosons should be lighter than 580 GeV/c 2 . 1 IntroductionAlthough the success of the standard SU (2) W ×U (1) Y gauge theory of the electroweak interactions is overwhelming, the Higgs boson sector in charge of spontaneous symmetry breaking has so far eluded experimental verification and is still a mystery. We all agree that the Higgs boson is one of our central concerns of the present experimental search and will be so even more in the future colliders, JLC, SSC and LHC.It has been known by now rather well that the mass of the Higgs boson, which is proportional to the Higgs quartic coupling, may be bounded from above, provided that the quartic coupling is not so large as to violate the validity of perturbative calculations [1,2]. In fact in the minimal standard model with a single Higgs doublet, Lee, Quigg and Thacker (LQT) [1] deduced the constraint from the perturbative unitarity which turned out to be m h < (8π Casalbuoni et al. [6] have raised a question which has close bearings on LQT's, namely, at what energy strong interaction phenomena would start to show up whenever one or more Higgs masses are sufficiently large. They examined models with two doublets, a doublet plus a singlet and also a supersymmetric model where there exist three Higgs supermultiplets.Maalampi et al. [7] have recently studied the two-doublet model in the same vein as LQT. They derived an upper bound of the neutral Higgs boson mass by a numerical analysis, which gave them more or less the same bound as of LQT. It should be pointed out herewith that they did not consider a broad class of scattering processes to derive constraints on all of the charged and neutral Higgs boson masses.The purpose of the present paper is to reexamine the two-doublet model to see whether one can derive an upper bounds for neutral as well as charged Higgs boson masses in the method of LQT. We will answer to this question in the affirmative by taking into our considerations sufficiently large number of scattering processes. Overall allowed regions of three neutral and one charged Higgs boson masses are explored and their maximally possible values are presented (see Eqs. (45)- (48)). Moreover we will argue that at least one of the Higgs bosons ought to be lighter considerably than might have been expected from the LQT' work (see Eqs. (49) and (50)).

Possible models of Yukawa interaction are discussed in the two Higgs doublet model (THDM) under the discrete symmetry imposed to avoid the flavor changing neutral current at the leading order. It is known that there are four types of such models corresponding to the possible different assignment of charges for the discrete symmetry on quarks and leptons. We first examine decay properties of Higgs bosons in each type model, and summarize constraints on the models from current experimental data. We then shed light on the differences among these models in collider phenomenology. In particular, we mainly discuss the so-called type-II THDM and type-X THDM.The type-II THDM corresponds to the model with the same Yukawa interaction as the minimal supersymmetric standard model. On the other hand, in the type-X THDM, additional Higgs bosons can predominantly decay into leptons. This scenario may be interesting because of the motivation for a light charged Higgs boson scenario such as in the TeV scale model of neutrino, dark matter and baryogenesis. We study how we can distinguish the type-X THDM from the minimal supersymmetric standard model at the Large Hadron Collider and the International Linear Collider.

We study new physics effects on the couplings of weak gauge bosons with the lightest CP-even Higgs boson ($h$), $hZZ$, and the tri-linear coupling of the lightest Higgs boson, $hhh$, at the one loop order, as predicted by the two Higgs doublet model. Those renormalized coupling constants can deviate from the Standard Model (SM) predictions due to two distinct origins; the tree level mixing effect of Higgs bosons and the quantum effect of additional particles in loop diagrams. The latter can be enhanced in the renormalized $hhh$ coupling constant when the additional particles show the non-decoupling property. Therefore, even in the case where the $hZZ$ coupling is close to the SM value, deviation in the $hhh$ coupling from the SM value can become as large as plus 100 percent, while that in the $hZZ$ coupling is at most minus 1 percent level. Such large quantum effect on the Higgs tri-linear coupling is distinguishable from the tree level mixing effect, and is expected to be detectable at a future linear collider.Comment: 52 pages, 10 figures, revtex