Analysis of an extended scalar sector with S3S_3 symmetry

We investigate the scalar potential of a general $S_3$-symmetric three-Higgs-doublet model. The outcome of our analysis does not depend on the fermionic sector of the model. We identify a decoupling limit for the scalar spectrum of this scenario. In view of the recent LHC Higgs data, we show our numerical results only in the decoupling limit. Unitarity and stability of the scalar potential demand that many new scalars must be lurking below 1 TeV. We provide numerical predictions for $h\to \gamma \gamma$ and $h\to Z \gamma$ signal strengths which can be used to falsify the theory.Comment: One Eq. added, minor changes in figures and subsequent texts, version accepted in Phys. Rev. D, appendix included in the arXiv versio

KK-number non-conserving decays: Signal of n = 2 excitations of Extra-Dimensional Models at the LHC

In the simplest universal extra-dimension models Kaluza-Klein (KK) parity distinguishes the states with odd and even KK-number. We calculate the coupling of a 2n-level top quark to a top quark and the Higgs scalar (both n = 0 states), absent at the tree level, which is mediated by strong interactions at one-loop. We show that the strength of this coupling is independent of n. We observe that the decay due to this coupling, which conserves KK-parity, can be a few per cent of the phase space suppressed decay to two n-level states which proceeds through tree-level couplings. We explore the prospects of verification of this result at the Large Hadron Collider through the production of an n = 2 KK top-antitop pair both of which subsequently decay to a zero mode top quark/antiquark and a Higgs boson.Comment: 11 pages, v2: One additional figure (published version

Constraints on Leptoquark Models from IceCube Data

Leptoquarks in the mass range of 500-1000 GeV can be resonantly produced in significant numbers by PeV neutrino interacting with nuclei at IceCube. We compute the event rates of leptoquark production and decay events and use the 3-year IceCube data for PeV energy events to find the allowed range of the leptoquarks mass and coupling parameter space. We use a low-scale quark lepton unification model based on the $SU(4)_C \otimes SU(2)_L\otimes U(1)_R$ gauge group where leptoquark couplings which give rise to proton decay are forbidden by the symmetry. We constrain the parameters of this model and point out signals of leptoquarks in this model which may be seen in PeV energy IceCube events in the future.Comment: 11 pages, 4 figures, 1 table; a few typos fixed; matches published versio

Constraining minimal and non-minimal UED models with Higgs couplings

Early indications from the LHC for the observed scalar boson imply properties close to the Standard Model Higgs, putting considerable constraints on TeV scale new physics scenarios. In this letter we consider flat extra dimensional scenarios with the fifth spatial dimension compactified on an S^1/Z_2 orbifold. We find in the minimal model the experimentally preferred effective Higgs couplings to gluon and photon at 95% confidence level disfavor the New Physics scale below 1.3 TeV. We demonstrate that a generalization of these models to include brane localized kinetic terms can relieve the tension to accommodate scales as low as 0.4 TeV.Comment: KK level mixing effects included, resembles published version, 8 pages, 4 figure

Implications of Unitarity and Charge Breaking Minima in Left-Right Symmetric Model

We examine the usefulness of the unitarity conditions in Left-Right symmetric model which can translate into giving a stronger constraint on the model parameters together with the criteria derived from vacuum stability and perturbativity. In this light, we demonstrate the bounds on the masses of the physical scalars present in the model and find the scenario where multiple scalar modes are in the reach of Large Hadron Collider. We also analyse the additional conditions that can come from charge breaking minima in this context.Comment: v2: Accepted for publication in Phys. Rev. D, reference added, minor change in the text, 16 pages, 2 figure

High-scale validity of a two-Higgs doublet scenario: a study including LHC data

We consider the conditions for the validity of a two-Higgs doublet model at high energy scales, together with all other low- and high-energy constraints. The constraints on the parameter space at low energy, including the measured value of the Higgs mass and the signal strengths in channels are juxtaposed with the conditions of vacuum stability, perturbativity and unitarity at various scales. We find that a scenario with an exact $\mathbb{Z}_2$ symmetry in the potential cannot be valid beyond about 10 TeV without the intervention of additional physics. On the other hand, when the $\mathbb{Z}_2$ symmetry is broken, the theory can be valid even up to the Planck scale without any new physics coming in. The interesting feature we point out is that such high-scale validity is irrespective of the uncertainty in the top quark mass as well as $\alpha_{s}(M_Z)$, in contrast with the standard model with a single Higgs doublet. It is also shown that the presence of a CP-violating phase is allowed when the $\mathbb{Z}_2$ symmetry is relaxed. The allowed regions in the parameter space are presented for each case. The results are illustrated in the context of a Type-II scenario.Comment: 38 pages, 12 figures. Major changes in the presentation of some of the plots, minor changes in the text, references added, typos corrected, matches with published versio