Cornering variants of Georgi-Machacek model using Higgs precision data

We show that in the absence of trilinear terms in the scalar potential of Georgi-Machacek model, heavy charged scalars do not necessarily decouple from the $h \to \gamma \gamma$ decay amplitude. In such scenarios, measurement of the Higgs to diphoton signal strength can place stringent constraints in the parameter space. Using the projected precisions at the High Luminosity LHC (HL-LHC) and the ILC, we find that the upper bound on the triplet vacuum expectation value can be as low as 10 GeV. We also found that when combined with the theoretical constraints from perturbative unitarity and stability, such variants may be ruled out altogether.Comment: 9 pages, 4 captioned figures. Accepted for publication in Phys. Rev.

Little Higgs after the little one

At the LHC, the Littlest Higgs Model with $T$-parity is characterised by various production channels. If the $T$-odd quarks are heavier than the exotic partners of the $W$ and the $Z$, then associated production can be as important as the pair-production of the former. Studying both, we look for final states comprising at least one lepton, jets and missing transverse energy. We consider all the SM processes that could conspire to contribute as background to our signals, and perform a full detector level simulation of the signal and background to estimate the discovery potential at the current run as well as at the scheduled upgrade of the LHC. We also show that, for one of the channels, the reconstruction of two tagged $b$-jets at the Higgs mass $(M_h = 125~{\rm GeV})$ provides us with an unambiguous hint for this model.Comment: 22 pages, 3 captioned figures, 8 Tables; minor modifications, version published in JHE

Revisiting the high-scale validity of Type-II seesaw model with novel LHC signature

The Type-II seesaw model is a well-motivated new physics scenario to address the origin of the neutrino mass issue. We show that this model can easily accommodate an absolutely stable vacuum until the Planck scale, however with strong limit on the exotic scalar masses and the corresponding mixing angle. We examine the model prediction at the current and future high luminosity run of the Large Hadron Collider (LHC) for the scalar masses and mixing angles fixed at such high-scale valid region. Specifically, we device the associated and pair production of the charged scalars as a new probe of the model at the LHC. We show that for a particular signal process the model can be tested with $5\sigma$ signal significance even at the present run of the LHC.Comment: Further clarification added, Table 2 updated, figure 5,8,9 and 10 modified, version accepted for publication in Phys.Rev.

125 GeV Higgs Boson and the Type-II Seesaw Model

We study the vacuum stability and unitarity conditions for a 125 GeV Standard Model (SM)-like Higgs boson mass in the type-II seesaw model. We find that, as long as the seesaw scale is introduced below the SM vacuum instability bound, there exists a large parameter space predicting a 125 GeV Higgs mass, irrespective of the exact value of the seesaw scale, satisfying both stability and unitarity conditions up to the Planck scale. We also study the model predictions for the Higgs partial decay widths in the diphoton and Z+photon channels with respect to their SM expectations and find that the decay rates for these two processes are correlated. We further show that for any given enhancement in the Higgs-to-diphoton rate over its SM expectation, there exists an upper bound on the type-II seesaw scale, and hence, on the masses of the associated doubly- and singly-charged Higgs bosons in the allowed parameter space. For instance, if more than 10% enhancement persists in the Higgs-to-diphoton channel, the upper limit on the type-II seesaw scale is about 450 GeV which is completely within the reach of the 14 TeV LHC. We believe this to be an encouraging result for the experimental searches of the singly- and doubly-charged Higgs bosons which, in combination with improved sensitivity in the Higgs-to-diphoton and Higgs-to-Z+photon signal strengths, could probe the entire allowed parameter space of the minimal type-II seesaw model, and establish/eliminate it as a single viable extension of the SM.Comment: 29 pages, 7 figures, 2 tables; corrected Eq. (5.11) and related discussion, updated Table 2 and Figures 5-

Thermoelectric response in two-dimensional nodal-point semimetals

In this review, we discuss the computation of thermoelectric properties in two-dimensional (2D) nodal-point semimetals with two bands, and show that the expressions of the thermoelectric coefficients take different values depending on the nature of the scattering mechanism responsible for transport. We consider scatterings arising from short-ranged disorder potential and screened charged impurities. In all the cases considered, an anisotropy in the band spectrum invariably affects the thermopower quite significantly. We illustrate this by comparing the results for a semi-Dirac semimetal with those for the isotropic case (captured by the dispersion of a single valley of graphene). We also consider the scenario when a magnetic field of magnitude $B$ is applied perpendicular to the plane of the 2D semimetal. For a weak external magnetic field, when we can ignore the formation of Landau levels, a complex dependence of the thermopower on $B$ emerges for the anisotropic case. We also describe the behaviour of the thermoelectric coefficients in the presence of a strong quantizing magnetic field. Overall, the interplay of anisotropy and strengths of the external fields provides a promising platform for achieving high thermoelectric figure-of-merit.Comment: invited review article; includes the results reported in arXiv:1811.0495

Thermopower in an anisotropic two-dimensional Weyl semimetal

We investigate the generation of an electric current from a temperature gradient in a two-dimensional Weyl semimetal with anisotropy in both the presence and absence of a quantizing magnetic field. We show that the anisotropy leads to doping dependences of thermopower and thermal conductivities which are different from those in isotropic Dirac materials. Additionally, we find that a quantizing magnetic field in such systems leads to an interesting magnetic field dependence of the longitudinal thermopower, resulting in unsaturated thermoelectric coefficients. Thus, the results presented here will serve as a guide to achieving high thermopower and a thermoelectric figure of merit in graphene-based materials, as well as organic conductors such as α-BEDT-TTF2I3.acceptedVersio