Search

We revisit the two real singlet extension of the Standard Model with a $Z_2\times Z_2^\prime$ symmetry. One of the singlet scalars $S_2$, by virtue of an unbroken $Z_2^\prime$ symmetry, plays the role of a stable dark matter candidate. The other scalar $S_1$, with spontaneously broken $Z_2$-symmetry, mixes with the SM Higgs boson and acts as the scalar mediator. We analyze the model by putting in the entire set of theoretical and recent experimental constraints. The latest bounds from direct detection Xenon1T experiment severely restricts the allowed region of parameter space of couplings. To ensure the dark matter satisfies the relic abundance criterion, we rely on the Breit-Wigner enhanced annihilation cross-section. Further, we study the viability of explaining the observed gamma-ray excess in the galactic center in this model with a dark matter of mass in the $\sim 36-51$ GeV window and present our conclusions., 14 pages, 9 figures

We study the discovery prospects of the charged Higgs boson in the context of multi-Higgs models in certain beyond the Standard Model scenarios. We classify models into three categories based on the charged Higgs coupling properties: gaugophobic, fermiophobic, and chromophobic. In each case, we identify viable modes of discovery and present LHC analysis for discovery. We find that extensions of the Standard Model in which the charged Higgs boson does not couple to colored particles offer the best possible avenues for discovery.

Models with extra gauge symmetry are well-motivated extensions of the Standard Model. In this paper, we study an extended gauge model with a heavy neutral gauge boson Z′ which is fermiophobic. Thus, the production of such particles can occur via vector boson fusion, with subsequent decays into WW or Zh. We investigate the collider phenomenology of such Z′ s in the context of both the 14 TeV LHC and the future Compact Linear Collider. We find that looking at ℓℓbb final states provides a rich opportunity to discover such new vector bosons where conventional search strategies in the dilepton channel would fail. In particular, we optimize our analysis by putting in kinematic cuts deriving model-independent values of σ×BR needed for a 5σ discovery at the LHC. We then translate this into the parameter space of a specific model for illustration purpose—our results show that fermiophobic Z′s are discoverable in the ℓℓbb channel for a wide range of parameter values.

We test the possibility that the newly-discovered 126 GeV boson is a pseudoscalar by examining the correlations among the loop-induced pseudoscalar decay branching fractions to $\gamma\gamma$, $ZZ^*$, $Z\gamma$, and $WW^*$ final states in a model-independent way. These four decays are controlled by only two effective operators, so that the rates in $Z\gamma$ and $WW^*$ are predicted now that the rates in $\gamma\gamma$ and $ZZ^*,Z\gamma^* \to 4 \ell$ have been measured. We find that the pseudoscalar possibility is disfavored but not conclusively excluded. Experimental exclusion of the $Z\gamma$ decay to well below $\sigma/\sigma_{\rm SM} \sim 170$ or conclusive observation of the $WW^*$ decay near the Standard Model rate would eliminate the pseudoscalar possibility. The $Z\gamma$ exclusion should be possible using existing data. The only loophole in our argument is the possibility that the $4\ell$ signal comes from pseudoscalar decays to a pair of new neutral gauge bosons with mass near the $Z$ pole., Comment: 8 pages, 2 figures, v2: references added, Fig. 1 improved,v3: minor error in numbers on last paragraph of pg5 fixed

A large class of deconstructed Higgsless model is known to satisfy the tree-level experimental bounds on the electroweak precision parameters. In particular, an approximate custodial symmetry insures that the tree-level $\rho$ parameter is exactly one, for arbitrary values of the model parameters, and regardless of fermion delocalization. In this note we expand on previous work by considering the fermionic one-loop contributions to $\rho$, which are essentially due to loops with top and bottom modes. We analyze the dependence on the number $N$ of internal SU(2) sites in models with a ``flat background''. We find that the new-physics contribution rapidly increases with $N$, to quickly stabilize for large values of $N$. Experimental upper bounds on $\rho$ translate into lower bounds on the mass of the heavy fermions. These, however, are weakly correlated to $N$, and the three-site model (N=1) turns out to be already an excellent approximation for the continuum model ($N\to\infty$)., Comment: 20 pages, 5 figures

We analyze the spectrum and properties of a highly-deconstructed Higgsless model with only three sites. Such a model contains sufficient complexity to incorporate interesting physics issues related to fermion masses and electroweak observables, yet remains simple enough that it could be encoded in a Matrix Element Generator program for use with Monte Carlo simulations. The gauge sector of this model is equivalent to that of the BESS model; the new physics of interest here lies in the fermion sector. We analyze the form of the fermion Yukawa couplings required to produce the ideal fermion delocalization that causes tree-level precision electroweak corrections to vanish. We discuss the size of one-loop corrections to b \to s \gamma, the weak-isospin violating parameter \alpha T and the decay Z \to b \bar{b}. We find that the new fermiophobic vector states (the analogs of the gauge-boson KK modes in a continuum model) can be reasonably light, with a mass as low as 380 GeV, while the extra (approximately vectorial) quark and lepton states (the analogs of the fermion KK modes) must be heavier than 1.8 TeV., Comment: 30 pages, JHEP.cls, axodraw. References and acknowledgements added, minor textual clarifications added and typos fixed, relationship to BESS model emphasized. Typos corrected, version to appear in PRD

Models of electroweak symmetry breaking with extended Higgs sectors are theoretically well motivated. In this study, we focus on models with a low energy spectrum containing a pair of charged scalars $H^\pm$, as well as a light scalar H and/or a pseudoscalar A. We study the $H^\pm tb$ associated production with $H^\pm \to AW/HW$, which could reach sizable branching fractions in certain parameter regions. With detailed collider analysis, we obtain the exclusion bounds as well as discovery reach at the 14 TeV LHC for the process $pp \to H^\pm tb \to AW^\pm tb/HW^\pm tb \to \tau\tau bbWW, bbbbWW$. We find that for a daughter particle mass of 70 GeV, the 95% C.L. exclusion reach in $\sigma$xBR varies from about 60 fb to 25 fb, for $m_{H^\pm}$ ranging from 150 GeV to 500 GeV with 300 fb$^{-1}$ integrated luminosity in the $\tau\tau$ mode. We further interpret these bounds in the context of Type II Two Higgs Doublet Model. The exclusion region in the $m_{H^\pm}-\tan\beta$ plane can be extended to $m_{H^\pm}=$ 600 GeV, while discovery is possible for $m_{H^\pm}\lesssim$ 400 GeV with 300 fb$^{-1}$ integrated luminosity. The exotic decay mode $H^\pm \to AW^\pm/HW^\pm$ offers a complementary channel to the conventional mode $H^\pm \to \tau\nu$ for charged Higgs searches.