Next to Minimal Higgs : Mass Bounds and Search Prospects

The Standard Model of electroweak interactions has one scalar doublet. The minimal extension of this sector is effected by adding a neutral, singlet scalar field. Depending on whether the singlet field has a non-zero vacuum expectation value, x, or not, the scenario has quite distinctive predictions. In particular, x unequal to 0 produces a mixing between the usual SU(2) doublet and the singlet, giving rise to two physical states and a goldstone boson with non-vanishing coupling to these. Presence of this coupling modifies the 2 jets + missing energy signal of the Bjorken process at LEP. We update the bounds on the Higgs mass using the LEP-1 data. We then explore, using parton-level Monte Carlo event generators, the production of these scalars at the LHC via gluon-gluon fusion and subsequent detection. We compare the signals with the expected backgrounds.Comment: 16 pages and 7 Postscript figures, Late

Mass bounds for Triplet Scalars of the Left-Right symmetric model and their future detection prospects

The standard formulation of the Left-Right symmetric model involves scalars transforming as a triplet under SU(2)L. This multiplet contains particles which are uncharged, singly-charged, and doubly-charged. We derive a bound on the uncharged scalar mass of 55.4 GeV using results from LEP-II and find that a range upto 110 GeV may be explored at the NLC at the 5sigma level. We also discuss search strategies for the singly- and doubly-charged scalars at the Tevatron and the LHC. Possible Standard Model backgrounds for the relevant modes are estimated and compared with the signal. At the LHC, the prospects of detecting the doubly-charged scalar are bright up to a mass of 850 GeV while the 5sigma discovery limit of the singly-charged mode extends to 240 GeV for an integrated luminosity of 100 inverse fb. At the Tevatron, with an integrated luminosity of 25 inverse fb, the doubly-charged state can be detected if its mass is less than 275 GeV while the reach for the singly charged scalar is 140 GeV.Comment: Latex, References added, some postscript figures modified, to appear in Phys. Rev.

Testing Gauge-Gravitino Coupling in Gauge-Mediated Supersymmetry Breaking Through Single Photon Events

We show that the process $e^+e^- \to \gamma+$ missing energy, arising from the pair production of neutralinos, can probe the \gamma-\tilde\gamma- \gravitino as well as the Z-\tilde Z-\gravitino couplings in Gauge Mediated Supersymmetry Breaking models. This enables one to study the mutual relationship of the Goldstino couplings of the different gauginos, a feature whose testability has not been emphasized so far. The Standard Model backgrounds get suppresed with the use of a right polarized electron beam. The energy and angular distribution of the emitted photon can distinguish such models from the minimal supersymmetric theory and its variants.Comment: Revised version to be published in Physics Letters B. Some minor changes were mad

On a Generalized Fifth-Order Integrable Evolution Equation and its Hierarchy

A general form of the fifth-order nonlinear evolution equation is considered. Helmholtz solution of the inverse variational problem is used to derive conditions under which this equation admits an analytic representation. A Lennard type recursion operator is then employed to construct a hierarchy of Lagrangian equations. It is explicitly demonstrated that the constructed system of equations has a Lax representation and two compatible Hamiltonian structures. The homogeneous balance method is used to derive analytic soliton solutions of the third- and fifth-order equations.Comment: 16 pages, 1 figur

Lepton Flavours at the Early LHC Experiments as the Footprints of the Dark Matter Producing Mechanisms

The mSUGRA parameter space corresponding to light sleptons well within the reach of LHC and relatively light squarks and gluinos (mass $\le$ 1 TeV) has three regions consistent with the WMAP data on dark matter relic density and direct mass bounds from LEP 2. Each region can lead to distinct leptonic signatures from squark-gluino events during the early LHC experiments (integrated luminosity $\sim 10 ~fb^{-1}$ or even smaller). In the much studied stau-LSP coannihilation region with a vanishing common trilinear coupling ($A_0$) at the GUT scale a large fraction of the final states contain electrons and / or muons and $e$ - $\mu$ - $\tau$ universality holds to a good approximation. In the not so well studied scenarios with non-vanishing $A_0$ both LSP pair annihilation and stau-LSP coannihilation could contribute significantly to the dark matter relic density for even smaller squark-gluino masses. Our simulations indicate that the corresponding signatures are final states rich in $\tau$-leptons while final states with electrons and muons are suppressed leading to a violation of lepton universality. These features may be observed to a lesser extent even in the modified parameter space (with non-zero $A_0$) where the coannihilation process dominates. We also show that the generic $m$-leptons + $n$-jets+ $\not! E_T$ signatures without flavour tagging can also discriminate among the three scenarios. However, the signals become more informative if the $\tau$ and $b$-jet tagging facilities at the LHC experiments are utilized.Comment: 28 page