We study the prospects of observing the non-resonant di-Higgs pair production in the Standard Model (SM) at the high luminosity run of the 14 TeV LHC (HL-LHC), upon combining multiple final states chosen on the basis of their yield and cleanliness. In particular, we consider the bbγγ, bbτ + τ − , bbW W * , W W * γγ and 4W channels mostly focusing on final states with photons and/or leptons and study 11 final states. We employ multivariate analyses to optimise the discrimination between signal and backgrounds and find it performing better than simple cut-based analyses. The various differential distributions for the Higgs pair production have non-trivial dependencies on the Higgs self-coupling (λ hhh ). We thus explore the implications of varying λ hhh for the most sensitive search channel for the double Higgs production, viz., bbγγ. The number of signal events originating from SM di-Higgs production in each final state is small and for this reason measurement of differential distributions may not be possible. In order to extract the Higgs quartic coupling, we have to rely on the total number of events in each final state and these channels can be contaminated by various new physics scenarios. Furthermore, we consider various physics beyond the standard model scenarios to quantify the effects of contamination while trying to measure the SM di-Higgs signals in detail. In particular, we study generic resonant heavy Higgs decays to a pair of SM-like Higgs bosons or to a pair of top quarks, heavy pseudoscalar decaying to an SM-like Higgs and a Z-boson, charged Higgs production in association with a top and a bottom quark and also various well-motivated supersymmetric channels. We set limits on the cross-sections for the aforementioned new physics scenarios, above which these can be seen as excesses over the SM background and affect the measurement of Higgs quartic coupling. We also discuss the correlations among various channels which can be useful to identify the new physics model. 2.5.3 The 4 final state 35 2.6 Summarising the non-resonant search results 36 3 Ramifications of varying the Higgs self-coupling 37 4 Contaminations to non-resonant di-Higgs processes 40 4.1 The hh(+X) channels 41 4.2 The h + X channels 46 4.3 Null Higgs channels 49 A Appendix A 68 B Appendix B 69

A multitude of searches have already been performed by the ATLAS and CMS collaborations at the LHC to probe the heavy Higgses of the Minimal Supersymmetric Standard Model (MSSM) through their decay to the Standard Model particles. In this paper, we study the decay of the MSSM heavy Higgses into neutralino and chargino pairs and estimate the maximum possible branching ratios for these 'ino' modes being consistent with the present LHC data. After performing a random scan of the relevant electroweakino parameters, we impose the SM 125 GeV Higgs constraints, low energy flavour data as well as current bounds on heavy Higgses from the LHC run-I and run-II data. The present limits on the electroweakino masses and couplings are also considered in our analysis. We choose a few representative benchmark points satisfying all the above-mentioned constraints, and then perform a detailed collider simulation, including fast detector effects, and analyze all the potential SM backgrounds in order to estimate the discovery reach of these heavy Higgses at the LHC. We restrict ourselves within the leptonic cascade decay modes of these heavy Higgses and study the mono-X + E / T (X=W,Z) and trilepton + E / T signatures in the context of high luminosity run of the 14 TeV LHC.

In this work, we show the importance of searches for heavy resonant scalars (H) and pseudoscalars (A). Taking cue from the present searches, we make projections for searches in an extended scalar sector at the high luminosity run of the Large Hadron Collider. We study the three most relevant search channels, i.e., H → hh, H/A → tt and bbH/A. Upon studying multifarious final states for the resonant double Higgs production, we find that the bbγγ (σ(pp → H → hh) ∈ [81.27, 14.45] fb for m H ∈ [300, 600] GeV at 95% C.L.) and bbbb ([5.4, 2.5] fb for m H ∈ [800, 1000] GeV at 95% C.L.) channels are the most constraining. For the bbH channel, we can exclude σ(pp → bbH) ∈ [22.2, 3.7] fb for m H ∈ [300, 500] GeV. Finally, we consider the phenomenological Minimal Supersymmetric Standard Model as an example and impose various present constraints and our future direct search-limits and obtain strong constraints on the m A − tan β parameter space, where m A and tan β are respectively the mass of the pseudoscalar and the ratio of the vacuum expectation values of the two Higgs doublets. Assuming that the heavy Higgs boson decays only to Standard Model (SM) states, we find that the H → hh → bbγγ (H → tt) channel excludes tan β as low as 4 (m A ∈ [400, 800] GeV) at 95% CL. This weakens up to ∼ 5.5 when the bbH channel dominates. Upon allowing for non-SM decay modes, the limits weaken.

40 pages, 21 figuresInternational audienceWe study the decay of 125 GeV Higgs boson to light LSP neutralino in the phenomenological minimal supersymmetric standard model in the context of collider searches and astrophysical experiments. We consider the parameter space for light neutralinos that can be probed via the invisible Higgs decays and higgsino searches at the ILC. We consider the cases where the light neutralino is compatible with the observed relic density or where the thermal relic is over-abundant, pointing to non-standard cosmology. In the former case, when the neutralino properties give rise to under-abundant relic density, the correct amount of relic abundance is assumed to be guaranteed by either additional DM particles or by non-thermal cosmology. We contrast these different cases. We assess what astrophysical measurements can be made, in addition to the measurements made at the ILC, which can provide a clue to the nature of the light neutralino. We find that a number of experiments, including Xenon-nT, PICO-250, LZ in conjunction with measurements made at the ILC on invisible Higgs width can pin down the nature of this neutralino, along with its cosmological implications. Additionally, we also point out potential LHC signatures that could be complementary in this region of parameter space

In this article we review the case for a light (