arXiv subjects

Harri Waltari

Publications and source records attributed to Harri Waltari.

22 records · Page 2Linked to original sources

arXiv2017

Resonant slepton production and right sneutrino dark matter in left-right supersymmetry

Right-handed sneutrinos are natural components of left-right symmetric supersymmetric models where the gauge sector is extended to include right-handed weak interactions. Unlike in other models where right-handed sneutrinos are gauge singlets, here the right sneutrino is part of a doublet and could be a dark matter candidate whose annihilation proceeds via gauge interactions. We investigate this possibility, and find that relic density, low-energy observable and direct supersymmetry search constraints can be satisfied when the lightest supersymmetric particle is a right-handed sneutrino. We introduce benchmarks for left-right supersymmetric realizations where either a sneutrino or a neutralino is the lightest superpartner. We then study the LHC signals arising through resonant right-handed slepton production via a $W_R$ gauge-boson exchange that lead to final states enriched in leptons, additionally containing a large amount of missing transverse momentum, and featuring a low jet multiplicity. We find that such a resonant production would boost the chances of discovering these weakly interacting supersymmetric particles for a mass range extending beyond 1 TeV already with a luminosity of 100 fb$^{-1}$. Finally, we compare sneutrino versus neutralino scenarios, and comment on differences with other sneutrino dark matter models.

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arXiv2016

Light top squarks in $U(1)_{R}$-lepton number model with a right handed neutrino and the LHC

We investigate the phenomenology of top squarks at the Large Hadron Collider (LHC) in a supersymmetric model where lepton number is identified with an approximate $U(1)_R$ symmetry in such a way that one of the left chiral sneutrinos can acquire a large vacuum expectation value ($vev$) and can play the role of the down-type Higgs. This $R$-symmetry allows a subset of trilinear $R$-parity violating interactions, which determine the collider phenomenology of this model in a significant way. The gauginos are Dirac particles and gluinos are relatively heavy in this class of models. The model contains a right handed neutrino superfield, which gives a tree level mass to one of the active neutrinos. An order one neutrino Yukawa coupling also helps enhance the Higgs boson mass at the tree level and results in a very light bino-like neutralino ($\widetilde χ_2^0$) with mass around a few hundred MeV, which is a carrier of missing (transverse) energy (\met). The model can accommodate two rather light top squarks, compatible with the observed mass of the Higgs boson. The lighter top squark (${\widetilde t}_1$) can decay into $t\widetildeχ_2^0$, and thus the signal would be similar to the signal of top quark pair production at the LHC. In addition, fully visible decays such as ${\widetilde t}_2 \rightarrow b e^+$ can give rise to interesting final states. Such signals at the LHC combined with other features like a heavy gluino could provide a strong evidence for this kind of a model. Our analysis shows that $m_{\widetilde t_1}\lsim 575~(750)$ GeV and $m_{\widetilde t_2}\lsim 1.2~(1.4)$ TeV can be probed with 5$σ$ statistical significance at the 13 TeV LHC with 300~(3000) fb$^{-1}$ of integrated luminosity. Finally, we observe that in the presence of super-light carriers of \met, the so-called `stealth' top squark scenario may naturally appear in our model.

hep-ph↗

arXiv2014

Left-right supersymmetry after the Higgs boson discovery

We perform a thorough analysis of the parameter space of the minimal left-right supersymmetric model in agreement with the LHC data. The model contains left- and right-handed fermionic doublets, two Higgs bidoublets, two Higgs triplet representations, and one singlet, insuring a charge-conserving vacuum. We impose the condition that the model complies with the experimental constraints on supersymmetric particles masses and on the doubly-charged Higgs bosons, and require that the parameter space of the model satisfy the LHC data on neutral Higgs signal strengths at $2σ$. We choose benchmark scenarios by fixing some basic parameters and scanning over the rest. The LSP in our scenarios is always the lightest neutralino. We find that the signals for $H\to γγ$ and $H \to VV^\star$ are correlated, while $H \to b \bar b$ is anti-correlated with all the other decay modes, and also that the contribution from singly-charged scalars dominate that of the doubly-charged scalars in $H\to γγ$ and $H \to Zγ$ loops, contrary to Type-II seesaw models. We also illustrate the range for mass spectrum of the LRSUSY model in light of planned measurements of the branching ratio of $H\to γγ$ to 10% level.

hep-ph↗

arXiv2014

Higgs sector in NMSSM with right-handed neutrinos and spontaneous R-parity violation

R-parity violation modifies the phenomenology of supersymmetric models considerably. We study a version of NMSSM, which contains right-handed neutrinos and in which spontaneous R-parity violation is possible. We study the ensuing effects of spontaneous breaking to the Higgs decay modes, taking into account the measured mass of the Higgs boson and experimental constraints, including rare decays. We find that a possible light scalar, dominantly a sneutrino, helps to increase the Standard Model (SM) Higgs-like scalar mass to the measured value. At the same time, a lighter stop than in the MSSM is allowed. The Higgs decay rates in the studied model can somewhat differ from the SM expectations, although the most prominent difference is a universal suppression in the couplings due to the mixing of doublet scalars with singlets. The charged, pseudoscalar, and other than the two lightest scalar Higgses are typically heavier than 1 TeV in the parameter region where R-parity is spontaneously broken.

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