It is known that there are AdS vacua obtained from compactifying the SM to 2 or 3 dimensions. The existence of such vacua depends on the value of neutrino masses through the Casimir effect. Using the Weak Gravity Conjecture, it has been recently argued by Ooguri and Vafa that such vacua are incompatible with the SM embedding into a consistent theory of quantum gravity. We study the limits obtained for both the cosmological constant Λ 4 and neutrino masses from the absence of such dangerous 3D and 2D SM AdS vacua. One interesting implication is that Λ 4 is bounded to be larger than a scale of order m 4 ν , as observed experimentally. Interestingly, this is the first argument implying a non-vanishing Λ 4 only on the basis of particle physics, with no cosmological input. Conversely, the observed Λ 4 implies strong constraints on neutrino masses in the SM and also for some BSM extensions including extra Weyl or Dirac spinors, gravitinos and axions. The upper bounds obtained for neutrino masses imply (for fixed neutrino Yukawa and Λ 4 ) the existence of upper bounds on the EW scale. In the case of massive Majorana neutrinos with a see-saw mechanism associated to a large scale M 10 10−14 GeV and Y ν 1 10 −3 , one obtains that the EW scale cannot exceed M EW 10 2 − 10 4 GeV. From this point of view, the delicate fine-tuning required to get a small EW scale would be a mirage, since parameters yielding higher EW scales would be in the swampland and would not count as possible consistent theories. This would bring a new perspective into the issue of the EW hierarchy.

Abstract:We study LHC signatures of displaced vertices and long-lived charged particles within the context of the Next-to-Minimal Supersymmetric Standard Model with righthanded (RH) sneutrinos. In this construction the RH neutrino can be produced directly from Higgs decays or in association with a RH sneutrino when the latter is the lightest supersymmetric particle. The RH neutrino is generally long-lived, since its decay width is proportional to the neutrino Yukawa, a parameter which is predicted to be small. The RH neutrino late decay can therefore give rise to displaced vertices at the LHC, which can be identified through the decay products, which involve two leptons (2ℓ + / E T ) or a lepton with two jets (ℓjj). We simulate this signal for the current LHC configuration (a centre of mass of 8 TeV and an integrated luminosity of L = 20 fb −1 ), and a future one (13 TeV and L = 100 fb −1 ). We show that a region of the parameter space of this model can be probed and that the RH neutrino mass can be reconstructed from the end-point of the two-lepton invariant mass distribution or the central value of the mass distribution for two jets plus one lepton. Another exotic signature of this construction is the production of a long-lived stau. If the stau is the next-to-lightest supersymmetric particle, it can decay through diagrams involving the small neutrino Yukawa, and would escape the detector leaving a characteristic trail. We also simulate this signal for various benchmark points and show that the model can be within the reach of the future run of the LHC.

We test the impact of the ATLAS and CMS multi-lepton searches performed at the LHC with 8 as well as 13 TeV center-of-mass energy (using only the pre-2018 results) on the chargino and neutralino sector of the NMSSM. Our purpose consists in analyzing the actual reach of these searches for a full model and in emphasizing effects beyond the MSSM that affect the performance of current (MSSMinspired) electroweakino searches. To this end, we consider several scenarios characterizing specific features of the NMSSM electroweakino sector. We then perform a detailed collider study, generating Monte-Carlo events through Pythia and testing against current LHC constraints implemented in the public tool CheckMATE. We find e.g. that SUSY decay chains involving intermediate singlino or Higgs-singlet states can modify the naive MSSM-like picture of the constraints by inducing finalstates with softer or less-easily identifiable SM particles -reversely, a compressed configuration with singlino NLSP occasionally induces final states that are rich with photons, which could provide complementary search channels.

The Triplet extension of the MSSM (TMSSM) alleviates the little hierarchy problem and provides a significant enhancement of the loop-induced diphoton rate of the lightest CP-even Higgs h. In this paper we pursue the analysis of the TMSSM Higgs phenomenology by computing for the first time the h → Zγ decay. Interestingly we find that the rates of loop-induced decays are correlated and their signal strengths can rise up to 40%-60% depending on the channel. We furthermore study the dark matter phenomenology of the TMSSM. The lightest neutralino is a good dark matter candidate in two regions. The first one is related to the Higgs and Z resonances and the LSP is mostly Bino. The second one is achieved for a mass larger than 90 GeV and the LSP behaves as the well-tempered neutralino. An advantage of the triplet contribution is that the well-tempered neutralino can be a Bino-Triplino mixture, relieving the problem of achieving M 2 ∼ M 1 in unified scenarios. The dark matter constraints strongly affect the Higgs phenomenology, reducing the potential enhancements of the diphoton and of the Zγ channels by 20% at most. In the near future, dark matter direct searches and collider experiments will probe most of the parameter space where the neutralino is the dark matter candidate.

In this work we present a new search strategy for the discovery of staus at the LHC in the context of the minimal supersymmetric standard model. The search profits from the large s-channel b-quark annihilation production of the heavy CP-even and CP-odd Higgs bosons (H/A) which can be attained in regions of tan β 1 that avoid the stringent H/A → τ + τ − searches via decays into stau pairs. We also focus on regions where the staus branching ratios are dominated by the decays into a tau lepton and the lightest neutralino. Thus the experimental signature consists of final states made up of a tau-lepton pair plus large missing transverse energy. We take advantage of the large stau-pair production cross sections via heavy Higgs boson decays, which are between one or two orders of magnitude larger than the usual electroweak production cross sections for staus. A set of basic cuts allow us to obtain significances of the signal over the SM backgrounds at the discovery level (5 standard deviations) in the next LHC run with a center-of-mass energy of 14 TeV and a total integrated luminosity of only 100 fb −