Probing the "μ\mu from ν\nu" supersymmetric standard model with displaced multileptons from the decay of a Higgs boson at the LHC

The "$\mu$ from $\nu$" supersymmetric standard model ($\mu\nu$SSM) cures the $\mu$-problem and concurrently reproduces measured neutrino data by using a set of usual right-handed neutrino superfields. Recently, the LHC has revealed the first scalar boson which naturally makes it tempting to test $\mu\nu$SSM in the light of this new discovery. We show that this new scalar while decaying to a pair of unstable long-lived neutralinos, can lead to a distinct signal with non-prompt multileptons. With concomitant collider analysis we show that this signal provides an unmistakable signature of the model, pronounced with light neutralinos. Evidence of this signal is well envisaged with sophisticated displaced vertex analysis, which deserves experimental attention.Comment: 5 pages, 3 figures, title, text, abstract and references modifie

Hunting physics beyond the standard model with unusual W±W^\pm and ZZ decays

Nonstandard on-shell decays of $W^\pm$ and $Z$ bosons are possible within the framework of extended supersymmetric models, i.e., with singlet states and/or new couplings compared to the minimal supersymmetric standard model. These modes are typically encountered in regions of the parameter space with light singlet-like scalars, pseudoscalars, and neutralinos. In this letter we emphasize how these states can lead to novel signals at colliders from $Z$- or $W^\pm$-boson decays with prompt or displaced multileptons/tau jets/jets/photons in the final states. These new modes would give distinct evidence of new physics even when direct searches remain unsuccessful. We discuss the possibilities of probing these new signals using the existing LHC run-I data set. We also address the same in the context of the LHC run-II, as well as for the future colliders. We exemplify our observations with the "$\mu$ from $\nu$" supersymmetric standard model, where three generations of right-handed neutrino superfields are used to solve shortcomings of the minimal supersymmetric standard model. We also extend our discussion for other variants of supersymmetric models that can accommodate similar signatures.Comment: New discussions and references added, 8 pages, 1 figure, matches with the published version in Phys. Rev.

Looking for the left sneutrino LSP with displaced-vertex searches

We analyze a displaced dilepton signal expected at the LHC for a tau left sneutrino as the lightest supersymmetric particle with a mass in the range $45$-$100$ GeV. The sneutrinos are pair produced via a virtual $W$, $Z$ or $\gamma$ in the $s$ channel and, given the large value of the tau Yukawa coupling, their decays into two dileptons or a dilepton plus missing transverse energy from neutrinos can be significant. The discussion is carried out in the $\mu \nu$SSM, where the presence of $R$-parity violating couplings involving right-handed neutrinos solves the $\mu$ problem and can reproduce the neutrino data. To probe the tau left sneutrinos we compare the predictions of the $\mu \nu$SSM with the ATLAS search for long-lived particles using displaced lepton pairs in $pp$ collisions at $\sqrt s= 8$ TeV, allowing us to constrain the parameter space of the model. We also consider an optimization of the trigger requirements used in existing displaced-vertex searches by means of a High Level Trigger that exploits tracker information. This optimization is generically useful for a light metastable particle decaying into soft charged leptons. The constraints on the sneutrino turn out to be more stringent. We finally discuss the prospects for the $13$ TeV LHC searches as well as further potential optimizations.Comment: Version published in PRD, discussions expanded, references added, LEP and LHC constraints discussed in more detail, 29 pages, 9 figures, 9 table

Right-handed neutrinos, domain walls and tadpoles in the superstring inspired μν\mu\nuSSM

We discuss the special role of right-handed neutrinos in the $\mu\nu$SSM for solving the $\mu$- and $\nu$-problems, simultaneously avoiding the potential domain wall and tadpole problems, In particular, embedding the $\mu\nu$SSM in the framework of superstrings implies that not all gauge invariant terms are necessarily present in the superpotential, and thus there is more flexibility to allow only those that avoid the domain wall and tadpole problems to be present. These can be non-renormalizable terms of dimension 4 or terms of higher dimensions. In addition, non-perturbative effects can also solve both problems. We discuss another implication of the superstring inspired $\mu\nu$SSM, since the right-handed neutrino is expected to have extra $U(1)$ charges at high energies. In this case, the cubic right-handed neutrino terms in the superpotential, helpful for generating Majorana masses and solving domain wall and tadpole problems, can arise through a variety of stringy mechanisms.Comment: 23 pages, 2 figure

An origin for small neutrino masses in the NMSSM

We consider the Next to Minimal Supersymmetric Standard Model (NMSSM) which provides a natural solution to the so-called mu problem by introducing a new gauge-singlet superfield S. We realize that a new mechanism of neutrino mass suppression, based on the R-parity violating bilinear terms mu_i L_i H_u mixing neutrinos and higgsinos, arises within the NMSSM, offering thus an original solution to the neutrino mass problem (connected to the solution for the mu problem). We generate realistic (Majorana) neutrino mass values without requiring any strong hierarchy amongst the fundamental parameters, in contrast with the alternative models. In particular, the ratio |mu_i/mu| can reach about 10^-1, unlike in the MSSM where it has to be much smaller than unity. We check that the obtained parameters also satisfy the collider constraints and internal consistencies of the NMSSM. The price to pay for this new cancellation-type mechanism of neutrino mass reduction is a certain fine tuning, which get significantly improved in some regions of parameter space. Besides, we discuss the feasibility of our scenario when the R-parity violating bilinear terms have a common origin with the mu term, namely when those are generated via a VEV of the S scalar component from the couplings lambda_i S L_i H_u. Finally, we make comments on some specific phenomenology of the NMSSM in the presence of R-parity violating bilinear terms.Comment: 21 pages, 5 figures, Latex fil

Phenomenological implications of sterile neutrinos in the μν\mu\nuSSM and dark matter

We analyze the role of sterile neutrinos in the framework of the $\mu\nu$SSM, where the presence of right-handed neutrinos provides a simultaneous solution to $\mu$- and $\nu$-problems in supersymmetry. We adopt a minimalistic approach, reproducing light neutrino masses and mixing angles at tree level using just two right-handed neutrinos as part of the seesaw mechanism. A third right-handed neutrino does not contribute significantly to the mass of the three active ones, behaving as a sterile neutrino with a mass in the range keV$-$MeV. Furthermore, a sterile neutrino of about $10$ keV can be a good candidate for dark matter with a lifetime larger than the age of the Universe. In particular, the three-body decay to active neutrinos gives the dominant contribution to its lifetime. The one-loop decay to gamma and active neutrino is subdominant, but relevant for observations such as astrophysical X-rays. We find regions of the parameter space of the $\mu\nu$SSM, with different values of the sterile neutrino mass, fulfilling not only these constraints but also collider constraints from the Higgs sector.Comment: Version published in Astroparticle Physics. Discussion improved including one figure. 24 pages, 7 figures, 2 table

The impact of the ATLAS zero-lepton, jets and missing momentum search on a CMSSM fit

Recent ATLAS data significantly extend the exclusion limits for supersymmetric particles. We examine the impact of such data on global fits of the constrained minimal supersymmetric standard model (CMSSM) to indirect and cosmological data. We calculate the likelihood map of the ATLAS search, taking into account systematic errors on the signal and on the background. We validate our calculation against the ATLAS determinaton of 95% confidence level exclusion contours. A previous CMSSM global fit is then re-weighted by the likelihood map, which takes a bite at the high probability density region of the global fit, pushing scalar and gaugino masses up.Comment: 16 pages, 7 figures. v2 has bigger figures and fixed typos. v3 has clarified explanation of our handling of signal systematic