Lightest Right-handed Sneutrino Research Articles

Vacuum (meta-)stability in the mu nu SSM

We perform an analysis of the vacuum stability of the neutral scalar potential of the mu -from-nu Supersymmetric Standard Model (mu nu SSM). As an example scenario, we discuss the alignment without decoupling limit of the mu nu SSM, for which the required conditions on the Higgs sector are derived. We demonstrate that in this limit large parts of the parameter space feature unphysical minima that are deeper than the electroweak minimum. In order to estimate the lifetime of the electroweak vacuum, we calculate the rates for the tunneling process into each unphysical minimum. We find that in many cases the resulting lifetime is longer than the age of the universe, such that the considered parameter region is not excluded. On the other hand, we also find parameter regions in which the electroweak vacuum is short-lived. We investigate how the different regions of stability are related to the presence of light right-handed sneutrinos. Accordingly, a vacuum stability analysis that accurately takes into account the possibility of long-lived metastable vacua is crucial for a reliable assessment of the phenomenological viability of the parameter space of the mu nu SSM and its resulting phenomenology at the (HL)-LHC.

Measuring neutrino dynamics in NMSSM with a right-handed sneutrino LSP at the ILC

We study the possibility of measuring neutrino Yukawa couplings in the Next-to-Minimal Supersymmetric Standard Model with right-handed neutrinos (NMSSMr) when the lightest right-handed sneutrino is the Dark Matter (DM) candidate, by exploiting a ‘dijet + dilepton + Missing Transverse Energy’ (MET or ) signature. We show that, contrary to the miminal realisation of Supersymmetry (SUSY), the MSSM, wherein the DM candidate is typically a much heavier (fermionic) neutralino state, this extended model of SUSY offers one with a much lighter (bosonic) state as DM that can then be produced at the next generation of e+e− colliders with energies up to 500 GeV or so. The ensuing signal, energing from chargino pair production and subsequent decay, is extremely pure so it also affords one with the possibility of extracting the Yukawa parameters of the (s)neutrino sector. Altogether, our results serve the purpose of motivating searches for light DM signals at such machines, where the DM candidate can have a mass around the Electro-Weak (EW) scale.

Lepton number violation in heavy Higgs boson decays to sneutrinos

We study the possibility of observing lepton number violation in the right-handed sneutrino sector of the Next-to-Minimal Supersymmetric Standard Model extended with right-handed neutrinos. The scalar potential introduces a lepton number violating mass term for the right-handed sneutrinos, which generates a phase difference that results in oscillations between the sneutrino and antisneutrino. If we have light higgsinos and right-handed sneutrinos, the sneutrino decay width is determined by the tiny Yukawa couplings, which allows the phase difference to accumulate before the sneutrino decays. We investigate the possibilities of producing sneutrino pairs resonantly through a heavy Higgs of such a model and the ability of seeing a lepton number violating signature emerging from sneutrinos at the Large Hadron Collider. We also discuss how a possible future signal of this type could be used to determine the neutrino Yukawa couplings.

Dark matter spin characterization in mono- Z channels

The $B-L$ Supersymmetric Standard Model (BLSSM) is an ideal testing ground of the spin nature of Dark Matter (DM) as it offers amongst its candidates both a spin-1/2 (the lightest neutralino) and spin-0 (the lightest right-handed sneutrino) state. We show that the mono-$Z$ channel can be used at the Large Hadron Collider (LHC) to diagnose whether a DM signal is characterised within the BLSSM by a fermionic or (pseudo)scalar DM particle. Sensitivity to either hypothesis can be obtained after only 100 fb$^{-1}$ of luminosity following Runs 2 and 3 of the LHC.

Long-lived B−L symmetric SSM particles at the LHC

We investigate the collider signatures of neutral and charged long-lived particles (LLPs), predicted by the supersymmetric $B\ensuremath{-}L$ extension of the Standard Model (BLSSM), at the Large Hadron Collider (LHC). The BLSSM is a natural extension of the minimal supersymmetric Standard Model (MSSM) that can account for nonvanishing neutrino masses. We show that the lightest right-handed sneutrino can be the lightest supersymmetric particle (LSP), while the next-to-the LSP (NLSP) is either the lightest left-handed sneutrino or the left-handed stau, which are natural candidates for the LLPs. We analyze the displaced vertex signature of the neutral LLP (the lightest left-handed sneutrino) and the charged tracks associated with the charged LLP (the left-handed stau). We show that the production cross sections of our neutral and charged LLPs are relatively large, namely of order $\mathcal{O}(1)\text{ }\text{ }\mathrm{fb}$. Thus, probing these particles at the LHC is quite plausible. In addition, we find that the displaced dilepton associated with the lightest left-handed sneutrino has a large impact parameter that discriminates it from other SM leptons. We also emphasize that the charged track associated with the left-handed stau has a large momentum with slow moving charged tracks, hence it is distinguished from the SM background, and therefore it can be accessible at the LHC.

Dark Matter in B–L supersymmetric Standard Model with inverse seesaw

We show that the B–L Supersymmetric Standard Model with Inverse Seesaw (BLSSMIS) provides new Dark Matter (DM) candidates (lightest right-handed sneutrino and lightest B–L neutralino) with mass of order few hundreds GeV, while most of other SUSY spectrum can be quite heavy, consistently with the current Large Hadron Collider (LHC) constraints. We emphasize that the thermal relic abundance and direct detection experiments via relic neutralino scattering with nuclei impose stringent constraints on the B–L neutralinos. These constraints can be satisfied by few points in the parameter space where the B–L lightest neutralino is higgsino-like, which cannot explain the observed Galactic Center (GC) gamma-ray excess measured by Fermi-LAT. The lightest right-handed sneutrino DM is analysed. We show that for a wide region of parameter space the lightest right-handed sneutrino, with mass between 80 GeV and 1.2 TeV, can satisfy the limits of the relic abundance and the scattering cross section with nuclei. We also show that the lightest right-handed sneutrino with mass \U0001d4aa(100) GeV can account for the observed GC gamma-ray results.

Very light right-handed sneutrino dark matter in the NMSSM

Very light right-handed (RH) sneutrinos in the Next-to-Minimal Supersymmetric Standard Model can be viable candidates for cold dark matter. We investigate the prospects for their direct detection, addressing their compatibility with the recent signal observed by the CoGeNT detector, and study the implications for Higgs phenomenology.We find that in order to reproduce the correct relic abundance very light RH sneutrinos can annihilate into either a fermion-antifermion pair, very light pseudoscalar Higgses or RH neutrinos. If the main annihilation channel is into fermions, we point out that RH sneutrinos could naturally account for the CoGeNT signal. Furthermore, the lightest Higgs has a very large invisible decay width, and in some cases the second-lightest Higgs too.On the other hand, if the RH sneutrino annihilates mostly into pseudoscalars or RH neutrinos the predictions for direct detection are below the current experimental sensitivities and satisfy the constraints set by CDMS and XENON. We also calculate the gamma ray flux from RH sneutrino annihilation in theGalactic centre,including as an interesting new possibility RH neutrinos in the final state. These are produced through a resonance with the Higgs and the resulting flux can exhibit a significant Breit-Wigner enhancement.

Right-handed sneutrino dark matter in supersymmetric B − L model

We show that the lightest right-handed sneutrino in TeV scale supersymmetric B-L model with inverse seesaw mechanism is a viable candidate for cold dark matter. We find that it accounts for the observed dark matter relic abundance in a wide range of parameter space. The spin-independent cross section of B-L right-handed sneutrino is consistent with the recent results CDMS II and XENON experiments and it is detectable in future direct detection experiments. Although the B-L right-handed sneutrinos annihilate into leptons, the PAMELA results can not be explained in this model unless a huge boost factor is considered. Also the muon flux generated by B-L right-handed sneutrino in the galactic center is smaller than Super-Kamiokande's upper bound.

Non-minimal sneutrino inflation, Peccei-Quinn phase transition and non-thermal leptogenesis

We consider a phenomenological extension of the minimal supersymmetricstandard model which incorporates non-minimal chaotic inflation,driven by a quartic potential associated with the lightestright-handed sneutrino. Inflation is followed by a Peccei-Quinnphase transition based on renormalizable superpotential terms,which resolves the strong CP and μ problems of the minimalsupersymmetric standard model provided that one related parameterof the superpotential is somewhat small. Baryogenesis occurs vianon-thermal leptogenesis, which is realized by the inflatondecay. Confronting our scenario with the current observationaldata on the inflationary observables, the baryon assymetry of theuniverse, the gravitino limit on the reheating temperature and theupper bound on the light neutrino masses, we constrain the effectiveYukawa coupling involved in the decay of the inflaton torelatively small values and the inflaton mass to values lower than1012GeV.

Neutrino masses, Baryon asymmetry, dark matter and the moduli problem — A complete framework

Recent developments in string theory have led to ``realistic string compactifications which lead to moduli stabilization while generating a hierarchy between the Electroweak and Planck scales at the same time. However, this seems to suggest a rethink of our standard notions of cosmological evolution after the end of inflation and before the beginning of BBN. This epoch is crucial for addressing the issues of neutrino masses, baryon asymmetry, Dark Matter (DM) abundance and the moduli (gravitino) problem. We argue that within classes of realistic string compactifications as defined above, there generically exists a light modulus with a mass comparable to that of the gravitino which is typically much smaller than the Hubble parameter during inflation. Therefore, it is destabilized and generates a large late-time entropy when it decays. Thus, all known elegant mechanisms of generating the baryon asymmetry of the Universe in the literature have to take this fact into account. In this work, we find that it is still possible to naturally generate the observed baryon asymmetry of the Universe as well as light left-handed neutrino masses from a period of Affleck-Dine (AD) leptogenesis shortly after the end of inflation, in classes of realistic string constructions with a minimal extension of the MSSM below the unification scale (consisting only of right-handed neutrinos) and satisfying certain microscopic criteria described in the text. The AD mechanism has already been used to generate the baryon asymmetry in the literature; however in this work we have embedded the above mechanism within a framework well motivated from string theory and have tried to describe the epoch from the end of inflation to the beginning of BBN in a complete and self-consistent manner. The consequences of our analysis are as follows. The lightest left-handed neutrino is required to be virtually massless. The moduli (gravitino) problem can be naturally solved in this framework both within gravity and gauge mediation. The observed upper bound on the relic abundance constrains the moduli-matter and moduli-gravitino couplings since the DM is produced non-thermally within this framework. Finally, although not a definite prediction, the framework naturally allows a light right-handed neutrino and sneutrinos around the electroweak scale which could have important implications for the nature of DM as well as the LHC.

Common Origin for Neutrino Anarchy and Charged Hierarchies

The generation of exponential flavor hierarchies from extra-dimensional wave function overlaps is reexamined. We find, surprisingly, that the coexistence of anarchic fermion mass matrices with such hierarchies is intrinsic and natural to this setting. The salient features of charged fermion and neutrino masses and mixings can thereby be captured within a single framework. Both Dirac and Majorana neutrinos can be realized. Implications for a variety of weak-scale scenarios, including warped compactification and supersymmetry, are discussed. When the new weak-scale physics is sensitive to the origin of flavor structure, Dirac neutrinos are preferred.

Thermal right-handed sneutrino dark matter in theFD-term model of hybrid inflation

We compute the relic abundance of the right-handed sneutrinos in the supersymmetric F-D-term model of hybrid inflation. As well as providing a natural solution to the mu- and gravitino overabundance problems, the F-D-term model offers a new viable candidate to account for the cold dark matter in the Universe: the lightest right-handed sneutrino. In particular, the F-D-term model predicts a new quartic coupling of purely right-handed sneutrinos to the Higgs doublets that thermalizes the sneutrinos and makes them annihilate sufficiently fast to a level compatible with the current cosmic microwave background data. We analyze this scenario in detail and identify favourable regions of the parameter space within the framework of minimal supergravity, for which the lightest right-handed sneutrino becomes the thermal dark matter, in agreement with WMAP observations of cosmological inflation. Constraints derived from direct dark matter searches experiments are presented.

Right-handed sneutrino as cold dark matter of the universe

We consider the minimal supersymmetric standard model (MSSM) extended by three right-handed neutrinos. Assuming that neutrino masses are purely Dirac-type, the lightest right-handed sneutrino ν̃R can be the lightest superparticle (LSP). We discuss the possibility that the LSP ν̃R becomes dark matter of the universe, paying attention to the production of ν̃R in the early universe. This work is based on collaboration with K. Ishiwata and T. Moroi [1, 2].

Right-handed sneutrino as cold dark matter of the Universe

We consider the minimal supersymmetric standard model (MSSM) extended by introducing three right-handed (s)neutrinos to account for neutrino masses in the oscillation experiments. Assuming that the neutrino masses are purely Dirac type, the lightest right-handed sneutrino ${\stackrel{\texttildelow{}}{\ensuremath{\nu}}}_{R}$ can be the lightest superparticle (LSP), which is a good candidate of cold dark matter (CDM) of the Universe. We study the possibility of realizing ${\stackrel{\texttildelow{}}{\ensuremath{\nu}}}_{R}$-CDM, paying special attention to the production of ${\stackrel{\texttildelow{}}{\ensuremath{\nu}}}_{R}$ via decay of the next-to-lightest superparticle after its freeze-out time. It is shown that the late decay of the MSSM-LSP (the LSP among superparticles in the MSSM) can produce a sufficient amount of ${\stackrel{\texttildelow{}}{\ensuremath{\nu}}}_{R}$ to explain the observed dark matter density, and that the ${\stackrel{\texttildelow{}}{\ensuremath{\nu}}}_{R}$-CDM scenario can be realized in a wide range of parameter space. We also consider the constraint on the decay of MSSM-LSP from the big bang nucleosynthesis; we found that the case with stau being the MSSM-LSP is severely constrained.

Stop decay into right-handed sneutrino LSP at hadron colliders

Right-handed neutrinos offer us the possibility of accommodating neutrino masses. In a supersymmetric model, this implies the existence of right-handed sneutrinos. Right-handed sneutrinos are expected to be as light as other supersymmetric particles if the neutrinos are Dirac fermions, or if the lepton-number breaking scale is at (or below) the supersymmetry (SUSY) breaking scale, assumed to be around the electroweak scale. Depending on the mechanism of SUSY breaking, the lightest right-handed sneutrino may be the lightest supersymmetric particle (LSP). We consider the unique hadron collider signatures of a weak scale right-handed sneutrino LSP, assuming R-parity conservation. For concreteness, we concentrate on stop pair-production and decay at the Tevatron and the Large Hadron Collider, and briefly comment on the production and decay of other supersymmetric particles.

Preheating curvaton perturbations

We discuss the potentially important role played by preheating in certain variants of the curvaton mechanism in which isocurvature perturbations of a D-flat (and F-flat) direction become converted to curvature perturbations during reheating. We discover that parametric resonance of the isocurvature components amplifies the superhorizon fluctuations by a significant amount. As an example of these effects we develop a particle physics motivated model which involves hybrid inflation with the waterfall field N being responsible for generating the ? term, the right-handed neutrino mass scale, and the Peccei-Quinn symmetry breaking scale. The role of the curvaton field can be played either by usual Higgs field, or the lightest right-handed sneutrino. Our new results show that it is possible to achieve the correct curvature perturbations for initial values of the curvaton fields of order the weak scale. In this model we show that the prediction for the spectral index of the final curvature perturbation only depends on the mass of the curvaton during inflation, where consistency with current observational data requires the ratio of this mass to the Hubble constant to be less-than-or-equals, slant 0.3.