Decays Of Sneutrinos Research Articles

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.

Gamma-ray signals from multicomponent scalar dark matter decays

Within a multicomponent dark matter scenario, novel gamma-ray signals may arise from the decay of the heavier dark matter component into the lighter. For a scalar dark sector of this kind, the decay ϕ2→ϕ1 γ is forbidden by the conservation of angular momentum, but the decay ϕ2 → ϕ1 γγ can have a sizable or even dominant branching ratio. In this paper we present a detailed study of this decay channel. We determine the width and photon energy spectrum generated in the decay, employing an effective theory approach, and in UV complete models where the scalar dark matter components interact with heavy or light fermions. We also calculate limits on the inverse width from current data of the isotropic diffuse photon flux, both for a hierarchical and a degenerate dark matter spectrum. Finally, we briefly comment on the prospects of observing the diphoton signal from sneutrino decay in the minimal supersymmetric standard model extended with right-handed neutrino superfields (ν̃MSSM) .

Sneutrinos as mixed inflaton and curvaton

We investigate a scenario where the supersymmetric partners of two right-handed neutrinos (sneutrinos) work as mixed inflaton and curvaton, motivated by the fact that the curvaton contribution to scalar perturbations can reduce the tensor-to-scalar ratio r so that chaotic inflation models with a quadratic potential are made consistent with the experimental bound on r. After confirming that the scenario evades the current bounds on r and the scalar perturbation spectral index ns, we make a prediction on the local non-Gaussianity in bispectrum, fNL, and one in trispectrum, τNL. Remarkably, since the sneutrino decay widths are determined by the neutrino Dirac Yukawa coupling, which can be estimated from the measured active neutrino mass differences in the seesaw model, our scenario has a strong predictive power about local non-Gaussianities, as they heavily depend on the inflaton and curvaton decay rates. Using this fact, we can constrain the sneutrino mass from the experimental bounds on ns, r and fNL.

Mono-jet, -photon and -Z signals of a supersymmetric (B − L) model at the Large Hadron Collider

Search for invisible final states produced at the Large Hadron Collider (LHC) by new physics scenarios are normally carried out resorting to a variety of probes emerging from the initial state, in the form of single-jet, -photon and -$Z$ boson signatures. These are particularly effective for models of Supersymmetry (SUSY) in presence of $R$-parity conservation, owing to the presence in their spectra of a stable neutralino as dark matter candidate. We assume here as theoretical framework Supersymmetric ($B-L$) extension of the Standard Model (BLSSM), wherein a mediator for invisible decays can be $Z'$ boson. The peculiarity of the signal is thus that the final state objects carry a very large (transverse) missing energy, since the $Z'$ is naturally massive and constrained by direct searches and electro-weak precision tests to be at least in TeV scale region. Under these circumstances the efficiency in accessing the invisible final state and rejecting the standard model background is very high. This somehow compensates the rather meagre production rates. Another special feature of this invisible BLSSM signal is its composition, which is often dominated by sneutrino decays (alongside the more traditional neutrino and neutralino modes). Sensitivity of the CERN machine to these two features can therefore help disentangling the BLSSM from more popular SUSY models. We assess in this analysis the scope of the LHC in establishing the aforementioned invisible signals through a sophisticated signal-to-background simulation carried out in presence of parton shower, hadronisation and detector effects. We find that significant sensitivity exists already after 300 fb$^{-1}$ during Run 2. We find that mono-jet events can be readily accessible at the LHC, so as to enable one to claim a prompt discovery, while mono-photon and -$Z$ signals can be used as diagnostic tools of the underlying scenario.

Gravitino dark matter with constraints from Higgs boson mass and sneutrino decays

Abstract We investigate gravitino dark matter produced thermally at high temperatures and in decays of a long-lived sneutrino. We consider the Non-Universal Higgs Model and a generalized gauge mediation model, and in each case identify sneutrino LOSP regions of the parameter space consistent with the mass of the Higgs-like boson observed at the LHC. We apply relevant collider and cosmological bounds, including constraints from Big Bang Nucleosynthesis and from warm dark matter on large scale structures. Generally, we find allowed values of the reheating temperature T R below 109 GeV, i.e. somewhat smaller than the values needed for thermal leptogenesis, even with a conservative lower bound of 122 GeV on the Higgs mass. Requiring mass values closer to 126 GeV implies T R below 107 GeV and the gravitino mass less than 10 GeV.

Gravitino Dark Matter with Constraints from Higgs Boson Mass and Sneutrino Decays

We investigate gravitino dark matter produced thermally at high temperatures and in decays of a long-lived sneutrino. We consider the Non-Universal Higgs Model and a generalized gauge mediation model, and in each case identify sneutrino LOSP regions of the parameter space consistent with the mass of the Higgs-like boson observed at the LHC. We apply relevant collider and cosmological bounds, including constraints from Big Bang Nucleosynthesis and from warm dark matter on large scale structures. Generally, we find allowed values of the reheating temperature T R below 109 GeV, i.e. somewhat smaller than the values needed for thermal leptogenesis, even with a conservative lower bound of 122 GeV on the Higgs mass. Requiring mass values closer to 126 GeV implies T R below 107 GeV and the gravitino mass less than 10 GeV.

RADIATIVE PRODUCTION OF LIGHTEST NEUTRALINOS IN e+e-COLLISIONS IN SUPERSYMMETRIC GRAND UNIFIED MODELS

We study the production of the lightest neutralinos in the radiative process [Formula: see text] in supersymmetric models with grand unification. We consider models wherein the standard model (SM) gauge group SU(3)c×SU(2)L×U(1)Yis unified into the grand unified gauge groups SU(5) or SO(10). We study this process at energies that may be accessible at a future International Linear Collider (ILC). We compare and contrast the dependence of the signal cross-section on the grand unified gauge group, and different representations of the grand unified gauge group, into which the SM gauge group is unified. We carry out a comprehensive study of the radiative production process which includes higher-order QED corrections in our calculations. In addition we carry out a detailed study of the background to the signal process coming from the SM radiative neutrino production [Formula: see text], as well as from the radiative production of the scalar partners of the neutrinos (sneutrinos) [Formula: see text]. The latter can be a major supersymmetric background to the radiative production of neutralinos when the sneutrinos decay invisibly. It is likely that the radiative production of the lightest neutralinos may be a viable channel to study supersymmetric partners of the SM particles at the first stage of an ILC, where heavier sparticles may be too heavy to be produced in pairs.

Radiative neutralino production in low energy supersymmetric models. II. The case of beam polarization

We study the production of the lightest neutralinos in the radiative process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}\ensuremath{\gamma}$ in low energy supersymmetric models for the International Linear Collider energies with longitudinally polarized electron and positron beams. For this purpose we consider the case of nonminimal supersymmetric standard model as well as the case of minimal supersymmetric standard model. At the first stage of a linear collider, with $\sqrt{s}=500\text{ }\text{ }\mathrm{GeV}$, the radiative production of the lightest neutralinos may be a viable channel to study supersymmetric partners of the standard model particles, especially if the other supersymmetric particles are too heavy to be pair produced. We consider in detail the effect of beam polarization on the production cross section. We compare and contrast the dependence of the signal cross section on the parameters of the neutralino sector of the nonminimal and minimal supersymmetric standard model when the electron and positron beams are longitudinally polarized. In order to assess the feasibility of experimentally observing the radiative neutralino production process, we consider the background to this process coming from the standard model process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}$ with longitudinally polarized electron and positron beams. We also consider the supersymmetric background to the radiative neutralino production process coming from the radiative production of the scalar partners of the neutrinos (sneutrinos) ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\stackrel{\texttildelow{}}{\ensuremath{\nu}}{\stackrel{\texttildelow{}}{\ensuremath{\nu}}}^{*}\ensuremath{\gamma}$, with longitudinally polarized beams. This process can be a background to the radiative neutralino production when the sneutrinos decay invisibly.

LEPTOGENESIS FROM SOFT SUPERSYMMETRY BREAKING: SOFT LEPTOGENESIS

Soft leptogenesis is a scenario in which the cosmic baryon asymmetry is produced from a lepton asymmetry generated in the decays of heavy sneutrinos (the partners of the singlet neutrinos of the seesaw) and where the relevant sources of CP violation are the complex phases of soft supersymmetry-breaking terms. We explain the motivations for soft leptogenesis, and review its basic ingredients: the different CP-violating contributions, the crucial role played by thermal corrections, and the enhancement of the efficiency from lepton flavor effects. We also discuss the high temperature regime T > 107 GeV in which the cosmic baryon asymmetry originates from an initial asymmetry of an anomalous R-charge, and soft leptogenesis reembodies in R-genesis.

Search forR-Parity Violating Decays of Sneutrinos toeμ,μτ, andeτPairs inpp¯Collisions ats=1.96 TeV

We present a search for supersymmetric neutrino ν˜ production using the Tevatron pp¯ collision data collected with the CDF II detector and corresponding to an integrated luminosity of 1 fb−1. We focus on the scenarios predicted by the R-parity violating (RPV) supersymmetric models in which sneutrinos decay to two charged leptons of different flavor. With the data consistent with the standard model expectations, we set upper limits on σ(pp¯→ν˜)×BR(ν˜→eμ,μτ,eτ) and use these results to constrain the RPV couplings as a function of the sneutrino mass.Received 10 May 2010DOI:https://doi.org/10.1103/PhysRevLett.105.191801© 2010 The American Physical Society

Flavoured soft leptogenesis and natural values of the B term

We revisit flavour effects in soft leptogenesis relaxing the assumption of universality for the soft supersymmetry breaking terms. We find that with respect to the case in which the heavy sneutrinos decay with equal rates and equal CP asymmetries for all lepton flavours, hierarchical flavour configurations can enhance the efficiency by more than two orders of magnitude. This translates in more than three order of magnitude with respect to the one-flavour approximation. We verify that lepton flavour equilibration effects related to off-diagonal soft slepton masses are ineffective for damping these large enhancements. We show that soft leptogenesis can be successful for unusual values of the relevant parameters, allowing for $B\sim {\cal O}({\rm TeV})$ and for values of the washout parameter up to $m_{\rm eff}/m_* \sim 5\times 10^{3}$.

Three-body decays of sleptons in models with non-universal Higgs masses

We compute the three-body decays of charged sleptons and sneutrinos into other sleptons. These decays are of particular interest in SUSY-breaking models with non-universal Higgs mass parameters, where the left-chiral sleptons can be lighter than the right-chiral ones, and lighter than the lightest neutralino. We present the formulas for the three-body decay widths together with a numerical analysis in the context of gaugino-mediated SUSY breaking with a gravitino LSP.

BARYOGENESIS VIA LEFT-RIGHT ASYMMETRY GENERATED BY AFFLECK – DINE MECHANISM IN DIRAC NEUTRINO MODEL

We reconsider a baryogenesis scenario in supersymmetric standard models with Dirac neutrinos proposed by Abel and Page. We introduce intermediate scale physics to stabilize the runaway potential along a right-handed sneutrino direction. If the lightest neutrino mass is small and/or thermal effects induce early oscillation, the right amount of baryon number asymmetry can be obtained even for higher reheating temperature without entropy production. We also discuss the right-handed sneutrino decay via SU (2)R gauge interaction as a solution to the problem of dark matter overproduction.

Baryogenesis via left-right asymmetry generation by the Affleck-Dine mechanism in a Dirac neutrino model

A baryogenesis scenario in supersymmetric standard models with Dirac neutrinos proposed by Abel and Page is reconsidered, introducing intermediate scale physics to stabilize the runaway potential along a right-handed sneutrino direction. Contrary to previous results, the baryon number asymmetry can be explained even for higher reheating temperature without entropy production if the lightest neutrino mass is small and/or thermal effects induce early oscillation. We also discuss the solution to the problem of dark matter overproduction from the right-handed sneutrino decay by $\mathrm{SU}(2{)}_{R}$ gauge interaction.

Increasing the effective number of neutrinos with decaying particles

We present models of decaying particles for increasing the effective number of neutrinosNν after big bang nucleosynthesis but before the structure formation begins. We point outthat our scenario not only solves the discrepancy between the constraints onNν from these two epochs, but also provides a possible answer to deeper inconsistency in theestimation of the matter power spectrum amplitude at small scales, represented byσ8, between the WMAP and some small scale matter power measurements such as theLyman-α forest and weak lensing. We consider (a) saxion decay into two axions; (b) gravitino decayinto axino and axion; (c) Dirac right-handed sneutrino decay into gravitino andright-handed neutrino.

Cosmological constraints on the gravitino LSP scenario with a sneutrino NLSP

We study the scenario where a sneutrino is the next to lightest supersymmetric particle (NLSP) which decays into a gravitino and standard model particles. The daughter particles such as neutrinos and quarks cause electromagnetic and hadronic showers and affect big-bang nucleosynthesis. It is found that, despite a small branching ratio, four-body processes including quarks in the final state give the most stringent constraint on the sneutrino abundance for gravitino mass of 1--100 GeV. Pion production by high-energy neutrinos is important when the sneutrinos decay at $\ensuremath{\sim}1\text{ }\text{ }\mathrm{sec}$. We also discuss the thermal leptogenesis in the sneutrino NLSP scenario.

Discovery potential of radiative neutralino production at the ILC

We study radiative neutralino production e{sup +}e{sup -}{yields}{chi}-tilde{sub 1}{sup 0}{chi}-tilde{sub 1}{sup 0}{gamma} at the linear collider with longitudinally polarized beams. We consider the standard model background from radiative neutrino production e{sup +}e{sup -}{yields}{nu}{nu}{gamma}, and the supersymmetric radiative production of sneutrinos e{sup +}e{sup -}{yields}{nu}-tilde{nu}-tilde*{gamma}, which can be a background for invisible sneutrino decays. We give the complete tree-level formulas for the amplitudes and matrix elements squared. In the minimal supersymmetric standard model, we study the dependence of the cross sections on the beam polarizations, on the parameters of the neutralino sector, and on the selectron masses. We show that for b-inolike neutralinos longitudinal polarized beams enhance the signal and simultaneously reduce the background, such that statistics is significantly enhanced. We point out that there are parameter regions where radiative neutralino production is the only channel to study SUSY particles, since heavier neutralinos, charginos and sleptons are too heavy to be pair-produced in the first stage of the linear collider with {radical}(s)=500 GeV.

Leptogenesis as the source of gravitino dark matter and density perturbations

We investigate the possibility that the entropy producing decay of a right-handed sneutrino condensate can simultaneously be the source of the baryon asymmetry, of gravitino dark matter, and of cosmological density perturbations. For generic values of soft supersymmetry breaking terms in the visible sector of 1--10 TeV, condensate decay can yield the dark matter abundance for gravitinos in the mass range 1 MeV to 1 TeV, provided that the resulting reheat temperature is below ${10}^{6}\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$. The abundance of thermally produced gravitinos before and after sneutrino decay is then negligible. We consider different leptogenesis mechanisms to generate a sufficient asymmetry, and find that low-scale soft leptogenesis works most naturally at such temperatures. The condensate can easily generate sufficient density perturbations if its initial amplitude is $\ensuremath{\sim}\mathcal{O}({M}_{\mathrm{G}\mathrm{U}\mathrm{T}})$, for a Hubble expansion rate during inflation $>{10}^{9}\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$. Right-handed sneutrinos may therefore at the same time provide a source for baryogenesis, dark matter, and the seed of structure formation.

Conditions for a successful right-handed Majorana sneutrino curvaton

We consider the conditions which must be satisfied for a Majorana RH sneutrino, a massive right-handed (RH) sneutrino associated with the see-saw mechanism of Majorana neutrino masses, to play the role of the curvaton. Planck-scale suppressed non-renormalizable terms in the RH neutrino superpotential must be eliminated to a high order if the RH sneutrino curvaton is to dominate the energy density before it decays, which can be achieved via an R-symmetry which is broken to R-parity by the Giudice-Maseiro mechanism. In order to satisfy the thermalization constraint, one RH neutrino mass eigenstate must have small Yukawa couplings to the Higgs and lepton doublets, corresponding to a lightest neutrino mass m_{nu_{1}} < 10^{-3} eV. A time-dependent lepton asymmetry will be induced in the RH sneutrino condensate by the Affleck-Dine mechanism driven by SUSY breaking B-terms associated with the RH neutrino masses. Requiring that the resulting baryon asymmetry and isocurvature perturbations are acceptably small imposes an upper bound on the RH neutrino mass. We show that a scenario consistent with all constraints is obtained for a RH neutrino mass in the range 10^{2} - 10^{4} GeV when the RH sneutrino decay temperature is greater than 100 GeV and lightest neutrino mass m_{nu_{1}} approx 10^{-3} GeV. Larger RH neutrino masses are possible for smaller m_{nu_{1}}. The resulting scenario is generally consistent with a solution of the cosmic string problem of D-term inflation.

SuperWIMP gravitino dark matter from slepton and sneutrino decays

Dark matter may be composed of superWIMPs, superweakly-interacting massive particles produced in the late decays of other particles. We focus on the case of gravitinos produced in the late decays of sleptons or sneutrinos and assume they are produced in sufficient numbers to constitute all of non-baryonic dark matter. At leading order, these late decays are two-body and the accompanying energy is electromagnetic. For natural weak-scale parameters, these decays have been shown to satisfy bounds from Big Bang nucleosynthesis and the cosmic microwave background. However, sleptons and sneutrinos may also decay to three-body final states, producing hadronic energy, which is subject to even more stringent nucleosynthesis bounds. We determine the three-body branching fractions and the resulting hadronic energy release. We find that superWIMP gravitino dark matter is viable and determine the gravitino and slepton/sneutrino masses preferred by this solution to the dark matter problem. In passing, we note that hadronic constraints disfavor the possibility of superWIMPs produced by neutralino decays unless the neutralino is photino-like.