R-parity Violation Research Articles

Charged lepton flavour violation at the CMS experiment

Charged lepton flavour violation (CLVF) processes can be directly related to neutrino masses and mixing and anomalous muon magnetic moment and therefore are very promising to find evidence for physics beyond the Standard Model (BSM). At CMS several searches for flavour violation have been performed in different channels and final state topologies. In particular they focussed on narrow resonances in same-sign dilepton mass spectra analyses, on heavy neutrinos with and without additional right-handed W bosons and on leptonic R-parity violating (RPV) supersymmetry (SUSY) searches. In none of these cases evidence of new physics BSM has been found and the relative exclusion limits on the cross-sections of these new processes have been placed.

Probing L-violating coupling via sbottom resonance production at the LHeC

We investigate the resonant production of the lighter sbottom at the proposed Large Hadron Electron Collider (LHeC) and its subsequent decay into e- + jet final state, under the single coupling dominance hypothesis in the framework of the R-parity-violating (RPV) minimal supersymmetric Standard Model (MSSM). It is concluded that the LHeC running at the high electron beam energy configuration of Ee = 150 GeV would provide excellent opportunities to search for the sbottom resonance and probe the lepton-number-violating [Formula: see text]-type Yukawa interaction. With about 1 fb-1 integrated luminosity expected in Ee = 150 GeV e-p collision at the LHeC, either the lighter sbottom RPV resonance could be directly detected up to 1 TeV, or the L-violating coupling [Formula: see text] could be constrained at an unprecedented level of precision compared with all the knowledge derived from indirect measurements.

Flavor and collider signatures of asymmetric dark matter

We consider flavor constraints on, and collider signatures of, asymmetric dark matter (ADM) via higher dimension operators. In the supersymmetric models we consider, $R$-parity-violating (RPV) operators carrying $B\ensuremath{-}L$ interact with $n$ dark matter particles $X$ through an interaction of the form $W={X}^{n}{\mathcal{O}}_{B\ensuremath{-}L}$, where ${\mathcal{O}}_{B\ensuremath{-}L}=q\ensuremath{\ell}{d}^{c}$, ${u}^{c}{d}^{c}{d}^{c}$, $\ensuremath{\ell}\ensuremath{\ell}{e}^{c}$. This interaction ensures that the lightest ordinary supersymmetric particle is unstable to decay into the $X$ sector, leading to a higher multiplicity of final state particles and reduced missing energy at a collider. Flavor-violating processes place constraints on the scale of the higher dimension operator, impacting whether the LOSP decays promptly. While the strongest limitations on RPV from $n\ensuremath{-}\overline{n}$ oscillations and proton decay do not apply to ADM, we analyze the constraints from meson mixing, $\ensuremath{\mu}\ensuremath{-}e$ conversion, $\ensuremath{\mu}\ensuremath{\rightarrow}3e$ and $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$. We show that these flavor constraints, even in the absence of flavor symmetries, allow parameter space for prompt decay to the $X$ sector, with additional jets and leptons in exotic flavor combinations. We study the constraints from existing 8 TeV LHC Supersymmetry (SUSY) searches with (i) 2--6 jets plus missing energy and (ii) 1--2 leptons, 3--6 jets plus missing energy, comparing the constraints on ADM-extended supersymmetry with the usual supersymmetric simplified models.

Constraining New Physics with D meson decays

Latest Lattice results on D form factors evaluation from first principles show that the Standard Model (SM) branching ratios prediction for the leptonic Ds→ℓνℓ decays and the semileptonic SM branching ratios of the D0 and D+ meson decays are in good agreement with the world average experimental measurements. It is possible to disprove New Physics hypothesis or find bounds over several models beyond the SM. Using the observed leptonic and semileptonic branching ratios for the D meson decays, we performed a combined analysis to constrain non-standard interactions which mediate the cs¯→lν¯ transition. This is done either by a model-independent way through the corresponding Wilson coefficients or in a model-dependent way by finding the respective bounds over the relevant parameters for some models beyond the Standard Model. In particular, we obtain bounds for the Two Higgs Doublet Model Type-II and Type III, the Left–Right model, the Minimal Supersymmetric Standard Model with explicit R-parity violation and Leptoquarks. Finally, we estimate the transverse polarization of the lepton in the D0 decay and we found it can be as high as PT=0.23.

Transition magnetic moment of Majorana neutrinos in the μνSSM

The nonzero vacuum expectative values of sneutrinos induce spontaneously R-parity and lepton number violation, and generate three tiny Majorana neutrino masses through the seesaw mechanism in the $\mu\nu$SSM, which is one of Supersymmetric extensions beyond Standard Model. Applying effective Lagrangian method, we study the transition magnetic moment of Majorana neutrinos in the model here. Under the constraints from neutrino oscillations, we consider the two possibilities on the neutrino mass spectrum with normal or inverted ordering.

Flavored dark matter and R-parity violation

AbstractMinimal Flavor Violation offers an alternative symmetry rationale to R-parity conservation for the suppression of proton decay in supersymmetric extensions of the Standard Model. The naturalness of such theories is generically under less tension from LHC searches than R-parity conserving models. The flavor symmetry can also guarantee the stability of dark matter if it carries flavor quantum numbers. We outline general features of supersymmetric flavored dark matter (SFDM) models within the framework of MFV SUSY. A simple model of top flavored dark matter is presented. If the dark matter is a thermal relic, then nearly the entire parameter space of the model is testable by upcoming direct detection and LHC searches.

Overview of SUSY results from the ATLAS experiment

The search for Supersymmetric extensions of the Standard Model (SUSY) remains a hot topic in high energy phisycs in the light of the discovery of the Higgs boson with mass of 125 GeV. Supersymmetric particles can cancel out the quadratically- divergent loop corrections to the Higgs boson mass and can explain presence of Dark Matter in the Universe. Moreover, SUSY can unify the gauge couplings of the Standard Model at high energy scales. Under certain theoretical assumptions, some of the super- symmetric particles are preferred to be lighter than one TeV and their discovery can thus be accessible at the LHC. The recent results from searches for Supersymmetry with the ATLAS experiment which utilized up to 21 fb −1 of proton-proton collisions at a center of mass energy of 8 TeV are presented. These searches are focused on inclusive production of squarks and gluinos, on production of third generations squarks, and on electroweak production of charginos and neutralinos. Searches for long-lived particles and R-parity violation are also summarized in the document.

Probing neutrino physics at LHC throughR-parity breaking supersymmetry

R-parity conservation is an ad-hoc assumption in the most popular versions of supersymmetric scenarios. Hence R-parity violation (RPV) not only is allowed but, if induced by bilinear terms (bRPV), it also provides an explanation for the observed neutrino masses and mixing. Here bRPV models are discussed, giving emphasis on the $\mu$-from-$\nu$ supersymmetric standard model, which is characterised by a rich Higgs sector that easily accommodates a 125-GeV Higgs boson. The phenomenology of such models at the Large Hadron Collider is reviewed and some recent results obtained by LHC experiments are presented. The possibility to extend such analyses to probe bRPV scenarios with a gravitino dark matter candidate is also explored.

Highlights from SUSY searches with ATLAS

Supersymmetry (SUSY) is one of the most relevant scenarios of new physics searched by the ATLAS experiment at the CERN Large Hadron Collider. In this writeup the principal search strategies employed by ATLAS are outlined and the most recent results for analyses targeting SUSY discovery are discussed. A wide range of signatures is covered motivated by various theoretical scenarios and topologies: strong production, third-generation fermions, long-lived particles and R-parity violation, among others. The results are based on up to ~5 fb-1 of data recorded during 2010-2011 at sqrt(s) = 7 TeV centre-of-mass energy by the ATLAS experiment at the LHC.

Large Hadron Collider constraints on a light baryon-number violating sbottom coupling to a top and a light quark

We investigate a model of R-parity violating (RPV) supersymmetry in which the right-handed sbottom is the lightest supersymmetric particle, and a baryon number violating coupling involving a top is the only non-negligible RPV coupling. This model evades proton decay and flavour constraints. We consider in turn each of the couplings lambda"_{313} and lambda"_{323} as the only non-negligible RPV coupling, and we recast two recent Large Hadron Collider (LHC) measurements and searches (CMS top transverse momentum p_T(t) spectrum and ATLAS multiple jet resonance search) in the form of constraints on the mass-coupling parameter planes. We delineate a large region in the parameter space of the mass of the sbottom (m_{b_R}) and the lambda"_{313} coupling that is ruled out by the measurements, as well as a smaller region in the parameter space of m_{b_R} and lambda"_{323}. A certain region of the m_{b_R}-lambda"_{313} parameter space was previously found to successfully explain the anomalously large ttbar forward backward asymmetry measured by Tevatron experiments. The entire region is excluded at the 95% CL by CMS measurements of the top p_T spectrum. We also present p_T(ttbar) distributions of the forward-backward asymmetry for this model.

Pulling out all the stops: searching for RPV SUSY with stop-jets

If the lighter stop eigenstate decays directly to two jets via baryonic R-parity violation, it could have escaped existing LHC and Tevatron searches in four-jet events, even for masses as small as 100 GeV. In order to recover sensitivity in the face of increasingly harsh trigger requirements at the LHC, we propose a search for stop pairs in the highly-boosted regime, using the approaches of jet substructure. We demonstrate that the four-jet triggers can be completely bypassed by using inclusive jet-H_T triggers, and that the resulting QCD continuum background can be processed by substructure methods into a featureless spectrum suitable for a data-driven bump-hunt down to 100 GeV. We estimate that the LHC 8 TeV run is sensitive to 100 GeV stops with decays of any flavor at better than 5-sigma level, and could place exclusions up to 300 GeV or higher. Assuming Minimal Flavor Violation and running a b-tagged analysis, exclusion reach may extend up to nearly 400 GeV. Longer-term, the 14 TeV LHC at 300/fb could extend these mass limits by a factor of two, while continuing to improve sensitivity in the 100 GeV region.

Unique R-parity violating sneutrino exchange signatures at e + e − linear colliders with polarized beams

We examine the possibility of uniquely identifying the indirect effects of s-channel R-parity violation sneutrino exchange against other kinds of new physics that can be parametrized by the four-fermion contact interactions, by means of double polarization asymmetry at the International Liner Collider with both e+e− beams being polarized.

Bs,d0→μμ¯andB→Xsγin theR-parity violating MSSM

The recent measurements of $B_s^0 \to \mu\bar{\mu}$ decay candidates at the LHC consistent with the standard model rate, and the improving upper limits for $B_d^0 \to \mu\bar{\mu}$ can strongly constrain beyond the standard model physics. For example, in supersymmetric models with broken R-parity (RpV), they restrict the size of the new couplings. We use the combination of the public software packages SARAH and SPheno to derive new bounds on several combinations of R-parity violating couplings. We improve existing limits for the couplings which open tree-level decay channels and state new limits for combinations which induce loop contributions. This is the first study which performs a full one-loop analysis of these observables in the context of R-parity violation. It turns out that at one-loop despite the strong experimental limits only combinations of R-parity violating couplings are constrained which include third generation fermions. We compare our limits with those obtained via $B\to X_s\gamma$ and discuss the differences.

Antiproton limits on decaying gravitino dark matter

We derive 95 % CL lower limits on the lifetime of decaying dark matter in the channels Zν, Wℓ and hν using measurements of the cosmic-ray antiproton flux by the PAMELA experiment. Performing a scan over the allowed range of cosmic-ray propagation parameters we find lifetime limits in the range of 8 × 1028 s to 5 × 1025 s for dark matter masses from roughly 100 GeV to 10 TeV. We apply these limits to the well-motivated case of gravitino dark matter in scenarios with bilinear violation of R-parity and find a similar range of lifetime limits for the same range of gravitino masses. Converting the lifetime limits to constraints on the size of the R-parity violating coupling we find upper limits in the range of 10−8 to 8 × 10−13.

R-broken SUSY Standard Model with right-handed neutrino

We consider the supersymmetric extension of the Standard Model with neutrino Yukawa interactions and R-parity violation. We found that R-parity breaking term λiν¯iHuHd leads to an additional F-type contribution to the Higgs scalar potential, and thus to the masses of supersymmetric Higgs bosons. The most interesting consequence is the modification of the tree-level expression for the lightest neutral supersymmetric Higgs boson mass. It appears that due to this contribution the tree bound on the lightest Higgs mass may be shifted upwards, thus taking into account radiative corrections might open the part of the model parameter space consistent with the observation of the Higgs boson at LHC, which is not natural in the MSSM. We also calculate one-loop corrections to physical neutrino masses in case of neutrino-neutralino mixing and discuss the influence of this mass shift on parameter constraints.

The same-sign top signature of R-parity violation

Abstract Baryonic R-parity violation could explain why low-scale supersymmetry has not yet been discovered at colliders: sparticles would be hidden in the intense hadronic activity. However, if the known flavor structures are any guide, the largest baryon number violating couplings are those involving the top/stop, so a copious production of same-sign top-quark pairs is in principle possible. Such a signal, with its low irreducible background and efficient identification through same-sign dileptons, provides us with tell-tale signs of baryon number violating supersymmetry. Interestingly, this statement is mostly independent of the details of the supersymmetric mass spectrum. So, in this paper, after analyzing the sparticle decay chains and lifetimes, we formulate a simplified benchmark strategy that covers most supersymmetric scenarios. We then use this information to interpret the samesign dilepton searches of CMS, draw approximate bounds on the gluino and squark masses, and extrapolate the reach of the future 14 TeV runs.

A collective breaking of R-parity

Supersymmetric theories with an R-parity generally yield a striking missing energy signature, with cascade decays concluding in a neutralino that escapes the detector. In theories where R-parity is broken the missing energy is replaced with additional jets or leptons, often making traditional search strategies ineffective. Such R-parity violation is very constrained, however, by resulting B and L violating signals, requiring couplings so small that LSPs will decay outside the detector in all but a few scenarios. In theories with additional matter fields, R-parity can be broken collectively, such that R-parity is not broken by any single coupling, but only by an ensemble of couplings. Cascade decays can proceed normally, with each step only sensitive to one or two couplings at a time, but B and L violation requires the full set, yielding a highly suppressed constraint. s-channel production of new scalar states, typically small for standard RPV, can be large when RPV is broken collectively. While missing energy is absent, making these models difficult to discover by traditional SUSY searches, they produce complicated many object resonances (MORes), with many different possible numbers of jets and leptons. We outline a simple model and discuss its discoverability at the LHC.

New physics contribution toBs→μ+μ−within R-parity violating supersymmetric models

We re-visit the problem of New Physics (NP) contribution to the branching ratio of the $B_s \to \mu^+ \mu^-$ decay in light of the recent observation of this decay by LHCb. We consider R-parity violating (RPV) supersymmetric models as a primary example - recently one has reported stringent constraints on the products of the RPV coupling constants that account for the $B_s \to \mu^+ \mu^-$ transition at the tree level. We argue that despite the LHCb measurement of the $B(B_s \to \mu^+ \mu^-)$ is in a remarkable agreement with the Standard Model (SM) prediction, there is still room for a significant New Physics contribution to the $B(B_s \to \mu^+ \mu^-)$, as the sign of the $B_s \to \mu^+ \mu^-$ transition amplitude may be opposite to that of the Standard Model; alternatively the amplitude may have a large phase. We conduct our analysis mainly for the case of real RPV couplings. We find that taking into account the scenario with the sign flip of the $B_s \to \mu^+ \mu^-$ amplitude (as compared to that of the SM) makes the bounds on the RPV coupling products significantly weaker. Also, we discuss briefly how our results are modified if the RPV couplings have large phases. In particular, we examine the dependence of the derived bounds on the phase of the NP amplitude.

Single-scale natural SUSY

We consider the prospects for natural SUSY models consistent with current data. Recent constraints make the standard paradigm unnatural so we consider what could be a minimal extension consistent with what we now know. The most promising such scenarios extend the MSSM with new tree-level Higgs interactions that can lift its mass to at least 125 GeV and also allow for flavor-dependent soft terms so that the third generation squarks are lighter than current bounds on the first and second generation squarks. We argue that a common feature of almost all such models is the need for a new scale near 10 TeV, such as a scale of Higgsing or confinement of a new gauge group. We consider the question whether such a model can naturally derive from a single mass scale associated with supersymmetry breaking. Most such models simply postulate new scales, leaving their proximity to the scale of MSSM soft terms a mystery. This coincidence problem may be thought of as a mild tuning, analogous to the usual mu problem. We find that a single mass scale origin is challenging, but suggest that a more natural origin for such a new dynamical scale is the gravitino mass, m_{3/2}, in theories where the MSSM soft terms are a loop factor below m_{3/2}. As an example, we build a variant of the NMSSM where the singlet S is composite, and the strong dynamics leading to compositeness is triggered by masses of order m_{3/2} for some fields. Our focus is the Higgs sector, but our model is compatible with a light stop (with the other generation squarks heavy, or with R-parity violation or another mechanism to hide them from current searches). All the interesting low-energy mass scales, including linear terms for S playing a key role in EWSB, arise dynamically from the single scale m_{3/2}. However, numerical coefficients from RG effects and wavefunction factors in an extra dimension complicate the otherwise simple story.

AMS-02 positrons from decaying Wino in the pure gravity mediation model

The AMS-02 collaboration has recently reported an excess of the cosmic-ray positron fraction, which turned out to be consistent with previous results reported by the PAMELA and Fermi-LAT collaborations. A decaying dark matter with the mass around 1 TeV can be responsible for the excess of the positron fraction when it is interpreted as a dark matter signal. Interestingly, the pure gravity mediation model provides such a dark matter, namely an almost pure neutral wino dark matter, when a tiny R-parity violation through $LLE^c$ interactions is introduced. We show that the decaying wino dark matter well reproduces the energy spectrum of the fraction with being consistent with constraints from cosmic-ray anti-proton and gamma-ray observations.