SUSY Particles Research Articles

Monophoton signals in light gravitino production at $$e^+ e^-$$ e + e - colliders

We revisit the monophoton plus missing energy signature at $$e^+e^-$$ colliders in supersymmetric (SUSY) models where the gravitino is very light. There are two possible processes which provide the signal: gravitino pair production and associated gravitino production with a neutralino, leading the monophoton final state via an additional photon radiation and via the neutralino decay, respectively. By using the superspace formalism, we construct a model that allows us to study the parameter space for the both processes. We show that the signal cross section and the photon spectra provide information on the masses of the SUSY particles as well as the SUSY breaking scale.

The latest IceCube results

The IceCube detector is unique. It uses the Antarctic glacial ice as an interaction and detection medium. An array of optical sensors observes Cherenkov light from secondary charged particles resulting from neutrino interactions. The high transparency of the ice enabled the realization of a 1km3 large detection volume in order to detect rarely interacting particles. Neutrinos are ideal probes of the deep universe because they rarely interact with matter and propagate in straight lines. Neutrinos are thought to be produced in hadronic processes at astronomical sources such as active galactic nuclei and gamma-ray bursts. IceCube aims to detect neutrinos from such astronomical sources. IceCube recently found 28 events in an energy range approximately from 50 TeV to 1 PeV. These events are not easily explained by background derived from atmospheric origin, and therefore represent the first evidence for high energy neutrinos from an extraterrestrial origin. IceCube can also perform elementary particle physics by searching for neutrinos from SUSY particles such as neutralinos and measuring atmospheric neutrino oscillations. An overview of the latest IceCube results is provided in this paper including the 28 candidate observations and the corresponding implications.

Compressed and split spectra in minimal SUSY SO(10)

The non-observation of supersymmetric signatures in searches at the Large Hadron Collider strongly constrains minimal supersymmetric models like the CMSSM. We explore the consequences on the SUSY particle spectrum in a minimal SO(10) with large D-terms and non-universal gaugino masses at the GUT scale. This changes the sparticle spectrum in a testable way and for example can sufficiently split the coloured and non-coloured sectors. The splitting provided by use of the SO(10) D-terms can be exploited to obtain light first generation sleptons or third generation squarks, the latter corresponding to a compressed spectrum scenario.

First evidence of the constrained minimal supersymmetric standard model is appearing soon

We explore the coannihilation region of the constrained minimal supersymmetric standard model (CMSSM) being consistent with current experimental/observational results. The requirements from the experimental/observational results are the 125 GeV Higgs boson mass and the relic abundances of both the dark matter and light elements, especially lithium-7. We put these requirements on the calculated values, and, thus, we obtain the allowed region. Then we give predictions to the mass spectra of the supersymmetric (SUSY) particles, the anomalous magnetic moment of the muon, the branching fractions of the $B$-meson rare decays, the direct detection of the neutralino dark matter, and the number of SUSY particles produced in a 14 TeV run at the LHC experiment. Comparing these predictions with current bounds, we show the feasibility of the test for this scenario in near future experiments.

Multiphoton signatures of goldstini at the LHC

We study models of gauge mediated SUSY breaking with more than one hidden sector. In these models the neutralino sector of the MSSM is supplemented with additional light neutral fermions, the nearly massless gravitino and the massive pseudo-goldstini. For the case where the Bino is the lightest ordinary SUSY particle, its preferred decay is to a photon and the heaviest pseudo-goldstino, which generically cascades down to lighter pseudo-goldstini, or to the gravitino, in association with photons. This gives rise to multiphoton plus missing energy signatures at the LHC. We investigate in detail simplified models where the SUSY spectrum consists of the right-handed sleptons, a Bino-like neutralino, the pseudo-goldstini and the gravitino. We compare against existing LHC searches and show that the sensitivity to our models could be significantly improved by relaxing the kinematic cuts and requiring additional final state particles. We propose inclusive searches in the final state with at least three photons plus missing energy and in the final state with at least two photons plus two leptons plus missing energy, the former being sensitive to any production mode and the latter being optimized for slepton pair production. We show that they could lead to an observation (or strong constraints) already with the data set from LHC Run I, and present prospects for LHC Run II.

Universal mass limits on gluino and third-generation squarks in the context of Natural-like SUSY spectra

In this paper, we present results based on a combination of four inclusive topology searches for supersymmetry (SUSY) from the CMS experiment, and use this to determine universal mass limits on gluino and third-generation squarks in the context of Natural-like SUSY spectra. This class of sparticle spectra is inspired by the argument of naturalness, which originates from both consideration of fine-tuning arguments, and the need to satisfy current experimental search constraints. The class of Natural-like SUSY spectra considered follows the typical Natural SUSY model made up of a gluino, third-generation squarks, and higgsino sparticles, but is extended to more complex spectra containing sleptons. We show that the limits obtained from the combination of inclusive topology searches are far more stable than those from individual searches, with respect to the assumed underlying complexity of the spectra, and hence these limits can be considered as universal mass limits on gluino and third-generation squarks, defined in the context of this broad class of Natural-like SUSY spectra. Furthermore, we present our results using a simple colour scheme that allows a straightforward interpretation of any Natural-like SUSY spectrum with our limits. Complementing the final results of the 2011 searches based on 5 fb-1 of integrated luminosity, with the first published results from 2012 searches using approximately 11 fb-1, we find that gluinos with a mass of [Formula: see text] and third-generation top and bottom squarks with masses of [Formula: see text] are excluded for low masses of the lightest SUSY particle (LSP). These limits weaken to [Formula: see text] and [Formula: see text], when the mass of the LSP is increased to several hundred GeV. Based on this result, we establish a prediction of how these limits might evolve when the full 2012 dataset is analysed, with both the CMS and ATLAS experiments combined. This outlook suggests that for low masses of the LSP, gluinos with a mass of [Formula: see text] and third-generation squarks with masses of [Formula: see text] are likely to be excluded. For high LSP masses, these limits are expected to decrease to [Formula: see text] and [Formula: see text]. Therefore, despite the fact that the LHC already probes a significant region of the SUSY parameter space, Natural SUSY scenarios based on rather stringent fine-tuning requirements may not be fully excluded by the data taken so far. This suggests that additional data is needed, to be recorded during the higher energy running of the LHC expected in 2015. The importance of combining relevant inclusive topology searches, in order to make the most universal interpretations possible, is a general recommendation for future experimental searches at the LHC.

The last vestiges of naturalness

Direct LHC bounds on colored SUSY particles now corner naturalness more than the measured value of the Higgs mass does. Bounds on the gluino are of particular importance, since it radiatively "sucks" up the stop and Higgs-up soft masses. As a result, even models that easily accommodate a 125 GeV Higgs are almost as tuned as the simplest version of SUSY, the MSSM: at best at the percent level. In this paper, we further examine how current LHC results constrain naturalness in three classes of models that may relax LHC bounds on sparticles: split families, baryonic RPV, and Dirac gauginos. In models of split families and bRPV, the bounds on the gluino are only slightly reduced, resulting in a few percent tuning. In particular, having a natural spectrum in bRPV models typically implies that tops, Ws, and Zs are easily produced in the cascade decays of squarks and gluinos. The resulting leptons and missing energy push the gluino mass limit above 1 TeV. Even when the gluino has a Dirac mass and does not contribute to the stop mass at one loop, tuning reappears in calculable models because there is no symmetry imposing the supersoft limit. We conclude that, even if sparticles are found at LHC-14, naturalness will not emerge triumphant.

Constraints on Heavy Neutrino and SUSY Parameters Derived from the Study of Neutrinoless Double Beta Decay

New constraints on the lepton number violating (LNV) parameters are derived from the analysis of the neutrinoless double beta (0νββ) decay in the hypothesis that this process would occur through the exchange of heavy neutrinos and/or SUSY particles. For derivation, we use new values of both phase space factors (PSFs) and nuclear matrix elements (NMEs) calculated with numerical codes developed recently, as well as the most recent experimental lifetimes. The NMEs are computed with a shell model (ShM) code for 48Ca, 76Ge, and 82Senuclei, while at present similar ShM results are available only for the first nucleus. We compare our results with similar ones from literature, obtained with ShM, QRPA, and IBM-2 methods, and conclude that more results are needed for a relevant analysis on the validity of NMEs associated with these decay mechanisms.

Muon g − 2 vs LHC in supersymmetric models

There is more than 3 sigma deviation between the experimental and theoretical results of the muon g-2. This suggests that some of the SUSY particles have a mass of order 100 GeV. We study searches for those particles at the LHC with particular attention to the muon g-2. In particular, the recent results on the searches for the non-colored SUSY particles are investigated in the parameter region where the muon g-2 is explained. The analysis is independent of details of the SUSY models. Future prospects of the collider searches are also discussed.

Third generation superpartners: Results from ATLAS and CMS

These proceedings discuss results from recent searches for third generation SUSY particles by the ATLAS and CMS experiments at the LHC. Analyses performed with 8 TeV data probing direct pair production of bottom and top squarks are presented.

SLAM, a Mathematica interface for SUSY spectrum generators

We present and publish a Mathematica package, which can be used to automatically obtain any numerical MSSM input parameter from SUSY spectrum generators, which follow the SLHA standard, like SPheno, SOFTSUSY, SuSeFLAV or Suspect. The package enables a very comfortable way of numerical evaluations within the MSSM using Mathematica. It implements easy to use predefined high scale and low scale scenarios like mSUGRA or mhmax and if needed enables the user to directly specify the input required by the spectrum generators. In addition it supports an automatic saving and loading of SUSY spectra to and from a SQL data base, avoiding the rerun of a spectrum generator for a known spectrum. Program summaryProgram title: SLAMCatalogue identifier: AERX_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERX_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 4387No. of bytes in distributed program, including test data, etc.: 37748Distribution format: tar.gzProgramming language: Mathematica.Computer: Any computer where Mathematica version 6 or higher is running providing bash and sed.Operating system: Linux.Classification: 11.1.External routines: A SUSY spectrum generator such as SPheno, SOFTSUSY, SuSeFLAV or SUSPECTNature of problem:Interfacing published spectrum generators for automated creation, saving and loading of SUSY particle spectra.Solution method:SLAM automatically writes/reads SLHA spectrum generator input/output and is able to save/load generated data in/from a data base.Restrictions:No general restrictions, specific restrictions are given in the manuscript.Running time:A single spectrum calculation takes much less than one second on a modern PC.

QCD corrections to quark (chromo)electric dipole moments in high-scale supersymmetry

Recent results from the LHC experiments, both for the Higgs mass measurement and the direct search for supersymmetric (SUSY) particles, might indicate that the SUSY breaking scale is much higher than the electroweak scale. Although it is difficult to investigate such a scenario at collider experiments, the measurement of the hadronic electric dipole moments is one of promising ways to detect the effects of the SUSY particles. These effects are expressed in terms of the CP-violating effective operators defined at the SUSY breaking scale, which involve quarks, gluons, photons, and gluinos. In this paper, we discuss the QCD corrections to the effective operators in the high-scale SUSY scenario. To appropriately evaluate the radiative corrections in the presence of large mass hierarchy among the SUSY particles, we exploit an effective theoretical approach based on the renormalization-group equations. As a result, it is found that the low-energy quark electric and chromoelectric dipole moments may differ from those evaluated in previous works by $ \mathcal{O} $ (100) % and $ \mathcal{O} $ (10) %, respectively.

Exotic Higgs decays in the [formula omitted] inspired SUSY models

We study the decays of the SM-like Higgs state within the E6 inspired supersymmetric (SUSY) models with exact custodial symmetry that forbids tree-level flavor-changing transitions and the most dangerous baryon and lepton number violating operators. In these models there are two states which are absolutely stable and can contribute to the dark matter density. One of them is the lightest SUSY particle (LSP) which is expected to be lighter than 1 eV forming hot dark matter in the Universe. The presence of another stable neutral state allows to account for the observed cold dark matter density. In the considered SUSY models next-to-lightest SUSY particle (NLSP) also tend to be light. We argue that the NLSP with GeV scale mass can result in the substantial branching ratio of the nonstandard decays of the lightest Higgs boson.

Non-decoupling MSSM Higgs sector and light superpartners

In the ``non-decoupling'' region of the Higgs sector in MSSM, the heavier CP-even Higgs boson (H^0) is Standard-Model-like and close to the charged Higgs bosons (H^\pm) in mass, while other neutral Higgs bosons (h^0,A^0) are lighter and near the Z mass. This scenario is consistent with the current Higgs search limits, although the improved sensitivity for a light charged Higgs boson search t -> H^+ b may result in certain degree of tension. We demonstrate that it can pass the stringent flavor constraints, provided there are other light SUSY particles to contribute in the loop induced processes. In turn, the non-decoupling Higgs sector implies the existence of light (left-handed) stop, sbottom and Wino-like gauginos, with mass all below 250 GeV. These light super-partners can still escape the current SUSY searches at the LHC. Dedicated searches for soft decay products should be devised for the LHC experiments to improve the searching sensitivity. The ILC would be able to cover the full spectrum region. The solutions for the viable SUSY parameters result from subtle cancellations and are often missed by the generic multiple dimensional scans, highlighting the importance of theoretical guidance in search for such special cases.

The string origin of SUSY flavor violation

We argue that in large classes of string compactifications with a MSSM-like structure substantial flavor violating SUSY-breaking soft terms are generically induced. We specify to the case of flavor dependent soft-terms in type IIB/F-theory SU(5) unified models, although our results can be easily extended to other settings. The Standard Model (SM) degrees of freedom reside in a local system of 7-branes wrapping a 4-fold S in the extra dimensions. It is known that in the presence of closed string 3-form fluxes SUSY-breaking terms are typically generated. We explore the generation dependence of these soft terms and find that non-universalities arise whenever the flux varies over the 4-fold S. These non-universalities are parametrically suppressed by (M GUT /M Pl)1/3. They also arise in the case of varying open string fluxes, in this case parametrically suppressed by $ \alpha_{\mathrm{GUT}}^{{{1 \left/ {2} \right.}}} $ . For a standard unification scheme with M GUT ≃ 1016 GeV and α GUT ≃ 1/24 these suppressions are very mild. Although limits from the kaon mass difference Δm K are easily obeyed for squark masses above the present LHC limits, constraints from the CP-violation parameter ϵ K imply squark masses in the multi-TeV region. The constraints from BR(μ → eγ) turn out to be the strongest ones, with slepton masses of order ~ 10 TeV or heavier required to obey the experimental limits. These sfermion masses are consistent with the observed large value m H ≃ 126 GeV of the Higgs mass. We discuss under what conditions such strong limits may be relaxed allowing for SUSY particle production at LHC.

Recent result of the AMS-02 experiment and decaying gravitino dark matter in gauge mediation

The AMS-02 collaboration has recently reported an excess of cosmic-ray positron fractions, which is consistent with previous results at PAMELA and Fermi-LAT experiments. The result indicates the existence of new physics phenomena to provide the origin of the energetic cosmic-ray positron. We pursue the possibility that the enhancement of the positron fraction is due to the decay of gravitino dark matter. We discuss that such a scenario viably fits into the models in which the soft SUSY breaking parameters are dominantly from gauge-mediation mechanism with superparticle masses of around 10 TeV. Our scenario is compatible with ~126 GeV Higgs boson, negative searches for SUSY particles, and non-observation of anomalous FCNC processes. We also point out that the scenario will be tested in near future by measuring the electric dipole moment of the electron and the lepton flavor violating decay of the muon.

Supersymmetric heavy Higgs bosons at the LHC

The search for heavy Higgs bosons is an essential step in the exploration of the Higgs sector and in probing the supersymmetric parameter space. This paper discusses the constraints on the ${M}_{A}$ and $\mathrm{tan}\ensuremath{\beta}$ parameters derived from the bounds on the different decay channels of the neutral $H$ and $A$ bosons accessible at the LHC, in the framework of the phenomenological minimal supersymmetric extension of the standard model. The implications from the present LHC results and the expected sensitivity of the 14 TeV data are discussed in terms of the coverage of the [${M}_{A}\ensuremath{-}\mathrm{tan}\ensuremath{\beta}$] plane. New channels becoming important at 13 and 14 TeV for low values of $\mathrm{tan}\ensuremath{\beta}$ are characterized in terms of their kinematics and the reconstruction strategies. The effect of QCD systematics, SUSY loop effects and decays into pairs of SUSY particles on these constraints are discussed in details.

One-loop on-shell renormalization of MSSM vertexes

The on-shell renormalization scheme for electroweak theory is well studied in the standard model (SM), but a consistent on-shell renormalization scheme for the minimal supersymmetric standard model (MSSM) is still unknown. In the MSSM, we study the on-shell scheme for three vertexes: and , with virtual SUSY particles (chargino, sneutrino, neutralino and slepton) at one-loop order. Instead of the amplitude of a single triangle diagram, the sum of the amplitude of triangle diagrams belonging to one suit can be renormalized in the on-shell scheme. One suit points out that the internal virtual particles are consistent. The zero-momentum scheme is also used for the renormalization. The two schemes can make the renormalized results decoupled, and in the MSSM some of the special characters of the on-shell scheme are shown. This work is propitious in completing the on-shell renormalization scheme in the MSSM.

Focus point in gaugino mediation — Reconsideration of the fine-tuning problem

We reconsider the fine-tuning problem in SUSY models, motivated by the recent observation of the relatively heavy Higgs boson and non-observation of the SUSY particles at the LHC. Based on this thought, we demonstrate a focus point-like behavior in a gaugino mediation model, and show that the fine-tuning is indeed reduced to about 2% level if the ratio of the gluino mass to wino mass is about 0.4 at the GUT scale. We show that such a mass ratio may arise naturally in a product group unification model without the doublet–triplet splitting problem. This fact suggests that the fine-tuning problem crucially depends on the physics at the high energy scale.

Direct search of dark matter in high-scale supersymmetry

We study direct detection of dark matter in supersymmetric (SUSY) model where most of SUSY particles have very high-scale masses beyond the weak scale. In the scenario, Wino-like or Higgsino-like neutralino is a good candidate for the dark matter in the universe. The neutralino scatters off nuclei by a Higgs-boson exchange diagram and also electroweak loop diagrams. It is found that the elastic-scattering cross section with nuclei is enhanced or suppressed due to constructive or deconstructive interference among the diagrams. Such a cross section is within the reach of future experiment in some parameter region.