Minimal Supergravity Model Research Articles

Constraining anR-parity violating supergravity model with the Higgs-induced Majorana neutrino magnetic moments

It is well known that $R$-parity violating supersymmetric models predict a nonzero magnetic moment for neutrinos. In this work we study the Majorana neutrino transition magnetic moments within an RpV modified minimal supergravity model. Specifically, we discuss the contributions coming from the charged Higgs bosons, Higgsinos, leptons, sleptons, charged gauge bosons, and charginos. We use the experimental results from the MUNU Collaboration to restrict the model's parameter space. A comparison with two other types of contributions (only trilinear RpV couplings and trilinear plus neutrino-neutralino mixing) is also presented. We have found that the presently discussed processes dominate significantly, exceeding in some cases even the experimental limits.

LHC discovery potential for supersymmetry withs=7 TeVand5–30 fb−1

We extend our earlier results delineating the supersymmetry (SUSY) reach of the CERN Large Hadron Collider operating at a centre-of-mass energy \sqrt{s}=7 TeV to integrated luminosities in the range 5 - 30 fb^{-1}. Our results are presented within the paradigm minimal supergravity model (mSUGRA or CMSSM). Using a 6-dimensional grid of cuts for the optimization of signal to background ratio -- including missing E_T-- we find for m(gluino) \sim m(squark) an LHC 5\sigma SUSY discovery reach of m(gluino) \sim 1.3,\ 1.4,\ 1.5 and 1.6 TeV for 5, 10, 20 and 30 fb^{-1}, respectively. For m(squark)>> m(gluino), the corresponding reach is instead m(gluino)\sim 0.8,\ 0.9,\ 1.0 and 1.05 TeV, for the same integrated luminosities.

Prospects for Higgs boson searches with the tribottom channel in unified supersymmetric models

We investigate the prospects for the discovery of a neutral Higgs boson produced in association with a $b$ quark, followed by the Higgs decay into a pair of bottom quarks, $pp \to b\phi^0 \to b b\bar{b} +X$, at the CERN Large Hadron Collider (LHC) within the framework of unified supersymmetric models. The Higgs boson $\phi^0$ can be a heavy scalar $H^0$ or a pseudoscalar $A^0$. Furthermore, this direct discovery channel is compared with the indirect Higgs searches in the rare decay $B_s \to \mu^+\mu^-$ at hadron colliders. Promising results are found for the minimal supergravity (mSUGRA) model, the anomaly mediated supersymmetry breaking (AMSB) model, and the gauge mediated supersymmetry breaking (GMSB) model. We find that the indirect search for $B(B_s \to \mu^+\mu^-) \ge 5\times 10^{-9}$ is complementary to the direct search for $b\phi^0 \to bb\bar{b}$ with $\sqrt{s} = 14$ TeV and an integrated luminosity ($L$) of 300 fb$^{-1}$. In the AMSB and GMSB models, $b\phi^0 \to bb\bar{b}$ with $L = 300$ fb$^{-1}$ covers a larger area in the parameter space than $B(B_s \to \mu^+\mu^-) \ge 5\times 10^{-9}$. In addition, we present constraints from $b \to s\gamma$ and muon anomalous dipole moment ($\Delta a_\mu$) on the parameter space.

Exploring neutralino dark matter resonance annihilation viabA,bH→bμ+μ−at the LHC

One of the main channels which allows for a large rate of neutralino dark matter annihilation in the early Universe is via the pseudoscalar Higgs A-resonance. In this case, the measured dark matter abundance can be obtained in the minimal supergravity (mSUGRA) model when tan(beta)\sim 50 and 2m_{\tz_1}\sim m_A. We investigate the reaction pp\to b\phi\to b\mu^+\mu^- +X (where \phi =A or H) at the CERN LHC where requiring the tag of a single b-jet allows for amplification of the signal-to-background ratio. The rare but observable Higgs decay to muon pairs allows for a precise measurement of the Higgs boson mass and decay width. We evaluate signal and background using CalcHEP, with muon energy smearing according to the CMS detector. We find that the Higgs width (\Gamma_A) can typically be determined with the accuracy up to \sim 8% (\sim 17%) for m_A\sim 400 (600) GeV assuming 10^3 fb^{-1} of integrated luminosity. Therefore, the pp\to b\phi\to b\mu^+\mu^- +X process provides a unique possibility for direct \Gamma_A measurement at the LHC. While the Higgs width is correlated with the parameter \tan\beta for a given value of m_A, extracting \tan\beta is complicated by an overlap of the A and H peaks, radiative corrections to the b and \tau Yukawa couplings, and the possibility that SUSY decay modes of the Higgs may be open. In the case where a dilepton mass edge from \tz_2\to\ell^+\ell^-\tz_1 is visible, it should be possible to test the relation that 2m_{\tz_1}\sim m_A.

Low mass neutralino dark matter in minimal supergravity and more general models in the light of LHC data

The $b\ensuremath{\tau}j\mathrm{E\ensuremath{\llap{\not\;}}}T$ signal at the ongoing LHC experiments is simulated with Pythia in the minimal supergravity (mSUGRA) and other models of supersymmetry (SUSY) breaking. Special attention is given to the compatibility of this signature with the low mass neutralino dark matter (LMNDM) scenario consistent with the Wilkinson Microwave Anisotropy Probe data. In the mSUGRA model the above signal as well as the LMNDM scenario are strongly disfavored due to the constraints from the ongoing SUSY searches at the LHC. This tension, however, originates from the model dependent correlations among the parameters in the strong and electroweak sectors of mSUGRA. That there is no serious conflict between the LMNDM scenario and the LHC data is demonstrated by constructing generic phenomenological models such that the strong sector is unconstrained or mildly constrained by the existing LHC data and parameters in the electroweak sector, unrelated to the strong sector, yield dark matter relic density consistent with the Wilkinson Microwave Anisotropy Probe data. The proposed models, fairly insensitive to the conventional SUSY searches in the $\mathrm{\text{jets}}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$ and other channels, yield observable signal in the suggested channel for $\mathcal{L}\ensuremath{\gtrsim}1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data. They are also consistent with the LMNDM scenario and can be tested by the direct dark matter search experiments in the near future. Some of these models can be realized by nonuniversal scalar and gaugino masses at the grand unified theory scale.

The MSSM confronts the precision electroweak data and the muon g − 2

We update the electroweak study of the predictions of the Minimal Supersymmetric Standard Model (MSSM) including the recent results on the muon anomalous magnetic moment, the weak boson masses, and the final precision data on the Z boson parameters from LEP and SLC. We find that the region of the parameter space where the slepton masses are a few hundred GeV is favored from the muon g-2 for \tan\beta \ltsim 10, whereas for \tan\beta \simeq 50 heavier slepton mass up to \sim 1000 GeV can account for the reported 3.2 \sigma difference between its experimental value and the Standard Model (SM) prediction. As for the electroweak measurements, the SM gives a good description, and the sfermions lighter than 200 GeV tend to make the fit worse. We find, however, that sleptons as light as 100 to 200 GeV are favored also from the electroweak data, if we leave out the jet asymmetry data that do not agree with the leptonic asymmetry data. We extend the survey of the preferred MSSM parameters by including the constraints from the b \to s \gamma transition, and find favorable scenarios in the minimal supergravity, gauge-, and mirage-mediation models of supersymmetry breaking.

Discovery potential of selectron or smuon as the lightest supersymmetric particle at the LHC

We investigate the LHC discovery potential of $R$-parity violating supersymmetric models with a right-handed selectron or smuon as the lightest supersymmetric particle. These particles arise naturally in $R$-parity violating minimal supergravity models. We classify the hadron collider signatures and perform for the first time within these models a detailed signal over background analysis. We develop an inclusive three-lepton search and give prospects for a discovery at a center-of-mass energy of $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ as well as $\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}$. There are extensive parameter regions which the LHC can already test with $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ and an integrated luminosity of $1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. We also propose a method for the mass reconstruction of the supersymmetric particles within our models at $\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}$.

What if the LHC does not find supersymmetry in thes=7TeV run?

We investigate the implications for supersymmetry from an assumed absence of any signal in the first period of LHC data taking at 7 TeV center-of-mass energy and with 1 to 7 fb^(-1) of integrated luminosity. We consider the zero-lepton plus four jets and missing transverse energy signature, and perform a combined fit of low-energy measurements, the dark matter relic density constraint and potential LHC exclusions within a minimal supergravity model. A non-observation of supersymmetry in the first period of LHC data taking would still allow for an acceptable description of low-energy data and the dark matter relic density in terms of minimal supergravity models, but would exclude squarks and gluinos with masses below 1 TeV.

Double Charm Decays of B Mesons in mSUGRA Model

Based on the low energy effective Hamiltonian with naive factorization, we calculate the branching ratios (BRs) and CP asymmetries (CPAs) for the twenty three double charm decays B/Bs → D(*)(s)D(*)(s) in both the standard model (SM) and the minimal supergravity (mSUGRA) model. Within the considered parameter space, we find that (a) the theoretical predictions for the BRs, CPAs and the polarization fractions in the SM and the mSUGRA model are all consistent with the currently available data within ±2σ errors; (b) For all the considered decays, the supersymmetric contributions in the mSUGRA model are very small, less than 7% numerically. It may be difficult to observe so small SUSY contributions even at LHC.

NEW CONSTRAINTS ON DARK MATTER FROM CMS AND ATLAS DATA

Constraints on dark matter from the first CMS and ATLAS SUSY searches are investigated. It is shown that within the minimal supergravity model, the early search for supersymmetry at the LHC has depleted a large portion of the signature space in dark matter direct detection experiments. In particular, the prospects for detecting signals of dark matter in the XENON and CDMS experiments are significantly affected in the low neutralino mass region. Here the relic density of dark matter typically arises from slepton coannihilations in the early universe. In contrast, it is found that the CMS and ATLAS analyses leave untouched the Higgs pole and the Hyperbolic Branch/Focus Point regions, which are now being probed by the most recent XENON results. Analysis is also done for supergravity models with non-universal soft breaking where one finds that a part of the dark matter signature space depleted by the CMS and ATLAS cuts in the minimal SUGRA case is repopulated. Thus, observation of dark matter in the LHC depleted region of minimal supergravity may indicate non-universalities in soft breaking.

Supersymmetry signals with small and large trilinear couplings at the LHC 7 TeV runs and neutralino dark matter

We propose the signal $1b+1l+N_j+\etslash$ along with appropriate selection criteria for the LHC 7 TeV run, where the number of jets $(N_j)$ is $\ge$ 2 or 4. These signals can complement the canonical $Jets + \etslash$ signature since they are sensitive to the trilinear soft breaking parameter $(A_0)$ and low values of the parameter tan$\beta$ in the minimal supergravity (mSUGRA) model. A large region of this mSUGRA parameter space within the reach of the ongoing experiments at the LHC is disfavoured by the bound on the lightest Higgs boson mass ($m_h \ge 114.4 $ GeV) unless $A_0$ has moderate to large negative values. Interestingly this parameter space with $A_0 \ne 0$ is also consistent with the observed dark matter relic density. A natural consequence of large $A_0$ is the existence of a light top squark ($\lstop$). The proposed signals primarily stem from direct $\lstop \lstop^*$ production and/or $\tilde g \ra \tilde t_{1} t $, if all squark-gluino events are considered. A thorough analysis of the signals and the corresponding backgrounds are presented using the event generator Pythia. We finally compare the signal size for $A_0 = 0$ and $A_0 \ne 0$.

DISCRIMINATION OF SUSY BREAKING MODELS USING SINGLE-PHOTON PROCESSES AT FUTURE e+e-LINEAR COLLIDERS

We examine the single-photon processes in the framework of supersymmetric models at future e+e-linear colliders. According to the recent experimental achievement, the optimistic polarization degrees for both electron and positron beams are taken into account to enhance the signal-to-noise ratio revealing the observable difference between supersymmetry breaking models. The minimal supergravity model and the minimal SU(5) grand unified model in gaugino mediation have been examined as examples. We see that after several years of accumulating data, the difference of the number of single-photon events between the two models received from the collider would be in excess of three times the statistical error, providing us the possibility to probe which model would be realized in nature. The result is well suitable for the future running of the International Linear Collider.

Search for squarks in R-parity violating supersymmetry in ep collisions at HERA

A search for squarks in R-parity violating supersymmetry is performed in e^+- p collisions at HERA using the H1 detector. The full data sample taken at a centre-of-mass energy sqrt{s}=319 GeV is used for the analysis, corresponding to an integrated luminosity of 255 pb^-1 of e^+ p and 183 pb^-1 of e^- p collision data. The resonant production of squarks via a Yukawa coupling lambda' is considered, taking into account direct and indirect R-parity violating decay modes. Final states with jets and leptons are investigated. No evidence for squark production is found and mass dependent limits on lambda' are obtained in the framework of the Minimal Supersymmetric Standard Model and in the Minimal Supergravity Model. In the considered part of the parameter space, for a Yukawa coupling of electromagnetic strength lambda'= 0.3, squarks of all flavours are excluded up to masses of 275 GeV at 95% confidence level, with down-type squarks further excluded up to masses of 290 GeV.

Realistic standard model fermion mass relations in generalized minimal supergravity (GmSUGRA)

Grand Unified Theories (GUTs) usually predict wrong Standard Model (SM) fermion mass relation m e /m μ = m d /m s toward low energies. To solve this problem, we consider the Generalized Minimal Supergravity (GmSUGRA) models, which are GUTs with gravity mediated supersymmetry breaking and higher dimensional operators. Introducing non-renormalizable terms in the super-and Kähler potentials, we can obtain the correct SM fermion mass relations in the SU(5) model with GUT Higgs fields in the 24 and 75 representations, and in the SO(10) model. In the latter case the gauge symmetry is broken down to SU(3) C × SU(2) L × SU(2) R × U(1) B−L , to flipped SU(5)×U(1) X , or to SU(3) C × SU(2) L × U(1)1 × U(1)2. Especially, for the first time we generate the realistic SM fermion mass relation in GUTs by considering the high-dimensional operators in the Kähler potential.

Supersymmetric discovery potential and benchmarks for early runs ats=7 TeVat the LHC

We carry out an analysis of the potential of the Large Hadron Collider (LHC) to discover supersymmetry in runs at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ with an accumulated luminosity of $(0.1--2)\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data. The analysis is done with both minimal supergravity and supergravity models with nonuniversal soft breaking. Benchmarks for early discovery with $(0.1--2)\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data are given. We provide an update of $b$-tagging efficiencies in PGS 4 appropriate for LHC analyses. A large number of signature channels are analyzed, and it is shown that each of the models exhibited are discoverable at the $5\ensuremath{\sigma}$ level or more above the standard model background in several signature channels which would provide cross checks for a discovery of supersymmetry. It is shown that some of the benchmarks are discoverable with $0.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data again with detectable signals in several channels.

R-parity violating resonant stop production at the Large Hadron Collider

We have investigated the resonant production of a stop at the Large Hadron Collider, driven by baryon number violating interactions in supersymmetry. We work in the framework of minimal supergravity models with the lightest neutralino being the lightest supersymmetric particle which decays within the detector. We look at various dilepton and trilepton final states, with or without b-tags. A detailed background simulation is performed, and all possible decay modes of the lighter stop are taken into account. We find that higher stop masses are sometimes easier to probe, through the decay of the stop into the third or fourth neutralino and their subsequent cascades. We also comment on the detectability of such signals during the 7 TeV run, where, as expected, only relatively light stops can be probed. Our conclusion is that the resonant process may be probed, at both 10 and 14 TeV, with the R-parity violating coupling {\lambda}"_{312} as low as 0.05, for a stop mass of about 1 TeV. The possibility of distinguishing between resonant stop production and pair-production is also discussed.

Bounds onR-parity violating couplings at the grand unification scale from neutrino masses

We consider the embedding of the supersymmetric standard model with broken R-parity in the minimal supergravity (mSUGRA) model. We restrict ourselves to the case of broken lepton number, the ${\mathrm{B}}_{3}$ mSUGRA model. We first study in detail how the tree-level neutrino mass depends on the mSUGRA parameters. We find, in particular, a strong dependence on the trilinear supersymmetry breaking $A$-parameter, even in the vicinity of the mSUGRA SPS1a point. We then reinvestigate the bounds on the trilinear R-parity violating couplings at the unification scale from the low-energy neutrino masses including dominant one-loop contributions. These bounds were previously shown to be very strict, as low as $\mathcal{O}({10}^{\ensuremath{-}6})$ for SPS1a. We show that these bounds are significantly weakened when considering the full mSUGRA parameter space. In particular the ratio between the tree-level and one-loop neutrino masses is reduced such that it may agree with the observed neutrino mass hierarchy. We discuss in detail how and in which parameter regions this effect arises.

Interplay between the charged Higgs and squark-gluino events at the LHC

In some extensions of the standard model with extended Higgs sectors, events from new particle production may pass the selection criteria for Higgs search in different channels at the LHC---14 TeV and mimic Higgs signals. This intriguing possibility is illustrated by PYTHIA based simulations using several representative points in the parameter space of the minimal supersymmetric standard model (MSSM) including a point in the minimal supergravity model consistent with the dark matter (DM) relic density data. Our simulations explore the interplay between the charged Higgs signal and typical squark-gluino events. We argue that the standard selections like the one based on the polarization properties of the $\ensuremath{\tau}$'s from charged Higgs decay, though adequate for handling the SM backgrounds, may not be very efficient in the presence of SUSY backgrounds. We then propose an alternative search strategy based on pure kinematics which sufficiently controls both the SM and the MSSM backgrounds. For charged Higgs masses (${H}^{\ifmmode\pm\else\textpm\fi{}}$) in the deep decoupling regime ($600\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{{H}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{\lesssim}800\text{ }\text{ }\mathrm{GeV}$) this method works well and extends the LHC reach close to 800 GeV for an integrated luminosity of $30\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ with or without the SUSY background. For a lighter charged Higgs a judicious combination of the old selections and some of the cuts proposed by us may disentangle the Higgs signal from the squark-gluino backgrounds quite effectively.

Supersymmetric dark matter at the LHC 7-TeV run

We have analysed the early LHC signatures of the minimal supergravity (mSUGRA) model. Our emphasis is on the 7 - $TeV$ run corresponding to an integrated luminosity of $\sim 1.0 ~fb^{-1}$ although we have also discussed briefly the prospects at LHC-10 $TeV$. We focus on the parameter space yielding relatively light squark and gluinos consistent with the darkmatter relic density data and the LEP bounds on the lightest Higgs scalar mass. This parameter space is only allowed for non-vanishing trilinear soft breaking term $A_0$. A significant region of the parameter space with large to moderate negative values of $A_0$ consistent with the stability of the scalar potential and relic density production via neutralino annihilation and/or neutralino - stau coannihilation yields observable signal via the jets + missing transverse energy channel. The one lepton + jets + missing energy signal is also viable over a smaller but non-trivial parameter space. The ratio of the size of the two signals - free from theoretical uncertainties - may distinguish between different relic density generating mechanisms. With efficient $\tau$-tagging facilities at 7 $TeV$ the discriminating power may increase significantly. We also comment on other dark matter relic density allowed mSUGRA scenarios and variants there of in the context of LHC-7 $TeV$.

Fine-tuning favors mixed axion/axino cold dark matter over neutralinos in the minimal supergravity model

Over almost all of minimal supergravity (mSUGRA or CMSSM) model parameter space, there is a large overabundance of neutralino cold dark matter (CDM). We find that the allowed regions of mSUGRA parameter space which match the measured abundance of CDM in the universe are highly fine-tuned. If instead we invoke the Peccei-Quinn-Weinberg-Wilczek solution to the strong CP problem, then the SUSY CDM may consist of an axion/axino admixture with an axino mass of order the MeV scale, and where mixed axion/axino or mainly axion CDM seems preferred. In this case, fine-tuning of the relic density is typically much lower, showing that axion/axino CDM (a\tilde{a}CDM) is to be preferred in the paradigm model for SUSY phenomenology. For mSUGRA with a\tilde{a}CDM, quite different regions of parameter space are now DM-favored as compared to the case of neutralino DM. Thus, rather different SUSY signatures are expected at the LHC in the case of mSUGRA with a\tilde{a}CDM, as compared to mSUGRA with neutralino CDM.