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Item 125 GeV Higgs Boson and the Type-II Seesaw Model(Published for SISSA by Springer, 2013-03) Okada, Nobuchika; University of Alabama TuscaloosaShow more We study the vacuum stability and unitarity conditions for a 125 GeV Standard Model (SM)-like Higgs boson mass in the type-II seesaw model. We find that, as long as the seesaw scale is introduced below the SM vacuum instability bound, there exists a large parameter space predicting a 125 GeV Higgs mass, irrespective of the exact value of the seesaw scale, satisfying both stability and unitarity conditions up to the Planck scale. We also study the model predictions for the Higgs partial decay widths in the diphoton and Z+photon channels with respect to their SM expectations and find that the decay rates for these two processes are anti- correlated. We further show that for any given enhancement in the Higgs-to-diphoton rate over its SM expectation, there exists an upper bound on the type-II seesaw scale, and hence, on the masses of the associated doubly- and singly-charged Higgs bosons in the allowed parameter space. For instance, if more than 10% enhancement persists in the Higgs-to-diphoton channel, the upper limit on the type-II seesaw scale is about 450 GeV which is completely within the reach of the 14 TeV LHC. We believe this to be an encouraging result for the experimental searches of the singly- and doubly-charged Higgs bosons which, in combination with improved sensitivity in the Higgs-to-diphoton and Higgs-to-Z+photon channels, could probe the entire allowed parameter space of the minimal type-II seesaw model, and establish/eliminate it as a single viable extension of the SM.Show more Item 125 GeV Higgs Boson Mass and Muon g−2 in 5D MSSM(2016-10-26) Okada, Nobuchika; University of Alabama TuscaloosaShow more In the minimal supersymmetric standard model (MSSM), the tension between the observed Higgs boson mass and the experimental result of the muon g − 2 measurement requires a large mass splitting between stops and smuons/charginos/neutralinos. We consider a five-dimensional (5D) framework of the MSSM with the Randall-Sundrum warped background metric, and show that such a mass hierarchy is naturally achieved in terms of geometry. In our setup, the supersymmetry is broken at the ultraviolet (UV) brane, while all the MSSM multiplets reside in the 5D bulk. An appropriate choice of the bulk mass parameters for the MSSM matter multiplets can naturally realize the sparticle mass hierarchy desired to resolve the tension. The gravitino is localized at the UV brane and hence becomes very heavy, while the gauginos spreading over the bulk acquire their masses suppressed by the fifth dimensional volume. As a result, the lightest sparticle neutralino is a candidate for the dark matter as usual in the MSSM. In addition to reproducing the SM-like Higgs boson mass of around 125 GeV and the measured value of the muon g − 2, we consider a variety of phenomenological constraints, and present the benchmark particle mass spectra that can be explored at the LHC Run-2 in the near future.Show more Item 125 gev higgs boson mass from 5d gauge-higgs unification(University of Alabama Libraries, 2015) Carson, Jason Carl; Okada, Nobuchika; University of Alabama TuscaloosaShow more In the context of a simple gauge-Higgs unification (GHU) scenario based on the gauge group SU(3)×U(1)′ in a 5-dimensional flat space-time, we investigate a possibility to reproduce the observed Higgs boson mass of around 125 GeV. We introduce bulk fermion multiplets with a bulk mass and a (half) periodic boundary condition. In our analysis, we adopt a low energy effective theoretical approach of the GHU scenario, where the running Higgs quartic coupling is required to vanish at the compactification scale. Under this "gauge-Higgs condition," we investigate the renormalization group evolution of the Higgs quartic coupling and find a relation between the bulk mass and the compactification scale so as to reproduce the 125 GeV Higgs boson mass. Through quantum corrections at the one-loop level, the bulk fermions contribute to the Higgs boson production and decay processes and deviate the Higgs boson signal strengths at the Large Hadron Collider (LHC) experiments from the Standard Model (SM) predictions. Employing the current experimental data which show the the Higgs boson signal strengths for a variety of Higgs decay modes are consistent with the SM predictions, we obtain lower mass bounds on the lightest mode of the bulk fermions.Show more Item 125 GeV Higgs boson mass from 5D gauge-Higgs unification(Oxford University Press, 2018) Carson, Jason; Okada, Nobuchika; University of Alabama TuscaloosaShow more In the context of a simple gauge-Higgs unification (GHU) scenario based on the gauge group SU(3) x U(1)' in a 5D flat space-time, we investigate the possibility of reproducing the observed Higgs boson mass of around 125 GeV. We introduce bulk fermion multiplets with a bulk mass and a (half-)periodic boundary condition. In our analysis, we adopt a low-energy effective theoretical approach of the GHU scenario, where the running Higgs quartic coupling is required to vanish at the compactification scale. Under this “gauge-Higgs condition,” we investigate the renormalization group evolution of the Higgs quartic coupling and find a relation between the bulk mass and the compactification scale so as to reproduce the 125 GeV Higgs boson mass. Through quantum corrections at the one-loop level, the bulk fermions contribute to the Higgs boson production and decay processes and deviate the Higgs boson signal strengths at the Large Hadron Collider experiments from the Standard Model (SM) predictions. Employing the current experimental data that show that the Higgs boson signal strengths for a variety of Higgs decay modes are consistent with the SM predictions, we obtain lower mass bounds on the lightest mode of the bulk fermions to be around 1 TeV.Show more Item 125 GeV Higgs, type III seesaw and gauge-Higgs unification(Elsevier, 2012-09-17) He, Bin; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University of Alabama TuscaloosaShow more Recently, both the ATLAS and CMS experiments have observed an excess of events that could be the first evidence for a 125 GeV Higgs boson. This is a few GeV below the (absolute) vacuum stability bound on the Higgs mass in the Standard Model (SM), assuming a Planck mass ultraviolet (UV) cutoff. In this Letter, we study some implications of a 125 GeV Higgs boson for new physics in terms of the vacuum stability bound. We first consider the seesaw extension of the SM and find that in type III seesaw, the vacuum stability bound on the Higgs mass can be as low as 125 GeV for the seesaw scale around a TeV. Next we discuss some alternative new physics models which provide an effective ultraviolet cutoff lower than the Planck mass. An effective cutoff Lambda similar or equal to 10(11) GeV leads to a vacuum stability bound on the Higgs mass of 125 GeV. In a gauge-Higgs unification scenario with five-dimensional flat spacetime, the so-called gauge-Higgs condition can yield a Higgs mass of 125 GeV, with the compactification scale of the extra-dimension being identified as the cutoff scale Lambda similar or equal to 10(11) GeV. Identifying the compactification scale with the unification scale of the SM SU(2) gauge coupling and the top quark Yukawa coupling yields a Higgs mass of 121 +/- 2 GeV. (C) 2012 Elsevier B.V. All rights reserved.Show more Item A 3x2 texture for neutrino oscillations and leptogenesis(Elsevier, 2008-03-06) Brahmachari, Biswajoy; Okada, Nobuchika; High Energy Accelerator Research Organization (KEK); University of Alabama TuscaloosaShow more In an economical system with only two heavy right-handed neutrinos, we postulate a new texture for 3 x 2 Dirac mass matrix m(D). This model implies one massless light neutrino and thus displays only two patterns of mass spectrum for light neutrinos, namely hierarchical or inverse-hierarchical. Both the cases can correctly reproduce all the current neutrino oscillation data with a unique prediction m(nu e nu e) = root Delta m(solar)(2)/3 and root Delta(2)(atm) for the hierarchical and the inverse-hierarchical cases, respectively, which can be tested in next generation neutrino-less double beta decay experiments. Introducing a single physical CP phase in in m(D), we examine baryon asymmetry through leptogenesis. Interestingly, through the CP phase there are correlations between the amount of baryon asymmetry and neutrino oscillation parameters. We find that for a fixed CP phase, the hierarchical case also succeeds in generating the observed baryon asymmetry in our universe, plus a non-vanishing U-e3 which is accessible in future baseline neutrino oscillation experiments. (c) 2008 Published by Elsevier B.V.Show more Item Almost No-Scale Supergravity(Published by Institute of Physics Publishing for SISSA/ISAS, 2003-05-16) Okada, Nobuchika; University of Alabama TuscaloosaShow more We construct an explicit 5-dimensional supergravity model that realizes the 'no scale' mechanism for supersymmetry breaking, with all moduli stabilized consistently by low-energy dynamics in the effective theory. Supersymmetry is broken by a constant superpotential localized on a brane, and the radion is stabilized by Casimir energy from supergravity and massive hypermultiplets. If the standard model gauge and matter fields are localized on a brane, visible sector supersymmetry breaking is dominated by gravity loops and flavor-violating hypermultiplet loops, and gaugino masses are smaller than scalar masses. A realistic model can be obtained by partly localizing the the standard model gauge fields. In this case visible sector supersymmetry breaking can be gaugino mediated, while masses of the gravitino and gravitational moduli are larger than the weak scale.Show more Item Alternative renormalizable SO(10) GUTs anddatafitting(Elsevier, 2020) Fukuyama, Takeshi; Okada, Nobuchika; Tran, Hieu Minh; Osaka University; University of Alabama Tuscaloosa; Hanoi University of Science & TechnologyShow more The alternative renormalizable minimal \(SO\left(10\right)\) model is composed of the Yukawa couplings with \(\text{10}\oplus \text{120}\) Higgs fields, whereas the right-handed (RH) neutrino Majorana masses are generated via the Witten mechanism. The gauge coupling unification is achieved together with a unique pattern of the fermion masses and mixing at the grand unification scale due to additional contributions of vector-like quarks to the standard model renormalization group equations. We perform the fitting of the model to the experimental data of charged fermion masses and the CKM matrix. The best fit point is obtained with large pulls for \({m}_{c}\), \({m}_{s}\), \({m}_{b}\), and \({m}_{\tau }\). For the modifications to the minimal model by adding either \({\text{10}}^{\prime }\) or \({\text{120}}^{\prime }\), a large deviation for the tau mass rules out all these models. In the case with the bottom and vector-like quark mixing, the mass matrices are well fitted the charged fermions but the bound on the light neutrino mass scale excludes this scenario. To ameliorate this deficit, we consider the two-step symmetry breaking scenario, \(SO\left(10\right)\to SU\left(5\right)\to SU{\left(3\right)}_{C}×SU{\left(2\right)}_{L}×U{\left(1\right)}_{Y}\), with the \(SO\left(10\right)\) breaking at the Planck scale leading to the radiatively generated RH neutrino Majorana masses being at the ordinary seesaw scale. For this case, we find the best fit point with \({\chi }^{2}=7.8\) consistent with experimental results including the neutrino sector. The largest deviation is 2.3σ corresponding to the strange quark mass. Hence, a more precise determination of the strange quark mass can test this model. For the best fit point, we find the effective Majorana neutrino mass of \({m}_{\beta \beta }=0.22\) meV and the sum of light neutrino masses as \(\Sigma =0.078\) eV, which are consistent with the current constraints from the search for the neutrinoless double beta decay and the CMB anisotropy measurement.Show more Item Alternative Signature of TeV Strings: Reduction in QCD Jet Production(2002-11-11) Okada, Nobuchika; University of Alabama TuscaloosaShow more In string theory, it is well known that any hard scattering amplitude inevitably suffers exponential suppression. We demonstrate that, if the string scale is Mₛ < 2TeV, this intrinsically stringy behavior leads to a dramatic reduction in the QCD jet production rate with very high transverse momenta pₜ >~ 2 TeV at CERN LHC. This suppression is sufficient to be observed in the first year of low-luminosity running. Our prediction is based on the universal behavior of string theory, and therefore is qualitatively model independent. This signature is alternative and complementary to conventional ones such as Regge resonance (or string ball or black hole) production.Show more Item Antineutrino neutral current interactions in MiniBooNE(University of Alabama Libraries, 2012) Dharmapalan, Ranjan; Stancu, Ion; University of Alabama TuscaloosaShow more The antineutrino nucleon neutral current elastic scattering cross section measured at the MiniBooNE experiment is reported. The data set corresponds to 10.1 × 10^20 protons on target which is a world record neutral current elastic antineutrino sample. An antineutrino to neutrino neutral current scattering cross section ratio is measured after accounting for all associated errors. This is the first time such a ratio has been experimentally reported. Previous MiniBooNE neutrino cross section measurements have indicated a higher value for the axial mass, M_A, as compared to the nominal value of M_A=1.0 GeV. A Χ^2 test was performed to find the best value of M_A which matches the antineutrino neutral current elastic data. Finally, an exciting possibility to search for dark matter in the MiniBooNE experiment, using the neutral current interactions is discussedShow more Item Bosonic Seesaw Mechanism in a Classically Conformal Extension of the Standard Model(2016-03-10) Okada, Nobuchika; University of Alabama TuscaloosaShow more We suggest the so-called bosonic seesaw mechanism in the context of a classically conformal U(1)B−L extension of the Standard Model with two Higgs doublet fields. The U(1)B−L symmetry is radiatively broken via the Coleman–Weinberg mechanism, which also generates the mass terms for the two Higgs doublets through quartic Higgs couplings. Their masses are all positive but, nevertheless, the electroweak symmetry breaking is realized by the bosonic seesaw mechanism. Analyzing the renormalization group evolutions for all model couplings, we find that a large hierarchy among the quartic Higgs couplings, which is crucial for the bosonic seesaw mechanism to work, is dramatically reduced toward high energies. Therefore, the bosonic seesaw is naturally realized with only a mild hierarchy, if some fundamental theory, which provides the origin of the classically conformal invariance, completes our model at some high energy, for example, the Planck scale. We identify the regions of model parameters which satisfy the perturbativity of the running couplings and the electroweak vacuum stability as well as the naturalness of the electroweak scale.Show more Item Bounds on heavy Majorana neutrinos in type-I seesaw and implications for collider searches(Elsevier, 2017-11-10) Das, Arindam; Okada, Nobuchika; Korea Institute for Advanced Study (KIAS); Seoul National University (SNU); University of Alabama TuscaloosaShow more The neutrino masses and flavor mixings, which are missing in the Standard Model (SM), can be naturally incorporated in the type-I seesaw extension of the SM with heavy Majorana neutrinos being singlet under the SM gauge group. If the heavy Majorana neutrinos are around the electroweak scale and their mixings with the SM neutrinos are sizable, they can be produced at high energy colliders, leaving characteristic signatures with lepton-number violations. Employing the general parametrization for the neutrino Dirac mass matrix in the minimal seesaw scenario, we perform a parameter scan and identify allowed regions to satisfy a variety of experimental constraints from the neutrino oscillation data, the electroweak precision measurements and the lepton-flavor violating processes. We find that the resultant mixing parameters between the heavy neutrinos and the SM neutrinos are more severely constrained than those obtained from the current search for heavy Majorana neutrinos at the LHC. Such parameter regions can be explored at the High-Luminosity LHC and a 100 TeV pp-collider in the future. (c) 2017 The Author(s). Published by Elsevier B.V.Show more Item Bounds on large extra dimensions from the simulation of black hole events at the Large Hadron Collider(University of Alabama Libraries, 2016) Hou, Shaoqi; Harms, B.; University of Alabama TuscaloosaShow more Large extra dimensions were originally proposed to solve the hierarchy problem of the Standard Model (SM) of elementary particle physics. The presence of large extra dimensions dilutes gravity, lowering the Planck scale, while SM particles are required to propagate only in the usual 4 dimensional spacetime, leaving the electroweak scale unchanged. If large extra dimensions exist and they are large enough, the Planck scale may be as low as a few TeV’s, so that the hierarchy problem is solved. A smaller Planck scale will bring about numerous phenomenological consequences; in particular, microscopic black holes may be produced in high-energy particle collisions at this energy scale. The decay of black holes, via the Hawking effect, into elementary particles enables the detection of the black hole events, which can be used to infer the existence of large extra dimensions. In this work, we simulate microscopic black hole formation at the Large Hadron Collider with the black hole event generator CATFISH, and compare the simulation results with the experimental data published by the Compact Muon Solenoid collaboration in 2013 at a center of mass energy $\sqrt{s}= 8$ TeV, corresponding to an integrated luminosity of 12.1 fb$^{-1}$. The goal of this work is to test the large extra dimension model and to determine the value of the Planck scale if large extra dimensions exist. The absence of observed black hole events in the experimental data allows us to set lower bounds on the Planck scale and various parameters related to microscopic black hole formation for a number (3 - 6) of large extra dimensions. Assuming no energy loss during high-energy particle collisions, our analysis sets lower bounds on the fundamental Planck scale ranging from 0.8 TeV to 4.9 TeV for black holes fully decaying into SM particles and 0.5 TeV to 3.0 TeV for black holes settling down to a charge neutral, invisible remnant, depending on the minimum allowed black hole mass at formation. Formation of black holes with mass less than 5.2 TeV to 6.5 TeV (SM decay) and 2.2 TeV to 4.0 TeV (remnant) is excluded at 95\% C.L. Further investigation takes into account the effects of the Generalized Uncertainty Principle (GUP), which is expected to play an important role because the mass of a microscopic black hole is only a few fundamental Planck masses. An analysis similar to the one carried out without including GUP effects reveals smaller lower bounds on the fundamental Planck scale ranging from 0.8 TeV to 1.4 TeV for black holes fully decaying into SM particles, only when $\alpha\ge0.9$, depending on the minimum allowed black hole mass at formation. Therefore, this work constrains not only the sizes of the large extra dimensions and the masses of the microscopic black holes, but also sets the lower limits on the energy scale where the effects of quantum gravity start to become significant.Show more Item Brane World Cosmological Solution to the Gravitino Problem(2005-01-19) Okada, Nobuchika; University of Alabama TuscaloosaShow more We investigate the thermal production of gravitinos in the context of the brane world cosmology. Since the expansion law is modified from the one in the standard cosmology, the Boltzmann equation for the gravitino production is altered. We find that the late-time gravitino abundance is proportional to the “transition temperature”, at which the modified expansion law in the brane world cosmology is connecting with the standard one, rather than the reheating temperature after inflation as in the standard cosmology. This means that, even though the reheating temperature is very high, we can avoid the overproduction of gravitinos by taking the transition temperature low enough. Therefore, the gravitino problem can be solved.Show more Item Bulk Standard Model in the Randall-Sundrum Background(2000-09-26) Okada, Nobuchika; University of Alabama TuscaloosaShow more We discuss issues in an attempt to put the standard model (SM) in five-dimensional anti–de Sitter spacetime compactified on S¹/Z₂. The recently proposed approach to the gauge hierarchy problem by using this background geometry, with the SM confined on a boundary, is extended to a situation where (some of) the SM particles reside in the five-dimensional bulk. In particular, we find a localization of zero modes of bulk fermions near the boundary with a negative tension. Unlike the compactification with the flat metric, these fermion zero modes couple to Kaluza-Klein (KK) excitations of the SM gauge bosons. Interestingly, only low-lying modes of such KK gauge bosons have non-negligible couplings. Current electroweak precision data give a constraint that the first KK mode be heavier than 9 TeV. We also argue that at least the Higgs field should be confined on the brane to utilize the Randall-Sundrum background as a solution to the gauge hierarchy.Show more Item Can WIMP Dark Matter Overcome the Nightmare Scenario?(2010-09-29) Okada, Nobuchika; University of Alabama TuscaloosaShow more Even if new physics beyond the standard model indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC), and the LHC could find only the Higgs boson but nothing else. This is the so-called “nightmare scenario.” On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral weakly interacting massive particle (WIMP) with mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the standard model gauge group, which only couples to the Higgs doublet at the lowest order, and investigate the possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.Show more Item Classically conformal B-L extended Standard Model(Elsevier, 2009-06-01) Iso, Satoshi; Okada, Nobuchika; Orikasa, Yuta; High Energy Accelerator Research Organization (KEK); Graduate University for Advanced Studies - Japan; University of Alabama TuscaloosaShow more Under a hypothesis of classically conformal theories, we investigate the minimal B-L extended Standard Model, which naturally provides the seesaw mechanism for explaining tiny neutrino masses. In this setup, the radiative gauge symmetry breaking is successfully realized in a very simple way: The B-L gauge symmetry is broken through the conformal anomaly induced by quantum corrections in the Coleman-Weinberg potential. Associated with this B-L symmetry breaking, the Higgs mass parameter is dynamically generated, by which the electroweak symmetry breaking is triggered. We find that a wide range of parameter space can satisfy both the theoretical and experimental requirements. (C) 2009 Elsevier B.V. All rights reserved.Show more Item Classically conformal U(1)' extended standard model, electroweak vacuum stability, and LHC Run-2 bounds(American Physical Society, 2016-06-29) Das, Arindam; Oda, Satsuki; Okada, Nobuchika; Takahashi, Dai-Suke; University of Alabama Tuscaloosa; Okinawa Institute of Science & Technology Graduate UniversityShow more We consider the minimal U(1)' extension of the standard model (SM) with the classically conformal invariance, where an anomaly-free U(1)' gauge symmetry is introduced along with three generations of right-handed neutrinos and a U(1)' Higgs field. Since the classically conformal symmetry forbids all dimensional parameters in the model, the U(1)' gauge symmetry is broken by the Coleman-Weinberg mechanism, generating the mass terms of the U(1)' gauge boson (Z' boson) and the right-handed neutrinos. Through a mixing quartic coupling between the U(1)' Higgs field and the SM Higgs doublet field, the radiative U(1)' gauge symmetry breaking also triggers the breaking of the electroweak symmetry. In this model context, we first investigate the electroweak vacuum instability problem in the SM. Employing the renormalization group equations at the two-loop level and the central values for the world average masses of the top quark (m(t) = 173.34 GeV) and the Higgs boson (m(h) = 125.09 GeV), we perform parameter scans to identify the parameter region for resolving the electroweak vacuum instability problem. Next we interpret the recent ATLAS and CMS search limits at the LHC Run-2 for the sequential Z' boson to constrain the parameter region in our model. Combining the constraints from the electroweak vacuum stability and the LHC Run-2 results, we find a bound on the Z' boson mass as m(Z') greater than or similar to 3.5 TeV. We also calculate self-energy corrections to the SM Higgs doublet field through the heavy states, the right-handed neutrinos and the Z' boson, and find the naturalness bound as m(Z') less than or similar to 7 TeV, in order to reproduce the right electroweak scale for the fine-tuning level better than 10%. The resultant mass range of 3.5 TeV less than or similar to m(Z') less than or similar to 7 TeV will be explored at the LHC Run-2 in the near future.Show more Item Classically Conformal U(1)′ Extended Standard Model and Higgs Vacuum Stability(American Physical Society, 2015-07-27) Okada, Nobuchika; University of Alabama TuscaloosaShow more We consider the minimal U(1)′ extension of the standard model (SM) with conformal invariance at the classical level, where in addition to the SM particle contents, three generations of right-handed neutrinos and a U(1)′ Higgs field are introduced. In the presence of the three right-handed neutrinos, which are responsible for the seesaw mechanism, this model is free from all the gauge and gravitational anomalies. The U(1)′ gauge symmetry is radiatively broken via the Coleman-Weinberg mechanism, by which the U(1)′ gauge boson (Z′ boson) mass as well as the Majorana mass for the right-handed neutrinos are generated. The radiative U(1)′ symmetry breaking also induces a negative mass squared for the SM Higgs doublet to trigger the electroweak symmetry breaking. In this context, we investigate a possibility to solve the SM Higgs vacuum instability problem. The model includes only three free parameters (U(1)′ charge of the SM Higgs doublet, U(1)′ gauge coupling and Z′ boson mass), for which we perform parameter scan, and identify a parameter region resolving the SM Higgs vacuum instability. We also examine naturalness of the model. The heavy states associated with the U(1)′ symmetry breaking contribute to the SM Higgs self-energy. We find an upper bound on Z′ boson mass, m_Z_′≲6 TeV, in order to avoid a fine-tuning severer than 10% level. The Z′ boson in this mass range can be discovered at the LHC Run-2 in the near future.Show more Item Collider phenomenology of heavy neutrinos(University of Alabama Libraries, 2016) Das, Arindam; Okada, Nobuchika; University of Alabama TuscaloosaShow more The existence of the neutrino mass has been established by the neutrino oscillation experiments. The so-called seesaw extension of the Standard Model is probably the simplest idea to naturally explain the existence of tiny neutrino mass through the lepton number violating Majorana mass term. There is another alternative way, commonly known as the inverse seesaw mechanism, where the small neutrino mass is obtained by the tiny lepton number violating parameters. In this work we investigate the signatures of such heavy neutrinos, having mass in the Electroweak scale at the high energy colliders. Based on a simple realization of inverse seesaw model we fix the model parameters to reproduce the neutrino oscillation data and to satisfy the other experimental constraints. We assume two flavor structures of the model and the different types of hierarchical light neutrino mass spectra. For completeness we consider the general parameterization for the model parameters by introducing an arbitrary orthogonal matrix and the nonzero Dirac and Majorana phases. Due to the smallness of the lepton number violating parameter this model can manifest the trilepton plus missing energy at the Large Hadron Collider(LHC). Using the recent LHC results for anomalous production of the multilepton events at $8$ TeV with a luminosity of $19.5$ fb$^{-1}$, we derive the direct upper bounds on the light-heavy neutrino mixing parameter as a function of the heavy neutrino mass. Using a variety of initial states such as quark-quark, quark-gluon and gluon-gluon as well as photon mediated processes for the Majorana heavy neutrinos we obtain direct upper bounds on the light-heavy neutrino mixing angles from the current LHC data at $8$ TeV. For the pseudo-Dirac heavy neutrinos produced from the various initial states using the recent anomalous multilepton search by the LHC at $8$ TeV with $19.5$ fb$^{-1}$ luminosity, we obtain upper bounds on the mixing angles.Show more