A natural extension of the standard $SU(2)_{\rm L} \times U(1)_{\rm Y}$ gauge model to accommodate massive neutrinos is to introduce one Higgs triplet and three right-handed Majorana neutrinos, leading to a $6\times 6$ neutrino mass matrix which contains three $3\times 3$ sub-matrices $M_{\rm L}$, $M_{\rm D}$ and $M_{\rm R}$. We show that three light Majorana neutrinos (i.e., the mass eigenstates of $ν_e$, $ν_μ$ and $ν_τ$) are exactly massless in this model, if and only if $M_{\rm L} = M_{\rm D} M_{\rm R}^{-1} M_{\rm D}^T$ exactly holds. This no-go theorem implies that small but non-vanishing neutrino masses may result from a significant but incomplete cancellation between $M_{\rm L}$ and $M_{\rm D} M_{\rm R}^{-1} M_{\rm D}^T$ terms in the Type-II seesaw formula, provided three right-handed Majorana neutrinos are of ${\cal O}(1)$ TeV and experimentally detectable at the LHC. We propose three simple Type-II seesaw scenarios with the $A_4 \times U(1)_{\rm X}$ flavor symmetry to interpret the observed neutrino mass spectrum and neutrino mixing pattern. Such a TeV-scale neutrino model can be tested in two complementary ways: (1) searching for possible collider signatures of lepton number violation induced by the right-handed Majorana neutrinos and doubly-charged Higgs particles; and (2) searching for possible consequences of unitarity violation of the $3\times 3$ neutrino mixing matrix in the future long-baseline neutrino oscillation experiments.
The Majorana nature of neutrinos is strongly motivated from the theoretical and phenomenological point of view. A plethora of neutrino mass models, known collectively as Seesaw models, exist that could generate both a viable neutrino mass spectrum and mixing pattern. They can also lead to rich, new phenomenology, including lepton number non-conservation as well as new particles, that may be observable at collider experiments. It is therefore vital to search for such new phenomena and the mass scale associated with neutrino mass generation at high energy colliders. In this review, we consider a…
We show that the longitudinal beam polarization option at a future electron-positron collider provides an unambiguous distinction between low-scale seesaw models of neutrino mass. This is possible due to the fact that the pair production cross section of the heavy neutrinos in seesaw models is sensitive to the polarization of the initial lepton beams, and for a suitable choice of the polarization, shows a clear enhancement over the unpolarized cross section. More interestingly, the choice of the beam polarization for which the enhancement is maximum is governed by the size of the light-heavy n…
We consider the Standard Model with right-handed neutrinos to explain the masses of active neutrinos by the seesaw mechanism. Since active neutrinos as well as heavy neutral leptons are Majorana fermions in this case, the lepton number violating process can be induced. We discuss the inverse neutrinoless double beta decay $e^- e^- \to W^- W^-$ in the framework of the seesaw mechanism and its detectability at future colliders. It is shown that the cross section can be 17 fb for $\sqrt{s}=3$ TeV even with the stringent constraint from the neutrinoless double beta decays if three (or more) right-…
Type-III seesaw is a simple extension of the Standard Model~(SM) with the SU$(2)_\text{L}$ triplet fermion with zero hypercharge. It can explain the origin of the tiny neutrino mass and flavor mixing. After the electroweak symmetry breaking the light neutrino mass is generated by the seesaw mechanism which further ensures the mixings between the light neutrino and heavy neutral lepton mass eigenstates. If the triplet fermions are around the electroweak scale having sizable mixings with the SM sector allowed by the correct gauge symmetry, they can be produced at the high energy colliders leavin…
We propose ways to distinguish between different mechanisms behind the collider signals of TeV-scale seesaw models for neutrino masses using kinematic endpoints of invariant mass variables. We particularly focus on two classes of such models widely discussed in literature: (i) Standard Model extended by the addition of singlet neutrinos and (ii) Left-Right Symmetric Models. Relevant scenarios involving the same "smoking-gun" collider signature of dilepton plus dijet with no missing transverse energy differ from one another by their event topology, resulting in distinctive relationships among t…
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 identi…
We review the TeV scale $B-L$ extension of the Minimal Supersymmetric Standard Model (BLSSM) where an inverse seesaw mechanism of light neutrino mass generation is naturally implemented and concentrate on its hallmark manifestations at the Large Hadron Collider (LHC).
Low-scale seesaw variants protected by lepton number symmetry provide a natural explanation of the smallness of neutrino masses but, unlike their higher-scale counterparts, with potentially testable phenomenology. The approximate lepton number symmetry arranges the heavy neutrinos in pseudo-Dirac pairs, which might be accessible at collider or even beam dump experiments if their mass is low enough and their mixing with the active neutrinos sufficiently large. Despite their pseudo-Dirac nature, their small mass splittings may lead to oscillations that prevent the cancellation of their potential…
We study the capability of the international linear collider (ILC) to probe extra dimensions via the seesaw mechanism. In the scenario we study, heavy Kaluza-Klein neutrinos generate tiny neutrino masses and, at the same time, have sizable couplings to the standard-model particles. Consequently, a Kaluza-Klein tower of heavy neutrinos (N) can be produced and studied at the ILC through the process: e+e- -> vN followed by N -> Wl decay. We show that the single lepton plus two-jets final states with large missing energy from this signal process will provide a good opportunity to measure the masse…
We investigate the production and decays of doubly-charged Higgs bosons for the Type-II seesaw mechanism at an $e^{+} e^{-}$ collider with two center of mass energies, $\sqrt{s}=380$ GeV and 3 TeV, and analyze the fully hadronic final states in detail. Lower mass ranges can be probed during the 380 GeV run of the collider, while high mass ranges, which are beyond the 13 TeV Large Hadron Collider discovery reach, can be probed with $\sqrt{s}=3$ TeV. For such a heavy Higgs boson, the final decay products are collimated, resulting in fat-jets. We perform a substructure analysis to reduce the back…
We discuss the scenario with TeV-scale right-handed neutrinos, which are accessible at future colliders, while holding down tiny seesaw-induced masses and sizable couplings to the standard-model particles. The signal with tri-lepton final states and large missing transverse energy is appropriate for studying collider signatures of the scenario with extra spatial dimensions. We show that the LHC experiment generally has a potential to discover the signs of extra dimensions and the origin of small neutrino masses.
We review the collider phenomenology of neutrino physics and the synergetic aspects at energy, intensity and cosmic frontiers to test the new physics behind the neutrino mass mechanism. In particular, we focus on seesaw models within the minimal setup as well as with extended gauge and/or Higgs sectors, and on supersymmetric neutrino mass models with seesaw mechanism and with $R$-parity violation. In the simplest Type-I seesaw scenario with sterile neutrinos, we summarize and update the current experimental constraints on the sterile neutrino mass and its mixing with the active neutrinos. We a…
We discuss the scenario with gauge singlet fermions (right-handed neutrinos) accessible at the energy of the Large Hadron Collider. The singlet fermions generate tiny neutrino masses via the seesaw mechanism and also have sizable couplings to the standard-model particles. We demonstrate that these two facts, which are naively not satisfied simultaneously, are reconciled in the five-dimensional framework in various fashions, which make the seesaw mechanism observable. The collider signal of tri-lepton final states with transverse missing energy is investigated for two explicit examples of the o…
In this work we study the viable parameter space of the scalar sector in the type-II seesaw model. In identifying the allowed parameter space, we employ constraints from low energy precision measurements, theoretical considerations and the 125-GeV Higgs data. These tools prove effective in constraining the model parameter space. Moreover, the triplet also offers a rich collider phenomenology from having additional scalars that have unique collider signatures. We find that direct collider searches for these scalars can further probe various parts of the viable parameter space. These parts can b…
The existence of the tiny neutrino mass and the flavor mixing can be naturally explained by type-I Seesaw model which is probably the simplest extension of the Standard Model (SM) using Majorana type SM gauge singlet heavy Right Handed Neutrinos (RHNs). If the RHNs are around the Electroweak(EW)-scale having sizable mixings with the SM light neutrinos, they can be produced at the high energy colliders such as Large Hadron Collider (LHC) and future $100$ TeV proton-proton (pp) collider through the characteristic signatures with same sign di-lepton introducing lepton number violations(LNV). On t…
The explanation of the small neutrino mass can be depicted using some handsome models like type-I and inverse seesaw where the Standard Model gauge singlet heavy right handed neutrinos are deployed. The common thing in these two models is a lepton number violating parameter, however, its order of magnitude creates a striking difference between them making the nature of the right handed heavy neutrinos a major play factor. In the type-I seesaw a large lepton number violating parameter involves the heavy right handed neutrinos in the form of Majorana fermions while a small lepton number violatin…
The DAMPE $e^+ e^-$ excess at around 1.4 TeV could be explained in the type-II seesaw model with a scalar dark mater $D$ which is stabilized by a discrete $Z_2$ symmetry. The simplest scenario is the annihilation $DD \to H^{++} H^{--}$ followed by the subsequent decay $H^{\pm\pm} \to e^\pm e^\pm$, with both the DM and triplet scalars roughly 3 TeV with a small mass splitting. In addition to the Drell-Yan process at future 100 TeV hadron colliders, the doubly-charged components could also be produced at lepton colliders like ILC and CLIC in the off-shell mode, and mediate lepton flavor violatin…
The same-sign tetralepton signature via mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-II seesaw model. In this paper, we study this signature at future lepton colliders, such as ILC, CLIC, and MuC. Constrained by direct search, $H^{\pm\pm}\to W^\pm W^\pm$ is the only viable decay mode for $M_{A^0}=400$ GeV at $\sqrt{s}=1$ TeV ILC. With an integrated luminosity of $\mathcal{L}=8~ \mathrm{ab}^{-1}$, the promising region with about 150 signal events corresponds to a narrow band in the range of $10^{-4}~\text{GeV}\lesssim v_Δ\lesssim…
The Randall-Sundrum model with gauge fields and fermions in the bulk has several attractive features including the gauge coupling unification, a candidate for the dark matter, and an explanation for the hierarchical Yukawa couplings. In this paper, we point out that the 1st Kaluza-Klein modes of right-handed neutrinos may be produced at colliders, for both Dirac and Majorana neutrino cases. Furthermore, we can see whether the neutrino masses are Dirac type or Majorana type from the mass spectrum of KK particles.
A general feature of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated via loop corrections, is an extended scalar (Higgs) sector. Another feature is the Majorana nature; e.g., introducing right-handed neutrinos with TeV-scale Majorana masses under the discrete symmetry, or otherwise introducing some lepton number violating interactions in the scalar sector. We study phenomenological aspects of these models at collider experiments. We find that, while properties of the extended Higgs sector of these models can be explored to some extent, the Majorana nature of the …
We investigate the potential of the International Linear Collider (ILC) to probe the mechanisms of neutrino mass generation and leptogenesis within the minimal seesaw model. Our results can also be used as an estimate for the potential of a Compact Linear Collider (CLIC). We find that heavy sterile neutrinos that simultaneously explain both, the observed light neutrino oscillations and the baryon asymmetry of the universe, can be found in displaced vertex searches at ILC. We further study the precision at which the flavour-dependent active-sterile mixing angles can be measured. The measurement…
We calculate the ratio $R_{\ell\ell}$ of same sign (SS) to opposite sign (OS) dileptons in type I and generalized inverse seesaw models and show that it can be anywhere between 0 and 1 depending on the detailed texture of the right-handed neutrino mass matrix. Measurement of $R_{\ell\ell}$ in hadron colliders can therefore provide a way to probe the nature of seesaw mechanism and also to distinguish between the two types of seesaw mechanisms. We work within the framework of left-right symmetric model as an example. We emphasize that coherence of the final states in the $W_R$ decay is crucial f…
We consider the TeV scale left-right symmetric theory which can accommodate low scale seesaw mechanisms consistent with neutrino oscillation data and find new physics contributions to neutrinoless double beta decay. The model facilitates natural type-II seesaw dominance and the presence of extra particles make the Dirac neutrino mass matrix $M_D$ large that leads to large light heavy neutrino mixing. The spontaneous symmetry breaking through doublets, triplets and bidoublet scalars at TeV scale offers rich phenomenology accessible to LHC. From the numerical studies of the new physics contribut…
We propose a left-right symmetric framework with universal seesaw mechanism for the generation of masses of the Standard Model quarks and leptons. Heavy vector-like singlet quarks and leptons are required for generation of Standard Model-like quark and lepton masses through seesaw mechanism. A softly broken $Z_2$ symmetry distinguishes the lepton sector and the quark sector of the model. This leads to the presence of some lepton-specific interactions that can produce unique collider signatures which can be explored at the current Large Hadron Collider run and also future colliders.
We investigate the collider phenomenology of the scalar triplet particles in the Type-II seesaw model at a 100 TeV $pp$ collider. Depending on triplet vacuum expectation value $v_Δ$, the dominant discovery channels could be $H^{++} H^{--}$ and $H^{\pm\pm}H^\mp$. We find the $H^{\pm\pm}H^\mp\to W^\pm W^\pm h W^\mp/\ell^\pm \ell^\pm h W^\mp$ channels are promising for both model discovery at relatively large $v_Δ$ and determination of the Higgs portal couplings $λ_4$ and $λ_5$. We also find that these two channels are complementary to indirect determination of $λ_4$ from future precise measureme…
The type-II seesaw model can explain neutrino masses and address the baryon asymmetry problem of the Universe simultaneously. In this letter, we explore its phase transition and the resulting gravitational wave signals. We find a strong first-order electroweak phase transition generically prefers a relatively light triplet in the $300\sim500$GeV range, which is ideal for collider searches and can generate gravitational waves within the sensitivity reach of BBO and Ultimate-DECIGO. While above $\sim$1TeV where a future 100TeV $pp$ collider will play a key role in model discovery, we integrate o…
Two of the important implications of the seesaw mechanism are: (i) a simple way to understand the small neutrino masses, and (ii) the origin of matter-anti-matter asymmetry in the universe via the leptogenesis mechanism. For TeV-scale seesaw models, successful leptogenesis requires that the right-handed neutrinos (RHNs) must be quasi-degenerate and if they have CP violating phases, they also contribute to the CP asymmetry. We investigate this in the TeV-scale left-right models for seesaw and point out a way to probe the quasi-degeneracy possibility with CP violating mixings for RHNs in hadron …
We investigate multilepton signatures, arising from the decays of doubly charged and singly charged Higgs bosons in the Type-II Seesaw model. Depending on the vacuum expectation value of the triplet $v_Δ$, the doubly and singly charged Higgs bosons can decay into a large variety of multi-lepton final states. We explore all possible decay modes corresponding to different regimes of $v_Δ$, that generate distinguishing four and five leptonic signatures. We focus on the 13 TeV Large Hadron Collider (LHC) and further extend the study to a very high energy proton-proton collider (VLHC) with a center…
The signature of heavy fermionic triplets belonging to Type III seesaw at the International Linear Collider (ILC) is probed. Presence of charged fermionic triplets upto a mass of about $ 750$ GeV could be established through single production at a 1 TeV ILC with moderate luminosity of 300 fb$^{-1}$, assuming a fermion triplet-electron mixing of about 0.05. Unlike the case of LHC, the production process is highly sensitive to the mixing, making the process interesting. The single production of neutral triplet is found to be somewhat harder, considering the large SM background present. Pair prod…
We discuss phenomenology of the radiative seesaw model in which spontaneous breaking of the U(1)$_{B-L}$ gauge symmetry at the TeV scale gives the common origin for masses of neutrinos and dark matter (Kanemura et al., 2012). In this model, the stability of dark matter is realized by the global U(1)$_{DM}$ symmetry which arises by the B$-$L charge assignment. Right-handed neutrinos obtain TeV scale Majorana masses at the tree level. Dirac masses of neutrinos are generated via one-loop diagrams. Consequently, tiny neutrino masses are generated at the two-loop level by the seesaw mechanism. This…
If kinematically accessible, hadron collider experiments provide an ideal laboratory for the direct production of heavy lepton partners in Seesaw models. In the context of the Type III Seesaw Mechanism, the $\mathcal{O}(α_s)$ rate and shape corrections are presented for the pair production of hypothetical, heavy $SU(2)_L$ triplet leptons in $pp$ collisions at $\sqrt{s}=$ 13, 14, and 100 TeV. The next-to-leading order (NLO) $K$-factors span, approximately, $K^{NLO}=1.1 - 1.4$ for both charged current and neutral current processes over a triplet mass range $m_T = 100~\text{GeV}-2~\text{TeV}$. To…
We study lepton-flavor violating slepton production and decay at a future e^+e^- linear collider in context with the seesaw mechanism in mSUGRA post-LEP benchmark scenarios. The present knowledge in the neutrino sector as well as improved future measurements are taken into account. We calculate the signal cross-sections σ(e^{+/-}e^- -> l_β^{+/-} l_α^- \tildeχ_b^0 \tildeχ_a^0); l_δ=e, μ, τ; α=|= βand estimate the main background processes. Furthermore, we investigate the correlations of these signals with the corresponding lepton-flavor violating rare decays l_α -> l_β γ. It is shown that these…
Precision Higgs Boson Probe of Type-II Seesaw Models
Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；Washington University, Saint Louis（华盛顿大学圣路易斯分校）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）
Seesaw Models under the Lens of Angular Distributions at $μ^+μ^-,\, μ^+ μ^+, \, μ^+ γ$ and $μ^+ e^-$ Colliders
Indian Institute of Technology Hyderabad（印度理工学院海德拉巴分校）；INFN, Gruppo Collegato di Cosenz & Dipartimento di Fisica, Università della Calabria（意大利国家核物理研究所科森扎合作组与卡塔尼亚大学物理系）；Theoretical Physics Division, Physical Research Laboratory（物理研究实验室理论物理部）
A low-scale neutrino seesaw may be probed or even reconstructed at colliders provided that supersymmetry is at the weak scale and the LSP is a sterile sneutrino. Because the neutrino Yukawa couplings are small, the NLSP is typically long-lived and thus a significant fraction of colored or charged NLSPs may stop in the detector material before decaying to the LSP and a charged lepton, gauge boson, or Higgs. For two-body NLSP decays, the energy spectrum of the visible decay product exhibits a monochromatic line for each sterile sneutrino which can be used to extract the sterile sneutrino masses …
Neutrino are massless in the Standard Model. The most popular mechanism to generate neutrino masses are the type I and type II seesaw, where right-handed neutrinos and a scalar triplet are augmented to the Standard Model, respectively. In this work, we discuss a model where a type I + II seesaw mechanism naturally arises via spontaneous symmetry breaking of an enlarged gauge group. Lepton flavor violation is a common feature in such setup and for this reason, we compute the model contribution to the $μ\rightarrow eγ$ and $μ\rightarrow 3e$ decays. Moreover, we explore the connection between the…
We study the search potential of heavy triplet leptons in Type III Seesaw mechanism at future high-energy and high-luminosity muon colliders. The impact of up-to-date neutrino oscillation results is taken into account on neutrino parameters and the consequent decay patterns of heavy leptons in Type III Seesaw. The three heavy leptons in the Casas-Ibarra parametrization with diagonal unity matrix are distinguishable in their decay modes. We consider the pair production of charged triplet leptons $E^+ E^-$ through both $μ^+μ^-$ annihilation and vector boson fusion (VBF) processes. The leading-or…
The Higgs boson can mix with a singlet scalar that dynamically generates the Majorana mass of the right-handed neutrino $N_R$. We show that even a tiny mixing between the Higgs boson and a `decoupled' singlet scalar allows for Higgs-mediated pair production of $N_R$ without significant mixings between the active neutrinos and $N_R$, and thus testable at colliders via a characteristic signal of two same-sign same-flavor lepton pairs, plus missing energy. We demonstrate that this search channel is mostly background-free in $pp$-collision and can be a highly sensitive probe of the Higgs-singlet m…
A natural extension of the standard model to accommodate massive neutrinos is to introduce one Higgs triplet and three right-handed Majorana neutrinos, leading to a 6 \times6 neutrino mass matrix. We show that three light Majorana neutrinos (i.e., the mass eigenstates of ν_e, ν_μand ν_τ) are exactly massless, if and only if M_L = M_D M^{-1}_R M^T_D exactly holds in this seesaw model. We propose three simple Type-II seesaw scenarios with broken A_4 \times U(1)_X flavor symmetry to interpret the observed neutrino mass spectrum and neutrino mixing pattern. Such a TeV-scale neutrino model can be t…
We study the potential of an e+- e- Linear Collider for charged lepton flavour violation studies in a supersymmetric framework where neutrino masses and mixings are explained by a type-I seesaw. Focusing on e-mu flavour transitions, we evaluate the background from standard model and supersymmetric charged currents to the e mu + missing E_T signal. We study the energy dependence of both signal and background, and the effect of beam polarisation in increasing the signal over background significance. Finally, we consider the mu- mu- + missing E_T final state in e- e- collisions that, despite bein…
We consider a class of gauged $U(1)$ extensions of the Standard Model (SM), where the light neutrino masses are generated by an inverse seesaw mechanism. In addition to the three right handed neutrinos, we add three singlet fermions and demand an extra $Z_2$ symmetry under which, the third generations of both of the neutral fermions are odd, which in turn gives us a stable dark matter candidate. We express the $U(1)$ charges of all the fermions in terms of the U(1) charges of the standard model Higgs and the new complex scalar. We study the bounds on the parameters of the model from vacuum sta…
The implementation of the Type III seesaw mechanism for neutrino masses in the context of left-right theories where parity is broken spontaneously is investigated. We propose a simple left-right symmetric theory where the neutrinos masses are generated through a double seesaw mechanism which is a combination of Type I and Type III seesaw. In this context we find a possible candidate for the cold dark matter in the Universe and discuss the Baryogenesis via Leptogenesis mechanisms. The spectrum of the theory, the phenomenological constraints and the possibility to test the theory at the Large Ha…
The simplest linear seesaw mechanism can accommodate the new CDF-II $W$ mass measurement. In addition to Standard Model particles, the model includes quasi-Dirac leptons, and a second, leptophilic, scalar doublet seeding small neutrino masses. Our proposal is consistent with electroweak precision tests, neutrino physics, rare decays and collider restrictions, requiring a new charged scalar below a few TeV, split in mass from the new degenerate scalar and pseudoscalar neutral Higgs bosons.
We explore an intriguing possibility to test the type-II seesaw mechanism of neutrino mass generation at the Large Hadron Collider (LHC). We show that the lepton-number-violating signatures of heavy Majorana neutrinos N_i (for i=1, 2, 3) and doubly-charged Higgs bosons H^++(H^--) can be closely correlated with each other in a class of TeV-scale type-II seesaw models. Taking the minimal version of such models for example, we calculate the cross sections of pp -> l^+_αl^+_βX (l^-_αl^-_βX) processes mediated separately by N_1 and H^++(H^--), and illustrate their nontrivial correlation at the LHC.
New physics coupling to the Higgs sector of the Standard Model can lead to dangerously large corrections to the Higgs mass. We investigate this problem in the type II seesaw model for neutrino mass, where a weak scalar triplet is introduced. The interplay of direct and indirect constraints on the type II seesaw model with its contribution to the Higgs mass is analyzed. The focus lies on testable triplet masses and (sub) eV-scale triplet vacuum expectation values. We identify scenarios that are testable in collider and/or lepton flavor violation experiments, while satisfying the Higgs naturalne…
We investigate a prospect of probing the type-III seesaw neutrino mass generation mechanism at various collider experiments by searching for a disappearing track and a displaced vertex signature originating from the decay of $SU(2)_L$ triplet fermion ($Σ$). Since $Σ$ is primarily produced at colliders through the electroweak gauge interactions, its production rate is uniquely determined by its mass. We find that a $Σ$ particle with a mass of a few hundred GeV produces a disappearing track signature from the decay of its charged component, which can be searched at the HL-LHC. Furthermore, we sh…
After outlining some popular ways to go beyond the standard model so as to generate non-zero but tiny neutrino masses, I focus on several typical seesaw mechanisms and discuss how to get a balance between their theoretical naturalness and their experimental testability. Besides possible collider signatures at the Large Hadron Collider, new and non-unitary CP-violating effects are also expected to show up in neutrino oscillations for type-I, type-(I+II), type-III and double seesaws at the TeV scale.
We study the production of heavy neutrinos at the Large Hadron Collider (LHC) through the dominant s-channel production mode as well as the vector boson fusion (VBF) process. We consider the TeV scale minimal linear seesaw model containing two heavy singlets with opposite lepton number. This model is fully reconstructible from oscillation data apart from an overall normalization constant which can be constrained from meta-stability of the electroweak vacuum and bounds coming from lepton flavor violation (LFV) searches. Dirac nature of heavy neutrinos in this model implies suppression of the co…
The signatures of heavy fermionic triplets ($Σ$) arising in scenarios like Type III seesaw model are probed through their direct production and subsequent decay at high energy electron-positron collider. Unlike the case of LHC, the production process has strong dependence on the mixing parameter ($V_{e,μ}$), making the leptonic collider unique to probe such mixing. We have established that with suitably chosen kinematic cuts, a 1 TeV $e^+e^-$ collider could probe the presence of $Σ$ of mass in the range of 500 GeV having $V_e=0.05$ with a few inverse femto barn luminosity through single produc…
A collider probe of the radiative seesaw models are considered. Two key ingredients of these models, the extended Higgs sector and the source of the Majorana mass, although these details differ model by model, would be studied at the TeV-scale electron-positron and electron-electron colliders. The searches and mass determinations in the inert doublet model, which is the extended Higgs sector of the Ma model, are summarized as an example.
The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons and propose the strategy to test this mechanism at the hadron and lepton colliders. The smoking gun evidence of the theory is Delta L=2 lepton number violation through events of a pair of like-sign leptons plus four jets without significant missing ener…
TeV-scale seesaw mechanisms are interesting due to their potential testability at existing collider experiments. Herein we propose an E$_6$-inspired model allowing a TeV-scale pseudo-Dirac singlet neutrino seesaw mechanism with naturally sizeable Yukawa couplings of $\mathcal{O}(10^{-2})$. The model also contains new U(1) gauge interactions (and associated $Z^\prime$ bosons with which the singlet neutrinos can be produced at colliders), typically long-lived colour triplet fermions, SU(2) doublet fermions, and a complex scalar - potentially all at the TeV-scale. Additionally we identify three p…
