Generations Of Right-handed Neutrinos Research Articles

Z′ induced forward dominant processes in μTRISTAN experiment

General U(1) extension of the Standard Model (SM) is a well motivated beyond the Standard Model (BSM) scenario where three generations of right handed neutrinos (RHNs) are introduced to cancel gauge and mixed gauge-gravity anomalies. After the U(1)X is broken, RHNs participate in the seesaw mechanism to generate light neutrino masses satisfying neutrino oscillation data. In addition to that, a neutral gauge boson Z′ is evolved which interacts with the left and right handed fermions differently manifesting chiral nature of the model which could be probed in future collider experiments. As a result, if we consider μ+e− and μ+μ+ collisions in μTRISTAN experiment Z′ mediated 2→2 scattering will appear in t− and u-channels depending on the initial and final states being accompanied by the photon and Z mediated interactions. This will result well motivated resulting forward dominant scenarios giving rise to sizable left-right asymmetry. Estimating constraints on general U(1) coupling from LEP-II and LHC for different U(1)X charges, we calculate differential and integrated scattering cross section and left-right asymmetry for μ+e−→μ+e− and μ+μ+→μ+μ+ processes which could be probed at μTRISTAN experiment further enlightening the interaction between Z′ and charged leptons and the U(1)X breaking scale.

Generation of neutrino dark matter, baryon asymmetry, and radiation after quintessential inflation

We construct a model explaining dark matter, baryon asymmetry, and reheating in a quintessential inflation model. Three generations of right-handed neutrinos having hierarchical masses and the light scalar field leading to the self-interaction of active neutrinos are introduced. The lightest sterile neutrino is a dark matter candidate produced by a Dodelson-Widrow mechanism in the presence of a new light scalar field, while the heaviest and next-heaviest sterile neutrinos produced by gravitational particle production are responsible for the generation of the baryon asymmetry. Reheating is realized by spinodal instabilities of the Standard Model Higgs field induced by the nonminimal coupling to the scalar curvature, which can solve the overproduction of gravitons and curvature perturbation created by the Higgs condensation.

Testing leptogenesis at the LHC and future muon colliders: A Z′ scenario

If the masses of at least two generations of right-handed neutrinos (RHNs) are near-degenerate, the scale of leptogenesis can be as low as $\sim$ 100 GeV. In this work, we study probing such resonant leptogenesis in the $B-L$ model at the LHC and future multi-TeV muon colliders via the process $Z'\to NN\to\ell^\pm\ell^\pm+{\rm jets}$, with $Z'$ the $U(1)_{B-L}$ gauge boson and $N$ the RHN. The same-sign dilepton feature of the signal makes it almost background-free, while the event number difference between positive and negative leptons is a hint for $CP$ violation, which is a key ingredient of leptogenesis. We found that resonant leptogenesis can be tested at the HL-LHC for $M_{Z'}$ up to 12 TeV, while at a 10 (30) TeV muon collider the reach can be up to $M_{Z'}\sim28~(100)$ TeV via the off-shell production of $Z'$.

Heavy dark matter, neutrino masses, and Higgs naturalness from a strongly interacting hidden sector

We consider the extension of the Standard Model (SM) with a strongly interacting QCD-like hidden sector, at least two generations of right-handed neutrinos and one scalar singlet. Once scalar singlet obtains a nonzero vacuum expectation value, active neutrino masses are generated through type-I seesaw mechanism. Simultaneously, the electroweak scale is generated through the radiative corrections involving these massive fermions. This is the essence of the scenario that is known as the "neutrino option" for which the successful masses of right-handed neutrinos are in the range $10^7-10^8$ GeV. The main goal of this work is to scrutinize the potential to accommodate dark matter in such a realization. The dark matter candidates are Nambu-Goldstone bosons which appear due to the dynamical breaking of the hidden chiral symmetry. The mass spectrum studied in this work is such that masses of Nambu-Goldstone bosons and singlet scalar exceed those of right-handed neutrinos. Having the masses of all relevant particles several orders of magnitude above $\mathcal{O}$(TeV), the freeze-out of dark matter is not achievable and hence we turn to alternative scenarios, namely freeze-in. The Nambu-Goldstone bosons can interact with particles that are not in SM but, however, have non-negligible abundance through their not-too-small couplings with SM. Utilizing this, we demonstrate that the dark matter in the model is successfully produced at temperature scale where the right-handed neutrinos are still stable. We note that the lepton number asymmetry sufficient for the generation of observable baryon asymmetry of the Universe can be produced in right-handed neutrino decays. Hence, we infer that the model has the potential to simultaneously address several of the most relevant puzzles in contemporary high-energy physics.

Anomaly-free 2HDMs with a gauged Abelian symmetry and two generations of right-handed neutrinos

Despite the popularity of two-Higgs-doublet models (2HDMs) with a gauged abelian flavor symmetry, the allowed Yukawa textures have only been partly explored so far. In this work, we classify and compare every anomaly-free instance, in the case of having two generations of right-handed neutrinos and a type-I seesaw mechanism. We found 16 valid implementations in total, out of which 11 agree well with current experimental bounds. To our knowledge, neither of these models have been considered previously.

Precise prediction for the Higgs-Boson masses in the {varvec{mu }}{varvec{nu }}SSM with three right-handed neutrino superfields

The mu nu mathrm {SSM} is a simple supersymmetric extension of the Standard Model (SM) capable of describing neutrino physics in agreement with experiments. We perform the complete one-loop renormalization of the neutral scalar sector of the mu nu mathrm {SSM} with three generation of right-handed neutrinos in a mixed on-shell/smash {overline{mathrm {DR}}} scheme. We calculate the full one-loop corrections to the neutral scalar masses of the mu nu mathrm {SSM}. The one-loop contributions are supplemented by available MSSM higher-order corrections. We obtain numerical results for a SM-like Higgs-boson mass consistent with experimental bounds, while simultaneously agreeing with neutrino oscillation data. We illustrate the distinct phenomenology of the mu nu mathrm {SSM} in scenarios in which one or more right-handed sneutrinos are lighter than the SM-like Higgs boson, which might be substantially mixed with them. These scenarios are experimentally accessible, on the one hand, through direct searches of the right-handed sneutrinos decaying into SM particles, and on the other hand, via the measurements of the SM-like Higgs-boson mass and its couplings. In this way the parameter space of the mu nu mathrm {SSM} can be probed without the need to propose model dependent searches at colliders. Finally, we demonstrate how the mu nu mathrm {SSM} can simultaneously accommodate two excesses measured at LEP and LHC at sim 96,, mathrm {GeV} at the 1sigma level, while at the same time reproducing neutrino masses and mixings in agreement with neutrino oscillation measurements.

The new \u03bdMSM (\u03bd\u03bdMSM): radiative neutrino masses, keV-scale dark matter and viable leptogenesis with sub-TeV new physics

We study the scenario in which the Standard model is augmented by three generations of right-handed neutrinos and a scalar doublet. The newly introduced fields share an odd charge under a ℤ2 parity symmetry. This model, commonly known as “Scotogenic”, was designed to provide a mechanism for active neutrino mass generation as well as a viable dark matter candidate. In this paper we consider a scenario in which the dark matter particle is at the keV-scale. Such particle is free from X-ray limits due to the unbroken parity symmetry that forbids the mixing between active and right-handed neutrinos. The active neutrino masses are radiatively generated from the new scalars and the two heavier right-handed states with ∼ mathcal{O} (100) GeV masses. These heavy fermions can produce the observed baryon asymmetry of the Universe through the combination of Akhmedov-Rubakov-Smirnov mechanism and recently proposed scalar decays. To the best of our knowledge, this is the first time that these two mechanisms are shown to be successful in any radiative model. We identify the parameter space where the successful leptogenesis is compatible with the observed abundance of dark matter as well as the measurements from the neutrino oscillation experiments. Interestingly, combining dark matter production and successful leptogenesis gives rise to strict limits from big bang nucleosynthesis which do not allow the mass of dark matter to lie above ∼ 10 keV, providing a phenomenological hint for considered low-scale dark matter. By featuring the keV-scale dark matter free from stringent X-ray limits, successful baryon asymmetry generation and non-zero active neutrino masses, the model is a direct analogue to the νMSM model proposed by Asaka, Blanchet and Shaposhnikov. Therefore we dub the presented framework as “The new νMSM” abbreviated as ννMSM.

Precise prediction for the Higgs-boson masses in the mu nu SSM

The mu nu mathrm {SSM} is a simple supersymmetric extension of the Standard Model (SM) capable of predicting neutrino physics in agreement with experiment. In this paper we perform the complete one-loop renormalization of the neutral scalar sector of the mu nu mathrm {SSM} with one generation of right-handed neutrinos in a mixed on-shell/{overline{mathrm {DR}}} scheme. The renormalization procedure is discussed in detail, emphasizing conceptual differences to the minimal (MSSM) and next-to-minimal (NMSSM) supersymmetric standard model regarding the field renormalization and the treatment of non-flavor-diagonal soft mass parameters, which have their origin in the breaking of R-parity in the mu nu mathrm {SSM}. We calculate the full one-loop corrections to the neutral scalar masses of the mu nu mathrm {SSM}. The one-loop contributions are supplemented by available MSSM higher-order corrections. We obtain numerical results for a SM-like Higgs boson mass consistent with experimental bounds. We compare our results to predictions in the NMSSM to obtain a measure for the significance of genuine mu nu mathrm {SSM}-like contributions. We only find minor corrections due to the smallness of the neutrino Yukawa couplings, indicating that the Higgs boson mass calculations in the mu nu mathrm {SSM} are at the same level of accuracy as in the NMSSM. Finally we show that the mu nu mathrm {SSM} can accomodate a Higgs boson that could explain an excess of gamma gamma events at sim 96 ,mathrm {GeV} as reported by CMS, as well as the 2,sigma excess of b bar{b} events observed at LEP at a similar mass scale.

Z′ -portal right-handed neutrino dark matter in the minimal U(1)X extended Standard Model

We consider a concise dark matter (DM) scenario in the context of a non-exotic U(1) extension of the Standard Model (SM), where a new U(1)$_X$ gauge symmetry is introduced along with three generation of right-handed neutrinos (RHNs) and an SM gauge singlet Higgs field. The model is a generalization of the minimal gauged U(1)$_{B-L}$ (baryon number minus lepton number) extension of the SM, in which the extra U(1)$_X$ gauge symmetry is expressed as a linear combination of the SM U(1)$_Y$ and U(1)$_{B-L}$ gauge symmetries. We introduce a $Z_2$-parity and assign an odd-parity only for one RHN among all particles, so that this $Z_2$-odd RHN plays a role of DM. The so-called minimal seesaw mechanism is implemented in this model with only two $Z_2$-even RHNs. In this context, we investigate physics of the RHN DM, focusing on the case that this DM particle communicates with the SM particles through the U(1)$_X$ gauge boson ($Z^\prime$ boson). This "$Z^\prime$-portal RHN DM" scenario is controlled by only three free parameters: the U(1)$_X$ gauge coupling ($\alpha_X$), the $Z^\prime$ boson mass ($m_{Z^\prime}$), and the U(1)$_X$ charge of the SM Higgs doublet ($x_H$). We consider various phenomenological constraints to identify a phenomenologically viable parameter space. The most important constraints are the observed DM relic abundance and the latest LHC Run-2 results on the search for a narrow resonance with the di-lepton final state. We find that these are complementary with each other and narrow the allowed parameter region, leading to the lower mass bound of $m_{Z^\prime} \gtrsim 2.7$ TeV.

Electroweak vacuum stability in classically conformal B-L extension of the standard model

We consider the minimal U(1)_{B-L} extension of the standard model (SM) with the classically conformal invariance, where an anomaly-free U(1)_{B-L} gauge symmetry is introduced along with three generations of right-handed neutrinos and a U(1)_{B-L} Higgs field. Because of the classically conformal symmetry, all dimensional parameters are forbidden. The B-L gauge symmetry is radiatively broken through the Coleman–Weinberg mechanism, generating the mass for the U(1)_{B-L} gauge boson (Z^prime boson) and the right-handed neutrinos. Through a small negative coupling between the SM Higgs doublet and the B-L Higgs field, the negative mass term for the SM Higgs doublet is generated and the electroweak symmetry is broken. In this model context, we investigate the electroweak vacuum instability problem in the SM. It is well known that in the classically conformal U(1)_{B-L} extension of the SM, the electroweak vacuum remains unstable in the renormalization group analysis at the one-loop level. In this paper, we extend the analysis to the two-loop level, and perform parameter scans. We identify a parameter region which not only solve the vacuum instability problem, but also satisfy the recent ATLAS and CMS bounds from search for Z^prime boson resonance at the LHC Run-2. Considering self-energy corrections to the SM Higgs doublet through the right-handed neutrinos and the Z^prime boson, we derive the naturalness bound on the model parameters to realize the electroweak scale without fine-tunings.

Composite states of two right-handed neutrinos

In this work, we develop a model for Higgs-like composites based on two generations of right handed neutrinos which condense. We analyze the Spontaneous Symmetry Breaking of the theory with two explicit breakings, setting the different scales of the model and obtaining massive bosons as a result. Finally, we calculate the gravitational wave imprint left by the phase transition associated to the symmetry breaking of a generic potential dictated by the symmetries of the composites.

Constraining minimal anomaly free U(1) extensions of the Standard Model

We consider a class of minimal anomaly free $\mathrm{U}(1)$ extensions of the Standard Model with three generations of right-handed neutrinos and a complex scalar. Using electroweak precision constraints, new 13 TeV LHC data, and considering theoretical limitations such as perturbativity, we show that it is possible to constrain a wide class of models. By classifying these models with a single parameter, $\kappa$, we can put a model independent upper bound on the new $\mathrm{U}(1)$ gauge coupling $g_z$. We find that the new dilepton data puts strong bounds on the parameters, especially in the mass region $M_{Z'}\lesssim 3~ \mathrm{TeV}$.

Classically conformalU(1)′extended standard model, electroweak vacuum stability, and LHC Run-2 bounds

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 $m_{Z'} \gtrsim 3.5$ 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 $m_{Z'} \lesssim 7$ 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 $\lesssim m_{Z'} \lesssim 7$ TeV will be explored at the LHC Run-2 in the near future.

ZBL′portal dark matter and LHC Run-2 results

We consider a concise dark matter scenario in the minimal gauged $B\ensuremath{-}L$ extension of the standard model (SM), where the global $B\ensuremath{-}L$ (baryon number minus lepton number) symmetry in the SM is gauged, and three generations of right-handed neutrinos and a $B\ensuremath{-}L$ Higgs field are introduced. Associated with the $B\ensuremath{-}L$ gauge symmetry breaking by a VEV of the $B\ensuremath{-}L$ Higgs field, the seesaw mechanism for generating the neutrino mass is automatically implemented after the electroweak symmetry breaking in the SM. In this model context, we introduce a ${Z}_{2}$-parity and assign an odd parity for one right-handed neutrino while even parities for the other fields. Therefore, the dark matter candidate is identified as the right-handed Majorana neutrino with odd ${Z}_{2}$ parity, keeping the minimality of the particle content intact. When the dark matter particle communicates with the SM particles mainly through the $B\ensuremath{-}L$ gauge boson (${Z}_{BL}^{\ensuremath{'}}$ boson), its relic abundance is determined by only three free parameters, the $B\ensuremath{-}L$ gauge coupling (${\ensuremath{\alpha}}_{BL}$), the ${Z}_{BL}^{\ensuremath{'}}$ boson mass (${m}_{{Z}^{\ensuremath{'}}}$) and the dark matter mass (${m}_{\mathrm{DM}}$). With the cosmological upper bound on the dark matter relic abundance we find a lower bound on ${\ensuremath{\alpha}}_{BL}$ as a function of ${m}_{{Z}^{\ensuremath{'}}}$. On the other hand, we interpret the recent LHC Run-2 results on search for ${Z}^{\ensuremath{'}}$ boson resonance to an upper bound on ${\ensuremath{\alpha}}_{BL}$ as a function of ${m}_{{Z}^{\ensuremath{'}}}$. Combining the two results we identify an allowed parameter region for this ``${Z}_{BL}^{\ensuremath{'}}$ portal'' dark matter scenario, which turns out to be a narrow window with the lower mass bound of ${m}_{{Z}^{\ensuremath{'}}}>2.5\text{ }\text{ }\mathrm{TeV}$.

Classically conformalU(1)′extended standard model and Higgs vacuum stability

We consider the minimal U(1)$^\prime$ 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)$^\prime$ 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)$^\prime$ gauge symmetry is radiatively broken via the Coleman-Weinberg mechanism, by which the U(1)$^\prime$ gauge boson ($Z^\prime$ boson) mass as well as the Majorana mass for the right-handed neutrinos are generated. The radiative U(1)$^\prime$ 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)$^\prime$ charge of the SM Higgs doublet, U(1)$^\prime$ gauge coupling and $Z^\prime$ 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)$^\prime$ symmetry breaking contribute to the SM Higgs self-energy. We find an upper bound on $Z^\prime$ boson mass, $m_{Z^\prime} \lesssim 6$ TeV, in order to avoid a fine-tuning severer than 10 % level. The $Z^\prime$ boson in this mass range can be discovered at the LHC Run-2 in the near future.

Dark matter andU(1)′symmetry for the right-handed neutrinos

We consider a $U{(1)}^{\ensuremath{'}}$ gauge symmetry acting on three generations of right-handed neutrinos. The $U{(1)}^{\ensuremath{'}}$ symmetry is broken at the TeV scale, and its remnant discrete symmetry makes one of the right-handed neutrinos stable. As a natural consequence of the anomaly cancellation, the neutrino mass matrix consists of a combination of type I (TeV scale) seesaw and radiative corrections. The stable right-handed neutrino communicates with the Standard Model via $s$-channel exchange of the Higgs field and the $U{(1)}^{\ensuremath{'}}$ gauge boson, so that the observed relic density for dark matter is obtained in a wide range of the parameter space. The experimental signatures in collider and other experiments are briefly discussed.

Leptogenesis and neutrino oscillations in the classically conformal standard model with the Higgs portal

The Standard Model with an added Higgs portal interaction and no explicit mass terms is a classically scale-invariant theory. In this case the scale of electroweak symmetry breaking can be induced radiatively by the Coleman-Weinberg mechanism operational in a hidden sector, and then transmitted to the Standard Model through the Higgs portal. The smallness of the generated values for the Higgs vev and mass, compared to the UV cutoff of our classically scale-invariant effective theory, is naturally explained by this mechanism. We show how these classically conformal models can generate the baryon asymmetry of the Universe without the need of introducing mass scales by hand or their resonant fine-tuning. The minimal model we consider is the Standard Model coupled to the Coleman-Weinberg scalar field charged under the U(1) B−L gauge group. Anomaly cancellation requires automatic inclusion of three generations of right-handed neutrinos. Their GeV-scale Majorana masses are induced by the Coleman-Weinberg field and lead to the generation of active neutrino masses through the standard see-saw mechanism. Leptogenesis occurs via flavour oscillations of right-handed sterile neutrinos and is converted to the baryon asymmetry by electroweak sphalerons.

Dark matter and strong electroweak phase transition in a radiative neutrino mass model

We consider an extension of the standard model (SM) with charged singlet scalars and right handed (RH) neutrinos all at the electroweak scale. In this model, the neutrino masses are generated at three loops, which provide an explanation for their smallness, and the lightest RH neutrino, N1, is a dark matter candidate. We find that for three generations of RH neutrinos, the model can be consistent with the neutrino oscillation data, lepton flavor violating processes, N1 can have a relic density in agreement with the recent Planck data, and the electroweak phase transition can be strongly first order. We also show that the charged scalars may enhance the branching ratio h→γγ, where as h→γZ get can get few percent suppression. We also discuss the phenomenological implications of the RH neutrinos at the collider.

A COMPLETE AND MINIMAL CATALOGUE OF MSSM GAUGE INVARIANT MONOMIALS

We present a complete and minimal catalogue of MSSM gauge invariant monomials. That is, the catalogue of Gherghetta, Kolda and Martin is elaborated to include generational structure for all monomials. Any gauge invariant operator can be built as a linear combination of elements of the catalogue lifted to nonnegative integer powers. And the removal of any one of the monomials would deprive the catalogue of this feature. It contains 712 monomials, plus 3 generations of right-handed neutrinos if one extends the model to the νMSSM. We note that νMSSM flat directions can all be lifted by the sixth-order superpotential compared to the ninth-order needed in MSSM.

Testability of the type I seesaw mechanism at the CERN LHC: Revealing the existence of theB−Lsymmetry

We study the possibility to test the type I seesaw mechanism for neutrino masses at the CERN Large Hadron Collider. The inclusion of three generations of right-handed neutrinos (${N}_{i}$) provides an attractive option of gauging the $B\ensuremath{-}L$ accidental symmetry in the standard model (as well as an extended symmetry $X=Y\ensuremath{-}5(B\ensuremath{-}L)/4$). The production mechanisms for the right-handed neutrinos through the ${Z}^{\ensuremath{'}}$ gauge boson in the $U(1{)}_{B\ensuremath{-}L}$ and $U(1{)}_{X}$ extensions of the standard model are studied. We discuss the flavor combinations of the charged leptons from the decays of ${N}_{i}$ in the $\ensuremath{\Delta}L=2$ channels. We find that the clean channels with dilepton plus jets and possible secondary vertices of the $N$ decay could provide conclusive signals at the LHC in connection with the hierarchical pattern of the light neutrino masses and mixing properties within the type I seesaw mechanism.