Extra Neutral Gauge Boson Research Articles

Revisiting sterile neutrino dark matter in gauged U(1)B−L model

We reexamine sterile neutrino dark matter in gauged $U(1)_{B-L}$ model. Improvements have been made by tracing and careful evaluation of the evolution of the number densities of sterile neutrinos $N$ and extra neutral gauge bosons $Z'$. As a result, the cosmologically-interesting gauge coupling of $U(1)_{B-L}$ for freeze-in sterile neutrinos turns out to be smaller than the values reported in the literature. This avoids the overproduction of $Z'$ so that it is consistent with the big bang nucleosynthesis and the cosmic microwave background constraints on the effective number of neutrino species. Similarly, the free-streaming length constraints exclude a large parameter space derived in previous studies. In addition to known freeze-in pair production of $N$ from the standard model fermion pairs, we find the case that $N$ is dominantly produced from a pair of $Z'$ at the temperature characterized by the $B-L$ breaking scalar mass. Thus, the naive truncation of the $U(1)_{B-L}$ scalar contribution made in the literature is not valid.

Contributions to ZZV^* (V=gamma ,Z,Z') couplings from CP violating flavor changing couplings

The one-loop contributions to the trilinear neutral gauge boson couplings ZZV^* (V=gamma ,Z,Z'), parametrized in terms of one CP-conserving f_5^{V} and one CP-violating f_4^{V} form factors, are calculated in models with CP-violating flavor changing neutral current couplings mediated by the Z gauge boson and an extra neutral gauge boson Z'. Analytical results are presented in terms of Passarino-Veltman scalar functions. Constraints on the vector and axial couplings of the Z gauge boson left| g_{{VZ}}^{tu}right| < 0.0096 and left| g_{{VZ}}^{tc}right| <0.011 are obtained from the current experimental data on the trightarrow Z q decays. It is found that in the case of the ZZgamma ^* vertex the only non-vanishing form factor is f_5^{gamma }, which can be of the order of 10^{-3}, whereas for the ZZZ^* vertex both form factors f_5^{Z} and f_4^{Z} are non-vanishing and can be of the order of 10^{-6} and 10^{-5}, respectively. Our estimates for f_5^{gamma } and f_5^{Z} are smaller than those predicted by the standard model, where f_4^{Z} is absent up to the one loop level. We also estimate the ZZ{Z'}^{*} form factors arising from both diagonal and non-diagonal Z' couplings within a few extension models. It is found that in the diagonal case f_{5}^{Z'} is the only non-vanishing form factor and its real and imaginary parts can be of the order of 10^{-1}–10^{-2} and 10^{-2}–10^{-3}, respectively, with the dominant contributions arising from the light quarks and leptons. In the non-diagonal case f_{5}^{Z^prime } can be of the order of 10^{-4}, whereas f_4^{Z'} can reach values as large as 10^{-7}–10^{-8}, with the largest contributions arising from the Z'tq couplings.

Singlet fermionic dark matter with dark Z

We present a fermionic dark matter model mediated by the hidden gauge boson. We assume the QED-like hidden sector which consists of a Dirac fermion and U(1)_X gauge symmetry, and introduce an additional scalar electroweak doublet field with the U(1)_X charge as a mediator. The hidden U(1)_X symmetry is spontaneously broken by the electroweak symmetry breaking and there exists a massive extra neutral gauge boson in this model which is the mediator between the hidden and visible sectors. Due to the U(1)_X charge, the additional scalar doublet does not couple to the Standard Model fermions, which leads to the Higgs sector of type I two Higgs doublet model. The new gauge boson couples to the Standard Model fermions with couplings proportional to those of the ordinary Z boson but very suppressed, thus we call it the dark Z boson. We study the phenomenology of the dark Z boson and the Higgs sector, and show the hidden fermion can be the dark matter candidate.

Probing new neutral gauge bosons with CEνNS and neutrino-electron scattering

The potential for probing extra neutral gauge boson mediators ($Z^\prime$) from low-energy measurements is comprehensively explored. Our study mainly focuses on $Z^\prime$ mediators present in string-inspired $E_6$ models and left-right symmetry. We estimate the sensitivities of coherent-elastic neutrino-nucleus scattering (CE$\nu$NS) and neutrino-electron scattering experiments. Our results indicate that such low-energy high-intensity measurements can provide a valuable probe, complementary to high-energy collider searches and electroweak precision measurements.

Constraining heavy neutral gauge boson Z′ in the 3 - 3 - 1 models by weak charge data of Cesium and proton

The recent experimental data of the weak charges of Cesium and proton is analyzed in the framework of the models based on the SU(3)C×SU(3)L×U(1)X (3-3-1) gauge group, including the 3-3-1 model with CKS mechanism (3-3-1CKS) and the general 3-3-1 models with arbitrary β (3-3-1β) with three Higgs triplets. We will show that at the TeV scale, the mixing among neutral gauge bosons plays significant effect. Within the present values of the weak charges of Cesium and proton we get the lowest mass bound of the extra heavy neutral gauge boson to be 1.27 TeV. The results derived from the weak charge data, perturbative limit of Yukawa coupling of the top quark, and the relevant Landau poles favor the models with β=±13 and β=0 while ruling out the ones with β=±3. In addition, there are some hints showing that in the 3-3-1 models, the third quark family should be treated differently from the first twos.

Minimally extended left-right symmetric model for dark matter with U(1) portal

A minimal extension of the left-right symmetric model for neutrino masses that includes a vector-like singlet fermion dark matter (DM) is presented with the DM connected to the visible sector via a gauged U(1) portal. We discuss the symmetry breaking in this model and calculate the mass and mixings of the extra heavy neutral gauge boson at the TeV scale. The extra gauge boson can decay to both standard model particles as well to dark matter. We calculate the relic density of the singlet fermion dark matter and its direct detection cross section and use these constraints to obtain the allowed parameter range for the new gauge coupling and the dark matter mass.

B-L extension of the SM - Z′ and heavy Higgs boson analysis at future e+ e− linear colliders ILC and CLIC

We propose a U(1)B−L (baryon minus lepton) extension to the Standard Model, which adds a complex singlet to the scalar sector where an extra neutral gauge boson Z′ corresponding to the U(1)B−L gauge symmetry and an extra SM like singlet scalar H (heavy Higgs) are predicted. We consider the mixture of the Z and Z′. The model also yields Majorana masses for three right handed neutrinos. We study the phenomenology of the light h and heavy H Higgs boson production and decay at future e+ e− linear colliders with center-of-mass energies of √s = 500 − 3000 GeV and integrated luminosities of ℒ = 500 − 2000 fb−1. The study includes the Higgs-strahlung processes e+ e− → (Z Z′) → Zh, e+ e− → (Z Z′) → ZH, and we complement our previous works with the addition of the process.

Model identification of new heavy Z′ bosons at ILC with polarized beams

Extra neutral gauge bosons, Z′s, are predicted by many theoretical scenarios of physics beyond the Standard Model, and intensive searches for their signatures will be performed at present and future high energy colliders. It is quite possible that Z′s are heavy enough to lie beyond the discovery reach expected at the CERN Large Hadron Collider LHC, in which case only indirect signatures of Z′ exchanges may occur at future colliders, through deviations of the measured cross sections from the Standard Model predictions. We here discuss in this context the expected sensitivity to Z′ parameters of fermion-pair production cross sections at the planned International Linear Collider (ILC), especially as regards the potential of distinguishing different Z′ models once such deviations are observed. Specifically, we evaluate the discovery and identification reaches on Z′ gauge bosons pertinent to the E6, LR, ALR, and SSM classes of models at the ILC.

Scalar production in association with a Z boson at the LHC and ILC: The mixed Higgs-radion case of warped models

The radion scalar field might be the lightest new particle predicted by extra-dimensional extensions of the Standard Model. It could thus lead to the first signatures of new physics at the LHC collider. We perform a complete study of the radion production in association with the Z gauge boson in the custodially protected warped model with a brane-localised Higgs boson addressing the gauge hierarchy problem. Radion-Higgs mixing effects are present. Such a radion production receives possibly resonant contributions from the Kaluza-Klein excitations of the Z boson as well as the extra neutral gauge boson (Z'). All the exchange and mixing effects induced by those heavy bosons are taken into account in the radion coupling and rate calculations. The investigation of the considered radion production at LHC allows to be sensitive to some parts of the parameter space but only the ILC program at high luminosity would cover most of the theoretically allowed parameter space via the studied reaction. Complementary tests of the same theoretical parameters can be realised through the high accuracy measurements of the Higgs couplings at ILC. The generic sensitivity limits on the rates discussed for the LHC and ILC potential reach can be applied to the searches for other (light) exotic scalar bosons.

FIMP and muon (g \u2212 2) in a U(1)L\u03bc\u2212L\u03c4 model

The tightening of the constraints on the standard thermal WIMP scenario has forced physicists to propose alternative dark matter (DM) models. One of the most popular alternate explanations of the origin of DM is the non-thermal production of DM via freeze-in. In this scenario the DM never attains thermal equilibrium with the thermal soup because of its feeble coupling strength (∼10−12) with the other particles in the thermal bath and is generally called the Feebly Interacting Massive Particle (FIMP). In this work, we present a gauged U(1)Lμ−Lτ extension of the Standard Model (SM) which has a scalar FIMP DM candidate and can consistently explain the DM relic density bound. In addition, the spontaneous breaking of the U(1)Lμ−Lτ gauge symmetry gives an extra massive neutral gauge boson Zμτ which can explain the muon (g − 2) data through its additional one-loop contribution to the process. Lastly, presence of three right-handed neutrinos enable the model to successfully explain the small neutrino masses via the Type-I seesaw mechanism. The presence of the spontaneously broken U(1)Lμ−Lτ gives a particular structure to the light neutrino mass matrix which can explain the peculiar mixing pattern of the light neutrinos.

Higgs mass and right-handed sneutrino WIMP in a supersymmetric3−3−1model

This work deals with right handed sneutrino as thermal cold dark matter candidate. This scalar emerges in a supersymmetric version of $SU(3)_c \otimes SU(3)_L \otimes U(1)_X$ gauge model where right handed neutrinos are a natural component of leptonic chiral scalar supermultiplets. We first consider the issue of a $125$~GeV Higgs boson mass in this model, showing that constraints on stop mass and trilinear soft coupling are considerably alleviated compared to MSSM. Then we investigate the region of parameter space that is consistent with right handed sneutrino as thermal cold dark matter, under the light of Planck results on the relic abundance and direct detection from LUX experiment. This sneutrino mainly annihilates through an extra neutral gauge boson, $Z^\prime$, and Higgs exchange, so that the physics of dark matter is somewhat related to the parameters determining Higgs and $Z^\prime$ masses. We then obtain that right handed sneutrino in this model must be heavier than $400$~GeV to conform with Planck and LUX, simultaneously constraining the $Z^\prime$ mass to be above 2400~GeV, which is in perfect agreement with LHC searches in a non-supersymmetric version of this model.

Freeze-in production of sterile neutrino dark matter in U(1)B−L model

With the advent of new and more sensitive direct detection experiments, scope for a thermal WIMP explanation of dark matter (DM) has become extremely constricted. The non-observation of thermal WIMP in these experiments has put a strong upper bound on WIMP-nucleon scattering cross section and within a few years it is likely to overlap with the coherent neutrino-nucleon cross section. Hence in all probability, DM may have some non-thermal origin. In this work we explore in detail this possibility of a non-thermal sterile neutrino DM within the framework of U(1)B−L model. The U(1)B−L model on the other hand is a well-motivated and minimal way of extending the standard model so that it can explain the neutrino masses via Type-I see-saw mechanism. We have shown, besides explaining the neutrino mass, it can also accommodate a non-thermal sterile neutrino DM with correct relic density. In contrast with the existing literature, we have found that W± decay can also be a dominant production mode of the sterile neutrino DM . To obtain the comoving number density of dark matter, we have solved here a coupled set of Boltzmann equations considering all possible decay as well as annihilation production modes of the sterile neutrino dark matter. The framework developed here though has been done for a U(1)B−L model, can be applied quite generally for any models with an extra neutral gauge boson and a fermionic non-thermal dark matter.

On probing Higgs couplings in H → Ze+e− and e+e−→ ZH

Two most popular GUT scenarios, namely, the left–right symmetric model (LRM) and models coming from [Formula: see text] grand unification (effective rank 5 models (ER5M’s)) are considered. Both models forecast existence of the extra neutral gauge boson. Its contributions to the decay of the Higgs boson being an analog of the Standard Model (SM) Higgs boson [Formula: see text] and the process of the associated Higgs production with [Formula: see text] boson (Higgsstrahlung) [Formula: see text] are found. For both processes, deviations from the SM predicted by the LRM prove to be larger than that predicted by the ER5M’s. It is shown that in the case of the decay [Formula: see text] it is impossible to observe these deviations at the condition of the High Luminosity Large Hadron Collider. Investigation of the Higgsstrahlung disclosed that with its help one could make a choice between the SM and the SM extensions under consideration.

Phenomenology of minimalZ’ models: from the LHC to the GUT scale

We consider a class of minimal abelian extensions of the Standard Model with an extra neutral gauge boson $Z'$ at the TeV scale. In these scenarios an extended scalar sector and heavy right-handed neutrinos are naturally envisaged. We present some of their striking signatures at the Large Hadron Collider, the most interesting arising from a $Z'$ decaying to heavy neutrino pairs as well as a heavy scalar decaying to two Standard Model Higgses. Using renormalisation group methods, we characterise the high energy behaviours of these extensions and exploit the constraints imposed by the embedding into a wider GUT scenario.

LHC Phenomenology of Z′ and Z″ bosons in the SU(4)L × U(1)X little Higgs model

We examine the direct limits on masses of extra neutral gauge bosons in the model with a little Higgs mechanism confronted with the Large Hadron Collider (LHC) data, especially by embedding an anomaly-free set of fermions. There exist two extra neutral gauge bosons, called and in this model. The lower exclusion limit of the mass of the lighter extra neutral gauge boson is about 3 TeV, while that of the heavier one is 5 TeV. For comparison, we examine the mass limit of the boson in the model as well and discuss the implication of our result in the model with a standard Higgs mechanism. We also discuss the discovery potential of and at the future LHC with a center-of-momentum energy of 14 TeV. Our results can be applicable to models with a regular Higgs mechanism if the same type of fermion family is assigned.

Lepton number violation within the conformal inverse seesaw

We present a novel framework within the conformal inverse seesaw scheme allowing large lepton number violation while the neutrino mass formula is still governed by the low-scale inverse seesaw mechanism. This model includes new contributions to rare low-energy lepton number violating processes like neutrinoless double beta decay. We find that the lifetime for this rare process due to heavy sterile neutrinos can saturate current experimental limits in contrast to the usual inverse seesaw where this process is suppressed. The characteristic collider signature of the present conformal inverse seesaw scheme includes, same-sign dilepton plus two jets and same-sign dilepton plus four jets. Finally, we comment on the testability of the model at the Large Hadron Collider since there are new scalars, new fermions and an extra neutral gauge boson with masses around few 100 GeV to few TeV.

A 3-form gauge potential in 5D in connection with a possible dark sector of 4D-electrodynamics

We here propose a 5-dimensional {\bf Abelian gauge} model based on the mixing between a $U(1)$ potential and an Abelian 3-form field by means of a topological mass term. An extended covariant derivative is introduced to minimally couple a Dirac field to the $U(1)$ potential, while this same covariant derivative non-minimally couples the 3-form field to the charged fermion. A number of properties are discussed in 5D; in particular, the appearance of a topological fermionic current. A 4-dimensional reduced version of the model is investigated and, { \bf in addition to the $U(1)$ electric- and magnetic-sort of fields,} there emerges an extra set of electric- and magnetic-like fields which contribute a negative pressure and may be identified as a possible fraction of dark energy. The role of the topological fermionic current is also contemplated upon dimensional reduction from 5D to 4D. Other issues we present in 4 space-time dimensions are the emergence {\bf of a pseudo-scalar massive particle,} an extra massive neutral gauge boson,{\bf which we interpret as a kind of paraphoton}, and the calculation of spin- and velocity-dependent interparticle potentials associated to the exchange of the intermediate bosonic fields of the model.

Determination of e+e- beam polarization for optimal gauge boson discovery limits

Extra neutral gauge bosons suggested by models beyond the standard model can indirectly show up in e+e- collisions through off-resonance deviations of various physical observables from the corresponding standard model values. We considered leptonic observables and studied the dependence of the deviations on the polarizations of the positron and electron beams. We showed that, for a given model, the magnitude of the deviation of a given observable can attain its maximum value if the polarizations of the positron and electron beams are properly chosen. We determined, for a given model, a single set of beam polarization so that if this set is employed in measuring all considered observables, it produces the highest extra gauge boson discovery limits.

Search for HZZ′ couplings at the LHC

New physics models predict the possibility of extra neutral gauge bosons associated with an extra gauge symmetry. We study the couplings of the Higgs boson to the Z boson and Z′ boson predicted by the new physics models. Since there is stringent limit on the Z′ boson mass from the channel at the LHC experiments, we use two benchmark models: the leptophobic which has no couplings with leptons and the eta which has small couplings with fermions. The couplings of the Z′ boson to quarks can also be investigated through the interactions. The accessible ranges of the parameter space have been searched for processes and at the LHC with .

Constraints on 3-3-1 models with electroweakZpole observables andZ′search at the LHC

In the framework of general 3-3-1 models, we perform a global ${\ensuremath{\chi}}^{2}$ fit at 95% C.L. to the updated $Z$ pole observables, including new data from atomic parity violation. We found scenarios where specific realizations of 3-3-1 models are largely excluded above the current limit on the extra neutral gauge boson (${Z}^{\ensuremath{'}}$) research at the LHC. We derive a relation between the $Z\text{\ensuremath{-}}{Z}^{\ensuremath{'}}$ mixing angle and the parameter $\mathrm{tan}(\ensuremath{\beta})$ of the effective two-Higgs-doublet model contained into the 3-3-1 spectrum. We show that particular versions of 3-3-1 models containing particles with exotic electric charges are disfavored by the electroweak precision observables in an ample region of the parameter space.