Scalar Doublet Field Research Articles

Light lepton portal dark matter meets the LHC

We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10 GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below mathcal{O}(10)textrm{GeV} and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run 2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-Z plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.

Fermion mass formulation in the Modified Left-Right Symmetry Model

The Modified Left Right Symmetry Model is an extension of the Standard Model. This model introduces left-handed neutrinos to the right sector and a doublet scalar field to the left sector. This model cannot yet explain the mass generation of fermions and neutrinos. This study is theoretical research using the literature review method. Generating the masses of fermions (quark up-down) and electrons through spontaneous symmetry breaking in Yukawa's Lagrangian term produces a particle mass in the left sector, the same as the calculations in the Standard Model. The masses of fermions (up-down quarks) and electrons for the right sector produced in this study are much more massive than those of fermions (up-down quarks) and the left sector. The neutrino masses produced in this study are by following the Seesaw Mechanism. That is, if one neutrino mass is massive, then the other neutrino masses will be light.©2022 JNSMR UIN Walisongo. All rights reserved.

Asymmetric mediator in scotogenic model

The scotogenic model is the Standard Model (SM) with Z2 symmetry and the addition of Z2 odd right-handed Majorana neutrinos and SU(2)L doublet scalar fields. We have extended the original scotogenic model by an additional Z2 odd singlet scalar field that plays a role in dark matter. In our model, the asymmetries of the lepton and Z2 odd doublet scalar are simultaneously produced through CP-violating right-handed neutrino decays. While the former is converted into baryon asymmetry through the sphaleron process, the latter is relaid to the DM density through the decay of SU(2)L doublet scalar that is named “asymmetric mediator”. In this way, we provide an extended scotogenic model that predicts the energy densities of baryon and dark matter being in the same order of magnitude, and also explains the low-energy neutrino masses and mixing angles.

Cosmological Evolution of a Statistical System of Degenerate Scalarly Charged Fermions with an Asymmetric Scalar Doublet. I. Two-Component System of Assorted Charges

Based on the mathematical model of a statistical system with scalar interaction of fermions formulated earlier, a cosmological model based on a two-component statistical system of scalar charged degenerate fermions interacting with an asymmetric scalar doublet, canonical and phantom scalar fields, is investigated. The asymptotic and limiting properties of the cosmological model are investigated, and it is shown that among all models there is a class of models with a finite lifetime. The asymptotic behavior of models near the corresponding singularities is investigated and numerical implementations of such models are constructed.

Probing doubly charged scalar bosons from the doublet at future high-energy colliders

The isospin doublet scalar field with hypercharge 3/2 is introduced in some new physics models such as tiny neutrino masses. Detecting the doubly charged scalar bosons from the doublet field can be a good probe of such models. However, their collider phenomenology has not been examined sufficiently. We investigate collider signatures of the doubly and singly charged scalar bosons at the LHC for the high-luminosity upgraded option (HL-LHC) by looking at transverse mass distributions etc. With the appropriate kinematical cuts we demonstrate the background reduction in the minimal model in the following two cases depending on the mass of the scalar bosons. (1) The main decay mode of the singly charged scalar bosons is the tau lepton and missing (as well as charm and strange quarks). (2) That is into a top bottom pair. In the both cases, we assume that the doubly charged scalar boson is heavier than the singly charged ones. We conclude that the scalar doublet field with $Y = 3/2$ is expected to be detectable at the HL-LHC unless the mass is too large.

Exceptional regions of the 2HDM parameter space

The exceptional region of the parameter space (ERPS) of the two Higgs doublet model (2HDM) is defined to be the parameter regime where the scalar potential takes on a very special form. In the standard parameterization of the 2HDM scalar potential with squared mass parameters $m_{11}^2$, $m_{22}^2$, $m_{12}^2$, and dimensionless couplings, $\lambda_1$, $\lambda_2$, $\ldots,\lambda_7$, the ERPS corresponds to $\lambda_1=\lambda_2$, $\lambda_7=-\lambda_6$, $m_{11}^2=m_{22}^2$ and $m_{12}^2=0$, corresponding to a scalar potential with an enhanced generalized CP symmetry called GCP2. Many special features persist if $\lambda_1=\lambda_2$ and $\lambda_7=-\lambda_6$ are retained while allowing for $m_{11}^2\neq m_{22}^2$ and/or $m_{12}^2\neq 0$, corresponding to a scalar potential with a softly-broken GCP2 symmetry, which we designate as the ERPS4. In this paper, we examine many of the special features of the ERPS4, as well as even more specialized cases within the ERPS4 framework in which additional constraints on the scalar potential parameters are imposed. By surveying the landscape of the ERPS4, we complete the classification of 2HDM scalar potentials that exhibit an exact Higgs alignment (where the tree-level couplings of one neutral scalar coincide with those of the Standard Model Higgs boson), due to a residual symmetry that is unbroken in the vacuum. One surprising aspect of the ERPS4 is the possibility that the scalar sector is CP-conserving despite the presence of a complex parameter of the scalar potential whose complex phase cannot be removed by separate rephasings of the two scalar doublet fields. The significance of the ERPS4 regime for custodial symmetry is also discussed, and the cases where a custodial symmetric 2HDM scalar potential preserves an exact Higgs alignment are elucidated.

Confinement and moduli locking of Alice strings and monopoles

We argue that strings (vortices) and monopoles are confined, when fields receiving nontrivial Aharonov-Bohm (AB) phases around a string develop vacuum expectation values (VEVs). We illustrate this in an SU(2)×U(1) gauge theory with charged triplet complex scalar fields admitting Alice strings and monopoles, by introducing charged doublet scalar fields receiving nontrivial AB phases around the Alice string. The Alice string carries a half U(1) magnetic flux and 1/4 SU(2) magnetic flux taking a value in two of the SU(2) generators characterizing the U(1) modulus. This string is not confined in the absence of a doublet VEV in the sense that the SU(2) magnetic flux can be detected at large distance by an AB phase around the string. When the doublet field develops VEVs, there appear two kinds of phases that we call deconfined and confined phases. When a single Alice string is present in the deconfined phase, the U(1) modulus of the string and the vacuum moduli are locked (the bulk-soliton moduli locking). In the confined phase, the Alice string is inevitably attached by a domain wall that we call an AB defect and is confined with an anti-Alice string or another Alice string with the same SU(2) flux. Depending on the partner, the pair annihilates or forms a stable doubly-wound Alice string having an SU(2) magnetic flux inside the core, whose color cannot be detected at large distance by AB phases, implying the “color” confinement. The theory also admits stable Abrikosov-Nielsen-Olesen string and a ℤ2 string in the absence of the doublet VEVs, and each decays into two Alice strings in the presence of the doublet VEVs. A monopole in this theory can be constructed as a closed Alice string with the U(1) modulus twisted once, and we show that with the doublet VEVs, monopoles are also confined to monopole mesons of the monopole charge two.

Generalizing the Scotogenic model

The Scotogenic model is an economical setup that induces Majorana neutrino masses at the 1-loop level and includes a dark matter candidate. We discuss a generalization of the original Scotogenic model with arbitrary numbers of generations of singlet fermion and inert doublet scalar fields. First, the full form of the light neutrino mass matrix is presented, with some comments on its derivation and with special attention to some particular cases. The behavior of the theory at high energies is explored by solving the Renormalization Group Equations.

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.

Cosmological unification, dark energy, and the origin of neutrino mass

We suggest that quintessential vacuum energy could be the source of right handed neutrino masses that feed the seesaw mechanism, which may provide observed small masses to light standard neutrinos. This idea is naturally implemented in the Cosmological Unification model based on the global $SO(1,1)$ symmetry, where early inflation and late accelerated expansion of the Universe are driven by the degrees of freedom of a doublet scalar field. In this model, the $SO(1,1)$ custodial symmetry naturally provides the quintessence to standard model singlet fermion couplings that source neutrino masses. We also show that the model predicts a highly suppressed contribution to relativistic degrees of freedom from quintessential quanta at any late Universe epoch, ensuring the consistency of the model.

Symmetries and mass degeneracies in the scalar sector

We explore some aspects of models with two and three SU(2) scalar doublets that lead to mass degeneracies among some of the physical scalars. In Higgs sectors with two scalar doublets, the exact degeneracy of scalar masses, without an artificial fine-tuning of the scalar potential parameters, is possible only in the case of the inert doublet model (IDM), where the scalar potential respects a global U(1) symmetry that is not broken by the vacuum. In the case of three doublets, we introduce and analyze the replicated inert doublet model, which possesses two inert doublets of scalars. We then generalize this model to obtain a scalar potential, first proposed by Ivanov and Silva, with a CP4 symmetry that guarantees the existence of pairwise degenerate scalar states among two pairs of neutral scalars and two pairs of charged scalars. Here, CP4 is a generalized CP symmetry with the property that (CP4)n is the identity operator only for integer n values that are multiples of 4. The form of the CP4-symmetric scalar potential is simplest when expressed in the Higgs basis, where the neutral scalar field vacuum expectation value resides entirely in one of the scalar doublet fields. The symmetries of the model permit a term in the scalar potential with a complex coefficient that cannot be removed by any redefinition of the scalar fields within the class of Higgs bases (in which case, we say that no real Higgs basis exists). A striking feature of the CP4-symmetric model is that it preserves CP even in the absence of a real Higgs basis, as illustrated by the cancellation of the contributions to the CP violating form factors of the effective ZZZ and ZWW vertices.

Multi-Higgs doublet models: the Higgs-fermion couplings and their sum rules

This is the second of a series of papers that explores the physical parameterization, sum rules and unitarity bounds arising from a non-minimal scalar sector of the Standard Model (SM) that consists of N Higgs doublets. In this paper, we focus on the structure and implication of the Yukawa interactions that couple the N scalar doublets to the SM fermions. We employ the charged Higgs basis, which is defined as the basis of scalar fields such that the neutral scalar field vacuum expectation value resides entirely in one of the N scalar doublet fields, and the charged components of the remaining N − 1 scalar doublet fields are the physical (mass-eigenstate) charged Higgs fields. Based on the structure of the Yukawa Lagrangian of the model (and as a consequence of tree-level unitarity), one may deduce numerous sum rules, several of which have not appeared previously in the literature. These sum rules can be used to uncover intimate relations between the structure of the Higgs-fermion couplings and the scalar/gauge couplings. In particular, we show that the approximate alignment limit, in which the W+W− and ZZ couplings to the observed Higgs boson are approximately SM-like, imposes significant constraints on the Higgs-fermion couplings.

Collapse and Nonlinear Instability of AdS Space with Angular Momentum.

We present a numerical study of rotational dynamics in AdS_{5} with equal angular momenta in the presence of a complex doublet scalar field. We determine that the endpoint of gravitational collapse is a Myers-Perry black hole for high energies and a hairy black hole for low energies. We investigate the time scale for collapse at low energies E, keeping the angular momenta J∝E in anti-de Sitter (AdS) length units. We find that the inclusion of angular momenta delays the collapse time, but retains a t∼1/E scaling. We perturb and evolve rotating boson stars, and find that boson stars near AdS space appear stable, but those sufficiently far from AdS space are unstable. We find that the dynamics of the boson star instability depend on the perturbation, resulting either in collapse to a Myers-Perry black hole, or development towards a stable oscillating solution.

Review of Standard Model Higgs results at the ATLAS experiment

The investigation of the mechanism of electroweak (EW) symmetry breaking has been one of the main goals of the ATLAS experiment [1] research program at the CERN Large Hadron Collider (LHC). In the Standard Model (SM) of particle physics, the breaking of the EW symmetry is realised by introducing a complex doublet scalar field which is related to the existence of a neutral particle, the Higgs boson. The Higgs scalar field is responsible of the mass of the other particles; the mass of its mediator, the Higgs boson, is the only free parameter in the theory. In 2012, the ATLAS and CMS collaborations discovered a new particle consistent with the SM Higgs boson and two years later measured its mass, in the H → γγ and H →ZZ* → 4l channels, to be mH=125.09±0.21 (stat) ±0.11 (sys) GeV with data collected in 2011 and 2012 (LHC Run 1). This document will cover the SM Higgs analyses performed with approximately 15 fb−1 of pp collision data collected until summer 2016 during the so-called Run 2 LHC data-taking at a center-of-mass energy ().

Testing the dark matter scenario in the inert doublet model by future precision measurements of the Higgs boson couplings

We evaluate radiative corrections to the Higgs boson couplings in the inert doublet model, in which the lightest component of the $Z_2^{}$ odd scalar doublet field can be a dark matter candidate. The one-loop contributions to the $hVV$, $hff$ and $hhh$ couplings are calculated in the on-shell scheme, where $h$ is the Higgs boson with the mass 125 GeV, $V$ represents a weak gauge boson and $f$ is a fermion. We investigate how the one-loop corrected Higgs boson couplings can be deviated from the predictions in the standard model under the constraints from perturbative unitarity and vacuum stability in the scenario where the model can explain current dark matter data. When the mass of the dark matter is slightly above a half of the Higgs boson mass, it would be difficult to test the model by the direct search experiments for dark matter. We find that in such a case the model can be tested at future collider experiments by either the direct search of heavier inert particles or precision measurements of the Higgs boson couplings.

Higgs phenomenology in the minimalSU(3)L×U(1)Xmodel

We investigate the phenomenology of a model based on the $SU(3)_c\times SU(3)_L\times U(1)_X$ gauge theory, the so-called 331 model. In particular, we focus on the Higgs sector of the model which is composed of three $SU(3)_L$ triplet Higgs fields, and this corresponds to the minimal form to realize phenomenologically acceptable scenario. After the spontaneous symmetry breaking $SU(3)_L\times U(1)_X\to SU(2)_L\times U(1)_Y$, our Higgs sector effectively becomes that with two $SU(2)_L$ doublet scalar fields, in which the first and the second generation quarks couple to the different Higgs doublet from that couples to the third generation quarks. This structure causes the flavour changing neutral current mediated by Higgs bosons at the tree level. By taking an alignment limit of the mass matrix for the CP-even Higgs bosons, which is naturally realized in the case with the breaking scale of $SU(3)_L\times U(1)_X$ to be much larger than that of $SU(2)_L\times U(1)_Y$, we can avoid current constraints from flavour experiments such as the $B^0$-$\bar{B}^0$ mixing even for the Higgs bosons masses being ${\cal O}(100)$ GeV. In this allowed parameter space, we clarify that a characteristic deviation in quark Yukawa couplings of the standard model-like Higgs boson is predicted, which has a different pattern from that seen in two Higgs doublet models with a softly-broken $Z_2$ symmetry. We also find that the flavour violating decay modes of the extra Higgs boson, e.g., $H/A \to tc$ and $H^\pm \to ts$ can be dominant, and they yield the important signature to distinguish our model from the two Higgs doublet models.

A 4 $$ {\mathbb{A}}_4 $$ symmetry at colliders and in the universe

Two puzzling facts of our time are the observed patterns in the fermion masses and mixings and the existence of non-baryonic dark matter, which are both often associated with extensions of the Standard Model at higher energy scales. In this paper, we consider a solution to these two problems with the flavour symmetry ${\mathbb A}_4\times {\mathbb Z}_2\times {\mathbb Z}_2^\prime$, in a model which has been shown before to explain large leptonic mixings with a specific texture. The model contains 3 generations of $SU(2)_L$-doublet scalar fields, arranged as an ${\mathbb A}_4$-triplet, that spontaneously break the electroweak symmetry, and a "dark sector" of ${\mathbb Z}_2$-odd fields, containing one Majorana neutrino and an ${\mathbb A}_4$-triplet $SU(2)_L$-doublet scalar field, the lightest of which provides a candidate for dark matter. Concerning the ${\mathbb Z}_2$-even scalar fields, compared to the Standard Model, we predict additional fields with masses at the electroweak scale. We therefore investigate present phenomenological constraints from lepton flavour violation experiments, obtaining a lower bound on the extra scalar masses of 140 GeV. Furthermore we consider the oblique parameters, Higgs boson decay properties and possible flavour violating signals at the LHC. Concerning the "dark sector", we study bounds from dark matter search experiments and identify the parameter space of the dark matter candidate that is compatible with the observed relic density. We find two allowed mass ranges for the dark matter within which the experimental constraints can be accommodated: the low-mass range is from 47 GeV to 74 GeV and the high-mass range is from 600 GeV and 3.6 TeV.

Enhancement of the H±W∓Z vertex in the three scalar doublet model

We compute one-loop induced trilinear vertices with physical charged Higgs bosons H± and ordinary gauge bosons, i.e., H±W∓Z and H±W∓γ, in the model with two active plus one inert scalar doublet fields under a Z2(unbroken) × $$ {\tilde{Z}}_2 $$ (softly-broken) symmetry. The Z2 and $$ {\tilde{Z}}_2 $$ symmetries are introduced to guarantee the stability of a dark matter candidate and to forbid the flavour changing neutral current at the tree level, respectively. The dominant form factor F Z of the H±W∓Z vertex can be enhanced by effects of extra scalar boson loop contributions. We find that, in such a model, |F Z |2 can be one order of magnitude larger than that predicted in two Higgs doublet models, under the constraints from vacuum stability, perturbative unitarity and the electroweak precision observables. In addition, the branching fraction of the H± → W±Z (H± → W±γ) mode can be of order 10 (1)% level when the mass of H± is below the top quark mass. Such a light H± is allowed by the so-called Type-I and Type-X Yukawa interactions which appear under the classification of the $$ \tilde{Z} $$ charge assignment of the quarks and leptons. We also calculate the cross sections for the processes H± → W±Z and H± → W±γ onset by the top quark decay t → H±b and electroweak H± production at the LHC.

Flavour dependent gauged radiative neutrino mass model

We propose a one-loop induced radiative neutrino mass model with anomaly free flavour dependent gauge symmetry: $\mu$ minus $\tau$ symmetry $U(1)_{\mu-\tau}$. A neutrino mass matrix satisfying current experimental data can be obtained by introducing a weak isospin singlet scalar boson that breaks $U(1)_{\mu-\tau}$ symmetry, an inert doublet scalar field, and three right-handed neutrinos in addition to the fields in the standard model. We find that a characteristic structure appears in the neutrino mass matrix: two-zero texture form which predicts three non-zero neutrino masses and three non-zero CP-phases from five well measured experimental inputs of two squared mass differences and three mixing angles. Furthermore, it is clarified that only the inverted mass hierarchy is allowed in our model. In a favored parameter set from the neutrino sector, the discrepancy in the muon anomalous magnetic moment between the experimental data and the the standard model prediction can be explained by the additional neutral gauge boson loop contribution with mass of order 100 MeV and new gauge coupling of order $10^{-3}$.

Predictive Model for Radiatively Induced Neutrino Masses and Mixings with Dark Matter

A minimal extension of the standard model to naturally generate small neutrino masses and provide a dark matter candidate is proposed. The dark matter particle is part of a new scalar doublet field that plays a crucial role in radiatively generating neutrino masses. The symmetry that stabilizes the dark matter also suppresses neutrino masses to appear first at three-loop level. Without the need of right-handed neutrinos or other very heavy new fields, this offers an attractive explanation of the hierarchy between the electroweak and neutrino mass scales. The model has distinct verifiable predictions for the neutrino masses, flavor mixing angles, colliders, and dark matter signals.