Scalar Multiplets Research Articles

Reissner-Nordström dyonic black holes with gauged scalar hair

For gauged scalar fields minimally coupled to Einstein-Maxwell theory, the Mayo-Bekenstein no-hair theorem can be circumvented when including appropriate scalar self-interactions, allowing static, electrically charged black holes to be endowed with (Abelian) gauged scalar hair. Here we show these spherically symmetric solutions can be extended to include a magnetic charge in a model with scalar multiplets. The resulting dyonic configurations share most of the properties of the electrically charged solutions, in particular satisfying the same resonance condition, with the existence of a mass gap with respect to the bald Reissner-Nordström dyonic black holes. A distinctive feature, however, is that no solitonic limit exists for a non-zero magnetic charge.

On the Addition of a Large Scalar Multiplet to the Standard Model

Abstract We consider the addition of a single $SU(2)$ multiplet of complex scalar fields to the Standard Model (SM). We explicitly consider the various possible values of the weak isospin J of that multiplet, up to and including $J = 7/2$. We allow the multiplet to have arbitrary weak hypercharge. The scalar fields of the multiplet are assumed to have no vacuum expectation value; the mass differences among the components of the multiplet originate in its coupling, present in the scalar potential (SP), to the Higgs doublet of the SM. We derive exact bounded-from-below and unitarity conditions on the SP, thereby constraining those mass differences. We compare those constraints to the ones that may be derived from the oblique parameters.

Unitarity constraints on large multiplets of arbitrary gauge groups

We impose partial-wave unitarity on 2→2 tree-level scattering processes to derive constraints on the dimensions of large scalar and fermionic multiplets of arbitrary gauge groups. We apply our results to scalar and fermionic extensions of the Standard Model, and also to the Grand Unified Theories (GUTs) based on the groups SU(5), SO(10), and E6. We find scenarios within the latter two GUTs that violate the unitarity condition; this may require a reevaluation of the validity of perturbation theory in those scenarios.

Neutrino masses from new Weinberg-like operators: phenomenology of TeV scalar multiplets

The unique dimension-5 effective operator, LLHH, known as the Weinberg operator, generates tiny Majorana masses for neutrinos after electroweak spontaneous symmetry breaking. If there are new scalar multiplets that take vacuum expectation values (VEVs), they should not be far from the electroweak scale. Consequently, they may generate new dimension-5 Weinberg-like operators which in turn also contribute to Majorana neutrino masses. In this study, we consider scenarios with one or two new scalars up to quintuplet SU(2) representations. We analyse the scalar potentials, studying whether the new VEVs can be induced and therefore are naturally suppressed, as well as the potential existence of pseudo-Nambu-Goldstone bosons. Additionally, we also obtain general limits on the new scalar multiplets from direct searches at colliders, loop corrections to electroweak precision tests and the W-boson mass.

W-boson mass anomaly from high-dimensional scalar multiplets

In light of the recently discovered W-boson mass anomaly by the CDF Collaboration, we discuss two distinct mechanisms that could possibly explain this anomaly through the introduction of high-dimensional SU(2)L scalar multiplets. The first mechanism is the tree-level W-boson mass correction induced by the vacuum expectation values of one or more SU(2)L scalar multiplets with odd dimensions of n≥3 and zero hypercharge of Y=0 in order to avoid the strong constraint from measurements of the Z-boson mass. The second mechanism is to consider the one-loop level W-boson mass correction from a complex multiplet. In particular, we focus on the case with an additional scalar octuplet with Y=7/2. As a result, we find that both mechanisms can explain the W-boson mass anomaly without violating any other theoretical or experimental constraints.

Probing grand unification with quantum sensors

We discuss how grand unification can be probed with experiments at low energies using quantum sensors. Specifically, we show that scalar multiplets coupled to the gauge sector of a grand unified theory provide a mechanism for a time-varying unified coupling which has low-energy consequences which can be probed with quantum sensors. We then assume that the multiplets represent ultra light dark matter. Constraints on ultra light dark matter couplings to regular matter are extracted using atomic clock comparisons, pulsar timing arrays (NANOGrav) and MICROSCOPE.

GUT origins of general electroweak multiplets and their oblique parameters

We survey the scalar electroweak multiplets that can originate from a grand unified theory (GUT) like SU(5), SO(10) or E6. We compute the oblique parameters S, T and U for a general scalar electroweak multiplet and then apply the results to the leptoquark, as well as the color sextet and octet cases, allowed by the GUT survey. Constraints from precision measurement data of the Standard Model W boson mass and ρ parameter to the mass splittings within each of these multiplets are presented. Extension to general vector electroweak multiplets is briefly discussed.

Unitarity bounds on extensions of Higgs sector

It is widely believed that extensions of the minimal Higgs sector is one of the promising directions for resolving many puzzles beyond the Standard Model (SM). In this work, we study the unitarity bounds on the models by extending the two-Higgs-doublet model with an additional real or complex Higgs triplet scalar. By noting that the SM gauge symmetries SU(2)L × U(1)Y are recovered at high energies, we can classify the two-body scattering states by decomposing the direct product of two scalar multiplets into their direct sum of irreducible representations of electroweak gauge groups. In such state bases, the s-wave amplitudes of two-body scalar scatterings can be written in the form of block-diagonalized scattering matrices. Then the application of the perturbative unitarity conditions on the eigenvalues of scattering matrices leads to the analytic constraints on the model parameters. Finally, we numerically investigate the complex triplet scalar extension of the two-Higgs-doublet model, finding that the perturbative unitarity places useful stringent bounds on the model parameter space.

An alternate left-right symmetric model with Dirac neutrinos

We study a different variant of left-right symmetric model, incorporating Dirac type neutrinos. In the absence of the bi-doublet scalars, the possibility of a universal seesaw type of mass generation mechanism for all the Standard Model charged fermions have been discussed. The model has been constructed by extending the Standard Model particle spectrum with heavy vector-like fermions as well as different scalar multiplets. We have shown that this model can generate non zero neutrino mass through loop mediated processes. The parameters which are involved in neutrino mass generation mechanism can satisfy the neutrino oscillation data for both normal and inverted hierarchy. The lightest charged Higgs plays a crucial role in neutrino mass generation mechanism and can have mass of {mathcal {O}}[text {GeV}]. We have systematically studied different constraints which are relevant for the charged Higgs phenomenology. In addition to that we also briefly discuss discovery prospects of the charged Higgs at different colliders.

One-loop algebras and fixed flow trajectories in adjoint multi-scalar gauge theory

We study the one loop renormalisation of 4d SU(N) Yang-Mills theory with M adjoint representation scalar multiplets related by O(M) symmetry. General M are of field theoretic interest, and the 4d one loop beta function of the gauge coupling g2 vanishes for the case M = 22, which is intriguing for string theory. This case is related to D3 branes of critical bosonic string theory in D = 22 + 4 = 26. An RG fixed point could have provided a definition for a purely bosonic AdS/CFT, but we show that scalar self-couplings λ ruin one-loop conformal invariance in the large N limit. There are real fixed flows (fixed points of λ/g2) only for M ≥ 406, rendering one-loop fixed points of the gauge coupling and scalar couplings incompatible.We develop and check an algebraic approach to the one-loop renormalisation group which we find to be characterised by a non-associative algebra of marginal couplings. In the large N limit, the resulting RG flows typically suffer from strong coupling in both the ultraviolet and the infrared. Only for M ≥ 406 fine-tuned solutions exist which are weakly coupled in the infrared.

W-boson mass anomaly from a general SU(2) L scalar multiplet* *Supported in part by the National Key Research and Development Program of China (2021YFC2203003, 2020YFC2201501) and the National Natural Science Foundation of China (NSFC) (12005254, 12147103)

We explain the W-boson mass anomaly by introducing an scalar multiplet with general isospin and hypercharge {in the case without its vacuum expectation value}. It is shown that the dominant contribution from the scalar multiplet to the W-boson mass arises at the one-loop level, which can be expressed in terms of the electroweak (EW) oblique parameters T and S at leading order. We first rederive the general formulae of T and S induced by a scalar multiplet of EW charges, confirming the results in literature. We then study several specific examples of great phenomenological interest by applying these general expressions. As a result, it is found that the model with a scalar multiplet in an real representation with cannot generate the required correction because it leads to vanishing values of T and S. However, the cases with scalars in a complex representation under with a general hypercharge can explain the excess observed by CDF-II owing to nonzero T and S. We further consider the strong constraints from the perturbativity and EW global fit of the precision data and vary the isospin representation and hypercharge of the additional scalar multiplet to assess the extent of the model to solve the W-boson mass anomaly. It turns out that these constraints play important roles in setting limits on the model parameter space. We also briefly describe the collider signatures of the extra scalar multiplet, especially when it contains long-lived, heavy, highly charged states.

Scale-invariant 3-3-1-1 model with B−L symmetry

Motivated by a possible interplay between the mechanism of dynamical symmetry breaking and the seesaw mechanism for generating fermion masses, we present a scale-invariant model that extends the gauge symmetry of the Standard Model electroweak sector to SU(3)$_L\otimes$U(1)$_X\otimes$U(1)$_N$, with a built-in $B-L$ symmetry. The model is based on the symmetry structure of the known 3-3-1 models and, thus, it relates the number of the three observed fermion generations with the cancellation of gauge anomalies. Symmetry breaking is triggered via the Coleman-Weinberg mechanism taking into account a minimal set of scalar field multiplets. We establish the stability conditions for the tree-level scalar potential imposing the copositivity criteria and use the method of Gildener-Weinberg for computing the one-loop effective potential when one has multiple scalar fields. With the addition of vectorial fermions, getting their mass mainly through the vacuum expectation value of scalar singlets at $10^3$ TeV, the $B-L$ symmetry leads to textures for the fermion mass matrices, allowing seesaw mechanisms for neutrinos and quarks to take place. In particular, these mechanisms could partly explain the mass hierarchies of the quarks. Once the breakdown of the SU(3)$_L$ symmetry is supposed to occur around 10 TeV, the model also predicts new particles with TeV-scale masses, such as a neutral scalar, $H_{1}$, a charged scalar, $H^\pm$, and the gauge bosons $Z^{\prime}$, $W^{\prime\pm}$ and $Y^0$, that could be searched with the high-luminosity LHC.

Vacuum stability of conformally invariant scalar dark matter models

We discuss vacuum structure and vacuum stability in classically scale-invariant renormalizable models with a scalar dark matter multiplet of global O(N) symmetry together with an electroweak singlet scalar mediator. Our conformally invariant scalar potential generates the electroweak symmetry breaking via the Coleman-Weinberg mechanism, and the new scalar singlet mediator acquires its mass through radiative corrections of the scalar dark matters as well as of the standard model particles. Taking into account the present collider bounds, we find the region of parameter space where the scalar potential is stable and all the massless couplings are perturbative up to the Planck scale. With the obtained parameter sets satisfying the vacuum stability condition, we present the allowed region of new physics parameters satisfying the recent measurement of relic abundance, and predict the elastic scattering cross section of the new scalar multiplet into target nuclei for a direct detection of the dark matter. We also discuss the collider signatures and future discovery potentials of the new scalars.

The linear regime of tachyonic preheating

Tachyonic preheating is realized when the inflaton repeatedly returns to a convex region of the potential during the post-inflationary oscillating phase. This will induce a strong tachyonic instability and lead to a rapid fragmentation of the coherent field that can complete within a fraction of an e-fold. In this paper, we study the linear regime of this process in a model-independent way. To this purpose, we construct simplified models that provide an analytic Floquet theoretic description of mode growth. This approach captures the essential features of well-motivated tachyonic preheating scenarios, including scenarios in which the inflaton is part of a larger scalar multiplet. We show that tachyonic preheating is efficient if the field excursions are sub-Planckian, can produce gravitational waves in the frequency range of current and future gravitational wave interferometers, and can be consistent with any experimentally allowed tensor-to-scalar ratio.

Alternative signatures of the quintuplet fermions at the LHC and future linear colliders

Large fermionic multiplets appear in different extensions of the Standard Model (SM), which are essential to predict small neutrino masses, relic abundance of the dark matter (DM) and the measured value of muon anomalous magnetic moment (muon (g-2)). Models containing quintuplet of fermions ($\Sigma$), along with other scalar multiplets, can address recent anomalies in the flavor sector while satisfying the constraints from the electroweak physics. In standard scenarios, the exotic fermions couple with the SM particles directly and there exists a strong limit on their masses from collider experiments such as the Large Hadron Collider (LHC). In this paper, we choose a particular scenario where the quintuplet fermions are heavier than the scalars, which is naturally motivated from the muon (g-2) data. A unique nature of these models is that they predict non-standard signatures at the colliders as the quintuplet fermions decay via the scalars once produced at the colliders. We study these non-standard interactions and provide alternative search strategies for these exotic fermions at the LHC and future linear colliders (such as $e^+e^-$ colliders). We also discuss their exclusion and discovery limits. For the doubly charged quintuplet fermion ($\Sigma^{\pm\pm}$), discovery is possible with 5$\sigma$ significance at integrated luminosity of 3000 fb$^{-1}$ at 14 TeV LHC if $M_\Sigma\leq 980$ GeV. For the singly charged quintuplet fermion ($\Sigma^\pm$), the discovery is challenging at LHC but there might be a possibility of 5 $\sigma$ discovery with 1000 fb$^{-1}$ luminosity at $e^+e^-$ collider for $M_\Sigma\leq 700$ GeV.

Triple-leptoquark interactions for tree- and loop-level proton decays

We study the impact of triple-leptoquark interactions on matter stability for two specific proton decay topologies that arise at the tree- and one-loop level if and when they coexist. We demonstrate that the one-loop level topology is much more relevant than the tree-level one when it comes to the proton decay signatures despite the usual loop-suppression factor. We subsequently present detailed analysis of the triple-leptoquark interaction effects on the proton stability within one representative scenario to support our claim, where the scenario in question simultaneously features a tree-level topology that yields three-body proton decay p → e+e+e− and a one-loop level topology that induces two-body proton decays p → π0e+ and p → π+ overline{nu} . We also provide a comprehensive list of the leading-order proton decay channels for all non-trivial cubic and quartic contractions involving three scalar leptoquark multiplets that generate triple-leptoquark interactions of our interest, where in the latter case one of the scalar multiplets is the Standard Model Higgs doublet.

Predestined dark matter varieties in the simplest left-right model

In the simplest left-right extension of the Standard Model of particle interactions with one scalar bidoublet and one SU(2)R triplet for seesaw Majorana neutrino masses, the addition of a variety of fermion and scalar multiplets automatically makes them stable (predestined) dark matter candidates. We discuss the interplay of this dark ensemble in relic abundance and direct searches.

Constraints on coloured scalars from global fits

We consider a simple extension of the electroweak theory, incorporating one SU(2)L doublet of colour-octet scalars with Yukawa couplings satisfying the principle of minimal flavour violation. Using the HEPfit package, we perform a global fit to the available data, including all relevant theoretical constraints, and extract the current bounds on the model parameters. Coloured scalars with masses below 1.05 TeV are already excluded, provided they are not fermiophobic. The mass splittings among the different (charged and CP-even and CP-odd neutral) scalars are restricted to be smaller than 20 GeV. Moreover, for scalar masses smaller than 1.5 TeV, the Yukawa coupling of the coloured scalar multiplet to the top quark cannot exceed the one of the SM Higgs doublet by more than 80%. These conclusions are quite generic and apply in more general frameworks (without fine tunings). The theoretical requirements of perturbative unitarity and vacuum stability enforce relevant constraints on the quartic scalar potential parameters that are not yet experimentally tested.

Parameter space exploration of the minimal SU(5) unification

We present phenomenological study of the most minimal realistic $SU(5)$ model that owns its predictivity solely to the gauge symmetry and the representational content. The model is built entirely out of the fields residing in the first five lowest dimensional representations that transform non-trivially under the $SU(5)$ gauge group. It has eighteen real parameters and fourteen phases, all in all, to address experimental observables of the Standard Model fermions and accomplishes that via simultaneous use of three different mass generation mechanisms. Furthermore, it inextricably links the origin of the neutrino mass to the experimentally observed difference between the down-type quark and charged lepton masses. The main predictions of the model are that $(i)$ the neutrinos are Majorana particles, $(ii)$ one neutrino is massless, $(iii)$ the neutrinos have normal mass ordering, and $(iv)$ there are four new scalar multiplets at or below a $120$ TeV mass scale. A one-loop analysis demonstrates that an improvement of the current $p \rightarrow \pi^0 e^+$ partial lifetime limit by a factor of $2$, $15$, and $96$ would require these four scalar multiplets to reside at or below the $100$ TeV, $10$ TeV, and $1$ TeV mass scales, respectively.

Vector dark matter from a gauged SU(2) symmetry

We propose a scenario of dark sector described by a hidden SU(2) gauge symmetry which is broken by a vacuum expectation value(VEV) of a scalar multiplet. We discuss a general mass relation among SU(2) gauge bosons after spontaneous symmetry breaking which is determined by weight of gauge group representation associated with a scalar multiplet developing VEV. Then a model with quintet and triplet scalar fields is discussed in which hidden gauge boson can be dark matter(DM) stabilized by remnant discrete Z2 symmetry and resonant dark matter annihilation is realized by mass relation between DM and mediator. We estimate relic density and spin independent DM-nucleon scattering cross section searching for allowed parameter region.