Non-standard Higgs Bosons Research Articles

The two Higgs doublet type-II seesaw model: Naturalness and [formula omitted] versus heavy Higgs masses

We extend the work [1] to a more general and detailed analysis through studying the naturalness problem and B physics constraints within the context of two higgs doublets model augmented with a complex scalar triplet field (2HDMcT). We first derive the modified Vetman conditions and show that naturalness problem might be evaded at the electroweak scale. Then, we evaluate the branching ratio of B¯→Xsγ radiative decay at the Next to leading order. Besides unitarity, boundedness from below constraints and the present collider data from Higgs signal rate measurements, the parameter space of 2HDMcT is then revisited to see how the modified Veltman conditions and B¯→Xsγ experimental bounds induce significant delimitations. Our analysis shows that the naturalness affects drastically the masses of heavy Higgs h3, A2, H2± and H±±. More specifically, we considered three benchmark scenarios corresponding to μ2>20,40,70 GeV. For μ2>40, we find stringent upper limits on mh2, mA1 and mH1± at 880, 920 and 918 GeV respectively. If, in addition, the measurements of B¯→Xsγ decay rate are also considered, the lower masses limits of nonstandard Higgs bosons (h2, h3, A1, A2, H1±, H2±, H±±) are pushed up to higher values located between 490 and 750 GeV. Besides, we also demonstrate that the B¯→Xsγ experimental limits can only be accommodated within 2HDMcT if two conditions are fullfilled: α1 parameter positive and the Higgs mass hierarchy mh3>mH2±>mH±±.

Prospects for light charged scalars in a three-Higgs-doublet model with Z3 symmetry

The stringent constraints from the direct searches for exotic scalars at the LHC as well as indirect bounds from flavor physics measurements have imposed severe restrictions on the parameter space of new physics models featuring extended Higgs sectors. In the Type-II 2HDM, this implies a lower bound on the charged Higgs masses of $\cal O$(600 GeV). In this work we analyze the phenomenology of a Z3HDM in the alignment limit focusing on the impact of flavor physics constraints on its parameter space. We show that the couplings of the two charged Higgs bosons in this model feature an additional suppression factor compared to Type-II 2HDM. This gives rise to a significant relaxation of the flavor physics constraints in this model, allowing the charged Higgs masses to be as low as $\cal O$(200 GeV). We also consider the constraints coming from precision electroweak observables and the observed diphoton decay rate of the 125 GeV Higgs boson at the LHC. The bounds coming from the direct searches of nonstandard Higgs bosons at the LHC, particularly those from resonance searches in the ditau channel, prove to be very effective in constraining this scenario further.

HiggsBounds-5: testing Higgs sectors in the LHC 13 TeV Era

We describe recent developments of the public computer code HiggsBounds. In particular, these include the incorporation of LHC Higgs search results from Run 2 at a center-of-mass energy of 13 TeV, and an updated and extended framework for the theoretical input that accounts for improved Higgs cross section and branching ratio predictions and new search channels. We furthermore discuss an improved method used in HiggsBounds to approximately reconstruct the exclusion likelihood for LHC searches for non-standard Higgs bosons decaying to tau tau final states. We describe in detail the new and updated functionalities of the new version HiggsBounds-5.

Dark-matter-spin effects at future e+e\u2212 colliders

We discuss the possibility to detect spin 0, 1 and raisebox{1ex}{1}!left/ !raisebox{-1ex}{2}right. dark matter (DM) at future e+e− colliders. The models considered here are simple, consistent and renormalizable field theories that provide correct DM abundance and satisfy direct detection, indirect detection and collider constraints. The intention of this paper was to verify to what extent it might be possible to disentangle models of different DM spins by the measurement of the cross section for e+e−→ Z + ⋯ at future e+e− colliders. We specialize to the case of the ILC operating at sqrt{s} = 250 GeV, however our results apply as well for the FCC-ee and the CEPC colliders. For each model the cross section maximized with respect to parameters was calculated and compared to the expected 95% CL cross-section limits estimated for the ILC. It turned out that near the 2mDM ≃ m1,2 resonances, where m1 and m2 are the SM Higgs boson and a non-standard Higgs boson masses, respectively, there exist substantial regions where the models are testable. A special attention has been payed to calculation of the cross section in the region where m1 ≃ m2.

Measurements of the Higgs boson by ATLAS and CMS

Recent results on Higgs boson production and decays in the ATLAS and CMS experiments at the LHC are reviewed. They are mostly based on the analyses of 13 TeV LHC proton-proton collision data accumulated during 2015–2016 or 2015–2017 year exposures. Production cross sections in five main decay channels are measured. These channels are combined to extract the Higgs boson signal strength, mass and couplings. All experimental results are found to be compatible with the Standard Model predictions. Upper limits on non-standard Higgs boson production in different decay modes are also derived.

Testing scalar versus vector dark matter

We investigate and compare two simple models of dark matter (DM): a vector and a scalar DM model. Both models require the presence of two physical Higgs bosons $h_1$ and $h_2$ which come from mixed components of the standard Higgs doublet $H$ and a complex singlet $S$. In the Vector model, the extra $U(1)$ symmetry is spontaneously broken by the vacuum of the complex field $S$. This leads to a massive gauge boson $X^\mu$ that is a DM candidate stabilized by the dark charge conjugation symmetry $S \to S^*$, $X^\mu\to -X^\mu$. On the other hand, in the Scalar model the gauge group remains the standard one. The DM field $A$ is the imaginary component of $S$ and the stabilizing symmetry is also the dark charge conjugation $S \to S^*$ ($A \to - A$). In this case, in order to avoid spontaneous breaking, the $U(1)$ symmetry is broken explicitly, but softly, in the scalar potential. The possibility to disentangle the two models has been investigated. We have analyzed collider, cosmological, DM direct and indirect detection constraints and shown that there are regions in the space spanned by the mass of the non-standard Higgs boson and the mass of the DM particle where the experimental bounds exclude one of the models. We have also considered possibility to disentangle the models at $e^+e^-$ collider and concluded that the process $e^+e^-\to Z + \text{DM}$ provides a useful tool to distinguish the models.

Precise prediction of the MSSM Higgs boson masses for low MA

Precise predictions for Higgs boson masses in the Minimal Supersymmetric Standard Model can be obtained by combining fixed-order calculations with effective field theory (EFT) methods for the resummation of large logarithms in case of heavy super-partners. This hybrid approach is implemented in the computer code FeynHiggs and has been applied in previous studies for calculating the mass of the lightest mathcal{C}mathcal{P} -even Higgs boson for low, intermediate and high SUSY scales. In these works it was assumed that the non-standard Higgs bosons share a common mass scale with the supersymmetric squark particles, leaving the Standard Model as the low-energy EFT. In this article, we relax this restriction and report on the implemention of a Two-Higgs-Doublet Model (THDM) as effective theory below the SUSY scale into our hybrid approach. We explain in detail how our EFT calculation is consistently combined with the fixed-order calculation within the code FeynHiggs. In our numerical investigation we find effects on the mass of the lightest mathcal{C}mathcal{P} -even Higgs boson h of up to 9GeV in scenarios with low MA, low tan β and high SUSY scales, when compared with previous versions of FeynHiggs. Comparisons to other publicly available pure EFT codes with a THDM show good agreement. Effects on the mass of the second lightest mathcal{C}mathcal{P} -even Higgs boson H are found to be negligible in the phenomenologically interesting parameter regions where H can be traded for h as the experimentally observed Higgs particle.

Higgs\u2013photon resonances

We study models that produce a Higgs boson plus photon (h^0gamma ) resonance at the LHC. When the resonance is a Z' boson, decays to h^0gamma occur at one loop. If the Z' boson couples at tree level to quarks, then the h^0gamma branching fraction is typically of order 10^{-5} or smaller. Nevertheless, there are models that would allow the observation of Z'rightarrow ,h^0gamma at sqrt{s}=13 TeV with a cross section times branching fraction larger than 1 fb for a Z' mass in the 200–450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The one-loop decay of the Z' into lepton pairs competes with h^0gamma , even if the Z' couplings to leptons vanish at tree level. We also present a model in which a Z' boson decays into a Higgs boson and a pair of collimated photons, mimicking an h^0gamma resonance. In this model, the h^0gamma resonance search would be the discovery mode for a Z' as heavy as 2 TeV. When the resonance is a scalar, although decay to h^0gamma is forbidden by angular momentum conservation, the h^0 plus collimated photons channel is allowed. We comment on prospects of observing an h^0gamma resonance through different Higgs decays, on constraints from related searches, and on models where h^0 is replaced by a nonstandard Higgs boson.

Two-loop corrections to the rho parameter in Two-Higgs-Doublet models

Models with two scalar doublets are among the simplest extensions of the Standard Model which fulfill the relation rho = 1 at lowest order for the rho parameter as favored by experimental data for electroweak observables allowing only small deviations from unity. Such small deviations varDelta rho originate exclusively from quantum effects with special sensitivity to mass splittings between different isospin components of fermions and scalars. In this paper the dominant two-loop electroweak corrections to varDelta rho are calculated in the CP-conserving THDM, resulting from the top-Yukawa coupling and the self-couplings of the Higgs bosons in the gauge-less limit. The on-shell renormalization scheme is applied. With the assumption that one of the CP-even neutral scalars represents the scalar boson observed by the LHC experiments, with standard properties, the two-loop non-standard contributions in varDelta rho can be separated from the standard ones. These contributions are of particular interest since they increase with mass splittings between non-standard Higgs bosons and can be additionally enhanced by tan beta and lambda _5, an additional free coefficient of the Higgs potential, and can thus modify the one-loop result substantially. Numerical results are given for the dependence on the various non-standard parameters, and the influence on the calculation of electroweak precision observables is discussed.

Search for Muonic Dark Forces at BABAR

Many models of physics beyond Standard Model predict the existence of light Higgs states, dark photons, and new gauge bosons mediating interactions between dark sectors and the Standard Model. Using a full data sample collected with the BABAR detector at the PEP-II $e^+e^-$ collider, we report searches for a light non-Standard Model Higgs boson, dark photon, and a new muonic dark force mediated by a gauge boson ($Z'$) coupling only to the second and third lepton families. Our results significantly improve upon the current bounds and further constrain the remaining region of the allowed parameter space.

Lepton flavor violating decay of 125 GeV Higgs boson to μτ channel and excess in tt̄H

A recent search for the lepton flavor violating (LFV) decays of the Higgs boson, performed by CMS collaboration, reports an interesting deviation from the Standard Model (SM). The search conducted in the channel [Formula: see text] and [Formula: see text] shows an excess of 2.4[Formula: see text] signal events with 19.6 fb[Formula: see text] data at a center-of-mass energy [Formula: see text] = 8 TeV. On the other hand, a search performed by CMS collaboration for the SM Higgs boson produced in association with a top quark pair [Formula: see text] also showed an excess in the same-sign dimuon final state. In this work, we try to find out if these two seemingly uncorrelated excesses are related or not. Our analysis reveals that a LFV Higgs decay [Formula: see text] can partially explain the excess in the same-sign dimuon final state in the [Formula: see text] search, infact brings down the excess well within 2[Formula: see text] error of the SM expectation. Probing such non-standard Higgs boson decay is of interest and might contain hints of new physics at the electroweak scale.

A 125 GeV fat Higgs at large tan β

We study the viability of regions of large $\tan \beta$ within the framework of Fat Higgs/$\lambda$-SUSY Models. We compute the one-loop effective potential to find the corrections to the Higgs boson mass due to the heavy non-standard Higgs bosons. As the tree level contribution to the Higgs boson mass is suppressed at large $\tan \beta$, these one-loop corrections are crucial to raising the Higgs boson mass to the measured LHC value. By raising the Higgsino and singlino mass parameters, typical electroweak precision constraints can also be avoided. We illustrate these new regions of Fat Higgs/$\lambda$-SUSY parameter space by finding regions of large $\tan \beta$ that are consistent with all experimental constraints including direct dark matter detection experiments, relic density limits and the invisible decay width of the $Z$ boson. We find that there exist regions around $\lambda = 1.25, \tan \beta = 50$ and a uniform psuedo-scalar $4~{\rm TeV} \lsim M_A \lsim 8$~TeV which are consistent will all present phenomenological constraints. In this region the dark matter relic abundance and direct detection limits are satisfied by a lightest neutralino that is mostly bino or singlino. As an interesting aside we also find a region of low $\tan \beta$ and small singlino mass parameter where a well-tempered neutralino avoids all cosmological and direct detection constraints.

Signatures of a nonstandard Higgs boson from flavor physics

We examine the constraints coming from incorporating the full Standard Model gauge symmetry into the effective field theory description of flavor processes, using semileptonic decays as paradigmatic examples. Depending on the dynamics triggering electroweak symmetry breaking, different patterns of correlations between the Wilson coefficients arise. Interestingly, this implies that flavor experiments are capable of shedding light upon the nature of the Higgs boson without actually requiring Higgs final states. Furthermore, the observed correlations can simplify model-independent analyses of these decays.

Applying exclusion likelihoods from LHC searches to extended Higgs sectors

LHC searches for non-standard Higgs bosons decaying into tau lepton pairs constitute a sensitive experimental probe for physics beyond the Standard Model (BSM), such as Supersymmetry (SUSY). Recently, the limits obtained from these searches have been presented by the CMS collaboration in a nearly model-independent fashion - as a narrow resonance model - based on the full 8 TeV dataset. In addition to publishing a 95% C.L. exclusion limit, the full likelihood information for the narrow resonance model has been released. This provides valuable information that can be incorporated into global BSM fits. We present a simple algorithm that maps an arbitrary model with multiple neutral Higgs bosons onto the narrow resonance model and derives the corresponding value for the exclusion likelihood from the CMS search. This procedure has been implemented into the public computer code HiggsBounds (version 4.2.0 and higher). We validate our implementation by cross-checking against the official CMS exclusion contours in three Higgs benchmark scenarios in the Minimal Supersymmetric Standard Model (MSSM), and find very good agreement. Going beyond validation, we discuss the combined constraints of the tau tau search and the rate measurements of the SM-like Higgs at 125 GeV in a recently proposed MSSM benchmark scenario, where the lightest Higgs boson obtains SM-like couplings independently of the decoupling of the heavier Higgs states. Technical details for how to access the likelihood information within HiggsBounds are given in the appendix. The program is available at http://higgsbounds.hepforge.org.

CP-odd component of the lightest neutral Higgs boson in the MSSM

The Higgs sector of the Minimal Supersymmetric Extension of the Standard Model may be described with a two Higgs doublet model with properties that depend on the soft supersymmetry breaking parameters. For instance, flavor independent CP-violating phases associated with the gaugino masses, the squark trilinear mass parameters and the Higgsino mass parameter $\mu$ may lead to sizable CP-violation in the Higgs sector. For these CP-violating effects to affect the properties of the recently observed SM-like Higgs resonance, the non-standard charged and neutral Higgs bosons masses must be of the order of the weak scale, and both $\mu$ as well as the trilinear stop mass parameter $A_t$ must be of the order or larger than the stop mass parameters. Constraints on this possibility come from direct searches for non-standard Higgs bosons, precision measurements on the lightest neutral Higgs properties, including its mass, and electric dipole moments. In this article, we discuss these constraints within the MSSM, trying to evaluate the possible size of the CP-odd component of the lightest neutral Higgs boson, and the possible experimental tests of this CP-violating effect at the LHC.

Constraints on models of the Higgs boson with exotic spin and parity using decays to bottom-antibottom quarks in the full CDF data set.

A search for particles with the same mass and couplings as those of the standard model Higgs boson but different spin and parity quantum numbers is presented. We test two specific alternative Higgs boson hypotheses: a pseudoscalar Higgs boson with spin-parity J^{P}=0^{-} and a gravitonlike Higgs boson with J^{P}=2^{+}, assuming for both a mass of 125 GeV/c^{2}. We search for these exotic states produced in association with a vector boson and decaying into a bottom-antibottom quark pair. The vector boson is reconstructed through its decay into an electron or muon pair, or an electron or muon and a neutrino, or it is inferred from an imbalance in total transverse momentum. We use expected kinematic differences between events containing exotic Higgs bosons and those containing standard model Higgs bosons. The data were collected by the CDF experiment at the Tevatron proton-antiproton collider, operating at a center-of-mass energy of sqrt[s]=1.96 TeV, and correspond to an integrated luminosity of 9.45 fb^{-1}. We exclude deviations from the predictions of the standard model with a Higgs boson of mass 125 GeV/c^{2} at the level of 5 standard deviations, assuming signal strengths for exotic boson production equal to the prediction for the standard model Higgs boson, and set upper limits of approximately 30% relative to the standard model rate on the possible rate of production of each exotic state.

Complementarity between nonstandard Higgs boson searches and precision Higgs boson measurements in the MSSM

Precision measurements of the Higgs boson properties at the LHC provide relevant constraints on possible weak-scale extensions of the Standard Model (SM). In the context of the Minimal Supersymmetric Standard Model (MSSM) these constraints seem to suggest that all the additional, non-SM-like Higgs bosons should be heavy, with masses larger than about 400 GeV. This article shows that such results do not hold when the theory approaches the conditions for "alignment independent of decoupling", where the lightest CP-even Higgs boson has SM-like tree-level couplings to fermions and gauge bosons, independently of the non-standard Higgs boson masses. The combination of current bounds from direct Higgs boson searches at the LHC, along with the alignment conditions, have a significant impact on the allowed MSSM parameter space yielding light additional Higgs bosons. In particular, after ensuring the correct mass for the lightest CP-even Higgs boson, we find that precision measurements and direct searches are complementary, and may soon be able to probe the region of non-SM-like Higgs boson with masses below the top quark pair mass threshold of 350 GeV and low to moderate values of $\tan\beta$.

Study of Decoupling Effects on SUSY Higgs Sector

The most likely scenario in the light of Higgs discovery is the decoupling limit in the MSSM Higgs sector. The decoupling limit in MSSM occurs when the pseudoscalar mass is large (i.e.mA» mZ ), then the CP-even (H0), CP-odd (A0) and charged (H±) Higgs are mass degenerate and the lightest CP-even Higgs boson (h) mimics the signature of the SM Higgs boson. In the decoupling limit of large mA the couplings of the lightest CP-even MSSM Higgs boson h to pairs of SM particles approach their SM values. Moreover, in the decoupling limit there exists a value of tanβ which is independent of the value of mA . Recently a Higgs like particle is reported to be discovered at CMS and ATLAS experiments at CERN LHC with a mass of about 125 GeV. This estimate is only valid in the so called decoupling limit where all non-standard Higgs bosons are significantly heavier than the Z gauge boson.

Probing the Standard Model with Higgs signal rates from the Tevatron, the LHC and a future ILC

We explore the room for possible deviations from the Standard Model (SM) Higgs boson coupling structure in a systematic study of Higgs coupling scale factor benchmark scenarios using the latest signal rate measurements from the Tevatron and LHC experiments. We employ chi-squared fits performed with HiggsSignals, which takes into account detailed information on signal efficiencies and major correlations of theoretical and experimental uncertainties. All considered scenarios allow for additional non-standard Higgs boson decay modes, and various assumptions for constraining the total decay width are discussed. No significant deviations from the SM Higgs boson coupling structure are found in any of the investigated benchmark scenarios. We derive upper limits on an additional (undetectable) Higgs decay mode under the assumption that the Higgs couplings to weak gauge bosons do not exceed the SM prediction. We furthermore discuss the capabilities of future facilities for probing deviations from the SM Higgs couplings, comparing the high luminosity upgrade of the LHC with a future International Linear Collider (ILC), where for the latter various energy and luminosity scenarios are considered. At the ILC model-independent measurements of the coupling structure can be performed, and we provide estimates of the precision that can be achieved.

Blind spots for neutralino dark matter in the MSSM with an intermediate mA

We study the spin-independent neutralino dark matter scattering off heavy nuclei in the minimal supersymmetric Standard Model. We identify analytically the blind spots in direct detection for intermediate values of ${m}_{A}$. In the region where $\ensuremath{\mu}$ and ${M}_{1,2}$ have opposite signs, there is not only a reduction of the lightest $CP$-even Higgs coupling to neutralinos, but also a destructive interference between the neutralino scattering through the exchange of the lightest $CP$-even Higgs and that through the exchange of the heaviest $CP$-even Higgs. At critical values of ${m}_{A}$, the tree-level contribution from the light Higgs exchange cancels the contribution from the heavy Higgs, so the scattering cross section vanishes. We denote these configurations as blind spots, since they provide a generalization of the ones previously discussed in the literature, which occur at very large values of ${m}_{A}$. We show that the generalized blind spots may occur in regions of parameter space that are consistent with the obtention of the proper neutralino relic density and can be tested by nonstandard Higgs boson searches and EWino searches at the LHC and future linear colliders.