CP-odd Scalar Research Articles

Probing a light long-lived pseudo-scalar from Higgs decay via displaced taus at the LHC

A light (GeV mass) long-lived (cτ around dozens of millimeters) CP-odd scalar can be readily predicted in new physics models. In this work we investigate the Higgs decay into such a light scalar plus a Z-boson and take the aligned two-Higgs-doublet model (2HDM) as an example. This light long-lived scalar, with the dominant decay to tau leptons, will fly over a distance from the production point and present a displaced vertex in an Inner Detector of a generally purposed experiment like ATLAS or CMS. In our study we focus on the LHC experiment and perform Monte Carlo simulations for the signal and backgrounds. We demonstrate some benchmark points for the aligned 2HDM and find the signal to be detectable when the luminosity is accumulated to 300 fb−1. So our study suggests an experimental search for this process in the ongoing LHC.

95 GeV excess in the Georgi-Machacek model: Single or twin peak resonance

In this work, we investigate the possibility to address the excess observed around 95 GeV in the γγ, ττ, and bb¯ channels as a scalar resonance(s) within the Georgi-Machacek model. In our analysis, we find that the excess can be easily accommodated in the channels (γγ and bb¯) simultaneously, where the 95 GeV candidate is a single peak resonance (SPR) due to a light CP-even scalar. We found that the excess in the ττ channel can be addressed simultaneously with γγ and bb¯ only if the 95 GeV candidate is a twin peak resonance (TPR), i.e., another CP-odd scalar in addition to the CP-even scalar. We demonstrate that the nature of the 95 GeV scalar resonance candidate (SPR or TPR) can be probed via the properties of its di-τ decay. Published by the American Physical Society 2024

Testing Z boson rare decays Z→H1γ,A1γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\rightarrow H_1 \\gamma , A_1 \\gamma $$\\end{document} with (g-2)μ,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(g-2)_\\mu ,$$\\end{document}MW,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ M_W,$$\\end{document} and BR(hSM→Zγ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$BR(h_{\ extrm{SM}}\\rightarrow Z\\gamma )$$\\end{document} in the NMSSM

We study the rare decay process of Z boson into photon, accompanied by a CP-even or CP-odd scalar. We present the analytical delineation of the processes through the model-independent parametrizations of the new physics couplings and, finally, consider the Next-to-Minimal Supersymmetric Standard Model to mark out the parameter space where the branching fraction can have the maximum value. As a part of the necessary phenomenological and experimental cross-checks, we aim to fit the anomalous magnetic moment of the muon and W boson mass anomaly through the supersymmetric contributions. We also find that the decays Z→H1γ,A1γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\rightarrow H_1 \\gamma , A_1 \\gamma $$\\end{document} can serve as an excellent complementary test to BR(hSM→Zγ).\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$BR(h_{\ extrm{SM}}\\rightarrow Z\\gamma ).$$\\end{document} In fact, to facilitate future searches, we unveil a few benchmark points that additionally satisfy the deviation of BR(hSM→Zγ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$BR(h_{\ extrm{SM}}\\rightarrow Z\\gamma )$$\\end{document} from the SM value based on the recent measurements of ATLAS and CMS. Future proposals such as ILC, CEPC, and FCC-ee are anticipated to operate for multiple years, focusing on center-of-mass energy near the Z pole. Consequently, these projects will be capable of conducting experiments at the Giga-Z(109\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(10^{9}$$\\end{document} of Z bosons) and Tera-Z(1012\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(10^{12}$$\\end{document} of Z bosons) phases, which may probe the aforesaid rare decay processes, thus the model as well. These unconventional yet complementary searches offer different routes to explore the supersymmetric models with extended Higgs sectors like NMSSM.

Light Scalars at FASER

FASER, the ForwArd Search ExpeRiment, is a currently operating experiment at the Large Hadron Collider (LHC) that can detect light long-lived particles produced in the forward region of the LHC interacting point. In this paper, we study the prospect of detecting light CP-even and CP-odd scalars at FASER and FASER 2. Considering a model-independent framework describing the most general interactions between a CP-even or CP-odd scalar and SM particles using the notation of coupling modifiers in the effective Lagrangian, we develop the general formalism for the scalar production and decay. We then analyze the FASER and FASER 2 reaches of light scalars in the large tan β region of the Type-I two Higgs double model as a case study, in which light scalars with relatively long lifetime could be accommodated. In the two benchmark scenarios we considered, the light (pseudo)scalar decay length varies in (10−8, 105) meters. Both FASER and FASER 2 can probe a large part of the parameter space in the large tan β region up to 107, extending beyond the constraints of the other existing experiments.

A scotogenic model with two inert doublets

In this work, we present a scotogenic model, where the neutrino mass is generated at one-loop diagrams. The standard model (SM) is extended by three singlet Majorana fermions and two inert scalar doublets instead of one doublet as in the minimal scotogenic model. The model scalar sector includes two CP-even, two CP-odd and two charged scalars in addition to the Higgs. The dark matter (DM) candidate could be either the light Majorana fermion (Majorana DM), or the lightest among the CP-even and the CP-odd scalars (scalar DM). We show that the model accommodates both Majorana and scalar DM within a significant viable parameter space, while considering all the relevant theoretical and experimental constraints such as perturbativity, vacuum stability, unitarity, the di-photon Higgs decay, electroweak precision tests and lepton flavor violating constraints. In addition to the collider signatures predicted by the minimal scotogenic model, our model predicts some novel signatures that can be probed through some final states such as .

Electroweak baryogenesis via bottom transport: Complementarity between LHC and future lepton collider probes

We study the complementarity between the Large Hadron Collider (LHC) and future lepton colliders in probing electroweak baryogenesis induced by an additional bottom Yukawa coupling ρbb. The context is general two Higgs doublet model (g2HDM) where such additional bottom Yukawa coupling can account for the observed baryon asymmetry of the Universe if Im(ρbb)≳0.058. We find that LHC would probe the nominal Im(ρbb) required for baryogenesis to some extent via bg→bA→bZh process if 300GeV≲mA≲450 GeV, where A is the CP-odd scalar in g2HDM. We show that future electron positron collider such as International Linear Collider with 500 GeV and 1 TeV collision energies may offer unique probe for the nominal Im(ρbb) via e+e−→Z⁎→AH process followed by A,H→bb¯ decays in four b-jets signature. For complementarity we also study the resonant diHiggs productions, which may give an insight into strong first-order electroweak phase transition, via e+e−→Z⁎→AH→Ahh process in six b-jets signature. We find that 1 TeV collision energy with O(1)ab−1 integrated luminosity could offer an ideal environment for the discovery.

Flavor and CP-violating Higgs sector in two Higgs doublet models with $$U(1)'$$

We investigate the role of a local $U(1)'$ symmetry for the problem of CP violation in the effective theory for two Higgs doublet models and its microscopic counterparts. First, in two Higgs doublet models with $U(1)'$, we show that the higher-dimensional operators in the scalar potential violate the CP symmetry with an interplay with the mixing mass parameter, giving rise to small mixings between CP-even and CP-odd scalars. Motivated by the $B$-meson anomalies in recent years, we take the flavored $U(1)'$ to be a benchmark model for specifying the flavor structure. Then, we calculate the electric dipole moment of electron (eEDM) at two loops due to the CP-violating higher-dimensional operators and identify the correlation between the masses of heavy Higgs bosons and the cutoff scale from the bound on eEDM. We also comment on the possibility of making an independent test of the CP violation in the collider searches for heavy Higgs bosons. Finally, we show how the obtained eEDM results in the effective theory can be used to constrain microscopic models with an explicit CP violation in the partially decoupled or dark sectors.

Higgs decay to light (pseudo)scalars in the semi-constrained NMSSM * *Supported by National Natural Science Foundation of China (NSFC) (11605123)

The next-to minimal supersymmetric standard model (NMSSM) with non-universal Higgs masses, i.e., the semi-constrained NMSSM (scNMSSM), extends the minimal supersymmetric standard model (MSSM) by a singlet superfield and assumes universal conditions, except for the Higgs sector. It can not only maintain the simplicity and grace of the fully constrained MSSM and NMSSM and relieve the tension they have been facing since the discovery of the 125-GeV Higgs boson but also allow for an exotic phenomenon wherein the Higgs decay into a pair of light ( ) singlet-dominated (pseudo)scalars (hereafter, in this paper, we use "scalar" for both scalars and pseudoscalars, considering pseudoscalars can also be called CP-odd scalars). This condition can be classified into three scenarios according to the identitiesof the SM-like Higgs and the light scalar: (i) the light scalar is CP-odd, and the SM-like Higgs is ; (ii) the light scalar is CP-odd, and the SM-like Higgs is ; and (iii) the light scalar is CP-even, and the SM-like Higgs is . In this work, we compare the three scenarios, checking the interesting parameter regions that lead to the scenarios, the mixing levels of the doublets and singlets, the tri-scalar coupling between the SM-like Higgs and a pair of light scalars, the branching ratio of Higgs decay to the light scalars, and sensitivities in the detection of the exotic decay at the HL-LHC and future lepton colliders such as CEPC, FCC-ee, and ILC. Finally, several interesting conclusions are drawn, which are useful for understanding the different delicate mechanisms of the exotic decay and designing colliders in future.

Probing electroweak baryogenesis induced by extra bottom Yukawa coupling via EDMs and collider signatures

We study the prospect of probing electroweak baryogenesis driven by an extra bottom Yukawa coupling ρbb in a general two Higgs doublet model via electric dipole moment (EDM) measurements and at the collider experiments. The parameter space receives meaningful constraints from 125 GeV Higgs h boson signal strength measurements as well as several heavy Higgs boson searches at the Large Hadron Collider (LHC). In addition, we show that the asymmetry of the CP asymmetry of inclusive B → Xsγ decay would provide complementary probe. A discovery is possible at the LHC via bg → bA → bZh process if |ρbb| ∼ 0.15 and 250 GeV≲ mA ≲ 350 GeV, where A is CP odd scalar. For mA> 2mt threshold, where mt is the top quark mass, one may also discover bg → bA → btoverline{t} at the high luminosity LHC run if an extra top Yukawa coupling |ρtt| ∼ 0.5, though it may suffer from systematic uncertainties. For completeness we study gg → toverline{t}A → toverline{t}boverline{b} but find it not promising.

Probing an additional bottom Yukawa coupling via bg→bA→bZH signature

The recent discovery of the bottom quark Yukawa coupling ($hbb$) of the 125 GeV scalar motivates one to search for extra bottom Yukawa coupling that may exist in the nature. The two Higgs doublet model without a discrete $Z_2$ symmetry allows the possibility of additional bottom Yukawa coupling $\rho_{bb}$. We show that $\rho_{bb}$ can be searched directly at the LHC via $bg\to b A \to b Z H$ and $gg \to b \bar b A \to b \bar b Z H$ processes, where $A$ and $H$ are the CP-odd and CP-even scalars respectively. We find that the $bg\to b A \to b Z H$ process could be discovered with $\sim300$ fb$^{-1}$ integrated luminosity if $ m_A \sim 300$ GeV, while the latter process may emerge in the high luminosity LHC (HL-LHC) data. A discovery might touch upon the parameter space required for the electroweak baryogenesis.

A light complex scalar for the electron and muon anomalous magnetic moments

The anomalous magnetic moments of the electron and the muon are interesting observables, since they can be measured with great precision and their values can be computed with excellent accuracy within the Standard Model (SM). The current experimental measurement of this quantities show a deviation of a few standard deviations with respect to the SM prediction, which may be a hint of new physics. The fact that the electron and the muon masses differ by two orders of magnitude and the deviations have opposite signs makes it difficult to find a common origin of these anomalies. In this work we introduce a complex singlet scalar charged under a Peccei-Quinn-like (PQ) global symmetry together with the electron transforming chirally under the same symmetry. In this realization, the CP-odd scalar couples to electron only, while the CP-even part can couple to muons and electrons simultaneously. In addition, the CP-odd scalar can naturally be much lighter than the CP-even scalar, as a pseudo-Goldstone boson of the PQ-like symmetry, leading to an explanation of the suppression of the electron anomalous magnetic moment with respect to the SM prediction due to the CP-odd Higgs effect dominance, as well as an enhancement of the muon one induced by the CP-even component.

Singlet scalar and 2HDM extensions of the Standard Model: CP-violation and constraints from (g \u2212 2)\u03bc and eEDM

We study popular scalar extensions of the Standard Model, namely the singlet extension, the 2-Higgs doublet model (2HDM) and its extension by a singlet scalar. We focus on the contributions of the added scalars to the anomalous magnetic moment of the muon, (g − 2)μ in the presence of CP-violation, and the electric dipole moment of the electron (eEDM) in these models. In the absence of CP-violation, CP-even and CP-odd scalars contribute with an opposite sign to the anomalous magnetic moment of the muon and as a result these models generally require very light scalars to explain the observed discrepancy in (g − 2)μ. We study the effect of CP-violation on the anomalous magnetic moment of the muon and its compatibility with the eEDM constraints. We show that given the current status of the global set of constraints applied on all values of cot β, in the CP-violating scalar extensions, there exist no viable parameter space in agreement with both aμ and eEDM bounds.

Dark Matter signals at the LHC from a 3HDM

We analyse new signals of Dark Matter (DM) at the Large Hadron Collider (LHC) in a 3-Higgs Doublet Model (3HDM) where only one doublet acquires a Vacuum Expectation Value (VEV), preserving a parity Z2. The other two doublets are inert and do not develop a VEV, leading to a dark scalar sector controlled by Z2, with the lightest CP-even dark scalar H1 being the DM candidate. This leads to the loop induced decay of the next-to-lightest scalar, {H}_2to {H}_1foverline{f}left(f=u,d,c,s,b,e,mu, tau right) , mediated by both dark CP-odd and charged scalars. This is a smoking-gun signal of the 3HDM since it is not allowed in the 2HDM with one inert doublet and is expected to be important when H2 and H1 are close in mass. In practice, this signature can be observed in the cascade decay of the SM-like Higgs boson, hto {H}_1{H}_2to {H}_1{H}_1foverline{f} into two DM particles and di-leptons/di-jets, where h is produced from either gluon-gluon Fusion (ggF) or Vector Boson Fusion (VBF). However, this signal competes with the tree-level channel qoverline{q}to {H}_1{H}_1{Z}^{ast}to {H}_1{H}_1foverline{f} . We devise some benchmarks, compliant with collider, DM and cosmological data, for which the interplay between these modes is discussed. In particular, we show that the resulting detector signature, , with invariant mass of foverline{f} much smaller than mZ, can potentially be extracted already during Run 2 and 3. For example, the H2 → H1γ* and γ* → e+e− case will give a spectacular QED mono-shower signal.

Classification of simple heavy vector triplet models

We investigate decay modes of spin-1 heavy vector bosons ($V'$) from the viewpoint of perturbative unitarity in a model-independent manner. Perturbative unitarity requires some relations among couplings. The relations are called unitarity sum rules. We derive the unitarity sum rules from processes that contain two fermions and two gauge bosons. We find the relations between $V'$ couplings to the SM fermions $(f)$ and $V'$ couplings to the SM gauge bosons ($V$). Using the coupling relations, we calculate partial decay widths for $V'$ decays into $VV$ and $ff$. We show that Br($W' \to WZ) \lesssim$ 2$\%$ in the system that contains $V'$ and CP-even scalars as well as the SM particles. This result is independent of the number of the CP-even scalars. We also show that contributions of CP-odd scalars help to make Br($W' \to WZ$) larger than Br($W' \to ff$) as long as the CP-odd scalars couple to both the SM fermions and the SM gauge bosons. The existence of the CP-odd scalar couplings is a useful guideline to construct models that predict Br($W' \to WZ) \gtrsim$ 2$\%$. Our analysis relies only on the perturbative unitarity of $f\bar{f} \to WW'$. Therefore our result can be applied to various models.

The impact of additional scalar bosons at the LHC

In this study we consider an effective model by introducing two hypothetical real scalars, H and χ - a dark matter candidate, where the masses of these scalars are 2mh < mH < 2mt and mχ ≈ mt/2 with mh and mt being the Standard Model Higgs boson and top quark masses, respectively. A distortion in the transverse momentum distributions of h in the intermediate region of the spectrum through the processes pp → H → hχχ could be observed in this model. An additional scalar, S, has been postulated to explain large H → hχχ branching ratios, assuming mh ≲ mS ≲ mH — mh and mS > 2mx. Furthermore, a scenario of a two Higgs doublet model (2HDM) is introduced and a detailed proposal at the present energies of the Large Hadron Collider to study the extra CP-even (h, H), CP-odd (A) and charged (H±) scalars has been pursued. With possible phenomenological implications, production and decay modes for these scalars are discussed. Based on the mass spectrum of H, A and H±, the production of multi-leptons and Z+jets+missing-energy events are predicted. A specific, Type-II 2HDM model is discussed in detail.

Precision tools and models to narrow in on the 750 GeV diphoton resonance

The hints for a new resonance at 750 GeV from ATLAS and CMS have triggered a significant amount of attention. Since the simplest extensions of the standard model cannot accommodate the observation, many alternatives have been considered to explain the excess. Here we focus on several proposed renormalisable weakly-coupled models and revisit results given in the literature. We point out that physically important subtleties are often missed or neglected. To facilitate the study of the excess we have created a collection of 40 model files, selected from recent literature, for the Mathematica package SARAH. With SARAH one can generate files to perform numerical studies using the tailor-made spectrum generators FlexibleSUSY and SPheno. These have been extended to automatically include crucial higher order corrections to the diphoton and digluon decay rates for both CP-even and CP-odd scalars. Additionally, we have extended the UFO and CalcHep interfaces of SARAH, to pass the precise information about the effective vertices from the spectrum generator to a Monte-Carlo tool. Finally, as an example to demonstrate the power of the entire setup, we present a new supersymmetric model that accommodates the diphoton excess, explicitly demonstrating how a large width can be obtained. We explicitly show several steps in detail to elucidate the use of these public tools in the precision study of this model.

Higgs-strahlung production process e+e− → hZ at the future Higgs factory in the SM extension with color-octet scalars

We investigate the Higgs-strahlung production process e+e− → hZ at the future Higgs factory in the Manohar-Wise model, which extends the SM by a family of color-octet and isospin-doublet scalars. We scan over the parameter space of the Manohar-Wise model considering the theoretical and experimental constraints from unitarity, electroweak data and LHC searches for the color-octet scalars and perform fits with the Higgs data from ATLAS and CMS. Then we calculate the cross section σ(e+e− → hZ) at s=240GeV by including the radiative corrections from loops mediated by color-octet scalars. We find that the deviation of the cross section in the Manohar-Wise model from its SM prediction can maximally reach 11%, and the large deviations are mainly due to the potentially large coupling of Higgs boson with CP-odd color-octet scalars SIA (i.e., the coupling hSIA∗SIB).

Extra neutral scalars with vectorlike fermions at the LHC

Many theories beyond the standard model (BSM) contain new CP-odd and CP-even neutral scalars $\phi = \{A,H\}$, and new vector-like fermions ($\psi_{VL}$). The couplings of the CP-odd scalar $A$ to two standard model (SM) gauge bosons cannot occur from renormalizable operators in a CP-conserving sector, but can be induced at the quantum loop level. We compute these effective couplings at the 1-loop level induced by the SM fermions and vector-like fermions, present analytical expressions for them, and plot them numerically. Using the 8~TeV Large Hadron Collider (LHC) $\gamma\gamma$, $\tau^{+} \tau^{-}$ and $t \bar t$ channel data, we derive constraints on the effective couplings of the $\phi$ to standard model gauge bosons and fermions. We present the gluon-fusion channel cross-sections of the $\phi$ at the 8~and~14~TeV LHC, and its branching-ratios into SM fermion and gauge-boson pairs. We present our results first model-independently, and then also for some simple models containing $\phi$ and $\psi_{VL}$ in the singlet and doublet representations of $SU(2)$. In the doublet case, we focus on the two-Higgs-doublet (2HDM) Type-II and Type-X models in the alignment limit.

Diboson anomaly: Heavy Higgs resonance and QCD vectorlike exotics

The ATLAS collaboration (and also CMS) has recently reported an excess over Standard Model expectations for gauge boson pair production in the invariant mass region $1.8-2.2$ TeV. In the light of these results, we argue that such signal might be the first manifestation of the production and further decay of a heavy CP-even Higgs resulting from a type-I Two Higgs Doublet Model. We demonstrate that in the presence of colored vector-like fermions, its gluon fusion production cross-section is strongly enhanced, with the enhancement depending on the color representation of the new fermion states. Our findings show that barring the color triplet case, any QCD "exotic" representation can fit the ATLAS result in fairly large portions of the parameter space. We have found that if the diboson excess is confirmed and this mechanism is indeed responsible for it, then the LHC Run-2 should find: (i) a CP-odd scalar with mass below $\sim 2.3$ TeV, (ii) new colored states with masses below $\sim 2$ TeV, (iii) no statistically significant diboson events in the $W^\pm Z$ channel, (iv) events in the triboson channels $W^\pm W^\mp\,Z$ and $ZZZ$ with invariant mass amounting to the mass of the CP-odd scalar.

Global fits of the two-loop renormalized Two-Higgs-Doublet model with soft Z 2 breaking

We determine the next-to-leading order renormalization group equations for the Two-Higgs-Doublet model with a softly broken $Z_2$ symmetry and CP conservation in the scalar potential. We use them to identify the parameter regions which are stable up to the Planck scale and find that in this case the quartic couplings of the Higgs potential cannot be larger than 1 in magnitude and that the absolute values of the S-matrix eigenvalues cannot exceed 2.5 at the electroweak symmetry breaking scale. Interpreting the 125 GeV resonance as the light CP-even Higgs eigenstate, we combine stability constraints, electroweak precision and flavour observables with the latest ATLAS and CMS data on Higgs signal strengths and heavy Higgs searches in global parameter fits to all four types of $Z_2$ symmetry. We quantify the maximal deviations from the alignment limit and find that in type II and Y the mass of the heavy CP-even (CP-odd) scalar cannot be smaller than 340 GeV (360 GeV). Also, we pinpoint the physical parameter regions compatible with a stable scalar potential up to the Planck scale. Motivated by the question how natural a Higgs mass of 125 GeV can be in the context of a Two-Higgs-Doublet model, we also address the hierarchy problem and find that the Two-Higgs-Doublet model does not offer a perturbative solution to it beyond 5 TeV.