A special Higgs challenge: measuring the mass and production cross section with ultimate precision at FCC-ee

The FCC-ee offers powerful opportunities to determine the Higgs boson parameters, exploiting over $$10^6$$ 10 6 $${ \hbox {e}^+\hbox {e}^- \rightarrow \hbox {ZH}}$$ e + e - → ZH events and almost $$10^5$$ 10 5 $${ \hbox {WW} \rightarrow \hbox {H}}$$ WW → H events at centre-of-mass energies around 240 and 365 GeV. This essay spotlights the important measurements of the ZH production cross section and of the Higgs boson mass. The measurement of the total ZH cross section is an essential input to the absolute determination of the HZZ coupling—a “standard candle” that can be used by all other measurements, including those made at hadron colliders—at the per-mil level. A combination of the measured cross sections at the two different centre-of-mass energies further provides the first evidence for the trilinear Higgs self-coupling, and possibly its first observation if the cross section measurement can be made accurate enough. The determination of the Higgs boson mass with a precision significantly better than the Higgs boson width (4.1 MeV in the standard model) is a prerequisite to either constrain or measure the electron Yukawa coupling via direct $${ \hbox {e}^+\hbox {e}^- \rightarrow \hbox {H}}$$ e + e - → H production at $$\sqrt{s} = 125$$ s = 125 GeV. Approaching the statistical limit of 0.1% and $${\mathcal {O}}(1)$$ O ( 1 ) MeV on the ZH cross section and the Higgs boson mass, respectively, sets highly demanding requirements on accelerator operation (ZH threshold scan, centre-of-mass energy measurement), detector design (lepton momentum resolution, hadronic final state reconstruction performance), theoretical calculations, and analysis techniques (efficiency and purity optimization with modern tools, constrained kinematic fits, control of systematic uncertainties). These challenges are examined in turn in this essay

Gluino-SUGRA scenarios in light of FNAL muon g – 2 anomaly

Gluino-SUGRA ($$ \overset{\sim }{g} $$ g ~ SUGRA), which is an economical extension of the predictive mSUGRA, adopts much heavier gluino mass parameter than other gauginos mass parameters and universal scalar mass parameter at the unification scale. It can elegantly reconcile the experimental results on the Higgs boson mass, the muon g − 2, the null results in search for supersymmetry at the LHC and the results from B-physics. In this work, we propose several new ways to generate large gaugino hierarchy (i.e. M3 » M1, M2) for $$ \overset{\sim }{g} $$ g ~ SUGRA model building and then discuss in detail the implications of the new muon g − 2 results with the updated LHC constraints on such $$ \overset{\sim }{g} $$ g ~ SUGRA scenarios. We obtain the following observations: (i) for the most interesting M1 = M2 case at the GUT scale with a viable bino-like dark matter, the $$ \overset{\sim }{g} $$ g ~ SUGRA can explain the muon g − 2 anomaly at 1σ level and be consistent with the updated LHC constraints for 6 ≤ M3/M1 ≤ 9 at the GUT scale; (ii) For M1 : M2 = 5 : 1 at the GUT scale with wino-like dark matter, the $$ \overset{\sim }{g} $$ g ~ SUGRA model can explain the muon g − 2 anomaly at 2σ level and be consistent with the updated LHC constraints for 3 ≤ M3/M1 ≤ 3.2 at the GUT scale; (iii) For M1 : M2 = 3 : 2 at the GUT scale with mixed bino-wino dark matter, the $$ \overset{\sim }{g} $$ g ~ SUGRA model can explain the muon g − 2 anomaly at 1σ level and be consistent with the updated LHC constraints for 6.9 ≤ M3/M1 ≤ 7.5 at the GUT scale. Although the choice of heavy gluino will always increase the FT involved, some of the 1σ/2σ survived points of $$ \Delta {a}_{\mu}^{\mathrm{combine}} $$ ∆ a μ combine can still allow low EWFT of order several hundreds and be fairly natural. Constraints from (dimension-five operator induced) proton decay are also discussed.

Muon g − 2 in gauge mediation without SUSY CP problem

We discuss gauge mediated supersymmetry breaking models which explain the observed muon anomalous magnetic moment and the Higgs boson mass simultaneously. The successful explanation requires the messenger sector which violates the relation motivated by the grand unification theory (GUT). The naive violation of the GUT relation, however, ends up with the CP problem. We propose a model in which the phases of the gaugino masses are aligned despite the violation of the GUT relation. We also consider a model which generates the μ-term and the additional Higgs soft masses squared without causing CP violation. As a result, we find a successful model which explains the muon anomalous magnetic moment and the Higgs boson mass. The model is also free from the CP, flavor-changing neutral current and the lepton flavor violation problems caused by the subdominant gravity mediation effects. The lightest supersymmetric particles are gravitino/goldstini and the next-to-lightest ones are the Wino/Higgsinos in the typical parameter space. We also study the LHC constraints.

Search for dark photons in Higgs boson production via vector boson fusion in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

A search is presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle and an isolated photon. The search is performed by the CMS collaboration at the LHC, using a data set corresponding to an integrated luminosity of 130 fb−1, recorded at a center-of-mass energy of 13 TeV in 2016–2018. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An upper limit is set on the product of the cross section for production via vector boson fusion and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a Higgs boson mass of 125 GeV, assuming the standard model production rates, the observed (expected) 95% confidence level upper limit on the branching fraction is 3.5 (2.8)%. This is the first search for such decays in the vector boson fusion channel. Combination with a previous search for Higgs bosons produced in association with a Z boson results in an observed (expected) upper limit on the branching fraction of 2.9 (2.1)% at 95% confidence level.

The naturalness in the BLMSSM and B-LSSM

In order to interpret the Higgs boson mass and its decays naturally, we hope to examine the BLMSSM and B-LSSM. In the both models, the right-handed neutrino superfields are introduced to better explain the neutrino mass problems. In this paper, we introduce the fine-tuning to acquire the physical Higgs boson mass. Besides, the method of $$\chi ^2$$ χ 2 analyses will be adopted in the BLMSSM and B-LSSM to fit the experimental data. Therefore, we can obtain the reasonable theoretical values of the Higgs decays and muon $$g-2$$ g - 2 that are in accordance with the experimental results respectively in the BLMSSM and B-LSSM.

The light MSSM Higgs boson mass for large $$\tan \beta $$ and complex input parameters

We discuss various improvements of the prediction for the light MSSM Higgs boson mass in the hybrid framework of the public code $$\texttt {FeynHiggs}$$ FeynHiggs , which combines fixed-order and effective field theory results. First, we discuss the resummation of logarithmic contributions proportional to the bottom-Yukawa coupling including two-loop $$\Delta _b$$ Δ b resummation. For large $$\tan \beta $$ tan β , these improvements can lead to large upward shifts of the Higgs mass compared to the existing fixed-order calculations. Second, we improve the implemented EFT calculation by fully taking into account the effect of $$\mathcal{CP}$$ CP -violating phases. As a third improvement, we discuss the inclusion of partial $$\hbox {N}^3$$ N 3 LL resummation. The presented improvements will be implemented into $$\texttt {FeynHiggs}$$ FeynHiggs .

Improving fermion mass hierarchy in grand gauge–Higgs unification with localized gauge kinetic terms

Grand gauge–Higgs unification of five dimensional SU(6) gauge theory on an orbifold $$S^1/Z_2$$ S 1 / Z 2 with localized gauge kinetic terms is discussed. The Standard model (SM) fermions on one of the boundaries and some massive bulk fermions coupling to the SM fermions on the boundary are introduced, so that they respect an SU(5) symmetry structure. The SM fermion masses including top quark are reproduced by mild tuning the bulk masses and parameters of the localized gauge kinetic terms. Gauge coupling universality is not guaranteed by the presence of the localized gauge kinetic terms and it severely constrains the Higgs vacuum expectation value. Higgs potential analysis shows that the electroweak symmetry breaking occurs by introducing additional bulk fermions in simplified representations. The localized gauge kinetic terms enhance the magnitude of the compactification scale, which helps Higgs boson mass large. Indeed the observed Higgs boson mass 125 GeV is obtained.