Search

The CDF collaboration recently reported a measurement of the $W$-bosos mass, $M_W$, showing a large positive deviation from the Standard Model (SM) prediction. The question arises whether extensions of the SM exist that can accommodate such large values, and what further phenomenological consequences arise from this. A different type of deviation from the SM has been observed experimentally in the searches for light Higgs bosons. CMS has observed two local $\sim 3\,\sigma$ excesses in the $\gamma\gamma$ and $\tau^+\tau^-$ final states for a hypothetical Higgs-boson mass of $\sim 95$ GeV. These two excesses are compatible with the corresponding ATLAS limits. A third excess was observed in the Higgs-boson searches at LEP in the $b \bar b$ final state at the local $\sim 2\,\sigma$ confidence level at about the same Higgs-boson mass. It was shown recently that the three excesses can be described the the 2HDM extended with a real singlet (N2HDM) of Yukawa type IV, while being in agreement with all other theoretical and experimental constraints. We demonstrate that the parameter space that accomodates the three excesses can also give a large contribution to $M_W$ in agreement with the recent CDF measurement. We discuss further phenomenological consequences of this scenario., Comment: 10 pages, 3 figures, v.2: discussion of Z-boson width included, matches published version. arXiv admin note: text overlap with arXiv:2203.13180

It has been recently shown that the discrepancy between the theoretical and experimental values of the anomalous magnetic moment of the muon can be fully accommodated by considering the contribution of few Kaluza-Klein (KK) states of the gauged lepton number with masses lighter than the LEP energy, consistently with present experimental limits. In this article, we construct the minimal embedding of the Standard Model (SM) into D-brane configurations with a gauged lepton number. In order to give rise to such KK modes, the lepton number gauge boson must live on an abelian $U(1)_L$ brane extended along at least one "large" extra dimension in the bulk, with a compactification scale $M_L\sim\mathcal{O}(10-10^2~{\rm GeV})$ for a string scale $M_s\sim 10~{\rm TeV}$. As a consequence, $U(1)_L$ cannot participate to the hypercharge linear combination. We show that the minimal realisation of this framework contains five stacks of branes: the SM color $U(3)_c$, weak $U(2)_w$ and abelian $U(1)$ stacks extended effectively only in four dimensions, the bulk $U(1)_L$, as well as a fifth $U(1)^{'}$ brane. With these five abelian factors, one finds besides the hypercharge a second anomaly-free linear combination which does not couple to the SM spectrum, both in the non-supersymmetric case as well as in the minimal supersymmetric extension of the model. It is also shown how the right-handed neutrino can be implemented in the spectrum, and how fermions arising from the two non-SM branes and coupled to the SM through the $U(1)_L$ KK modes can provide Dark Matter candidates. Finally, the possibility of breaking Lepton Flavour Universality is studied by replacing $U(1)_L$ with a brane gauging only the muonic lepton number, avoiding most experimental constraints and enlarging the parameter space for explaining the discrepancy on the muon magnetic moment., Comment: 20 pages. Published version

The particle discovered in the Higgs boson searches at the LHC with a mass of about 125 GeV is compatible within the present uncertainties with the Higgs boson predicted in the Standard Model (SM), but it could also be identified with one of the neutral Higgs bosons in a variety of beyond the SM (BSM) theories with an extended Higgs sector. The possibility that an additional Higgs boson (or even more than one) could be lighter than the state that has been detected at 125 GeV occurs generically in many BSM models and has some support from slight excesses that were observed above the background expectations in Higgs searches at LEP and at the LHC. The couplings between additional Higgs fields and the electroweak gauge bosons in BSM theories could be probed by model-independent Higgs searches at lepton colliders. We present a generator-level extrapolation of the limits obtained at LEP to the case of a future $e^+e^-$ collider, both for the search where the light Higgs boson decays into a pair of bottom quarks and for the decay-mode-independent search utilising the recoil method. We find that at the ILC with a centre-of-mass energy of 250 GeV, an integrated luminosity of 500 fb$^{-1}$ and polarised beams, the sensitivity to a light Higgs boson with reduced couplings to gauge bosons is improved by more than an order of magnitude compared to the LEP limits and goes much beyond the projected indirect sensitivity of the HL-LHC with 3000 fb$^{-1}$ from the rate measurements of the detected state at 125 GeV.

We describe the new developments in version 4 of the public computer code HiggsBounds. HiggsBounds is a tool to test models with arbitrary Higgs sectors, containing both neutral and charged Higgs bosons, against the published exclusion bounds from Higgs searches at the LEP, Tevatron and LHC experiments. From the model predictions for the Higgs masses, branching ratios, production cross sections and total decay widths—which are specified by the user in the input for the program—the code calculates the predicted signal rates for the search channels considered in the experimental data. The signal rates are compared to the expected and observed cross section limits from the Higgs searches to determine whether a point in the model parameter space is excluded at 95 % confidence level. In this paper we present a modification of the HiggsBounds main algorithm that extends the exclusion test in order to ensure that it provides useful results in the presence of one or more significant excesses in the data, corresponding to potential Higgs signals. We also describe a new method to test whether the limits from an experimental search performed under certain model assumptions can be applied to a different theoretical model. Further developments discussed here include a framework to take into account theoretical uncertainties on the Higgs mass predictions, and the possibility to obtain the χ2 likelihood of Higgs exclusion limits from LEP. Extensions to the user subroutines from earlier versions of HiggsBounds are described. The new features are demonstrated by additional example programs., This work has been supported by the Helmholtz Alliance “Physics at the Terascale” and the Collaborative Research Center SFB676 of the DFG, “Particles, Strings, and the early Universe”. The work of S.H. was supported in part by CICYT (grant FPA 2010–22163-C02- 01) and by the Spanish MICINN’s Consolider-Ingenio 2010 Program under grant MultiDark CSD2009-00064. The work of T.S. was partially funded by the Bonn-Cologne-Graduate-School. O.S. is supported by the Swedish Research Council (VR) through the Oskar Klein centre.