arXiv subjects

Dario Mueller

Publications and source records attributed to Dario Mueller.

4 recordsLinked to original sources

arXiv2021

Correlating $h\toμ^+μ^-$ to the Anomalous Magnetic Moment of the Muon via Leptoquarks

Recently, both ATLAS and CMS measured the decay $h\toμ^+μ^-$, finding a signal strength with respect to the Standard Model expectation of $1.2\pm0.6$ and $1.19\substack{+0.41+0.17\\-0.39 -0.16}$, respectively. This provides, for the first time, evidence that the Standard Model Higgs couples to second generation fermions. This measurement is particularly interesting in the context of the intriguing hints for lepton flavor universality violation, accumulated within recent years, as new physics explanations could also be tested in the $h\toμ^{+}μ^{-}$ decay mode. Leptoquarks are prime candidates to account for the flavor anomalies. In particular, they can provide the necessary chiral enhancement (by a factor $m_t/m_μ$) to address $a_μ$ with TeV scale new physics. In this letter we point out that such explanations of $a_μ$ also lead to enhanced effects in $h\toμ^+μ^-$ and we examine the correlations between $h\toμ^+μ^-$ and $a_μ$ within leptoquark models. We find that the effect in the branching ratio of $h\toμ^+μ^-$ ranges from several percent up to a factor three, if one aims at accounting for $a_μ$ at the $2\,σ$ level. Hence, the new ATLAS and CMS measurements already provide important constraints on the parameter space, rule out specific $a_μ$ explanations and will be very important to test the flavor anomalies in the future.

hep-ph↗

arXiv2021

Leptoquarks in Oblique Corrections and Higgs Signal Strength: Status and Prospects

Leptoquarks (LQs) are predicted within Grand Unified Theories and are well motivated by the current flavor anomalies. In this article we investigate the impact of scalar LQs on Higgs decays and oblique corrections as complementary observables in the search for them. Taking into account all five LQ representations under the Standard Model gauge group and including the most general mixing among them, we calculate the effects in $h\toγγ$, $h\to gg$, $h \to Z γ$ and the Peskin-Takeuchi parameters $S$, $T$ and $U$. We find that these observables depend on the same Lagrangian parameters, leading to interesting correlations among them. While the current experimental bounds only yield weak constraints on the model, these correlations can be used to distinguish different LQ representations at future colliders (ILC, CLIC, FCC-ee and FCC-hh), whose discovery potential we are going to discuss.

hep-ph↗

arXiv2018

Large $h\to b s$ in generic two-Higgs-doublet models

We investigate the possible size of $h\to bs$ in two-Higgs-doublet models with generic Yukawa couplings. Even though the corresponding rates are in general expected to be small due to the indirect constraints from $B_s\toμ^{+}μ^{-}$ and $B_s$--$\overline{B}_s$ mixing, we find regions in parameter space where $h\to bs$ can have a sizable branching ratio well above 10\%. This requires a tuning of the neutral scalar masses and their couplings to muons, but then all additional constraints such as $B\to X_s γ$, $(g-2)_μ$, and $h\toμ^{+}μ^{-}$ are satisfied. In this case, $h\to bs$ can be a relevant background in $h\to b\bar{b}$ searches and vice versa due to the imperfect $b$-tagging purity. Furthermore, if $h\to bs$ is sizeable, one expects two more scalar resonances in the proximity of $m_h$. We briefly comment on other flavour violating Higgs decays and on the 95 GeV $γγ$ resonance within generic two-Higgs-doublet models.

hep-ph↗

arXiv2018

Correlating Lepton Flavour (Universality) Violation in $B$ Decays with $μ\to eγ$ using Leptoquarks

Motivated by the measurements of $b\to s\ell^+\ell^-$ transitions, including $R(K)$ and $R(K^*)$, we examine lepton flavour (universality) violation in $B$ decays and its connections to $μ\to eγ$ in generic leptoquark models. Considering all 10 representations of scalar and vector leptoquarks under the Standard Model gauge group we compute the tree-level matching for semileptonic $b$-quark operators as well as their loop effects in $\ell\to\ell^\primeγ$. In our phenomenological analysis we correlate $R(K)$, $R(K^*)$ and the other $b\to sμ^+μ^-$ data to $μ\to eγ$ and $b\to sμe$ transitions for the three leptoquark representations that generate left-handed currents in $b\to s\ell^+\ell^-$ transitions and, therefore, provide a good fit to data. We find that while new physics contributions to muons are required by the global fit, also couplings to electrons can be sizeable without violating the stringent bounds from $μ\to eγ$. In fact, if the effect in electrons in $b\to s\ell^+\ell^-$ has opposite sign than the effect in muons the bound from $μ\to eγ$ can always be avoided. However, unavoidable effects in $b\to sμe$ transitions (i.e. $B_s\toμe$, $B\to Kμe$, etc.) appear which are within the reach of LHCb and BELLE II.

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