Towards the Ultimate SM Fit to Close in on Higgs Physics

Abstract: With the discovery of the Higgs at the LHC, experiments have finally addressed all aspects of the Standard Model (SM). At this stage, it is important to understand which windows for beyond the SM (BSM) physics are still open, and which are instead tightly closed. We address this question by parametrizing BSM effects with dimension-six operators and performing a global fit to the SM. We separate operators into different groups constrained at different levels, and provide independent bounds on their Wilson coefficients taking into account only the relevant experiments. Our analysis allows to assert in a model-independent way where BSM effects can appear in Higgs physics. In particular, we show that deviations from the SM in the differential distributions of h->Vff are related to other observables, such as triple gauge-boson couplings, and are then already constrained by present data. On the contrary, BR(h-> Z+gamma) can still hide large deviations from the SM.

• The paper provides a comprehensive global fit using dimension-six operators to quantify potential deviations from the Standard Model in Higgs observables.
• It leverages precise experimental data from Z-pole measurements, W mass, and LHC triple gauge-boson analyses to set stringent bounds on new physics.
• The study highlights less constrained Higgs decay channels as promising windows for uncovering BSM phenomena and guiding future LHC searches.

Overview of "Towards the Ultimate SM Fit to Close in on Higgs Physics"

The paper entitled "Towards the Ultimate SM Fit to Close in on Higgs Physics" by Alex Pomarol and Francesco Riva embarks upon a meticulous exploration of the Standard Model (SM) in light of the Higgs discovery at the Large Hadron Collider (LHC). The authors aim to refine the understanding of the leeway available for exploring Beyond the Standard Model (BSM) physics. They achieve this by examining dimension-six operators and performing a global fit to the SM. The research seeks to ascertain which potential deviations from the SM remain plausible and how they might manifest in associated Higgs physics experiments.

Global Fit to the Standard Model

At the heart of the study lies the employment of dimension-six operators as a diagnostic tool for characterizing BSM effects when the scale of BSM physics is higher than the electroweak scale. The approach cleverly circumvents model dependencies and allows for a universal framework under which deviations can be quantified using the Wilson coefficients of these operators. The fit uses an exhaustive compilation of precise experimental data, with primary contributions from the $Z$-pole measurements, the W mass, and LHC data, categorizing operators according to the observables they influence.

Experimental Constraints and Analysis

The paper divides the experimentally related operators into groups based on the extent and precision of constraints available:

1. $Z$-pole and Low-energy Constraints: These provide stringent bounds on deviations affecting the $W/Z$ propagators and gauge-boson couplings to fermions. With constraints sometimes at the per-mille level, these bounds are crucial for limiting the parameter space available for new physics.
2. Triple Gauge-Boson Couplings (TGCs): The analysis extends to TGCs which offer weaker constraints but are critical for directions in parameter space unbounded by previous groups. The TGCs present potential discovery tools, specifically through processes at high-energy scales such as those at the LHC.
3. Higgs Physics: The study elucidates the indirect constraints on Higgs interactions, noting that deviations in branching ratios, specifically $BR(h \to Z \gamma)$, remain less tightly bound compared to other observables like $h \to V \bar{f}f$. This aspect underlines opportunities for observing BSM signals in Higgs channels.

Implications for Higgs Physics and the Broader SM

This research presents a nuanced view of BSM explorations through the Higgs sector. The LHC's potential for improving constraints on TGCs, and through them on dimension-six operators, is emphasized over other processes, highlighting a direct path to more effective probes of new physics. The analysis implies that significant deviations in Higgs processes might be directly traceable through their connection to well-constrained TGCs, amplifying LHC's role in BSM searches.

The theoretical implications are substantial, inviting further investigation into operators which might reveal new physics in less-constrained Higgs decay channels. Practically, it suggests strategic directions for experimental focus, leveraging indirect constraints from established precision data to hone in on less-explored Higgs observables.

Future Prospects

The methodology employed here not only reinforces the robustness of the SM in light of Higgs physics but also maps out promising avenues for the discovery of novel phenomena. Future work might focus on enhancing the precision of Higgs property measurements and extending the theoretical groundwork to incorporate more sophisticated models of symmetry breaking.

In conclusion, Pomarol and Riva deliver a comprehensive, precise approach to Higgs physics that bolsters the SM while providing cogent strategies for uncovering new physics beyond its scope. Their analysis forms a critical resource for upcoming experimental endeavors and theoretical explorations in high-energy physics.