Interpreting electroweak precision data including the $W$-mass CDF anomaly

Abstract: We perform a global fit of electroweak data, finding that the anomaly in the $W$ mass claimed by the CDF collaboration can be reproduced as a universal new-physics correction to the $T$ parameter or $| H^\dagger D_\mu H|^2$ operator. Contributions at tree-level from multi-TeV new physics can fit the anomaly compatibly with collider bounds: we explore which scalar vacuum expectation values (such as a triplet with zero hypercharge), $Z'$ vectors (such as a $Z'$ coupled to the Higgs only), little-Higgs models or higher-dimensional geometries provide good global fits. On the other hand, new physics that contributes at loop-level must be around the weak scale to fit the anomaly. Thereby it generically conflicts with collider bounds, that can be bypassed assuming special kinematics like quasi-degenerate particles that decay into Dark Matter (such as an inert Higgs doublet or appropriate supersymmetric particles).

• The paper demonstrates that a universal correction to the T parameter can reconcile the CDF 7σ W-boson mass anomaly with electroweak precision data.
• It employs a comprehensive global fit that incorporates tree-level contributions from multi-TeV new physics models, including scalar VEVs, Z′ vectors, and little-Higgs scenarios.
• The analysis highlights that loop-level contributions require weak-scale new physics with specific kinematic conditions to meet current collider constraints.

Analysis of Electroweak Precision Data and the $W$-Mass CDF Anomaly

In this paper, Alessandro Strumia conducts a comprehensive analysis of electroweak precision data with a focus on the $W$-boson mass anomaly reported by the CDF collaboration. The anomaly presents a significant deviation - at a level of $7\sigma$ - from the Standard Model (SM) predictions, specifically a measured $W$ mass of 80.433 GeV compared to the SM prediction of 80.357 GeV, and also disagrees with previous global data combinations. Strumia explores the feasibility of reconciling this anomaly through the introduction of new physics via modifications to the $T$ parameter or the $|H^\dagger D_\mu H|^2$ operator.

Key Findings and Approach

Strumia's analysis employs a global fit of electroweak precision data, integrating the anomalous CDF $W$ mass measurement. The anomaly can be explained by introducing new physics as a universal correction to the $T$ parameter. In this scenario, new physics arising at tree level involving multi-TeV scale phenomena, such as scalar vacuum expectation values, $Z'$ vectors interacting with the Higgs, and particular little-Higgs models, provide a compatible fit without conflicting with existing collider bounds. Models inducing changes at loop level require new physics to be around the weak scale, which poses challenges with current collider constraints unless special kinematic conditions are considered.

Implications

The implications of this research are multifaceted, both in terms of theoretical physics and practical considerations. Notably:

• Universal heavy new physics described by effective operators contributes to the global electroweak fit, successfully accommodating the observed $W$ mass anomaly. Most notably, corrections stem from dimension-6 operators that involve weak gauge bosons and the Higgs field, parameterized by alterations in the $\widehat S$, $\widehat T$, $W$, and $Y$ coefficients.
• Tree-level contributions from heavy scalars, $Z'$ vectors, and little-Higgs models are viable solutions, providing specific mechanisms through which the anomaly can be explained without violating existing large hadron collider (LHC) results.
• Loop-level contributions necessitate lighter new physics which aligns with weak-scale models that could navigate current collider bounds by exploiting quasi-degenerate particle states or decay invisibly into dark matter candidates.
• Specific attention is given to $Z'$ models, where flavor-universal anomaly-free vectors provide strong candidates for reconciling the anomaly while considering collider constraints.

Future Directions

Theoretical exploration on heavy new physics, particularly at higher-dimensional representations and advanced little-Higgs models, could shed further light on mechanisms satisfactorily resolving the $W$-mass discrepancy. Special attention should be given to collider tests that are sensitive to loop-level effects as new potential candidates could sit within the currently viable regions and benefit from refined analytical approaches.

Moreover, investigation of log-enhanced one-loop effects and their nuances in affecting the global fit, as highlighted, offers another avenue for understanding the dynamical complexities of electroweak interactions. The constraints on effective operators mediated by TeV-scale physics provide vital clues for further empirical verification at emerging collider platforms.

Conclusion

Strumia's study presents a robust attempt to address the electroweak precision data anomaly identified by the CDF collaboration pertaining to the $W$-boson mass. The acknowledgment of specific new physics as contributing factors provides depth to this anomaly analysis, highlighting the intricate balance between theoretical predictions and experimental data compatibility. Continuing advancements in collider data assimilation and theoretical modeling will prove pivotal in confirming or refuting the potential sources and frameworks proposed within this work.