[Paper Review] Constraints on CP-Odd Gauge-Higgs Operators

Siddharth Dwivedi, Dilip Kumar Ghosh+2 more|arXiv (Cornell University)|May 21, 2015

Particle physics theoretical and experimental studies51 references3 citations

TL;DR

This paper constrains CP-odd gauge-Higgs operators of dimension six within the Standard Model effective field theory framework, using electroweak precision data, LHC Higgs data (especially the diphoton channel), and electric dipole moment measurements. It finds that electric dipole moments provide the strongest constraints, while LHC diphoton data is the most sensitive probe for operators contributing to γγh vertices.

ABSTRACT

We consider the most general set of $SU(2) imes U(1)$ invariant CP-violating operators of dimension six, which contribute to $VVh$ interactions ($V = W, Z, \gamma$). Our aim is to constrain any CP-violating new physics above the electroweak scale via the effective couplings that arise when such physics is integrated out. For this purpose, we use, in turn, electroweak precision data, global fits of Higgs data at the Large Hadron Collider and the electric dipole moments of the neutron and the electron. We thus impose constraints mainly on two parameter and three parameter spaces. We find that the constraints from the electroweak precision data are the weakest. The contributions to electric dipole moments mostly lead to the strongest constraints, though somewhat fine-tuned combinations of more than one parameters with large magnitudes are allowed. As for the LHC data, the diphoton channel for the Higgs is by far the strongest limitor of those operators that contribute to it. However, there can be non-trivial constraints from the $\gamma Zh$ vertex also, mainly through the vector boson fusion and $Vh$ associated production modes.

Motivation & Objective

• To identify and constrain the most general set of CP-violating dimension-six operators involving gauge and Higgs bosons in the context of $SU(2) \times U(1)$ invariance.
• To determine the sensitivity of various experimental probes—electroweak precision data, LHC Higgs data, and electric dipole moments—to these CP-odd operators.
• To assess the relative strength of constraints across different parameter spaces, particularly two- and three-parameter scenarios.
• To evaluate the role of the $\gamma Zh$ vertex and vector boson fusion modes in constraining CP-violating couplings.

Proposed method

• Construct the complete set of $SU(2) \times U(1)$-invariant, dimension-six CP-odd operators contributing to $VVh$ interactions ($V = W, Z, \gamma$).
• Integrate out new physics above the electroweak scale to derive effective couplings that modify $VVh$ vertices.
• Apply constraints from electroweak precision observables, including $S$, $T$, and other oblique parameters.
• Use global fits of LHC Higgs data, especially the $\gamma\gamma h$ and $Zh$ production channels, to constrain operator strengths.
• Compute contributions to the neutron and electron electric dipole moments (EDMs) and compare with experimental bounds.
• Perform combined global fits in two- and three-parameter spaces to identify allowed regions and dominant constraints.

Experimental results

Research questions

• RQ1 Which CP-odd gauge-Higgs operators of dimension six are consistent with current electroweak precision data?
• RQ2 How sensitive is the LHC Higgs data—particularly the $\gamma\gamma h$ channel—to CP-violating $VVh$ couplings?
• RQ3 To what extent do electric dipole moment measurements constrain the parameter space of CP-odd operators?
• RQ4 What role do the $\gamma Zh$ vertex and associated production modes play in constraining CP-violating interactions?
• RQ5 Are there fine-tuned combinations of large-magnitude parameters that evade the strongest constraints?

Key findings

• Electroweak precision data impose the weakest constraints on CP-odd gauge-Higgs operators compared to other probes.
• Electric dipole moment measurements provide the strongest constraints overall, though certain fine-tuned combinations of large-magnitude parameters remain allowed.
• The $\gamma\gamma h$ channel at the LHC is the most powerful single channel for constraining operators that contribute to this vertex.
• Non-trivial constraints also arise from the $\gamma Zh$ vertex, primarily through vector boson fusion and $Vh$ associated production modes.
• Constraints from the $\gamma Zh$ vertex are significant even when the $\gamma\gamma h$ channel is not directly sensitive, highlighting the importance of multiple production modes.
• The interplay between multiple operators in three-parameter spaces allows for regions of parameter space that evade individual constraints, though EDMs still provide strong overall suppression.