Vector Higgs-portal dark matter and the invisible Higgs (1111.4482v3)

Abstract: The Higgs sector of the Standard Model offers a unique probe of the hidden sector. In this work, we explore the possibility of renormalizable Higgs couplings to the hidden sector vector fields which can constitute dark matter (DM). Abelian gauge sectors with minimal field content, necessary to render the gauge fields massive, have a natural Z_2 parity. This symmetry ensures stability of the vector fields making them viable dark matter candidates, while evading the usual electroweak constraints. We illustrate this idea with the Stueckelberg and Higgs mechanisms. Vector DM is consistent with the WMAP, XENON100, and LHC constraints, while it can affect significantly the invisible Higgs decay. Due to the enhanced branching ratio for the Higgs decay into the longitudinal components of the vector field, the vector Higgs portal provides an efficient way to hide the Higgs at the LHC. This could be the reason why the latest combined ATLAS/CMS data did not bring evidence for the existence of the Higgs boson.

• The paper reveals that a vector dark matter candidate interacting via the Higgs portal can significantly enhance the invisible decay width of the Higgs boson.
• It demonstrates that Higgs-mediated annihilations reconcile the model with relic abundance constraints and provide testable predictions for direct detection experiments.
• The analysis contrasts vector and scalar dark matter, showing that energy-dependent vector interactions yield pronounced phenomenological signatures at colliders.

Analysis of Vector Higgs-Portal Dark Matter and Invisible Higgs Decay

The paper "Vector Higgs–portal dark matter and the invisible Higgs" by Oleg Lebedev, Hyun Min Lee, and Yann Mambrini explores the interaction of dark matter (DM) via a vector Higgs portal with the Standard Model (SM) Higgs field. This research addresses two significant issues in particle physics: the elusive nature of dark matter constituting approximately 85% of matter in the universe, and the mechanism behind electroweak symmetry breaking facilitated by the Higgs boson.

Theoretical Framework and Model

The authors propose a scenario where vector dark matter interacts with the SM through the Higgs portal. In this framework, a hidden U(1) vector field can serve as a viable dark matter candidate by gaining mass through mechanisms such as the Stueckelberg process or a hidden Higgs mechanism, without conflicting with the SM's electroweak constraints. An essential feature is a natural $Z_2$ parity, which ensures the stability of the vector field $X_\mu$, rendering it a suitable dark matter candidate.

The considered interaction incorporates the only dimension-two gauge-invariant operator in the SM, $\bar{H}H$, coupled to the hidden sector field $X_\mu$ through a renormalizable dimension-four interaction. Notably, this results in significant phenomenological effects, including contributions to the invisible decay width of the Higgs boson.

Phenomenological Implications

The implications for cosmology and accelerator-based experiments are pivotal:

1. Relic Abundance and Direct Detection: The thermal relic abundance is consistent with WMAP constraints, with appreciable contributions from Higgs-mediated annihilations. Direct detection prospects are analyzed concerning XENON100 data, leading to predictive cross-sections that could be probed by future experiments like XENON1T.
2. Invisible Higgs Decay: Perhaps the most intriguing implication is the potential for a substantial invisible decay width for the Higgs boson into dark matter states, especially for light dark matter candidates ($m_X < m_h/2$). This results in a diminished visible Higgs decay signal at the LHC, affecting the interpretation of Higgs search results.
3. LHC Constraints: By impacting the branching ratios of various decay channels, this model could explain why signatures for the Higgs particle might have been absent or obscured in the LHC data at the time.

Comparison with Scalar Dark Matter

An intriguing point made in the paper is the comparative analysis of vector versus scalar Higgs-portal dark matter. Vector fields, due to their derivative nature and hard mass terms, can have enhanced contributions to the Higgs invisible decay width, surpassing those of scalar dark matter. This difference stems from the energy-dependent interactions of the absorbed Goldstone bosons in vector Higgs decays.

Future Directions

The potential detection of associated signals in future direct detection experiments and updated results from the LHC might require adjustments or refinements in dark matter models. The paper invites exploration into the UV-completion of such theories, understanding field dependencies, and exploring mixed dark matter models that can exhibit both vector and scalar characteristics, which could be tested in colliders and cosmological observations for comprehensive dark matter detection.

In conclusion, the vector Higgs-portal model of dark matter offers a promising avenue in reconciling dark matter with observable Higgs signatures, with substantial implications for ongoing investigations at particle colliders and direct detection experiments. As progress in experimental methodologies continues, this model serves as a critical conceptual tool in probing the dark sector and informs future theoretical explorations in high-energy physics.