Emergence of the electroweak scale through the Higgs portal

Topic

natural sciences

Frequently Asked Questions (FAQ)

What is the Electroweak Scale and why is its smallness a problem? The electroweak scale (v ~ 246 GeV) determines the masses of fundamental particles in the Standard Model (SM), like the W and Z bosons. Its smallness compared to the Planck scale (MPl ~ 1019 GeV), where gravity becomes important, poses a problem known as the hierarchy problem. This vast difference in scales is difficult to explain naturally within the SM.
What is the Coleman-Weinberg mechanism and how does it address the hierarchy problem? The Coleman-Weinberg (CW) mechanism is a way to generate mass scales radiatively from dimensionless couplings. It exploits the fact that running couplings can induce spontaneous symmetry breaking, leading to a non-zero vacuum expectation value (vev) for a scalar field. This vev sets the mass scale of the theory. In a theory with no explicit mass scales, the CW mechanism naturally generates a vev exponentially smaller than the UV cutoff, addressing the naturalness aspect of the hierarchy problem.
What is the main limitation of the original Coleman-Weinberg scenario? While elegant, the original CW scenario, when applied to the SM, predicts a Higgs boson much lighter than the observed ~125 GeV. This is because the Higgs mass is directly linked to the masses of the W and Z bosons and is suppressed compared to them.
How does the Higgs portal model help overcome the limitations of the Coleman-Weinberg mechanism in the SM? The Higgs portal model introduces a new scalar field (φ) coupled to the SM Higgs (H) via a portal interaction (λP). The key idea is to generate the mass scale in a “hidden sector”, where φ undergoes CW symmetry breaking, and then transmit this scale to the SM through the portal coupling. This breaks the direct link between the SM gauge boson masses and the Higgs mass, allowing the Higgs to have its observed value.
How does dimensional transmutation work in the Higgs portal model? In the Higgs portal model with CW in the hidden sector, no explicit mass scales are present initially. The CW mechanism generates a vev for φ in the hidden sector, breaking the U(1)hidden gauge symmetry. This vev is then transmitted to the SM Higgs via the portal interaction, inducing a mass term for the Higgs. Dimensional transmutation ensures both vevs are naturally small compared to the UV cutoff.
What are the key arguments supporting vanishing mass terms at the origin of the potential in the Higgs portal model? The vanishing of mass terms at the origin of the potential is crucial for dimensional transmutation. Two arguments support this choice: Dimensional regularisation: This scheme preserves scale invariance maximally, making the condition of vanishing masses at the origin self-consistent. UV Fixed Point: Restricting the theory to trajectories ending in the UV fixed point, where only marginal operators with logarithmic running are excited, naturally leads to vanishing mass terms at the origin.
What are the phenomenological consequences and predictions of the Higgs portal model with Coleman-Weinberg symmetry breaking? The model predicts a new hidden Higgs (h2) and a massive U(1)hidden gauge boson (X). The phenomenological signatures include: Modifications to the SM Higgs (h1) branching ratios and couplings due to mixing with h2. Potential decay of h1 into two h2, if kinematically allowed. Decays of h2 into SM particles via its mixing with h1, possibly with displaced vertices for very small mixing. Resonant structures in di-Higgs searches due to h2 production.
How can this model be tested experimentally? Precision measurements of the Higgs boson properties: Deviations in couplings and total width can reveal mixing with the hidden Higgs. Searches for new resonances: Direct searches for h2 and the gauge boson X in various decay channels. Low energy measurements: Constraints from fifth force experiments and stellar evolution can probe very light hidden Higgses. A future linear collider would be particularly well-suited for precisely measuring the Higgs properties and thus constraining the model parameters.

Significance

Understanding these findings helps advance our knowledge and inform better decisions. This research represents an important contribution to the field. For the full details, watch the video above and explore the linked resources.

Resources & Further Watching

Read the research paper written by Christoph Englert, Joerg Jaeckel, Valentin V. Khoze, Michael Spannowsky: https://arxiv.org/abs/1301.4224

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emergence of the electroweak scale through the higgs portal

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