Equation 2 · Part 4 · From Origins to Frontier: A History of Particle Physics Beyond the Standard Model

Symbol c_i

\mathcal{L}_{\text{SMEFT}} = \mathcal{L}_{\text{SM}} + \sum_i \frac{c_i}{\Lambda^{2}} \mathcal{O}_i^{(6)} + \mathcal{O}\!\left(\frac{1}{\Lambda^{4}}\right)

c_i

What this part means

a dimensionless Wilson coefficient encoding the strength and structure of whatever heavy new physics generated it.

Its job in the formula

$c_i$ occurs above the fraction bar. The numerator is divided by the entire denominator below it.

Full expressionSymbol c_iArticle meaning

Where the article explains it

Here each $\mathcal{O}_i^{(6)}$ is a dimension-six operator built from Standard Model fields respecting its gauge symmetries, and $c_i$ is a dimensionless Wilson coefficient encoding the strength and structure of whatever heavy new physics generated it.

The passage around this formula

…new physics scale $\Lambda$ , to the ordinary Standard Model Lagrangian: $\mathcal{L}_{\text{SMEFT}} = \mathcal{L}_{\text{SM}} + \sum_i \frac{c_i}{\Lambda^{2}} \mathcal{O}_i^{(6)} + \mathcal{O}\!\left(\frac{1}{\Lambda^{4}}\right)$ . Here each $\mathcal{O}_i^{(6)}$ is a dimension-six operator built from Standard Model fields respecting its gauge symmetries, and $c_i$ is a dimensionless Wilson coefficient encoding the strength and structure of whatever heavy new physics generated it. This is not a discovery claim; it is a bookkeeping device, and its value is precisely that it is agnostic about what the new physics is. A single measured deviation — in a Higgs…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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