Exploring T and S parameters in Vector Meson Dominance models of strong electroweak symmetry breaking

We present a one-loop calculation of the oblique S parameter within Higgsless models of electroweak symmetry breaking and analyze the phenomenological implications of the available electroweak precision data. We use the most general effective Lagrangian with at most two derivatives, implementing the chiral symmetry breaking SU (2) L ⊗ SU (2) R → SU (2) L+R with Goldstones, gauge bosons and one multiplet of vector and axial-vector massive resonance states. Using the dispersive representation of Peskin and Takeuchi and imposing the short-distance constraints dictated by the operator product expansion, we obtain S at the NLO in terms of a few resonance parameters. In asymptotically-free gauge theories, the final result only depends on the vector-resonance mass and requires M V > 1.8 TeV (3.8 TeV) to satisfy the experimental limits at the 3σ (1σ) level; the axial state is always heavier, we obtain M A > 2.5 TeV (6.6 TeV) at 3σ (1σ). In strongly-coupled models, such as walking or conformal technicolour, where the second Weinberg sum rule does not apply, the vector and axial couplings are not determined by the short-distance constraints; but one can still derive a lower bound on S, provided the hierarchy M V < M A remains valid. Even in this less constrained situation, we find that in order to satisfy the experimental limits at 3σ one needs M V,A > 1.8 TeV.

“…(23) (the couplings κ and σ), as it was already realized in Refs. [47][48][49]. This result was known in QCD from the one-loop study of the pion form factor in RχT [39,41,42].…”

Section: Wsr Constraints At One Loopmentioning

confidence: 87%

“…The tree-level contributions to the gauge-boson vacuum polarization Π 30 (s) are shown in Figure 1 and lead to the well-known leading-order (LO) result [35,[47][48][49]:…”

Section: Nlo Calculation Of Smentioning

confidence: 96%

“…5 However, the second WSR cannot be used in Conformal Technicolour models [49] and its validity is questionable in most Walking Technicolour scenarios [62].…”

Section: Weinberg Sum Rulesmentioning

confidence: 99%

“…Several one-loop estimates of the electroweak S and T parameters in the three-site [46] and more general [47][48][49] Higgless models have appeared recently. The results of Refs.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

One-loop calculation of the oblique S parameter in higgsless electroweak models

Pich

Rosell

Sanz-Cillero

2012

Oblique S and T constraints on electroweak strongly-coupled models with a light Higgs

Pich

Rosell

Sanz-Ciller

2014

Using a general effective Lagrangian implementing the chiral symmetry breaking SU(2) L ⊗ SU(2) R → SU(2) L+R , we present a one-loop calculation of the oblique S and T parameters within electroweak strongly-coupled models with a light scalar. Imposing a proper ultraviolet behaviour, we determine S and T at next-to-leading order in terms of a few resonance parameters. The constraints from the global fit to electroweak precision data force the massive vector and axial-vector states to be heavy, with masses above the TeV scale, and suggest that the W + W − and ZZ couplings of the Higgs-like scalar should be close to the Standard Model value. Our findings are generic, since they only rely on soft requirements on the short-distance properties of the underlying strongly-coupled theory, which are widely satisfied in more specific scenarios.

The S parameter for a light composite Higgs: a dispersion relation approach

Orgogozo

Rychkov

2013

Self Cite

We derive a dispersion relation for the S parameter in the SO(5)/SO(4) Minimal Composite Higgs model. This generalizes the Peskin-Takeuchi formula to the case when a light Higgs boson is present in the spectrum. Our result combines an IR effect due to the reduction in the Higgs boson couplings with a UV contribution from the strong sector. It also includes a finite matching term, achieving a very good relative accuracy O(m h /m ρ ). We apply our formula in several toy examples, modeling the UV spectral density via Vector Meson Dominance.