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1. Boundaries of universal theories

   https://doi.org/10.1103/PhysRevD.111.015031  

   McCullough, Matthew; Riembau, Marc; Ricci, Lorenzo (January 2025, Physical Review D)

   Universal theories are a broad class of well-motivated microscopic dynamics of the electroweak sector that go beyond the Standard Model description. The long distance physics is described by electroweak parameters which correspond to local operators in the effective field theory. We show how unitarity and analyticity constrain the space of parameters. In particular, the $W$and $Y$parameters are constrained to be positive and are necessarily the leading terms in the low-energy expansion. We assess the impact of unitarity on the interpretation of Drell-Yan data. In passing, we uncover an unexpected Wilson coefficient transcendental cancellation at the $\mathcal{O}(<{10}^{-3})$level. Published by the American Physical Society2025 

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2. Lam-Tung relation breaking in $Z$ boson production as a probe of standard model effective field theory effects

   https://doi.org/10.1103/PhysRevD.111.073007  

   Li, Xu; Yan, Bin; Yuan, C-P (April 2025, Physical Review D)

   The violation of the Lam-Tung relation in the high- $p_T^{\ell \ell }$region of the Drell-Yan process at the LHC presents a longstanding discrepancy with the standard model prediction at $\mathcal{O}\left({\alpha }_s^3\right)$accuracy. In this paper, we employed a model-independent analysis to investigate this phenomenon within the framework of the standard model effective field theory (SMEFT). Our findings revealed that the leading contributions from SMEFT to this violation appear at the $1/{\mathrm{\Lambda }}^4$order with $\mathcal{O}\left({\alpha }_s\right)$accuracy in quantum chromodynamics (QCD) interaction. Notably, we demonstrated that the quadratic effect of dimension-6 dipole operators, associated with the $Z$boson, dominates the breaking effects induced by various dimension-6 and dimension-8 operators. This provides a possible explanation for the observed discrepancy with the Standard Model predictions at the LHC. Furthermore, the breaking effects could also serve as a powerful tool for constraining $Z$-boson dipole interactions, highlighting their importance among potential sources of new physics in the Drell-Yan process. Published by the American Physical Society2025 

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3. Revisiting $C$ and $CP$ violation in $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ decay

   https://doi.org/10.1103/PhysRevD.110.055039  

   Shi, Jun; Liang, Jian; Gardner, Susan (September 2024, Physical Review D)

   The decay $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$is an ideal process in which to study flavor-conserving $C$and $CP$violation beyond the Standard Model. We deduce the $C$- and $CP$-odd quark operators that contribute to $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$originating from the mass-dimension-six Standard Model effective field theory. The corresponding hadron-level operators that generate a nonvanishing $I=0$amplitude at order $p^6$in the chiral effective theory are presented for the first time, to the best of our knowledge, in addition to the leading-order operators ascribed to the $I=2$final state. By fitting the KLOE-2 and the most recent BESIII experimental data, we determine the coefficients of the lowest-order $I=0$and $I=2$amplitudes and estimate the potential new physics energy scale. We also perform an impact study of the future $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$experiments. Published by the American Physical Society2024 

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4. Universal density shift coefficients for the thermal conductivity and shear viscosity of a unitary Fermi gas

   https://doi.org/10.1103/PhysRevResearch.6.L042021  

   Li, Xiang; Huang, J; Thomas, J E (October 2024, Physical Review Research)

   We measure universal temperature-independent density shifts for the thermal conductivity ${\kappa }_T$and shear viscosity $\eta$, relative to the high temperature limits, for a normal phase unitary Fermi gas confined in a box potential. We show that a time-dependent kinetic theory model enables extraction of the hydrodynamic transport times ${\tau }_{\eta }$and ${\tau }_{\kappa }$from the time-dependent free decay of a spatially periodic density perturbation, yielding the static transport properties and density shifts, corrected for finite relaxation times. Published by the American Physical Society2024 

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5. Field-theory action for the constructive standard model

   https://doi.org/10.1103/PhysRevD.110.105008  

   Christensen, Neil (November 2024, Physical Review D)

   We introduce a field-theory framework in which fields transform under the little group, rather than the Lorentz group, specific to each particle type. By utilizing these fields, along with spinor products and the $x$ factor, we construct a field-theory action that naturally reproduces the vertices of the constructive standard model (CSM). This approach eliminates unphysical components, significantly reduces the degrees of freedom compared to traditional field theory, and offers deeper insights into the power of constructive amplitudes. Our action is momentum-conserving, Lorentz-invariant, Hermitian, and nonlocal. We also discuss this as a framework for developing new constructive field theories, discussing their essential properties and potential applicability in renormalization theory and nonperturbative calculations. Published by the American Physical Society2024 

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