Testing Minimal U(2)3 Right-Handed Flavor Breaking in a Singlet-Scalar Vector-Like Quark Portal
Abstract
We study a portal of a Z2-odd singlet scalar and a vector like down quark, in which a right handed flavor breaking spurion extends the portal coupling from bR to dR and sR. This single coupling vector links the b→ s, b→ d, and s→ d transitions. We compute the one loop dipole and ΔF=2 Wilson coefficients, and show that a real scalar generates no ΔF=2 amplitude at one loop. Using a seven observable profile likelihood of B meson mixing, εK, and radiative decays, with the CKM, lattice, and short distance inputs treated as nuisance parameters, we compare a generic spurion, minimal U(2)3 with a free size of the light quark couplings, and a CKM-aligned ansatz. We have found that the present data cannot yet test the flavor structure: the Standard Model is compatible with the data, with a pseudo experiment p-value of $0.20$, and no direction of the light quark couplings can be excluded at 95% CL. For MD≃ m𝒮=1 TeV and |λb|=1, the relative light quark coupling εR is bounded at 95% CL by $0.227$ for a generic spurion and by $0.211$ for minimal U(2)3. More precise measurements of the Bs mixing phase at the LHC and of sin2β at LHCb and Belle-II, together with improved lattice and CKM inputs, can make the minimality of the flavor structure testable if a deviation from the Standard Model is observed.
Related
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BibTeX
@misc{salam2026testing,
title = {{Testing Minimal $U(2)^3$ Right-Handed Flavor Breaking in a Singlet-Scalar Vector-Like Quark Portal}},
author = {Qazi Maaz Us Salam},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15911},
eprint = {2610.15911},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15911},
}
RIS
TY - UNPB
TI - Testing Minimal U(2)^3 Right-Handed Flavor Breaking in a Singlet-Scalar Vector-Like Quark Portal
AU - Qazi Maaz Us Salam
PY - 2026
DA - 2026/10/11
PB - arXiv
DO - 10.48550/arxiv.2610.15911
UR - https://arxiv.org/abs/2610.15911
AB - We study a portal of a Z_2-odd singlet scalar and a vector like down quark, in which a right handed flavor breaking spurion extends the portal coupling from b_R to d_R and s_R. This single coupling vector links the b→ s, b→ d, and s→ d transitions. We compute the one loop dipole and ΔF=2 Wilson coefficients, and show that a real scalar generates no ΔF=2 amplitude at one loop. Using a seven observable profile likelihood of B meson mixing, ε_K, and radiative decays, with the CKM, lattice, and short distance inputs treated as nuisance parameters, we compare a generic spurion, minimal U(2)^3 with a free size of the light quark couplings, and a CKM-aligned ansatz. We have found that the present data cannot yet test the flavor structure: the Standard Model is compatible with the data, with a pseudo experiment p-value of $0.20$, and no direction of the light quark couplings can be excluded at 95% CL. For M_D≃ m_𝒮=1 TeV and |λ_b|=1, the relative light quark coupling ε_R is bounded at 95% CL by $0.227$ for a generic spurion and by $0.211$ for minimal U(2)^3. More precise measurements of the B_s mixing phase at the LHC and of sin2β at LHCb and Belle-II, together with improved lattice and CKM inputs, can make the minimality of the flavor structure testable if a deviation from the Standard Model is observed.
ER -