C006 $\mathcal{B}(D^0\to e^\pm\mu^\mp)$

Anarchic warped flavor already generates nonuniversal \(c\)- and \(u\)-quark couplings through localization and KK exchange. C006 additionally requires lepton-flavor violation, so it is not a quark-only \(\Delta F=2\) constraint. In a lepton-extended RS pipeline it would constrain four-fermion \((\bar u\Gamma c)(\bar e\Gamma\mu)\) structures, flavor-changing \(Z\)-like couplings combined with lepton flavor violation, scalar exchange, or explicit leptoquark/R-parity-violating UV completions. It is therefore a roadmap process for joint up-sector and charged-lepton flavor alignment.

The arXiv:0804.1954 RS-flavor baseline CsakiFalkowskiWeiler2008:CompositeFlavor predates the modern \(D^0\to e\mu\) search sequence. Belle's 2010 result Belle2010:D0EMu set the combined charge-mode limit at \(2.6\times10^{-7}\), BaBar's 2012 continuum-charm search BaBar2012:D0EeMuMuEMu gave \(3.3\times10^{-7}\), and LHCb's 2016 hadron-collider analysis LHCb2016:D0EMu became the current PDG-used input at \(1.3\times10^{-8}\). The LHCb source describes this as an order-of-magnitude improvement over the previous limit and notes sensitivity to leptoquark and R-parity-violating SUSY parameter space.

The experimental upper limit is a clean LFV null result. The RS interpretation is model dependent: the quark-only scan has no charged-LFV \(c\to u e\mu\) operator, and different chiral structures map differently onto the two-body \(D^0\) rate. A conservative future use should compare the limit to a defined \(\Delta C=1\) LFV Wilson basis, with the \(D^0\) decay constant and lepton mass effects stated explicitly, rather than reusing the neutral-meson mixing basis.

NO. The sidecar code\_coverage block records the required greps across quarkConstraints/, qcd/, flavorConstraints/, neutrinos/, yukawa/, warpConfig/, solvers/, scanParams/, and tests/ found no \(D^0\to e^\pm\mu^\mp\), \(c\to u e\mu\), or rare-charm LFV implementation. Nearby hits are different observables: \(D^0\) mixing is configured at quarkConstraints/deltaf2.py:252 and evaluated at quarkConstraints/deltaf2.py:941; the modern policy surface lists only neutral \(D^0\) mixing at quarkConstraints/modern/phenomenology.py:23 and evaluates that bridge at quarkConstraints/modern/phenomenology.py:668. The \(\mu\to e\gamma\) dipole checker at flavorConstraints/muToEGamma.py:75, called from scanParams/scan.py:524, is a separate charged-LFV observable.

MEDIUM. A first live constraint would need a new \(\Delta C=1\) LFV operator normalization and a \(D^0\to e\mu\) branching-ratio wrapper. It should not require a global fit or the existing \(\Delta F=2\) RG machinery, but the current neutral-meson SLL/SLR/VLL/VRR/LR basis is not sufficient.

Process-local keys before bibliography consolidation: PDG2026:D0EMu, LHCb2016:D0EMu, Belle2010:D0EMu, BaBar2012:D0EeMuMuEMu, and CsakiFalkowskiWeiler2008:CompositeFlavor.