Radiative decays of heavy-light mesons and the $$ {f}_{H,{H}^{\ast },{H}_1}^{(T)} $$ decay constants

The on-shell matrix elements, or couplings $$ {g}_{H{H}^{\ast}\left({H}_1\right)\upgamma} $$ g H H ∗ H 1 γ , describing the $$ B{(D)}_q^{\ast } $$ B D q ∗ → B(D)qγ and B1q → Bqγ (q = u, d, s) radiative decays, are determined from light-cone sum rules at next-to-leading order for the first time. Two different interpolating operators are used for the vector meson, providing additional robustness to our results. For the D*-meson, where some rates are experimentally known, agreement is found. The couplings are of additional interest as they govern the lowest pole residue in the B(D) → γ form factors which in turn are connected to QED-corrections in leptonic decays B(D) → ℓ$$ \overline{\nu} $$ ν ¯ . Since the couplings and residues are related by the decay constants $$ {f}_{H^{\ast}\left({H}_1\right)} $$ f H ∗ H 1 and $$ {f}_{H^{\ast}\left({H}_1\right)}^T $$ f H ∗ H 1 T , we determine them at next-leading order as a by-product. The quantities $$ \left\{{f}_{H^{\ast}}^T,{f}_{H_1}^T\right\} $$ f H ∗ T f H 1 T have not previously been subjected to a QCD sum rule determination. All results are compared with the existing experimental and theoretical literature.

Radiative neutrino masses, lepton flavor mixing and muon g − 2 in a leptoquark model

We propose a leptoquark model with two scalar leptoquarks $$ {S}_1\left(\overline{3},1,\frac{1}{3}\right) $$ S 1 3 ¯ 1 1 3 and $$ {\tilde{R}}_2\left(3,2,\frac{1}{6}\right) $$ R ˜ 2 3 2 1 6 to give a combined explanation of neutrino masses, lepton flavor mixing and the anomaly of muon g − 2, satisfying the constraints from the radiative decays of charged leptons. The neutrino masses are generated via one-loop corrections resulting from a mixing between S1 and $$ {\tilde{R}}_2 $$ R ˜ 2 . With a set of specific textures for the leptoquark Yukawa coupling matrices, the neutrino mass matrix possesses an approximate μ-τ reflection symmetry with (Mν)ee = 0 only in favor of the normal neutrino mass ordering. We show that this model can successfully explain the anomaly of muon g − 2 and current experimental neutrino oscillation data under the constraints from the radiative decays of charged leptons.

A theoretical analysis of the semileptonic decays $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$ and $$\eta ^\prime \rightarrow \eta l^+l^-$$

A complete theoretical analysis of the C- conserving semileptonic decays $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$ η ( ′ ) → π 0 l + l - and $$\eta ^\prime \rightarrow \eta l^+l^-$$ η ′ → η l + l - ($$l=e$$ l = e or $$\mu $$ μ ) is carried out within the framework of the Vector Meson Dominance (VMD) model. An existing phenomenological model is used to parametrise the VMD coupling constants and the associated numerical values are obtained from an optimisation fit to $$V\rightarrow P\gamma $$ V → P γ and $$P\rightarrow V\gamma $$ P → V γ radiative decays ($$V=\rho ^0$$ V = ρ 0 , $$\omega $$ ω , $$\phi $$ ϕ and $$P=\pi ^0$$ P = π 0 , $$\eta $$ η , $$\eta ^{\prime }$$ η ′ ). The decay widths and dilepton energy spectra for the two $$\eta \rightarrow \pi ^0l^+l^-$$ η → π 0 l + l - processes obtained using this approach are compared and found to be in good agreement with other results available in the published literature. Theoretical predictions for the four $$\eta ^{\prime }\rightarrow \pi ^0l^+l^-$$ η ′ → π 0 l + l - and $$\eta ^\prime \rightarrow \eta l^+l^-$$ η ′ → η l + l - decay widths and dilepton energy spectra are calculated and presented for the first time in this work.

Radiative decays of charged leptons as constraints of unitarity polygons for active-sterile neutrino mixing and CP violation

We calculate the rates of radiative $$\beta ^- \rightarrow \alpha ^- + \gamma $$ β - → α - + γ decays for $$(\alpha , \beta ) = (e, \mu )$$ ( α , β ) = ( e , μ ) , $$(e, \tau )$$ ( e , τ ) and $$(\mu , \tau )$$ ( μ , τ ) by taking the unitary gauge in the $$(3+n)$$ ( 3 + n ) active-sterile neutrino mixing scheme, and make it clear that constraints on the unitarity of the $$3\times 3$$ 3 × 3 Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix U extracted from $$\beta ^- \rightarrow \alpha ^- + \gamma $$ β - → α - + γ decays in the minimal unitarity violation scheme differ from those obtained in the canonical seesaw mechanism with n heavy Majorana neutrinos by a factor 5/3. In such a natural seesaw case we show that the rates of $$\beta ^- \rightarrow \alpha ^- + \gamma $$ β - → α - + γ can be used to cleanly and strongly constrain the effective apex of a unitarity polygon, and compare its geometry with the geometry of its three sub-triangles formed by two vectors $$U^{}_{\alpha i} U^*_{\beta i}$$ U α i U β i ∗ and $$U^{}_{\alpha j} U^*_{\beta j}$$ U α j U β j ∗ (for $$i \ne j$$ i ≠ j ) in the complex plane. We find that the areas of such sub-triangles can be described in terms of the Jarlskog-like invariants of CP violation $${{\mathcal {J}}}^{ij}_{\alpha \beta }$$ J α β ij , and their small differences signify slight unitarity violation of the PMNS matrix U.