arXiv subjects

Hakan Akdag

Publications and source records attributed to Hakan Akdag.

5 recordsLinked to original sources

arXiv2024

Correlations of $C$ and $CP$ violation in $η\to π^0\ell^+\ell^-$ and $η'\to η\ell^+\ell^-$

Based on recent progress in the systematic analysis of $C$ and $CP$ violation in the light-meson sector, we calculate the $C$-odd transition amplitudes $η\toπ^0\ell^+\ell^-$ and $η'\toη\ell^+\ell^-$. Focusing on long-distance contributions driven by the lowest-lying hadronic intermediate states, we work out the correlations between these beyond-the-Standard-Model signals and the Dalitz-plot asymmetries in $η\rightarrow π^0 π^+ π^-$ and $η' \rightarrow ηπ^+ π^- $, using dispersion theory.

hep-ph↗

arXiv2023

$C$ and $CP$ violation in effective field theories

The quest for new sources of the simultaneous violation of $C$ and $CP$ symmetry was popular in the 1960s and has since been mostly neglected for more than half a century. In this work we revisit fundamental quark-level operators that break $C$ and $CP$ up to and including mass dimension 8 for flavor-conserving transitions, relying on the complete operator sets of the so-called Standard Model effective field theory and the low-energy effective field theory. With the formalism of chiral perturbation theory, we match these quark operators to light-meson physics, derive $C$- and $CP$-odd Lagrangians for several processes in the $η$, $η'$, and pion sectors, and furthermore, as a proof of principle, give estimates for the respective observables in explicit dependence of the underlying high-energy scale for new physics.

hep-ph↗

arXiv2023

Patterns of $C$- and $CP$-violation in hadronic $η$ and $η'$ three-body decays

We construct hadronic amplitudes for the three-body decays $η^{(\prime)}\toπ^+π^-π^0$ and $η'\toηπ^+π^-$ in a non-perturbative fashion, allowing for $C$- and $CP$-violating asymmetries in the $π^+π^-$ distributions. These amplitudes are consistent with the constraints of analyticity and unitarity. We find that the currently most accurate Dalitz-plot distributions taken by the KLOE-2 and BESIII collaborations confine the patterns of these asymmetries to a relative per mille level. Our dispersive representation allows us to extract the individual coupling strengths of the $C$- and $CP$-violating contributions arising from effective isoscalar and isotensor operators in $η^{(\prime)}\toπ^+π^-π^0$ and an effective isovector operator in $η'\toηπ^+π^-$, while the strongly different sensitivities to these operators can be understood from chiral power counting arguments.

hep-ph↗

arXiv2022

Pole position of the $a_1(1260)$ resonance in a three-body unitary framework

Masses, widths, and branching ratios of hadronic resonances are quantified by their pole positions and residues with respect to transition amplitudes on the Riemann sheets of the complex energy-plane. In this study we discuss the analytic structure in the physical energy region of three-body scattering amplitudes on such manifolds. As an application, we determine the pole position of the $a_1(1260)$ meson from the ALEPH experiment by allowing for $πρ$ coupled channels in S- and D-wave. We find it to be $\sqrt{s_0}=(1232^{+15+9}_{-0-11}-i266^{+0+15}_{-22-27})~\text{MeV}$.

hep-ph↗

arXiv2021

Dalitz plots and lineshape of $a_1(1260)$ from a relativistic three-body unitary approach

We formulate the final state interaction of the $a_1(1260)$ resonance decay in a manifestly three-body unitary parameterization and fit it to the $a_1(1260)$ lineshape measured by the ALEPH experiment. Dalitz plots calculated from this fit are presented. The work demonstrates the feasibility to numerically solve a previously derived amplitude and its generalization to isobars with spin and coupled channels. The model can also be applied to other meson decays and modified for the finite-volume problem as it arises in lattice QCD due to its manifest unitarity.

nucl-th↗